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The caviomorph Octodon degus is likely the most studied Chilean mammal species. Several studies have centered in its natural history, ecology, behavior, and physiology; in addition, the species is used as model organism in biomedicine and neurobiology research. However, basic aspects such as its genetic and morphological variation throughout its distribution have not been adequately assessed. In fact, the last taxonomic study focused on populations of O. degus dates to the first half of the last century. Here we integrate morphologic (137 specimens from 23 localities) and genetic (cytochrome-b gene sequences of 47 individuals from 17 localities) evidence to assess the level and pattern of geographic variation along the whole species distribution. We found that specimens of O. degus present one of two morphotypes that are quali and quatitative differentiable. A gracile morphotype is found towards the north and a robust morphotype towards the south. Skull size variation correlates with precipitation, temperature and primary productivity. In addition, genealogical analysis uncovered two mains clades, one of them formed by haplotypes from specimens from the north and the other formed by haplotypes from specimens from the south of the distribution. We consider these differences warrant recognition at the subspecies level. As such, after assigning a neotype for Sciurus degus (= O. degus) that attaches this name to the southern morph, we described and named a new subspecies for the northern populations of O. degus.

El género Spalacopus incluye una sola especie, S. cyanus, endémica de la región central del Chile, siendo una de las especies mejor adaptada a la vida subterránea de la familia Octodontidae. Miembro del linaje que consiste en Octodontomys como hermano de Octodon y el clado representado por Spalacopus y Aconaemys. Si bien la morfología externa y cráneo-dentarias en S. cyanus han sido bien estudiadas, su morfología postcraneal es pobremente conocida. Por las peculiaridades de su estilo de vida y locomoción entre los miembros de la familia, es interesante caracterizar detalles de la morfología del esqueleto postcraneal de esta especie e inferir sus aspectos funcionales de la morfología. Se revisaron 29 ejemplares con material de postcráneo disponibles en dos colecciones sistemáticas: Museo de La Plata (MLP), La Plata, Buenos Aires, Argentina y Colección de Mamíferos del Instituto de Ciencias Ambientales y Evolutivas (UACH), Universidad Austral de Chile, Valdivia, Chile. Para la descripción detallada de la morfología de los elementos óseos se dividió al esqueleto en las siguientes regiones: esqueleto axial, cintura escapular y miembros anteriores, y cintura pélvica y miembros posteriores. Las estructuras incluidas en el esqueleto axial fueron descriptas principalmente en sentido cráneo-caudal y en los miembros en sentido próximo-distal. La observación de las estructuras se realizó con las lupas estereoscópicas Leica Wild M3Z y Nikon SMZ 745T, incluyendo fotografías para ilustrar las descripciones. En la morfología postcraneal de S. cyanus se observan características que se consideran altamente conservadas entre los miembros de la familia Octodontidae, pero algunos caracteres son exclusivos de la especie. El esqueleto axial está compuesto por siete vértebras cervicales, 12 ó 13 torácicas, seis o siete lumbares, cuatro sacras, entre 16 y 18 caudales, 12 ó 13 pares de costillas y un esternón compuesto por cinco esternebras. Los elementos óseos de las cinturas pectoral y pélvica como de los miembros anterior y posterior se describen en detalle, excepto los carpos y tarsos debido al mal estado de preservación o ausencia de los mismos. El patrón morfológico que presenta el postcráneo de S. cyanus se ajusta a un plan anatómico típico de especies terrestres y en algunos elementos óseos (húmero y ulna principalmente) se observan características típicamente asociadas con la habilidad excavadora. Los datos generados permitirán a futuro una mejor interpretación de los atributos postcraneales funcionalmente relacionados con los diferentes estilos de vida, evaluar sus estrategias locomotoras, así como también comprender la evolución de estos rasgos en un contexto filogenético. The genus Spalacopus includes only one species, S. cyanus, endemic to central Chile and one of the species best adapted to a subterranean lifetyle in the family Octodontidae. It is a member of the lineage consisting in Octodontomys as a sister clade containing Octodon and of a clade represented by Spalacopus and Aconaemys. Although the external and cranio-dental morphology have been well studied, little is known of the postcranial morphology of S. cyanus. Because of the peculiarities of its lifestyle and locomotion among the members of the family, it is interesting to characterize details of the morphology of the postcranial skeleton of this species and to infer their functional aspects of the morphology. Twenty-nine specimens with postcranial material stored in two collections were studied: Museo de La Plata (MLP), La Plata, Buenos Aires, Argentina and Colección de Mamíferos del Instituto de Ciencias Ambientales y Evolutivas (UACH), Universidad Austral de Chile, Valdivia, Chile. To describe in detail the morphology of the bone elements, the skeleton was divided in the following regions: axial skeleton, scapular girdle and forelimb, and pelvis girdle and hindlimb. The structures included in the axial skeleton were mainly described in cranial-caudal orientation and the limbs in proximal-distal orientation. All structures were observed with stereoscopic microscopes Leica Wild M3Z and Nikon SMZ 745T including pictures to illustrate the descriptions. Highly conservative characteristics among members of the family Octodontidae were observed in the postcranial morphology of S. cyanus, although some characters are exclusive to this species. The axial skeleton has seven cervical vertebrae, 12 or 13 thoracic, six or seven lumbar, four sacral, 16 to 18 caudal vertebrae, 12 or 13 ribs and a sternum with five sternebrae. The elements of the scapular and pelvic girdles as well as forelimbs and hindlimbs are described in detail, except the carpus and tarsus due to their poor state of conservation, or because they not available. The morphological pattern observed in the postcranial skeleton of S. cyanus conforms to a typical anatomical plan for terrestrial species, and some bones (mainly humerus and ulna) present characteristics associated with digging. The information obtained provided will allow a better interpretation of the postcranial attributes, functionally related with different lifestyle, in a future, as well as the evolution of the traits in a phylogenetic context. Fil: Pérez, María Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Investigación de Biodiversidad Argentina; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Conservación de los Murciélagos de Argentina; Argentina Fil: Díaz, María Mónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Investigación de Biodiversidad Argentina; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Conservación de los Murciélagos de Argentina; Argentina. Fundación Miguel Lillo; Argentina

Viscacha rats (genus Tympanoctomys Yepes, 1942) are ecologically, physiologically, and behaviorally unusual octodontid rodents endemic to the Monte and Patagonian desert biomes of Argentina. The geographic ranges of the different species of Tympanoctomys have been described in general terms but have not been associated with spatial and climate data. Within species, populations are patchily distributed and genetically distinct. We investigated the predicted distribution of Tympanoctomys and the influence of climate fluctuations on their geographic range in historical, current, and future, scenarios. Our objectives were to characterize the environmental niche of the genus, propose a paleoclimatic context for the oldest fossils, characterize the environmental niches for T. barrerae and T. kirchnerorum, and forecast potential future distributions for these taxa. Ecological niche models were constructed using occurrence records from 1941 to the present wherein we identified several precipitation and temperature variables as important predictors of the geographic distributions of the genus, and the species T. barrerae and T. kirchnerorum. Based on our models’ results, we hypothesize that the distribution of Tympanoctomys has contracted from historical to modern times. At the species level, T. kirchnerorum likely experienced the most dramatic change, suffering a large contraction of its historical distribution resulting in its limited present distribution. Given these findings, projected future climate fluctuations and global warming are expected to affect the distributions and persistence of these species.

This study includes the first neoichnologic characterization of the burrow systems of Tympanoctomys barrerae (Rodentia: Octodontidae) and also considers sedimentologic features of the modern nebkhas where they occur. Tympanoctomys is a South American solitary and fossorial rodent that has ecomorphofunctional adaptations for living in saline environments and constructs its burrow in nebkhas with halophyte shrubs. The purpose of this work is to identify the ichnologic signatures of T. barrerae burrow systems and to provide combined ichnologic-sedimentologic criteria for identification of Cenozoic nebkha deposits. Tympanoctomys barrerae burrow systems are subhorizontal, typically with ten or more entrances, two or three levels, closed circuits, average complexity of 48, average tortuosity of 3.25, and an average ratio of total chamber volume to total tunnel volume of 0.04. The size of the tunnels averages 85 mm in horizontal diameter and 64 mm in vertical diameter, and cross-section shape ranges from elliptical flattened to plano-convex with incipient bilobed floor. Surface ornamentation is typified by a coexistence of primary (sets of four claw traces forming an arcuate pattern produced during digging) and secondary (numerous arthropod burrows excavated from the burrow lumen) surface ornamentation. Nebkha deposits in upper Cenozoic sequences can be recognized by the combination of ichnologic and sedimentologic features: fossil burrows having the ichnologic features characteristic of T. barrerae burrow systems and presence of rhizoliths of shrubby plants occurring in well-sorted sandy deposits with low-angle crossbedding. These criteria can be potentially applied to fossil sequences dating back to the early Oligocene.

Hearing in subterranean rodents exhibits numerous peculiarities, including low sensitivity and restriction to a narrow range of comparatively low frequencies. Past studies provided two conflicting hypotheses explaining how these derived traits evolved: structural degeneration and adaptive specialization. To further elucidate this issue, we recorded auditory brainstem responses from three species of social subterranean rodents that differ in the degree of specialization to the underground habitat: the naked mole-rat (Heterocephalus glaber) and the Mashona mole-rat (Fukomys darlingi), which represent the ancient lineage of African mole-rats (Bathyergidae), and the coruro (Spalacopus cyanus), a South American rodent (Octodontidae) that adopted a subterranean lifestyle in more recent geological time. Additionally, we measured call amplitudes of social vocalizations to study auditory vocal coupling. We found elevated auditory thresholds and severe hearing range restrictions in the African mole-rats, with hearing in naked mole-rats tending to be more sensitive than in Mashona mole-rats, in which hearing notably deteriorated with increasing age. In contrast, hearing in coruros was similar to that of epigeic rodents, with its range extending into ultrasonic frequencies. However, as in the mole-rats, the coruros’ region of best hearing was located at low frequencies close to 1 kHz. We argue that the auditory sensitivity of African mole-rats, although remarkably poor, has been underestimated by recent studies, whereas data on coruros conform to previous results. Considering the available evidence, we propose to be open to both degenerative and adaptive interpretations of hearing physiology in subterranean mammals, as each may provide convincing explanations for specific auditory traits observed.

We report the finding of 2 species of Pudica (Nematoda: Heligmonellidae: Pudicinae) in 2 rodents endemic to Chile, the common degu Octodon degus (Octodontidae) and the Bennett's chinchilla rat Abrocoma bennettii (Abrocomidae). Pudica degusi (Babero and Cattan, 1975) n. comb., originally described as a species of Longistriata (Heligmosomidae), was found in the common degu; through the study of its synlophe, the species is reassigned to the Heligmonellidae: Pudicinae and the genus Pudica, and it is revalidated through comparison with the remaining species of the genus. Pudica cattani n. sp. is described from both O. degus and A. bennettii. It is characterized by its large body size, bursal pattern of type 1-3-1 on right lobe, 1-3-1 tending to 1-4 on left lobe, synlophe with 11 ridges including a careen, dorsal ray of the bursa dividing proximally and bursal rays 9 and 10 relatively short. Pudica degusi n. comb. and Pudica cattani n. sp. were found in the same host species but not as coparasitic in the same individuals. The common degu is confirmed as the sole and primary host of Pudica degusi n. comb. It is unlikely that it is the primary host for Pudica cattani n. sp., whose host affinities are less clear mainly due to the scarcity of data. Pudica cattani n. sp. is the first helminth reported from the Bennett's chinchilla rat. Both findings enlarge the host range of the Pudicinae to the families Octodontidae and Abrocomidae, i.e., 9 out of the 11 extant families of caviomorphs, thereby establishing the presence of this nematode subfamily as typical parasites of the Neotropical Hystricognathi. Fil: Digiani, Maria Celina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Landaeta Aqueveque, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Serrano, Paula Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Notarnicola, Juliana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Due to their flexibility, sutures are regions that experience greater strains than the surrounding rigid cranial bones. Cranial sutures differ in their degree of interdigitation or complexity. There is evidence indicating that a more convoluted suture better enables the absorption of high stresses coming from dynamic masticatory forces, and other functions. The Order Rodentia is an interesting clade to study this because of its taxa with diverse chewing modes. Due to repeated loading resulting from gnawing and grinding, energy absorption by the sutures might be a crucial factor in these mammals. Species within the infraorder Caviomorpha were chosen as a case study because of their ecomorphological and dietary diversity. This study compared five sutures from the rostrum and cranial vault across seven caviomorph families, and assessed their complexity by means of the relative length and fractal dimension. Across these rodents, cranial sutures are morphologically quite diverse. We found that the sutures connecting the rostrum with the vault were relatively more interdigitated than those in the cranial vault itself, especially premaxillofrontal sutures. Suture interdigitation was higher in species that display chisel-tooth digging and burrowing behaviors, especially in the families Ctenomyidae and Octodontidae, than those in families Dasyproctidae and Cuniculidae, which have more gracile masticatory systems. The reconstruction of the ancestral character state, on family and species phylogeny, points toward low suture interdigitation (i.e., low length ratio) as a likely ancestral state for interfrontal, premaxillofrontal and maxillofrontal sutures. Interspecific differences in suture morphology shown here might represent adaptations to different mechanical demands (i.e., soft vs. tough foods) or behaviors (e.g., chisel-tooth digging), which evolved in close association with the diverse environments occupied by caviomorph rodents.

A new argasid (Argasidae) tick is herein described based on morphology and molecular data obtained from larvae parasitizing Octodon degus and from ticks collected inside burrows in northern Chile. Unfed laboratory-reared larvae were mounted in slides for morphometrical and morphological analyses. Larvae of Ornithodoros octodontus n. sp. share morphological traits with Ornithodoros quilinensis and Ornithodoros xerophylus, two species associated with rodents in the Argentinean Chaco. However, a longer hypostome with two rows of 21 and 22 denticles each one, and conspicuous leaf-shaped anal plates separate O. octodontus. While nymphal stages of O. octodontus lack cheeks and possess a micromammillated dorsal integument, adults have cheeks and exhibit markedly irregular mammillae along their dorsal surface. Phylogenetic analyses of neotropical Argasidae based on mitochondrial 16S rDNA sequences point that O. octodontus forms a monophyletic group with O. xerophylus and an unidentified Ornithodoros sp. from Bolivia, all of them associated with burrow-dweller rodents. Ornithodoros aragaoi and Ornithodoros davisi, two rare species collected once only in the Peruvian Andean Plateau during 1955 are morphologically closely related with adults and nymphs of O. octodontus. Biological observations of O. octodontus revealed autogenic females. For the moment, subgeneric classification of this new species depends on further biological studies. The fauna of ticks occurring in Chile is now represented by 22 species, 11 belonging to the Argasidae family.

Caviomorph rodents represent a major adaptive radiation of Neotropical mammals. They occupy a variety of ecological niches, which is also reflected in their wide array of locomotor behaviors. It is expected that this radiation would be mirrored by an equivalent disparity of tarsal-metatarsal morphology. Here, the tarsal-metatarsal complex of Erethizontidae, Cuniculidae, Dasyproctidae, Caviidae, Chinchillidae, Octodontidae, Ctenomyidae, and Echimyidae was examined, in order to evaluate its anatomical variation and functional-adaptive relevance in relation to locomotor behaviors. A qualitative study in functional morphology and a geometric morphometric analysis were performed. We recognized two distinct tarsal-metatarsal patterns that represent the extremes of anatomical variation in the foot. The first, typically present in arboreal species, is characterized by features that facilitate movements at different levels of the tarsal-metatarsal complex. The second pattern, typically present in cursorial caviomorphs, has a set of features that act to stabilize the joints, improve the interlocking of the tarsal bones, and restrict movements to the parasagittal plane. The morphological disparity recognized in this study seems to result from specific locomotor adaptations to climb, dig, run, jump and swim, as well as phylogenetic effects within and among the groups studies.

Vision has long been considered purposeless in the dark underground ecotope. However, recent anatomical studies revealed an unexpected diversity of ocular and retinal features and various degrees of development of the visual system in mammals with predominantly subterranean activity, and have suggested retention of basic visual capabilities even in some strictly subterranean mammals such as the African mole-rats. Behavioural tests assessing image-forming vision have not yet been conducted in subterranean mammals. Here, we investigated the visual capacities in three species of the African mole-rats, namely the giant mole-rat Fukomys mechowii, the Mashona mole-rat Fukomys darlingi and the silvery mole-rat Heliophobius argenteocinereus, in the fossorial coruro Spalacopus cyanus and the inbred C57L/J mouse. The behavioural assays performed in this study revealed severe visual deficits in all three species of mole-rats. The absence of the visual placing reflex suggested impairment of either image-forming vision or visuomotor integration. The random choice between the shallow and the deep side of a visual cliff clearly demonstrated inability of mole-rats to perceive depth. The nesting assay did not yield conclusive evidence regarding the capacity for visually guided spatial orientation in the only tested species, the giant mole-rat. In contrast, both the coruro and the mouse exhibited a clear placing reaction and preferred the shallow side of the visual cliff, implying functional image-forming vision. Thus, the behavioural data gathered in this study show that vision is seriously compromised in the strictly subterranean, congenitally microphthalmic African mole-rats but efficient (i.e. comparable to that of surface-dwelling rodents) in a species with regular surface activity, the coruro.

The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhabiting pre-Andean pre-Puna and Puna environments of tropical South America. In order to understand the phylogeographic patterns of Octodontomys gliroides, we sequenced 579 bp of the mitochondrial DNA control region from 100 individuals collected from 20 populations across its entire distributional range. The phylogenetic and parsimony network, in conjunction with analysis of molecular variance (AMOVA), revealed a structured pattern of geographic differentiation of O. gliroides, with the occurrence of two well-defined evolutionary lineages: lineage A, restricted to Bolivia and Chile, and lineage B, restricted mainly to Argentina. Analysis of population structure inferred three genetic clusters along the distribution of O. gliroides that mostly agree with the four major barriers inferred by BARRIER analysis (e.g. rivers, salt flats, deserts, and mountain systems). In addition to the significant differentiation found among all levels studied, a positive correlation was identified between genetic and geographic distance, similar to as expected under the isolation-by-distance model. The most recent common ancestor of O. gliroides was estimated as c. 5.99 Mya, and the divergence between lineages A and B is estimated to have occurred by the Middle Pleistocene, about 0.69 Mya. The mismatch distributions and neutrality tests suggested a signal of population range expansion for both lineages coincident with major climatic changes that occurred during the wet–dry events of the Pleistocene in the Andean Puna region. Bayesian skyline plots (BSPs) for lineage A suggest a long history of constant population size followed by a period of slight to moderate demographic expansion at c. 0.04 Mya, whereas lineage B remained unclear after BSP analysis, probably because of the limited sample size.

Octodontoidea is the most species-rich clade among hystricomorph rodents, and has a fossil record going back to at least the late Oligocene. Affinities of fossils previous to the late Miocene differentiation of the extant families Abrocomidae, Echimyidae and Octodontidae are controversial, essentially because these fossils may share few apomorphies with modern species. In fact, pre-late Miocene representatives of Abrocomidae had not been recognised until very recently. Here we revise the early Miocene genus Acarechimys, originally assigned to Echimyidae, and alternatively to stem Octodontoidea or to Octodontidae. A systematic and parsimony-based phylogenetic analysis of the species traditionally included in Acarechimys showed that this genus is part of stem Abrocomidae. These results are primarily supported by morphology of the mandible and lower molars. Acarechimys is here restricted to three species, A. minutus, A. pulchellus and Acarechimys pascuali sp. nov., while another species, A. constans, is here transferred to a new abrocomid genus. The remaining species were nested within Octodontidae. According to these results, Abrocomidae might have been as diverse as its sister clade Octodontidae-Echimyidae during the late Oligocene–early Miocene. Extinction of this diversity would have resulted in marked loss of evolutionary history, with extant abrocomids being currently restricted to late-diverged euhypsodont representatives. Fil: Verzi, Diego Hector. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados. Sección de Mastozoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Olivares, Adriana Itati. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados. Sección de Mastozoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Morgan, Cecilia Clara. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados. Sección de Mastozoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The convergent evolution of subterranean rodents is an excellent model to study how natural selection operates and the genetic bases of these adaptations, but the study on the different taxa has been very uneven and still insufficient. In the octodontoid caviomorph rodent superfamily there are two independent lineages where they have recently evolved into totally underground lifestyles: the genera Ctenomys (tuco-tucos) and Spalacopus (coruro). The underground habitat is characterized by an hypoxic and hypercapnic atmosphere, thus gas exchange is one of the most important challenges for these animals. The invasion of the underground niche could have modified the selective regimes of proteins involved in the respiration and transport of O2 of these rodents, positively selecting mutations of higher affinity for O2. Here we examine the sequence variation in the beta globin gene in these two lineages, within a robust phylogenetic context. Using different approaches (classical and Bayesian maximum likelihood (PAML/Datamonkey) and alternatives methods (TreeSAAP)) we found at least three sites with evidence of positive selection in underground lineages, especially the basal branch that leads to the Octodontidae family and the branch that leads to the coruro, suggesting some adaptive changes to the underground life. We also found a convergence with another underground rodent, which cannot be identified by the above methods.

Octodontomys Palmer, 1903 Octodon: P. Gervais and d’Orbigny, 1844:22. Part (description of gliroides); not Octodon Bennett, 1832. Neoctodon Thomas, 1902:114. Type species Neoctodon simonsi Thomas (= Octodon gliroides P. Gervais and d’Orbigny) by original designation; preoccupied by Neoctodon Bedel, 1892 (Insecta: Coleoptera). Octodontomys Palmer, 1903:873. Replacement name for Neoctodon Thomas. CONTEXT AND CONTENT. Order Rodentia, suborder Hystricomorpha, infraorder Hystricognathi, family Octodontidae. This species was originally placed within the genus Octodon but later raised to generic status by Thomas (1902) as Neoctodon. The name Neoctodon Thomas was preoccupied by Neoctodon Bedel, 1892, a genus of beetle, Palmer (1903) assigned Octodontomys as a substitute name. Octodontomys is monotypic., Published as part of Pérez, M. Julieta & Díaz, M. Mónica, 2018, Octodontomys gliroides (Rodentia: Octodontidae), pp. 74-83 in Mammalian Species 50 (963) on page 74, DOI: 10.1093/mspecies/sey010, http://zenodo.org/record/4573547, {"references":["PALMER, T. S. 1903. Some new generic names of mammals. Science, n. s. 17: 873.","BENNETT, E. T. 1832. Characters of a new genus of rodent Mammalia, presented by Mr. Cuming. Proceedings of the Committee of Science and Correspondence of the Zoological Society of London, Part 2: 46 - 48.","THOMAS, O. 1902. On two new genera and rodents from the highlands of Bolivia. Proceedings of the Zoological Society of London 1: 114 - 117.","BEDEL, L. 1892. Revision des Scarabaeus palearctiques. L'Abeille; journal d'entomologie 27: 281 - 288."]}

Pérez, M. Julieta, Díaz, M. Mónica (2018): Octodontomys gliroides (Rodentia: Octodontidae). Mammalian Species 50 (963): 74-83, DOI: 10.1093/mspecies/sey010, URL: http://dx.doi.org/10.1093/mspecies/sey010

Octodontomys gliroides (P. Gervais and d’Orbigny, 1844) Mountain Degu Octodon gliroides P. Gervais and d’Orbigny, 1844:22. Type locality “des Andes boliviennes, à Lapaz;” La Paz, Bolivia. Neoctodon simonsi Thomas, 1902:115. Type locality “Mountainous region south and south- east of the Titicaca- Poopo basin. Potosí, 4400 metres,” Bolivia. Octodontomys gliroides: Thomas, 1913:143. First use of current name combination. CONTEXT AND CONTENT. Context as for genus. Octodontomys gliroides is monotypic (Verzi et al. 2015a). Mountain Degu Octodon gliroides P. Gervais and d’Orbigny, 1844:22. Type locality “des Andes boliviennes, à Lapaz;” La Paz, Bolivia. Neoctodon simonsi Thomas, 1902:115. Type locality “Mountainous region south and south- east of the Titicaca- Poopo basin. Potosí, 4400 metres,” Bolivia. Octodontomys gliroides: Thomas, 1913:143. First use of current name combination. CONTEXT AND CONTENT. Context as for genus. Octodontomys gliroides is monotypic (Verzi et al. 2015a). DIAGNOSIS Octodontomys gliroides (Fig. 1) resembles other members of the family Octodontidae, being most similar to the mountain viscacha rat Octomys mimax and species of the genus Tympanoctomys; however, O. gliroides has upper and lower molariforms with an asymmetrical occlusal pattern (Octomys and Tympanoctomys have a figure-8 occlusal pattern—Reig and Quintana 1991; Hutterer 1994; Kramarz 2005). Other distinctive features of the teeth and skull of O. gliroides (Fig. 2) include: the alveolar portion of the 1st molariform tooth (DP4) is slightly inclined anteriorly, medial to the incisor; as a result, an anterior extension of the maxillaries into the posterior margins of the incisive foramina, where DP4 is inserted, is scarcely developed to nearly absent (Verzi 2001; Verzi et al. 2015a). The molariform teeth have folds (flexi or flexids) that are shallow or absent; the maxillary cheek teeth have the anterior lobe protruding as in Octodon, but without a penetrating lingual fold (hypoflexus— Verzi and Carrín Iglesias 1999; Verzi 2001; Verzi et al. 2015a). The auditory bullae are of medium size (14.6 ± 0.7 mm) and slightly inflated compared with other desert-adapted octodontids such as Octomys (15.8 ± 0.3 mm) and Tympanoctomys (17.2 ± 0.9 mm—Mares et al. 2000). GENERAL CHARACTERS Octodontomys gliroides is a medium- to large-sized octodontid, with a body mass ranging from 100–200 g; total length, 200–380 mm; length of tail, 100–190 mm; length of hind foot, 33–40 mm; length of ear, 24–35 mm (Díaz 1999; Mares et al. 2000; Díaz and Barquez 2002; Verzi et al. 2015a). It is a semisubterranean genus of the family Octodontidae and, like Octodon and Tympanoctomys, has large eyes, ears, and hind feet (Lacey and Ebensperger 2007). The pelage is relatively long and silky; dorsal coloration is grayish drab streaked with black; tail has a reddish buffy brush; the venter has white hairs with gray bases, except on the chin and throat where they are pure white, which contrasts sharply with the dorsum (Thomas 1902; Ipinza et al. 1971; Mares et al. 2000; Verzi et al. 2015a). The ears are large, finely covered by short grayish hairs, with white tufts on the anterior ends (Ipinza et al. 1971; Díaz and Barquez 2002). Feet are hairy with the claw covered by hair, the plantar surfaces bear fine granulations (Thomas 1902; Contreras et al. 1987; Díaz and Barquez 2002), and plantar pads are prominent (Ipinza et al. 1971). The tail is nearly 80% of the head and body length; it is bicolored, with an elongated, brown or ochraceous brush extending from the tip. Juveniles are darker with a grayer venter and have an essentially unicolored tail that terminates in a short, black or dark drab brush (Díaz and Barquez 2002; Verzi et al. 2015a). The rostrum is relatively long and narrow; postorbital processes are absent or reduced; interorbital region is relatively broad and divergent with breadth slightly less than the breadth of the rostrum (9.23 mm versus 7.41 mm); lacrimal is large and triangular; palate is short, and the mesopterygoid fossa has an inverted “V” shape, not extending beyond M1; pterygoids leaning on the bullae (Díaz 1999; Mares et al. 2000). Incisive foramina are large with the posterior most ends behind the premaxillary-maxillary suture; the lateral edges of the posterior bor- der of the incisive foramina are not raised (Mares et al. 2000). The lateral flange of the canal for the infraorbital nerve is well developed and has the dorsal end free, not joined to the maxillary (Glanz and Anderson 1990; Verzi et al. 2015a). Masseteric crest and the tubercle for the insertion of the M. masseter medialis pars infraorbitalis are discontinuous (Verzi et al. 1999, 2001; Kramarz 2005). The zygomatic arches are little expanded, with a low and slightly deep jugal fossa for the posterior masseter muscle; shape of suture of jugal and zygomatic process of squamosal squared or rounded (Mares et al. 2000; Verzi et al. 2015a). The lateral supraoccipital processes show greatest development, with the long process extending to the squamosal process and then turning conspicuously downward (Glanz and Anderson 1990). Woods (1984:424, 428) mentioned a “slight lateral supraoccipital process” in both Ctenomyidae and Octodontidae, but Glanz and Anderson (1990) considered this description slightly misleading because the supraoccipital process is well developed in O. gliroides. The paraoccipital processes are small, thick, and incompletely joined to the bullae, with each root directed medially due to the development of the mastoid bullae (Mares et al. 2000; Verzi et al. 2015a). The mandible is slender, low, and moderately hystricognathous; the coronoid process is small; the condylar process is broad and slightly behind the angular process, the latter being short, slender, and slightly flattened; the lunar notch is shallow (Díaz 1999; Mares et al. 2000; Verzi et al. 2015a); the masseteric crest is not prominent (Verzi 2002). Mean cranial measurements (mm, ± SD, sample size in parentheses—Mares et al. 2000, specimens from Argentina and Bolivia) were: greatest length of skull, 45.3 ± 1.3 (25); basal length, 39.6 ± 1.3 (22); zygomatic breadth, 23.3 ± 0.7 (26); mastoid breadth, 22.1 ± 0.7 (21); least interorbital breadth, 9.4 ± 0.4 (29); length of nasals, 16.6 ± 0.9 (26); breadth of rostrum, 8.2 ± 0.3 (26); length of diastema, 11.5 ± 0.5 (28); length of maxillary toothrow, 8.1 ± 0.6 (28); length of bulla, 14.6 ± 0.7 (23); width of bulla, 11.3 ± 0.3 (23); width of zygomatic plate, 1.9 ± 0.2 (26); length of mandibular toothrow, 8.5 ± 0.6 (27); length of mandible, 27.5 ± 0.9 (28). Mean cranial measurements (mm, ± SD, sample size in parentheses—Díaz 1999, specimens from Argentina) were: condyle incisive length, 42.2 ± 1.2 (11); occipitonasal length, 43.8 ± 1.5 (10); braincase breadth, 17.9 ± 0.5 (11); zygomatic breadth, 23.0 ± 0.8 (10); mastoid breadth, 14.2 ± 2.1 (9); least interorbital breadth, 9.3 ± 0.4 (11); length of rostrum, 17.9 ± 0.7 (9); breadth of rostrum, 7.8 ± 0.5 (10); length of nasals, 15.9 ± 0.9 (4); length of diastema, 11.5 ± 0.4 (11); length of maxillary toothrow, 8.7 ± 0.5 (11); greatest alveolar length of M1, 2.7 ± 0.2 (10); alveolar width of M1, 2.08 ± 0.11 (6; please note this was original reported incorrectly as 4 ± 5.7 (10)); greatest length of incisive foramina, 4.07 ± 0.7 (10); palate length, 16.8 ± 0.7 (11); maxima distance between the external border of M3, 7.5 ± 0.5 (11); length of bulla, 14.0 ± 0.9 (10); length of mandibular toothrow, 9.2 ± 0.5 (11); length of mandible, 25.8 ± 1.2 (11). These 2 cited publications differ in mastoid breadth; it is possible that Mares et al. (2000) included part of the bulla in their measurement. The upper incisors are orthodont or slightly proodont, orange, narrow, and short; the lower incisors are orange, high, narrow, with a suboval section, straight lingual enamel edge, and curved labial edge; on the labial side, the enamel extends beyond one-half of the tooth face (Verzi et al. 1999; Verzi 2002). Like all octodontids, O. gliroides is characterized by ever-growing (hypsodont) molar teeth. In the upper molariforms, the folds (flexi) are absent in the adult and the posterior lobe is not extended labially. The molariforms are asymmetrical with no reentrant folds (Hutterer 1994), except in juveniles, which have flexids and fossettids (Verzi 1994; Verzi et al. 2016). Lower molariform teeth have an asymmetrical occlusal pattern, nearly figure-8 shaped, with slightly oblique and rounded lobes and shallow traces of folds; deciduous dp4 with mesoflexid reduced or absent and hypoflexid barely visible (Verzi 1994; Verzi et al. 2015a); the mesoflexid of m1 and m2 remains open in advanced stages of wear (Kramarz 2005); with mesoflexid less evident than hypoflexid (Verzi 1994); last upper and lower molars (M3/m3) reduced in size (Verzi 2002; Verzi et al. 2015a). O. gliroides has oblique, posterolabial-anterolingual, unilateral chewing (anterolingual jaw displacement and alternate occlusion); according to phylogenetic analyses, this is primitive for octodontids (Verzi 2001; Olivares et al. 2004). The masticatory direction (in molariform teeth, defined as asymmetry in dentine wear relative to the sagittal plane) is 58° in Octodontomys (Vassallo and Verzi 2001). Hutterer (1994) considered the occlusal pattern of Octodontomys to be plesiomorphic, because it matches with the molars of the Oligocene Platypittamys, a putative octodontid. The similarities in the cranial morphology of O. gliroides and the basal octodontoid rodent Prospaniomys make O. gliroides an optimal species for reconstructing masticatory muscle origins and insertions of this extinct species (Álvarez and Arnal 2015). The data matrix of Olivares et al. (2012) and Verzi et al. (2016) should be consulted for additional cranial and dental characters for O. gliroides. Álvarez et al. (2011) and Álvarez et al. (2015) examined 2- and 3-dimensional craniomandibular geometric morphometric characters in an evolutionary context. DISTRIBUTION Octodontomys gliroides has a disjunct distribution (Fig. 3) in the Andean and Sub-Andean areas of southwestern Bolivia (from La Paz Department to Tarija Department), northern Chile (Arica- Parinacota and Tarapacá regions), and northwestern Argentina (several localities in Salta and Jujuy provinces, one in La Rioja Province, being highly probably in Catamarca Province—Cabrera 1961; Mann Fischer 1978; Pine et al. 1979; Contreras et al. 1987; Mares et al. 2000; Muñoz-Pedreros 2000; Díaz and Barquez 2002; Díaz and Verzi 2006; Díaz and Barquez 2007; Verzi et al. 2015a; Rivera et al. 2016). In Argentina, this species occupies the High Andes, Monte Desert of Mountains and Isolated Valleys, and Puna ecoregions (Díaz and Verzi 2006). Ojeda et al. (2011) mentioned that O. gliroides is restricted to northern Monte of Mountains and Isolated Valleys. It is found on both sides of the Andes, a distribution marked by an east to west gradient of decreasing rainfall that results in east and west (from theAndes) populations with contrasting differences in the abundance and patchiness of vegetation cover (Rivera et al. 2014, 2016). This species has an elevation range from about 1,200 m at Villa Union in La Rioja Province, Argentina to about 4,400 m in Potosí, Bolivia. Verzi et al. (2015a) indicated that the lowest altitude for the distribution of this species is 200– 300 m. However, this information is incorrect because the data taken from Diaz and Ojeda (1999) correspond to measurements of precipitation (200–300 mm), and this information was misinterpreted by editors during the final process of editing the book Mammals of South America (Patton et al. 2015). FOSSIL RECORD Although Octodontomys gliroides has no fossil record, it is the most primitive extant octodontid. Its cranial and dental anatomy resemble some species from the Miocene and Pliocene of Argentina (Verzi and Carrín Iglesias 1999; Verzi et al. 1999; Verzi 2002; Verzi et al. 2014), suggesting that it may be an early octodontid offshoot (Verzi et al. 2015b). Gallardo and Kirsch (2001) mentioned that Verzi (1994) considered hypsodonty in Ctenomys and Octodontomys to be indicative of common ancestry and re-erected the subfamily Ctenomyinae to include these 2 genera; however, their interpretation of Verzi’s conclusion was erroneous because Verzi stated “hypsodonty has originated independently several times in rodents” (see Verzi 1994:92) and thus does not support the idea of common ancestry. Opazo (2005) estimated the divergence of Octodontomys from its sister clade (Octodon + Spalacopus + Aconaemys) at 6.07 ± 1.34 million years ago, near the end of the Miocene. This value agrees with the results of both Gallardo and Kirsch (2001), who used DNA hybridization data, and Verzi et al. (2016), using morphological and molecular data, to obtain an estimated divergence of 5–7 million years ago; but it is older than the estimate of Honeycutt et al. (2003; 2.9–4.1 million years ago) based on molecular data (nucleotide sequence data from nuclear receptor and mitochondrial genes nucleotide sequence). The morphology of the lower incisor is shared with the extinct octodontid Neophanomys, but whether this character state is primitive or derived is difficult to determine (Verzi et al. 1999). Octodontomys has been recorded in the archaeological site Inca Cueva 5 site, Jujuy Province, Argentina (2,120 ± 120 to 780 ± 100 years before present) based on 3 left mandibular rami; the area corresponds to the oriental border of the Puna steppe (Teta and Ortiz 2002). Octodontomys gliroides produces middens (amalgamations of plant remains, bones, insects, feathers, and rodent feces, glued together within a crystallized matrix of rodent urine), which have proven to be important sources of paleontological evidence (Betancourt and Saavedra 2002; Latorre et al. 2005). In the Atacama (Chile), middens have been recorded from possibly the Quaternary for O. gliroides as well as other families of rodents (e.g., Chinchillidae, Abrocomidae, and Muridae—Latorre et al. 2005). Arnal and Vucetich (2015a, 2015b) used extant species of the family Octodontidae, including O. gliroides, to revise the taxonomy of the fossil rodent Acaremys (Hystricognathi, Octodontoidea, Acaremyidae) and to analyze phylogenetic relationships of the Pan-Octodontoidea group. FORM AND FUNCTION Dental formula for Octodontomys gliroides is i 1/1, c 0/0, p 1/1, m 3/3, total 20. Buccal surfaces of the upper teeth are progressively rotated more distally from the distal to the mesial ends of the arches, with DP4 being nearly transverse to the line of the arch (Miles and Grigson 1990). O. gliroides has simplified teeth without reentrant angles or cement (Glanz and Anderson 1990). In hypsodont rodents, the enamel of the molariforms typically has a different structure on the side of first contact (leading edge) and the opposite face (trailing edge); O. gliroides is more primitive compared to Ctenomys in this regard, with Hunter– Schreger bands limited to some areas. In a study of ultrastructure of the incisor enamel and delineated morphofunctional traits among octodontoid genera with disparate digging adaptations, O. gliroides had an enamel thickness more than double that of the other taxa studied (e.g., Ctenomys, Octodon, Dactylomys — Vieytes et al. 2007). The relative thickness of external index showed the lowest values in the fossorial O. gliroides and the arboreal Bolivian bamboo rat Dactylomys boliviensis than the other species studied, and this has been interpreted by Vieytes et al. (2007) as indicative of low wear resistance. The middle ear of O. gliroides has 3 cavities: bulla, anterior, and posterior recesses. The bulla is divided into 8–10 large pneumatized air cells, and the cochlea protrudes into the tympanic cavity medially (Heller et al. 1976). In the normal ear, these structures have fairly uniform radiolucency without evidence of thickening of the septae of the bulla or areas of bony sclerosis (Heller et al. 1976). In extant species of fossorial rodents, the degree of reduction in size of the eye indicates the adaptation level to the subterranean lifestyle (Pearson 1984). The size of the orbital cavity provides information about the size of the eye and can be estimated using the zygomatic index (see Verzi 2002:316). The comparative analysis of Verzi (2008) showed that echyimid rodents have relatively larger orbits than octodontids (for O. gliroides, mean index value of 1.22, range 1.13–1.38). The eyes of O. gliroides are much larger than those of Octodon, matching the inferred crepuscular or nocturnal habits of this species (Rowlands 1974, not seen cited in Wilson and Kleiman 1974) compared to the apparently diurnal habits of Octodon (Wilson and Kleiman 1974). Vasallo and Mora (2007) included O. gliroides in an allometric analysis of the effect of size on skull attributes (development of the mandibular angle and masseteric crest, and the robustness of incisors) in ctenomyid and octodontid rodents. They concluded that in Octodontomys, as in other octodontids and in ctenomyids, mandibular width and cross-sectional shape of the incisors show a significant and positive association with basicranium length. They also noted that O. gliroides clearly differs from Ctenomys by the intensification of the hystricognath condition (lateral expansion of the mandibular angle and masseteric crest) in Ctenomys. The glans penis of Octodontomys has 2 long spines on each side of the intromittent sac (2-2 pattern), although some specimens show a 2-3 pattern (Spotorno 1979; Contreras et al. 1993); these spines are the longest among octodontids (average length 5.6 mm—Contreras et al. 1993). These features indicate that O. gliroides is more closely related to generalist and subterranean species than to Octomys or Tympanoctomys, as the 1-1 pattern is interpreted to be ancestral and the 2-2 pattern derived in extant octodontid rodents (Contreras et al. 1993). O. gliroides shows the longest baculum among octodontids, which gradually tapers from the base to the tip (Contreras et al. 1993). The vaginal wall of O. gliroides shows a hardened surface and does not have a complementary space to hold the spikes in a distal or lateral position, suggesting that they can be accommodated only when pointing backwards (Contreras et al. 1993). Cummin, Published as part of Pérez, M. Julieta & Díaz, M. Mónica, 2018, Octodontomys gliroides (Rodentia: Octodontidae), pp. 74-83 in Mammalian Species 50 (963) on pages 75-80, DOI: 10.1093/mspecies/sey010, http://zenodo.org/record/4573547, {"references":["THOMAS, O. 1902. On two new genera and rodents from the highlands of Bolivia. Proceedings of the Zoological Society of London 1: 114 - 117.","THOMAS, O. 1913. On small mammals collected in Jujuy by Senor E. Budin. Annals and Magazine of Natural History, Including Zoology, Botany and Geology, London 8: 136 - 143.","VERZI, D. H., M. M. DiAZ, AND R. M. BARQUEZ. 2015 a. Genus Octodontomys. Pp. 1043 - 1048 in Mammals of South America. Vol. 2, rodents (J. L. Patton, U. F. J. Pardinas, and G. 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T 15091 A 4493577. http: // dx. doi. org / 10.2305 / IUCN. UK. 2008. RLTS. T 15091 A 4493577. in. Accessed 24 November 2015.","OJEDA, R. A. 2012. Family Octodontidae. Pp. 189 - 191 in Libro rojo, mamiferos amenazados de la Argentina (R. A. Ojeda, V. Chillo, and G. B. Diaz Isenrath, eds.). Sociedad Argentina para el Estudio de los Mamiferos (SAREM), Buenos Aires, Argentina."]}

Identifying high-quality habitats across large areas is a central goal in biodiversity conservation. Remotely sensed data provide the opportunity to study different habitat characteristics (e.g., landscape topography, soil, vegetation cover, climatic factors) that are difficult to identify at high spatial and temporal resolution on the basis of field studies. Our goal was to evaluate the applicability of remotely sensed information as a potential tool for modeling habitat suitability of the viscacha rat (Octomys mimax), a rock-dwelling species that lives in a desert ecosystem.We fitted models considering raw indices (i.e., green indices, Brightness Index (BI) and temperature) and their derived texture measures on locations used by and available for the viscacha rat. The habitat preferences identified in our models are consistent with results of field studies of landscape use by the viscacha rat. Rocky habitats were well differentiated by the second-order contrast of BI, instead of BI only, making an important contribution to the global model by capturing the heterogeneity of the substratum. Furthermore, rocky habitats are able to maintain more vegetation than much of the surrounding desert; hence, their availability might be estimated using SATVI (Soil Adjusted Total Vegetation Index) and its derived texture measures: second-order contrast and entropy. This is the first study that evaluates the usefulness of remotely sensed data for predicting and mapping habitat suitability for a small-bodied rock dwelling species in a desert environment. Our results may contribute to conservation efforts focused on these habitat specialist species by using good predictors of habitat quality. Fil: Campos, Valeria Evelin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Universidad Nacional de San Juan. Interacciones Biológicas del Desierto; Argentina Fil: Gatica, Mario Gabriel. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales. Instituto y Museo de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico San Juan; Argentina Fil: Bellis, María Laura. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Cordoba. Instituto de Diversidad y Ecologia Animal; Argentina

Tuco-tucos (Ctenomys) and related coruros (Spalacopus) are South American subterranean rodents. An energetically demanding lifestyle within the hypoxic/hypercapnic underground atmosphere may change the selective regime on genes involved in O2 transport in blood. In addition, some species of tuco-tucos may be found at high altitude, thus facing additional reductions in changes O2 availabily. We examined sequence variation in the alpha globin subunit gene of hemoglobine in these lineages, within a robust phylogenetic context. Using different approaches (classical and Bayesian maximum likelihood (PAML/Datamonkey) and alternatives methods (TreeSAAP)) we found at least 2 sites with evidence of positive selection in the basal branch of Octodontidae, but not in tuco-tucos. These results suggest some adaptive changes associated to fossoriality, but not strictly to life underground.

Don E. Wilson, Thomas E. Lacher, Jr, Russell A. Mittermeier (2016): Octodontidae. In: Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I. Barcelona: Lynx Edicions: 536-541, ISBN: 978-84-941892-3-4, DOI: http://doi.org/10.5281/zenodo.6615351

2. Kirchners’ Viscacha Rat Tympanoctomys kirchnerorum French: Octodon des Kirchner / German: KirchnerViscacharatte / Spanish: Rata vizcacha de Patagonia Taxonomy. Tympanoctomys kirchnerorum Teta et al, 2014, “ Argentina, Province of Chubut, department of Gastre, 18 km NNE by road of Los Adobes, conjunction between Ruta Provincial 58 and Zanjon El Colorado (43°13'51.6", 68°38'49.1", 517m).” This species is monotypic. Distribution. S Argentina, known distribution limited to the type locality and surrounding areas in Chubut Province. Descriptive notes. Head-body 111-136 mm, tail 111-120 mm, ear 14-15 mm, hindfoot 29-35 mm; weight 50-80 g. Kirchners’ Viscacha Rat is slightly smaller than the Red Viscacha Rat (T. barrerae). Its skull is more bowed in dorsal profile than the Red Viscacha Rat. Color of Kirchners’ Viscacha Rat is pale brown dorsally and whitish to white ventrally. Tail is relatively long (43-50% of head-body length), with a medium terminal brush. Short, thick, and whitish hairs cover forefeet and hindfeet. Oral bristle bundles are well developed. Kirchners’ Viscacha Rat has 2n = 102, similar to that of Red Viscacha Rat. Karyotype has 32 pairs of metacentric to submetecentric chromosomes and 18 pairs of subtelocentric chromosomes. Sex chromosomes could not be discriminated but probably resembled those of the Red Viscacha Rat. Sperm morphology of Kirchners’ Viscacha Rat is smaller in size but similar in shape to that of the Red Viscacha Rat. Habitat. Sandy terrain in a general badland landscape within the Chuquiraga avellanedae (Asteraceae) steppe of the Patagonian Ecoregion at an elevation of 500 m. Burrows of Kirchners’ Viscacha Rat have typical semicircular entrances c.10 cm high, are well curved above and flat below, and are usually placed under Atriplex (Amaranthaceae) bushes. Plant cover near burrows is sparse, consisting mostly of low shrubs, such as Atriplex, C. avellanedae, Prosopis sp. and Prosopidastrum sp. (both Fabaceae), and Schinus johnstonii (Anacardiaceae). Food and Feeding. There is no specific information for this species, but Kirchners’ Viscacha Rat probably feeds mainly on halophytic vegetation (e.g. Atriplex). Breeding. There is no information available for this species. Activity patterns. There is no specific information available for this species, but Kirchners’ Viscacha Rat is apparently nocturnal. Movements, Home range and Social organization. There is no specific information available for this species, but Kirchners’ Viscacha Rat is probably solitary. Status and Conservation. As a newly described species, Kirchners’ Viscacha Rat has not been assessed on The IUCN Red List. No information is available aboutits conservation status, but its very limited distribution (restricted to the type locality) together with its recent extirpation (Late Holocene) from the Chubut River Valley and potential impact of mining in central Patagonia suggest that Kirchners’ Viscacha Rat has a high risk of extinction in the short term. Bibliography. Gallardo et al. (2009), Leon et al. (1998), Ojeda et al. (2007), Pardinas et al. (2012), Sauthier et al. (2009), Teta et al. (2014).

9. Coastal Degu Octodon lunatus French: Octodon a dents de lune / German: Kistendegu / Spanish: Degu de costa Other common names: Moon-toothed Degu Taxonomy. Octodon lunatus Osgood, 1943, “Olmue, Province of Valparaiso, Chile.” M. Tamayo and D. Frassinetti in 1980 included O. lunatus in O. bridgesii. The two are very similar and hard to distinguish, but O. lunatus has a karyotype distinct from O. bridgesii. Monotypic. Distribution. Chile’s Coastal Mountain Range W of the Central Valley, from Bosque Fray Jorge National Park (Coquimbo Region) to Quilpué (Valparaiso Region). Descriptive notes. Head—body 167-221 mm, tail length 152-161 mm; weight averaging 233 g. Proportions and color of the Coastal Degu are similar to Bridges’s Degu (O. bridgesii). Tail of the Coastal Degu is straight and shorter than head-body length (45% ofits total length), with a terminal brush. Ears are large. Pelage is dense and is a uniform ocher-brown, with white spots under axillary and inguinal parts. Chromosome complement is 2n = 78, FN = 114. Habitat. Rocky areas with dense scrublands and small forests along the coast from sea level to 1200 m. Food and Feeding. The Coastal Degu is mainly herbivorous and eats leaves, seeds, grass, and small amount of insects. In Tiltil (Santiago Metropolitan Region), diet is 75% plant tissue, 23% seeds, and 2% insects. Breeding. There is no information available for this species. Activity patterns. Apparently the Coastal Degu has variable activity patterns. Some authors reported crepuscular-nocturnalactivity, while others studies suggested diurnal activity. Movements, Home range and Social organization. There is no information available for this species. Status and Conservation. Classified as Near Threatened on The IUCN Red List. The Coastal Degu was classified as Vulnerable in 2008. Major threat is loss of habitat from agricultural expansion and livestock grazing. Bibliography. Iriarte (2008), Lessa et al. (2010), Munoz-Pedreros (2000), Munoz-Pedreros & Yanez (2009), Osgood (1943), Spotorno et al. (1995), Tamayo & Frassinetti (1980), Woods & Kilpatrick (2005)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on pages 540-541, DOI: 10.5281/zenodo.6615351

3. Golden Viscacha Rat Pipanacoctomys aureus French: Octodon doré / German: Goldene Viscacharatte / Spanish: Rata vizcacha dorada Taxonomy. Pipanacoctomys aureus Mares et al., 2000, “28 km S, 9-3 km W Andalgala; Departamento Poman, Catamarca Province, Argentina, 27° 50’ 03” 8° 66’ 15” 59” W; elevation 680 m,” Salar de Pipanaco, Saujil Department. R. M. Barquez and colleagues in 2002 treated it as Tympanoctomys based on morphological characteristics, howeverit lacks of a formal description. C. A. Woods and C. W. Kilpatrick in 2005 and M. H. Gallardo and colleagues in 2007 have continued to recognize Pipanacoctomys as a valid genus. This last revision has been followed here. Morphological data suggest a sister taxon relationship with Salinoctomys and very close relationship with Tympanoctomys. Monotypic. Distribution. NW Argentina, known only from the type locality in the Salar de Pipanaco, S Catamarca Province. Descriptive notes. Head—body 166-178 mm,tail 127-145 mm, ear 19-22 mm, hindfoot 32-40 mm. The Golden Viscacha Rat is medium-sized to large-sized. It has large and inflated auditory bullae. Dorsal pelage is golden blond, and venteris white to pale cream. Tail is long (76-85% ofits head-body length), with well-developed terminal rufous brush. Whitish hairs cover forefeet and hindfeet. Buccal bristles are present but not as developed as in the Red Viscacha Rat (7. barrerae). The Golden Viscacha Rat has a karyotype of 2n = 92, with 44-45 pairs of biarmed chromosomes and a biarmed X-chromosome and uniarmed Y-chromosome. Habitat. Edge ofsalt pans associated with peri-saline shrublands of Heterostachys sp., Atriplex lampa, and Suaeda divaricata (all Amaranthaceae). The Golden Viscacha Rat lives in a restricted, narrow band of halophytic plants that lays between bare salt flats and more typical Monte Desert habitats of Prosopis (Fabaceae), Larrea (Zygophyllaceae), and other shrubs of the Monte. Complex burrow systems are shallow and have several openings. Food and Feeding. The Golden Viscacha Rat is herbivorous and specializes on halophytic plants. It forages on Heterostachysritteriana, which has compressed leaves that form small, salt-filled balls. High salt content of these leaves cannot be reduced via mechanical means (as can leaves of Atriplex) and buccal brushes of Pipanacoctomys seem to be less well developed than those of Tympanoctomys. Breeding. Birth of a Golden Viscacha Rat was observed in October. Newborn was well haired, and eyes and ears were open within a few hours after birth. Activity patterns. There is no specific information for this species, but the Golden Viscacha Rat is considered to be nocturnal. Movements, Home range and Social organization. The Golden Viscacha Ratis ground dwelling, and apparently more than one individual can inhabit a single mound—different from the Red Viscacha Rat. Status and Conservation. Classified as Critically Endangered on The IUCN Red List. Extent of occurrence of the Golden Viscacha Rat is less than 100 km?, and its area of occupancy is less than 10 km®. All individuals occurin a single location, and extent and quality of habitat continues to decline there. Major threat to the Golden Viscacha Rat is loss of habitat to expanding olive plantations. Bibliography. Barquez et al. (2002), Gallardo et al. (2007), Mares, Braun et al. (2000), Mares, Morello & Goldstein (1985), Ojeda & Bidau (2013g), Woods & Kilpatrick (2005).

12. Chilean Rock Rat Aconaemys fuscus French: Tunduco du Chili / German: Stidamerikanische Felsenratte / Spanish: Tunduco de Chile Other common names: Great Rock Rat Taxonomy. Schizodon fuscus Waterhouse, 1842, “from Chile.” Modified by G. R. Waterhouse in 1848 to the Valle de las Cuevas near the Volcano of Peteroa, Argentina. G. R. Waterhouse in 1842 described A. fuscus based on two specimens collected by T. Bridges but never designated a type specimen, which was formally designed by O. Thomas in 1927. O. P. Pearson in 1984 summarized taxonomic history of A. fuscus. Monotypic. Distribution. Andean areas of C Chile, between Curic6 (Maule Region) and Temuco (Araucania Region) and CW Argentina (Mendoza Province), between 33° S and 41°S. Descriptive notes. Head-body 150-170 mm,tail 55-78 mm, ear 8-12 mm; weight 80-230 g. The Chilean Rock Ratis small-sized to medium-sized. Tail is relatively short (31% of its total length), without a terminal tuff, unlike other species of octodontids. Ears are small. Forelegs are strong, with long claws. Pelage is dark brown dorsally, and venteris lighter brownish yellow. Hands and feet are grayish. Karyotype is 2n = 56, FN = 108. Habitat. Rocky outcrops in highland forests of Araucaria araucana (Araucariaceae) to above Andean tree and shrub lines and flat, sandy areas covered with xerophytic shrubs and grasses such as Poa lanuginosus (Poaceae), Acacia caven (Fabaceae), Ephedra (Ephedraceae), Rosa, and Rubus (both Rosaceae), at elevations of 1000-4000 m. Food and Feeding. The Chilean Rock Rat is herbivorous and eats mainly grasses, seeds, bulbs, and roots. It also feeds on pine nuts and roots of A. aracucana and subterranean bulbs of Amarylidaceae and Alstromeriaceae. It can accumulate and store food in chambers in their burrows. Breeding. Newborn young and pregnant female Chilean Rock Rats have been recorded in spring (October-November). Activity patterns. The Chilean Rock Rat is mainly nocturnal, although daytime activity has also been reported. They only leave their burrows during the day, searching for food or to take short excursions. They have high frequency vocalizations., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 541, DOI: 10.5281/zenodo.6615351

7. Bridges’s Degu Octodon bridgesii French: Octodon de Bridges / German: Walddegu / Spanish: Degu de Bridges Other common names: Bridges's Octodon Taxonomy. Octodon bridgesii Waterhouse, 1845, “Chile.” Restricted by O. Thomas in 1927 to “Rio Teno, Colchagua,” O’Higgins, Chile. This species is monotypic. Distribution. Chile’s Coastal Mountain Range in Cauquenes (Maule Region), Tomé (Bio Bio Region), and Nahuelbuta National Park (L.a Araucania Region) W of the Central Valley, and through the Chilean Andes from Banos de Cauquenes (O’Higgins Region) to Banos del Rio Blanco (La Araucania Region) and adjacent Argentina (Lanin National Park, Neuquén Province). Latitudinal range 34-40° S. Descriptive notes Head-body 150-200 mm, tail length 102-167 mm; weight averaging 92 g. Bridges’s Degu is medium-sized. Ears are large. Tail is short (44-46% ofits total length) and straight, with a terminal brush of black hairs. Pelage is soft and is ocherbrown, with white spots underaxillary and inguinal parts. Karyotype is 2n = 58, FN = 116. Habitat. Rocky and dense scrublands in Chile and dense forests, especially of Nothofagus (Nothofagaceae), in Argentina, at elevations from sea level to 1200 m. Bridges’s Degu prefers low densities oftrees, bare ground, and dead branches. It is scansorial but can climb and build nests in vegetation. In Chile, habitats are dominated by Baccharis sp. and Podanthus mitiqui (both Asteraceae); Aristotelia chilensis (Elaeocarpaceae); Eupatorium salvia (Asteraceae); Lithraea caustic and Schinus latifolius (both Anacardiaceae); Adesmia arborea (Fabaceae); and Beilschmiedia miersii (Lauraceae). Food and Feeding. Bridges’s Degu is herbivorous and eats leaves, seeds, and grasses. The most important item on the diet is Pinus radiata (Pinaceae). Breeding. Reproductive activity of Bridges’s Degu occurs in April-December. Litter sizes are 2-3 young. Activity patterns. Bridges’s Degu is nocturnal. It can climb with help from its straight tail that rests on the ground. It is rarely seen, but its presence can be detected by its noisy alarm calls. Movements, Home range and Social organization. Average home range of the Bridges’s Degu is estimated to be 1242 m*. Status and Conservation. Classified as Vulnerable on The IUCN Red List. Major threat to Bridges’s Degu is deforestation from forestry and agricultural activities. It disappeared from the Andean range in central Chile due to habitat clearing for horticultural development, and it was extirpated in the coastal range by local intensification of agriculture in areas previously unused by local farmers. Bibliography. Gallardo (1992), Gallardo et al. (2007), Iriarte (2008), Munoz & Murua (1987), Munoz-Pedreros (2000), Mufoz-Pedreros & Yanez (2009), Ojeda & Bidau (2013c), Pearson (1995), Podesta et al. (2000), Redford & Eisenberg (1992), Saavedra (2003), Simonetti (1989a, 1994), Simonetti & Saavedra (1998), Thomas (1927a), Verzi & Alcover (1990), Waterhouse (1845)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 540, DOI: 10.5281/zenodo.6615351

4. Chalchalero Viscacha Rat Salinoctomys loschalchalerosorum French: Octodon des Chalchaleros / German: Chalchaleros-Viscacharatte / Spanish: Rata vizcacha de Los Chalchaleros Taxonomy. Salinoctomys loschalchalerosorum Mareset al., 2000, “26 km SW Quimilo, Departamento Chamical, La Rioja Province, Argentina, (30° 02’ 43.4” S, 65° 31’ 13.4” W; elevation 581 m. ” R. M. Barquez and colleagues in 2002 treated it as Tympanoctomys based on morphological characteristics, howeverit lacks of a formal description. C. A. Woods and C. W. Kilpatrick in 2005 and M. H. Gallardo and colleagues in 2007 have continued to recognize Salinoctomys as a valid genus. This last revision has been followed here. Morphological analyses suggest that Salinoctomys, which is not represented in any molecular analysis, is member of the desert-adapted clade (Octomys [Tympanoctomys + Pipanacoctomys]), with a sister relationship with Pipanacoctomys. Monotypic. Distribution. W Argentina, known only from the type locality in NE La Rioja Province. Descriptive notes. Head-body 144-156 mm, tail 111-119 mm, ear 17 mm, hindfoot 28-30 mm. The Chalchalero Viscacha Rat is medium-sized. It has large and inflated auditory bullae. Pelage is brownish black dorsally and white ventrally. Tail is long (more than 75% of head-body length) with black tuft. Whitish to pale brownish hairs cover forefeet and hindfeet. Buccal bristles are present, but they are not well developed. Karyotype is unknown. Habitat. Peri-saline shrublands associated with the Salinas Grandes salt flat at elevations of 500-600 m. The Chalchalero Viscacha Ratlives in a burrow system restricted to a narrow band of halophytic plants thatlies between bare salt flat and dense thornscrub of cacti, trees, and shrubs, typical of the Gran Chaco. Food and Feeding. The Chalchalero Viscacha Rat specializes on halophytic vegetation and seems to forage mainly on Heterostachys ritteriana (Amaranthaceae)—often most abundant in the immediate vicinity of its burrow system. It has been found in food stores in burrows. Breeding. A pregnant Chalchalero Viscacha Rat with two embryos was collected in July. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. There is no information available for this species. Status and Conservation. Classified as Critically Endangered on The IUCN Red List. Extent of occurrence of the Chalchalero Viscacha Rat is less than 100 km?, and its area of occupancy is less than 10 km? All known individuals are in a single location, and extent and quality of its habitat continues to decline. Bibliography. Barquez et al. (2002), Gallardo et al. (2007), Mares et al. (2000), Ojeda & Bidau (2013h), Woods & Kilpatrick (2005).

2. Kirchners’ Viscacha Rat Tympanoctomys kirchnerorum French: Octodon des Kirchner / German: KirchnerViscacharatte / Spanish: Rata vizcacha de Patagonia Taxonomy. Tympanoctomys kirchnerorum Teta et al, 2014, “ Argentina, Province of Chubut, department of Gastre, 18 km NNE by road of Los Adobes, conjunction between Ruta Provincial 58 and Zanjon El Colorado (43°13'51.6", 68°38'49.1", 517m).” This species is monotypic. Distribution. S Argentina, known distribution limited to the type locality and surrounding areas in Chubut Province. Descriptive notes. Head-body 111-136 mm, tail 111-120 mm, ear 14-15 mm, hindfoot 29-35 mm; weight 50-80 g. Kirchners’ Viscacha Rat is slightly smaller than the Red Viscacha Rat (T. barrerae). Its skull is more bowed in dorsal profile than the Red Viscacha Rat. Color of Kirchners’ Viscacha Rat is pale brown dorsally and whitish to white ventrally. Tail is relatively long (43-50% of head-body length), with a medium terminal brush. Short, thick, and whitish hairs cover forefeet and hindfeet. Oral bristle bundles are well developed. Kirchners’ Viscacha Rat has 2n = 102, similar to that of Red Viscacha Rat. Karyotype has 32 pairs of metacentric to submetecentric chromosomes and 18 pairs of subtelocentric chromosomes. Sex chromosomes could not be discriminated but probably resembled those of the Red Viscacha Rat. Sperm morphology of Kirchners’ Viscacha Rat is smaller in size but similar in shape to that of the Red Viscacha Rat. Habitat. Sandy terrain in a general badland landscape within the Chuquiraga avellanedae (Asteraceae) steppe of the Patagonian Ecoregion at an elevation of 500 m. Burrows of Kirchners’ Viscacha Rat have typical semicircular entrances c.10 cm high, are well curved above and flat below, and are usually placed under Atriplex (Amaranthaceae) bushes. Plant cover near burrows is sparse, consisting mostly of low shrubs, such as Atriplex, C. avellanedae, Prosopis sp. and Prosopidastrum sp. (both Fabaceae), and Schinus johnstonii (Anacardiaceae). Food and Feeding. There is no specific information for this species, but Kirchners’ Viscacha Rat probably feeds mainly on halophytic vegetation (e.g. Atriplex). Breeding. There is no information available for this species. Activity patterns. There is no specific information available for this species, but Kirchners’ Viscacha Rat is apparently nocturnal. Movements, Home range and Social organization. There is no specific information available for this species, but Kirchners’ Viscacha Rat is probably solitary. Status and Conservation. As a newly described species, Kirchners’ Viscacha Rat has not been assessed on The IUCN Red List. No information is available aboutits conservation status, but its very limited distribution (restricted to the type locality) together with its recent extirpation (Late Holocene) from the Chubut River Valley and potential impact of mining in central Patagonia suggest that Kirchners’ Viscacha Rat has a high risk of extinction in the short term. Bibliography. Gallardo et al. (2009), Leon et al. (1998), Ojeda et al. (2007), Pardinas et al. (2012), Sauthier et al. (2009), Teta et al. (2014)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 538, DOI: 10.5281/zenodo.6615351

4. Chalchalero Viscacha Rat Salinoctomys loschalchalerosorum French: Octodon des Chalchaleros / German: Chalchaleros-Viscacharatte / Spanish: Rata vizcacha de Los Chalchaleros Taxonomy. Salinoctomys loschalchalerosorum Mareset al., 2000, “26 km SW Quimilo, Departamento Chamical, La Rioja Province, Argentina, (30° 02’ 43.4” S, 65° 31’ 13.4” W; elevation 581 m. ” R. M. Barquez and colleagues in 2002 treated it as Tympanoctomys based on morphological characteristics, howeverit lacks of a formal description. C. A. Woods and C. W. Kilpatrick in 2005 and M. H. Gallardo and colleagues in 2007 have continued to recognize Salinoctomys as a valid genus. This last revision has been followed here. Morphological analyses suggest that Salinoctomys, which is not represented in any molecular analysis, is member of the desert-adapted clade (Octomys [Tympanoctomys + Pipanacoctomys]), with a sister relationship with Pipanacoctomys. Monotypic. Distribution. W Argentina, known only from the type locality in NE La Rioja Province. Descriptive notes. Head-body 144-156 mm, tail 111-119 mm, ear 17 mm, hindfoot 28-30 mm. The Chalchalero Viscacha Rat is medium-sized. It has large and inflated auditory bullae. Pelage is brownish black dorsally and white ventrally. Tail is long (more than 75% of head-body length) with black tuft. Whitish to pale brownish hairs cover forefeet and hindfeet. Buccal bristles are present, but they are not well developed. Karyotype is unknown. Habitat. Peri-saline shrublands associated with the Salinas Grandes salt flat at elevations of 500-600 m. The Chalchalero Viscacha Ratlives in a burrow system restricted to a narrow band of halophytic plants thatlies between bare salt flat and dense thornscrub of cacti, trees, and shrubs, typical of the Gran Chaco. Food and Feeding. The Chalchalero Viscacha Rat specializes on halophytic vegetation and seems to forage mainly on Heterostachys ritteriana (Amaranthaceae)—often most abundant in the immediate vicinity of its burrow system. It has been found in food stores in burrows. Breeding. A pregnant Chalchalero Viscacha Rat with two embryos was collected in July. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. There is no information available for this species. Status and Conservation. Classified as Critically Endangered on The IUCN Red List. Extent of occurrence of the Chalchalero Viscacha Rat is less than 100 km?, and its area of occupancy is less than 10 km? All known individuals are in a single location, and extent and quality of its habitat continues to decline. Bibliography. Barquez et al. (2002), Gallardo et al. (2007), Mares et al. (2000), Ojeda & Bidau (2013h), Woods & Kilpatrick (2005)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 539, DOI: 10.5281/zenodo.6615351

6. Mountain Degu Octodontomys gliroides French: Octodon a longue queue / German: Pinselschwanzratte / Spanish: Degu del Monte Other common names: Chozchori, Long-tailed Octodon Taxonomy. Octodon gliroides P. Gervais & d’Orbigny, 1844, “des Andes boliviennes, a Lapaz,” La Paz, Bolivia. Phylogenetic position of Octodontomys remains uncertain. Most molecular studies support a sister relationship with the Chilean clade (Octodon [Aconaemys + Spalacopus]), while others place it basal to the desert-adapted Argentinean clade (Octomys [Tympanoctomys + Pipanacoctomys]). Monotypic. Distribution. Andean and sub-Andean zones of SW Bolivia, N Chile, and NW Argentina. Descriptive notes. Head-body 161-182 mm, tail 100-190 mm; weight 100-200 g. The Mountain Degu is mediumsized to large-sized. Skull is nearly similar to that of species of Octomys. Rostrum is relatively long and narrow. Tympanic bullae are large and well developed, like other desert-adapted octodontids. Pelage is long and silky. Dorsal fur is grayish brown, and venteris white, with gray bases to hairs. Chin and throat are pure white. Ears are large and covered with short grayish hairs. Tail is long (c.80% of head-body length) and bicolored, with well-developed, brown-ocher brush extending from tip. Chromosome complement is 2n = 38, FN = 64. Habitat. Open, xeric, and rocky areas of the Puna, dominated by columniform cacti (Browningia, Cereus, Trichocereus, and Opuntia, Cactaceae), shrubs, and herbaceous plants, at elevations of 2000-5000 m. The Mountain Degu is a scansorial species, but it can make superficial burrows in patches of columnar and ground-level cacti or shrubs, where they feed on vegetation, hide from predators, and rear offspring. Tail is used for substrate support when climbing. Food and Feeding. The Mountain Degu is herbivorous and eats on cacti and pods and seeds of acacia (Acacia, Fabaceae). Individuals feed on acacia sheaths in winter and cactus fruits in summer; they also eat leaves and bark of resinous shrubs and can use cactus tissues to satisfy water requirements. Breeding. Gestation of the Mountain Degu is 100-109 days, with litter sizes of 1-3 offspring. Precocial young are born completely furred and with open eyes. Juveniles in various stages of development have been found in November, and pregnant females and young in January and May. Activity patterns. The Mountain Degu is nocturnal. Its activity is highest after sunset and decreases after sunrise. Movements, Home range and Social organization. The Mountain Degu is social and communicates with gurgles, twitters, and squeaks in low, mid-, and high frequencies. A recent study of two populations of Mountain Degus identified social groups of 2-3 or 2—4 individuals. Mountain Degus from the same social group always used one burrow system for resting and hiding. Males have larger home ranges than females. Status and Conservation. Classified as Least Concern on The IUCN Red List. The Mountain Degu has no apparent conservation threats, and it can live in areas of high human densities. It has a wide distribution and presumably a large overall population. Bibliography. Contreras, Torres-Mura, Spotorno & Walker (1994), Contreras, Torres-Mura & Yanez (1987), Diaz, G.B. & Ojeda (2000), Diaz, M.M. (1999), Gallardo (1992), Gallardo & Kirsch (2001), George & Weir (1972b), Honeycutt et al. (2003), Iriarte (2008), Mann (1978), Munoz-Pedreros (2000), Opazo (2005), Pine et al. (1979), Reig (1986), Rivera (2013), Rivera et al. (2014), Rowe etal. (2010), Tirira, Boada, Weksler et al. (2008a), Upham & Patterson (2012), Weir (1974)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on pages 539-540, DOI: 10.5281/zenodo.6615351

1. Red Viscacha Rat Tympanoctomys barrerae French: Octodon de Barrera / German: Rote Viscacharatte / Spanish: Rata vizcacha colorada Other common names: Plains Viscacha Rat, Red Viscacha-rat Taxonomy. Octomys barrerae Lawrence, 1941, “La Paz, Mendoza Province, Argentina.” This species is monotypic. Distribution. Patchily in arid regions of W & C Argentina, known only from 13 localities in San Juan, Mendoza, La Pampa, and Neuquén provinces (between 29° S and 38° 8S). Descriptive notes. Head-body 125-160 mm, tail 93-147 mm, ear 13-19 mm, hindfoot 30-36 mm; weight 52-104 g. Males tend to be larger than females. The Red Viscacha Rat has a relatively large head; cranial width is greater than cranial length due to extremely developed auditory bullae that are more than 45% of greatest length of skull. Dorsal pelage is reddish brown; ventral pelage is white. Tail is long (82% ofits head-body length) and terminates in a black brush. Whitish hairs cover forefeet and hindfeet. It has a specialized oral bundle of rigid hairs behind upper incisors. Kidneys are specialized with an elongated renal papilla able to concentrate urine at a maximum of 7080 mOsm/liter, similar to other desert rodents that forage on halophytic vegetation. The Red Viscacha Rat has a 2n = 102, FN = 200 karyotype, the largest in both diploid and fundamental number among mammals. Karyotype is composed of completely biarmed chromosomes that include 36 pairs of metacentric to submetacentric chromosomes, 14 pairs of subtelocentric autosomes, and a XY sex chromosome system. Sperm morphology is peculiar with a paddle-like sperm head, and sperm lengths are the largest reported for rodents. The Red Viscacha Rat was proposed to be the first tetraploid mammal known, but other studies presented evidence that its genomeis diploid rather than polyploid. Habitat. Salt basins and sand dunes in the lowland habitats of Monte and Patagonian deserts at elevations of 300-1400 m. The Red Viscacha Rat lives in complex burrow systems built in soft soil associated with sand dunes and salty environments. Each burrow system has several entry holes that connect with internal tunnels and galleries. Orientation of holes changes seasonally; in winter, holes are mostly oriented toward sunlight, and galleries are constructed so that they receive direct sunlight in winter and indirect sunlight in summer. Food and Feeding. The Red Viscacha Rat has a strictly and highly specialized herbivorous diet and feeds mainly on halophytic vegetation (e.g. Atriplex, Allenrolfea, Heterostachys, and Suaeda, all Amaranthaceae). Low proportions of species of true grasses (Poaceae) are detected in diets and are eaten in lower proportions than available. The Red Viscacha Rat scrapes surfaces of Atriplex leaves with lower incisors and oral bundle of rigid hairs behind upper incisors before consumption, which helps remove and discard salt excess on leaves and reduces salt ingestion. Breeding. On average, captive female Red Viscacha Rats have four litters per year. Neonates have closed eyes and weigh 4 g at birth. At five days of age, they weighed 8 g and opened their eyes after six days. Juveniles start to consume plants at c.10 days old, although weaning is not complete. Juveniles scrape Atriplex leaves as their mothers do. Activity patterns. The Red Viscacha Rat is normally considered to be nocturnal, but it is sometimes active during the day. Movements, Home range and Social organization. The Red Viscacha Rat is a grounddwelling solitary species and occurs at low densities. One individual lives in each burrow system. Anecdotal reports indicate that a male and a female occupy the same burrow system, probably during mating; in another case, two males were trapped in the same burrow. Isolated, patchy populations of Red Viscacha Rats are, in some cases, separated by hundreds of kilometers. Status and Conservation. Classified as Near Threatened on The IUCN Red List. Several attributes of the Red Viscacha Rat (e.g. patchy distribution, habitat and trophic specialization, and low densities) increase its vulnerability. Change from Vulnerable to Near Threatened since the last assessment reflected a better understanding of its biology within its distribution. In particular, occurrence and area of occupancy (new population records) were extended. Recent studies have detected genetic distinctiveness in some populations that could have important implications for conservation and management of the Red Viscacha Rat. Bibliography. Berman (2003), Diaz & Ojeda (1999), Diaz et al. (2000), Gallardo, Bickham et al. (1999), Gallardo, Gonzalez & Cebrian (2006), Gallardo, Kausel et al. (2004), Gallardo, Sauthier et al. (2009), Giannoni et al. (2000), Grzimek (2004), Lawrence (1941), Mares, Braun & Channell (1997), Mares, Ojeda et al. (1997), Ojeda, A.A. (2010), Ojeda, A.A. et al. (2007), Ojeda, R.A. & Bidau (2013j), Ojeda, R.A. & Diaz (1997), Ojeda, R.A., Gonnet et al. (1996), Ojeda, R.A., Roig et al. (1989), Reca et al. (1996), Sauthier et al. (2009), Svartman et al. (2005), Torres et al. (2003), Torres-Mura et al. (1989), Verzi et al. (2002), Woods & Kilpatrick (2005), Yepes (1942)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 538, DOI: 10.5281/zenodo.6615351

11. Porter’s Rock Rat Aconaemys porter French: Tunduco de Porter / German: PorterFelsenratte / Spanish: Tunduco de Porter Taxonomy. Aconaemys porteri Thomas, 1917, “Osorno, S. Chile,” slopes of Volcan Osorno, Los Lagos Region. O. P. Pearson in 1984 synonymized A. porteri with A. fuscus, but M. H. Gallardo and D. Reise in 1992 confirmed that the two were morphologically and chromosomally distinct species. Based on molecular data, A. porteri is clearly distinct from the other two species of Aconaemys and has a basal phylogenetic position to the sister pair of A. fuscus and A. sagei. Monotypic. Distribution. Andes of Argentina and Chile, in Chile it occurs from Villarica to Puyehue volcanoes (Los Lagos Region) and in Argentina it extends from Lanin to Nahuel Huapi national parks (Neuquén Province). Descriptive notes. Head-body 148-192 mm, tail 68-85 mm, ear 20-22 mm, hindfoot 30-37 mm; weight 105-160 g. Ears are small. Forelegs have long claws. Pelage is dark brown dorsally and bright rufous on ventral parts. Main feature of dentition is long and wide incisors. Karyotype is 2n = 58, FN= 112. Habitat. Mountain plains with gentle slopes, occurring in dense bamboo and southern beech forests (Nothofagus dombeyi, Nothofagaceae) at elevations of 900-2000 m. Food and Feeding. Porter’s Rock Rat is herbivorous and feed on leaves, sprouts,little branches of bamboo, and pine nuts of araucarias. Breeding. There is no specific information for this species, but an anecdotal report indicated that one female Porter’s Rock Rat had three embryos at the end of October. Activity patterns. Porter’s Rock Rat is mainly nocturnal, but it can be active during the day. During winter,it is active under snow. Movements, Home range and Social organization. Porter’s Rock Ratis colonial and fossorial. It builds networks of interconnected superficial tunnels, with entrances 1 m from each other. It lives in small groups of up to seven individuals in communal burrow systems. In some burrows, thin bamboo stems and aggregations offeces are found. Porter’s Rock Rat makes a very strong group squeak. Status and Conservation. Classified as Data Deficient on The IUCN Red List. There is an absence of information about recent extent of occurrence, conservation threats, and ecological requirements. Porter’s Rock Rat is considered rare in the Los Lagos Region of Chile. Bibliography. Chapman (2008), Gallardo & Reise (1992), Honeycutt et al. (2003), Ipinza et al. (1971), Iriarte (2008), Munoz-Pedreros (2000), Opazo (2005), Pearson (1983, 1984), Thomas (1917a), Woods & Kilpatrick (2005)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 541, DOI: 10.5281/zenodo.6615351

10. Common Degu Octodon degus French: Octodon du Chili / German: Degu / Spanish: Degli comun Other common names: Degu Taxonomy. Sciurus degus Molina, 1782, “St. Jago.” Clarified by W. H. Osgood in 1943 to “Santiago, Chile.” This species is monotypic. Distribution. NC Chile, in the lower slopes of the Andes between Atacama and Valparaiso regions (from 28° S to 35° S). Descriptive notes. Head-body 169-212 mm, tail 81-138 mm; weight 200-300 g. The Common Degu is the smallest species of Octodon. Males tend to be larger than females. Ears and eyes are large. Tail is long (40% ofthe total length) and curved and terminates in well-developed tuft with black tip. Fur is soft but coarser than in other members of the genus. Dorsal color is yellowish brown, and ventral parts are cream. Albino individuals are occasionally observed. Karyotype is 2n = 58, FN = 116. Habitat. Semiarid and Mediterranean scrubland habitats (“matorral”) on western slopes of the Andes in central Chile from sea level to 2000 m. The Common Degu occurs in open areas with limited vegetation cover, characteristic of zones with steppes dominated by Acacia caven (Fabaceae). Food and Feeding. The Common Degu is herbivorous and feeds on grasses, seeds, fruits, roots, and bark of plants such as Stipa plumosa (Poaceae), Cestrum parqui (Solanaceae), Mimosa cavenia (Fabaceae), Erodium cicutarium (Geraniaceae), Chenopodium petiolare (Amaranthaceae), Proustia cuneifolia (Asteraceae), Atriplex repanda (Amaranthaceae), and A. caven. Common Degus choose food items that reduce fiber and increase nitrogen and moisture in their diets (e.g. young leaves). They feed exclusively aboveground and have been observed climbing low shrubs while foraging. They can spend 5-6 hours/day foraging. Common Degus perform coprophagy, usually at night, which allows them to maximize their digestive efficiency. It has also been reported that Common Degus collect food and storesit in their burrows for winter consumption. Breeding. Reproduction of the Common Degu occurs in July-October. Gestation is ¢.90 days. Four to six offspring are born mainly in spring (September—October) and summer (December—January). Young are precocial, with open eyes and fur and ability to eat vegetation at c.6—10 days of age. Young are weaned at 4-5 weeks and become sexually mature at 12-16 weeks of age. In captivity, Common Degus reproduced very easily. Activity patterns. The Common Degu exhibits diurnal activity, although they are most active in morning and evening. They construct underground burrows and nest in subterranean chambers; they spend part of the time aboveground. Movements, Home range and Social organization. Common Degus are highly social and live in groups of 2-5 adult females with their young. Number of adult males per group is unclear; some authors indicate there is only one adult male per group, while others report groups with several adult males. Common Degus dig extensive communal burrow systems where members of a social group share the same burrow system, including a communal nest site. Within social groups, individuals seem to cooperate. Some individuals contribute to excavation of tunnels; in this way, they reduce per capita energetic cost of tunnel construction allowing them to construct more extensive tunnels than would be possible for one individual. They also provide communal care of young within groups. They are highly vocal and use various calls to communicate with one another, including alarm calls, mating calls, and communication between parents and young. Young Common Degus reportedly make high ultrasonic calls to elicit care from an adult. Dust bathing plays an important role in social communication among unfamiliar, same-sex conspecifics. Home ranges are small (0-04-0-71 ha). Food availability influences seasonal variation in size and location of adult homes ranges. Males and females have similar home range areas independent of season, suggesting that home ranges are influenced more by availability of food than breeding activity. Densities are c.123 ind/ha in winter and ¢.210 ind/ha in summer. Status and Conservation. Classified as a Least Concern species on The IUCN Red List. There are no major conservation threats facing the Common Degu. Bibliography. Aglero & Simonetti (1988), Contreras et al. (1987), Ebensperger (2000), Ebensperger & Bozinovic (2000a, 2000b), Ebensperger & Caiozzi (2002), Ebensperger & Hurtado (2005), Ebensperger, Hurtado et al. (2004), Ebensperger, Sobrero et al. (2008), Fernandez (1968), Fulk (1976), Iriarte (2008), Kenagy et al. (2002), Lacey & Ebensperger (2007), Lee (2004), Long (2007 2009), Mann (1978), Mella et al. (2002), Mufoz-Pedreros (2000), Ojeda & Bidau (2013e), Osgood (1943), Quirici et al. (2010), Soto-Gamboa (2004), Woods & Boraker (1975), Yanez (1976), Zunino et al. (1992)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 541, DOI: 10.5281/zenodo.6615351

Don E. Wilson, Thomas E. Lacher, Jr, Russell A. Mittermeier (2016): Octodontidae. In: Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I. Barcelona: Lynx Edicions: 536-541, ISBN: 978-84-941892-3-4, DOI: http://doi.org/10.5281/zenodo.6615351

5. Common Viscacha Rat Octomys mimax French: Octodon vizcacha / German: Viscacharatte / Spanish: Rata vizcacha del Monte Other common names: Mountain Viscacha Rat, Viscacha Rat Taxonomy. Octomys mimax Thomas, 1920, “La Puntilla, near Tinogasta...a few miles | out from Tinogasta toward Copacabana, at an altitude of about 1000 metres,” Catamarca Province, Argentina. No fossils of O. mimax are known. Monotypic. Distribution. W Argentina, in Catamarca, La Rioja, San Juan, San Luis, and Mendoza provinces. Descriptive notes. Head-body 140-330 mm,tail 105-179 mm, ear 21-4-27-4 mm, hindfoot 32:3-36-6 mm; weight averaging 95-8 g. No sexual dimorphism in body weight. The Common Viscacha Rat is mediumsized. Skull is long and slender, with large and well-developed tympanic bullae butless developed than in species of Tympanoctomys. Dorsal fur is light brown and venteris white. Tail is long (c.50% ofits total length), bicolored, and hairy, with conspicuous terminal tuft. Oral vibrissae are present, but function is unknown. Chromosome complement is 2n = 56, FN = 108. Karyotype is composed of five small submetacentric chromosomes, 21 small metacentric chromosomes, and one small subtelocentric chromosome. Xand Y-chromosomes are a small subtelocentric and medium-sized metacentric, respectively. Habitat. [Lowland deserts with abundant rocks, foothills, low scrub areas, ravines, and gorges at elevations up to 800 m. The Common Viscacha Ratis a saxicolous and surface-dwelling rodent; it is a habitat specialist that lives and constructs burrows in rock formations. It also occurs in rocky macrohabitats with creosote bush (Larrea, Zygophyllaceae), “chical” (rocky substrate dominated by Ramorinoa girolae, Fabaceae, a species endemic to the temperate Monte Desert), and columnar cactus slopes. Food and Feeding. The Common Viscacha Ratis strictly herbivorous. Diets are mainly leaves of shrubs and trees but include cacti throughout the year and seeds and fruits, principally Prosopis (Fabaceae), in the wet season. They also include Larrea, cacti, species of Amaranthaceae, and drupe-type fruits (e.g. Lycium, Solanaceae) from which it may obtain preformed water. Diet also includes seedsrich in carbohydrates, a potential source of metabolic water (e.g. Prosopis). Breeding. Most observations regarding breeding of Common Viscacha Rats are anecdotal from captured young individuals in the same trap in November at Valle de la Luna, San Juan Province; they suggest that breeding occurs at the end of winter (August) or beginning of spring (September). Activity patterns. Common Viscacha Rats are nocturnal and most active after sunset; activity decreases substantially after sunrise. They are good thermoregulators, enabling nocturnal activity. Ambient temperatures can drop below freezing at nightin the Monte Desert. Individuals use rock crevices for refuge and resting sites because they provide thermally stable environments (especially in summer). Movements, Home range and Social organization. The Common Viscacha Rat ranges over large areas and exhibits low spatial overlap; overlap among conspecificsis similar for both sexes. Average home ranges (males and females combined) are 12,370 m? however, male Common Viscacha Rats have larger home ranges than females. Common Viscacha Rats are solitary and do not share resting sites during the day. Status and Conservation. Classified as a Least Concern on The IUCN Red List. Updated information on status of populations of the Common Viscacha Rat is needed, and if current agricultural trends persist, it may qualify for a Near Threatened status. It was considered as Vulnerable in a regional IUCN assessment of threatened mammals in Argentina. Bibliography. Berman (2003), Bozinovic & Contreras (1990), Campos & Giannoni (2013), Campos, Andino et al. (2013), Campos, Giannoni et al. (2015), Contreras et al. (1994), Ebensperger et al. (2008), Gallardo (1992), Gallardo et al. (2007), Mares (1980), Mares et al. (2000), Ojeda, A.A. et al. (2013), Ojeda, R.A. & Bidau (2013f), Ojeda, R.A., Borghi & Roig (2002), Ojeda, R.A., Gonnet et al. (1996), Oyarce et al. (2003), Redford & Eisenberg (1992), Sobrero et al. (2010), Woods & Kilpatrick (2005)., Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 539, DOI: 10.5281/zenodo.6615351

Rivera, Daniela S., Vianna, Juliana A., Ebensperger, Luis A., Palma, R. Eduardo (2016): Phylogeography and demographic history of the Andean degu, Octodontomys gliroides (Rodentia: Octodontidae). Zoological Journal of the Linnean Society 178 (2): 410-430, DOI: 10.1111/zoj.12412, URL: http://dx.doi.org/10.1111/zoj.12412

Many social animals develop vocal communications to send and receive information efficiently in a group. In alarm communication, call recipients in a social group evaluate alarm calls, enhancing their probability of survival in the face of predatory threats. Calls from naive and younger group members might be less evocative, in terms of rendering group members vigilant, than calls from more experienced adults because adults are generally more reliable. It remains uncertain, however, what acoustic characteristics render an alarm call reliable. Here, we report that adult degus, Octodon degus (Rodentia, Octodontidae), produced an alarm with a frequency-modulated (FM) syllable, accompanied by low bandwidth and entropy, to evoke a high-vigilance response amongst receivers. Unlike adults, subadult degus did not emit the FM syllable in the warning context, and their call without the FM syllable evoked less vigilance than the adult alarm. We suggest that the FM structure of the adult-produced syllable serves as the primary feature characterizing a reliable alarm call. Our results are consistent with those found in other social rodents, e.g., ground squirrels and gerbils, also produce FM alarm calls in high-urgency situations supports the importance of the FM syllable in alarm communication.

Despite a century of paleontological work in Neogene sequences of northwestern Argentina there is still much to learn about the biotic diversity in this area during Pliocene times. We report a rich microvertebrate assemblage recovered from Late Pliocene deposits of Uquia Formation, Jujuy Province, northernmost Argentina. Taxa represented in the studied sample include members of Bufonidae (Amphibia: Anura), Iguanoidea (Reptilia: Squamata), Passeriformes (Aves), Argyrolagidae, Didelphidae, Caviidae, Ctenomyidae, Octodontidae, and Cricetidae (Mammalia). Taphonomic attributes indicate that the bone concentration was produced by owls. The remains were disposed highly concentrated suggesting that the assemblage would have been generated in a short lapse, indicating a low time-averaging, retaining the main ecological signals of the past living community. The studied assemblage is noteworthy because it encompasses at least five new genera of cricetid rodents, illustrating the oldest record in northwestern Argentina for this diverse family of mammals. In spite of clear taxonomic differences at specific and generic levels, the structure of the assemblage is ecologically comparable to modern small mammal communities in terms of body mass distribution, trophic structure and abundance, with a dominance of cricetids over marsupials and caviomorph rodents. Striking differences in taxonomic composition between the Uquian assemblage and the coeval record from central Argentina indicate biogeographical distinctions since the Late Pliocene. The new Uquian cricetids show that the early divergence times for phyllotine genera proposed by several authors cannot be supported. The dominance of phyllotines in the assemblage as well as the record of Microcavia and an octodontid allow inferring arid or semiarid paleoenvironment conditions, in a more or less open habitat. The studied assemblage reflects a noteworthy faunal turnover, which implies the establishment of cricetid rodents as the dominant group in the small mammal communities. This faunal change can be associated to increasing aridity during Late Pliocene worldwide.

Great genome size (GS) variations described in desert-specialist octodontid rodents include diploid species ( Octomys mimax and Octodontomys gliroides ) and putative tetraploid species ( Tympanoctomys barrerae and Pipanacoctomys aureus ). Because of its high DNA content, elevated chromosome number, and gigas effect, the genome of T. barrerae is claimed to have resulted from tetraploidy. Alternatively, the origin of its GS has been attributed to the accumulation of repetitive sequences. To better characterize the extent and origin of these repetitive DNA, self-genomic in situ hybridization (self-GISH), whole-comparative genomic hybridization (W-CGH), and conventional GISH were conducted in mitotic and meiotic chromosomes. Self-GISH on T. barrerae mitotic plates together with comparative self-GISH (using its closest relatives) discriminate a pericentromeric and a telomeric DNA fraction. As most of the repetitive sequences are pericentromeric, it seems that the large GS of T. barrerae is not due to highly repeated sequences accumulated along chromosomes arms. W-CGH using red-labeled P. aureus DNA and green-labeled O. mimax DNA simultaneously on chromosomes of T. barrerae revealed a yellow–orange fluorescence over a repetitive fraction of the karyotype. However, distinctive red-only fluorescent signals were also detected at some centromeres and telomeres, indicating closer homology with the DNA sequences of P. aureus. Conventional GISH using an excess of blocking DNA from either P. aureus or O. mimax labeled only a fraction of the T. barrerae genome, indicating its double genome composition. These data point to a hybrid nature of the T. barrerae karyotype, suggesting a hybridization event in the origin of this species.

The evolutionary pattern of the molar morphology of the small caviomorph (Octodontidae) Neophanomys from the late Miocene Cerro Azul Formation of central Argentina is analyzed. Two new species (chronomorphs) are recognized, which constitute an anagenetically evolving lineage with a gradual and directional pattern of increasing molar hypsodonty. Dental changes related to increasing hypsodonty are comparable to those of the octodontid lineage Chasichimys also recovered from the Cerro Azul Formation. However, Neophanomys shows comparatively less variation in gross morphology and there are no evidences that this lineage achieved euhypsodonty. In contrast, important changes in enamel microstructure (schmelzmuster) are observed among different populations of Neophanomys, supporting the hypothesis that these changes can occur at least partially independently from modifications in dental gross morphology. The patterns of dental evolution detected in the Neophanomys and Chasichimys-Xenodontomys lineages and the unequivocal polarity of the changes involved, related to increasing hypsodonty, reinforce the hypothesis that chronological differences exist among late Miocene outcroppings of Cerro Azul Formation in central Argentina.

Among the ecomorphologically diverse Octodontoidea rodents, fossorial habits are prevalent in Ctenomyidae and Octodontidae and occur in some members of Echimyidae. To detect traits linked to scratch-digging, we analyzed morpho-structural variation in the carpus and metacarpus of 27 species of extinct and living octodontoids with epigean, fossorial and subterranean habits. Within a context of relative morphological uniformity, we detected the following specialized traits in the burrowing Clyomys (Echimyidae), Spalacopus (Octodontidae), Ctenomys and †Eucelophorus (Ctenomyidae): broad shortened carpus, robust metacarpals, markedly broad and short metacarpal V, and predominance of ray III (mesaxony, incipient in Spalacopus). In addition, the specialized subterranean Ctenomys presented an enlarged scapholunar in extensive contact with the unciform, and with a complex-shaped proximal articular surface. These features are interpreted as responses to mechanical requirements of scratch-digging, providing greater carpal rigidity and resistance to direct forces exerted during the digging stroke. In Ctenomys, the radius-scapholunar joint restricts movement at wrist level. The phylogenetic distribution of traits shows that the most derived carpal and metacarpal morphologies occur among subterranean octodontoids, also possessing important craniodental adaptations, and supports the hypothesis that the acquisition of digging specializations would have been linked to increasing burrowing frequency in some lineages. Nevertheless, octodontoids with less morphological specializations have metacarpal modifications advantageous for digging, suggesting that scratch-digging specialization preceded the acquisition of tooth-digging traits, in agreement with the general claim that scratch-digging is the primary digging strategy in burrowing mammals.

On the basement of the library model of satellite DNA evolution is the differential amplification of subfamilies through lineages diversification. However, this idea has rarely been explored from an experimental point of view. In the present work, we analyzed copy number and sequence variability of RPCS (repetitive PvuII Ctenomys sequence), the major satellite DNA present in the genomes of the rodents of the genus Ctenomys, in a closely related group of species and forms inhabiting the Iberá marsh in Argentina. We studied the dependence of these two parameters at the intrapopulation level because in the case of interbreeding genomes, differences in RPCS copy number are due to recent amplification/contraction events. We found an inverse relationship among RPCS copy number and sequence variability: amplifications lead to a decrease in sequence variability, by means of biased homogenization of the overall satellite DNA, prevailing few variants. On the contrary, the contraction events that involve tandems of homogeneous monomers contribute—by default—minor variants to become “evident”, which otherwise were undetectable. On the other hand, all the RPCS sequence variants are totally or partially shared by all the studied populations. As a whole, these results are comprehensible if these RPCS variants preexisted in the common ancestor of this Ctenomys group. Fil: Caraballo, Diego Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentina Fil: Belluscio, Pablo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentina Fil: Rossi, Maria Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentina

SUMMARYPatterns of infection among hosts in a population are often driven by intrinsic host features such as age or sex, as well as by positive or negative interactions between parasite species. We investigated helminth parasitism in 2 South American rodent species,Ctenomys australisandC. talarum(Octodontidae), to determine whether the unusual solitary and subterranean nature of these hosts would impact their patterns of infection. We applied generalized linear models to infection data on a total of 7 helminth species (1 inC. australisand 6 inC. talarum). Host age and season of capture influenced infection levels in some of the helminth species, but none were influenced by host body condition. InC. talarum, 4 pairs of helminth species showed significant associations, either asymmetrical or symmetrical, and with 3 of the 4 being positive; strong inter-specific facilitation appears likely in 1 case. Also, we found that female hosts, especially non-pregnant ones, harboured heavier infections of 2 nematode species than male hosts. This is in sharp contrast to the general male-bias reported for most studies of nematodes in wild mammals, and we develop explanations for these results based on the unusual ecology of these subterranean rodents.

Reproductive success depends on a precise synchronization of organisms’ activities with the environment, determining the evolution of mechanisms controlling reproductive behaviour. In temperate zones mammals exhibit pronounced seasonal reproduction because of thermoregulation costs imposed by low winter temperatures and limited food availability. Even occupying burrows that buffer external ambient conditions, these restrictions also affect subterranean rodents inhabiting these latitudes. Tuco-tucos (genus Ctenomys ) are subterranean herbivorous rodents that have a Neotropical distribution between 17 and 54° of latitude S. Ctenomys rionegrensis is one of the three species occurring in Uruguay and generated interest due to chromatic polymorphism in a restricted area (50×60 km). Here we describe the timing of breeding in C. rionegrensis based on the reproductive status of free-living females and the proportion of juveniles in the population, and describe the characteristics of the estrous cycle of the species using cytological techniques. As expected, the data showed a clear seasonality in female breeding and provided evidence of the occurrence of post-partum estrous. The reproductive activity began in late austral autumn and the highest proportion of pregnant females was observed in winter. At the beginning of the austral spring, the prevalence of lactating females increased as a consequence of the first births and remained high until early summer. This pattern of breeding seasonality was clearly correlated with the annual temperature variation. The estrous cycle showed four phases characterized by both different cellular types and the abundance and appearance of mucus, which allows a clear determination of female's reproductive status.

Rodents are important components of nearly every terrestrial ecosystem and display considerable ecological diversity. Nevertheless, a lack of data on the ecomorphology of rodents has led to them being largely overlooked in palaeoecological reconstructions. Here, geometric and linear morphometrics are used to examine how cranial and dental shapes reflect the diets of living rodent species. Although most rodents are omnivores or generalist herbivores, some species have evolved highly specialized carnivorous, insectivorous, and herbivorous diets. Results show that living rodents with similar diets display convergent morphology, despite their independent evolutionary histories. Carnivores have relatively elongate incisors, elongate and narrow incisor blades, orthodont incisor angles, reduced cheek tooth areas, and enlarged temporal fossae. Insectivores display relatively degenerate dentition, elongate rostra, narrow and thin zygomatic arches, and smaller temporal fossae. Herbivores are characterized by relatively broader incisor blades, longer molar tooth rows, larger cheek tooth areas, wider skull and rostrum, thicker and broader zygomatic arches, and larger temporal fossae. These results suggest that cranial and dental morphology can be used to accurately infer extinct rodent diets regardless of ancestry. Application to extinct beavers suggests that most had highly specialized herbivorous diets.

Several competing hypotheses attempt to explain how environmental conditions affect mass-independent basal metabolic rate (BMR) in mammals. One of the most inclusive is the hypothesis that associates BMR with food habits, including habitat productivity. The effects of food habits have been widely investigated at the interspecific level, and variation between individuals and populations has been largely ignored. Intraspecific analysis of physiological traits has the potential to compensate for many pitfalls associated with interspecific analyses and serve as a useful approach for evaluating hypotheses regarding metabolic adaptation. Here we tested the effects of climatic variables (mean annual rainfall=PP, mean annual temperature=T(A)), net primary productivity (NPP) and the de Martonne index (DMi) of aridity on mass-independent BMR among four populations of the caviomorph rodent Octodon degus along a geographic gradient in Chile. BMR was measured on animals maintained in a common garden acclimation set-up, thus kept under the same environment and diet quality for at least 6 months. Mass-independent BMR was significantly different among degu populations showing a large intraspecific spread in metabolic rates. A very large fraction of interpopulational variability in mass-independent BMR was explained by NPP, PP and DMi. Our results were conclusive about the effects of habitat productivity on setting the level of mass-independent BMR at the intraspecific-interpopulational level.

The vomeronasal system (VNS) of rodents participates in the regulation of a variety of social and sexual behaviours related to semiochemical communication. All rodents studied so far possess two parallel pathways from the vomeronasal organ (VNO) to the accessory olfactory bulb (AOB). These segregated afferences express either Gi2 or Go protein alpha-subunits and innervate the rostral or caudal half of the AOB, respectively. In muroid rodents, such as rats and mice, both subdivisions of the AOB are of similar proportions; as there is no anatomical feature indicative of the segregation, histochemical detection has been required to portray its boundary. We studied the AOB of Octodon degus, a diurnal caviomorph rodent endemic to central Chile, and found several distinctive traits not reported in a rodent before: (i) the vomeronasal nerve innervates the AOB from its lateral aspect, in opposition to the medial innervation described in rabbits and muroids, (ii) an indentation that spans all layers delimits the boundary between the rostral and caudal AOB subdivisions (rAOB and cAOB, respectively), (iii) the rAOB is twice the size of the cAOB and features more and larger glomeruli, and (iv) the rAOB, but not the cAOB, shows male-biased sexual dimorphisms in size and number of glomeruli, while the cAOB, but not the rAOB, shows a male-biased dimorphism in mitral cell density. The heterogeneities we describe here within AOB subdomains suggest that these segregated regions may engage in distinct operationalities. We discuss our results in relation to conspecific semiochemical communication in O. degus, and present it as a new animal model for the study of VNS neurobiology and evolution.

By comparison with murine rodents such as rats, the middle ear structures of many subterranean mammals appear to be enlarged and thus adapted toward low-frequency sound transmission. However, comparison with closely related terrestrial outgroups has not always been undertaken, and apparent specializations in some cases might reflect phylogeny rather than habitat. Examination of the middle ear of the nonsubterranean degu (Octodon degus) under light microscopy revealed a septated middle ear cavity, a circular tympanic membrane lacking a pars flaccida, a malleus with elongated head, synostosed with the incus, a typically bicrurate stapes, and no stapedius muscle. Many of these features are shared with closely related, subterranean octodontoids in the genera Ctenomys (tuco-tucos) and Spalacopus (coruro). Caviomorph rodents in general share a very similar middle ear morphology, regardless of habitat, which suggests that sensitive low-frequency hearing is plesiomorphic for this group, rather than being specifically associated with a subterranean lifestyle.

To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 267–283. ADDITIONAL KEYWORDS: behaviour – Ctenomyidae – evolutionary morphology – Octodontidae – subterranean niche.

Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.