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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.

Athene cunicularia is a very common opportunistic raptor inhabiting diverse environments of South America. It has variable hunting behavior and diet habits, feeding mostly on arthropods and nocturnal and diurnal micromammals. We evaluated taphonomically mammal bones accumulated in pellet samples produced by this raptor recovered from different areas of Central Argentina. The sum of the observed taphonomic attributes on consumed skeletal elements (digestion, relative abundance, indexes, and breakage) allow assigning this species to the category of moderate modification, but with several attributes located in a different category with respect to previous classification. This difference may be linked with the representation and body mass of prey; when the sample has larger prey (e.g. caviomorph rodents), there is a higher degree of modification in bones. Results of this evaluation were used for comparison with paleontological and archaeological sites in Argentina, where this owl was indicated as one of the possible accumulator agents. We propose that only large fossil samples allow a good evaluation of taxonomic diversity and therefore of the prey body mass representation. Here, we applied a new categorization of rodent skull breakage. Finally, this evaluation of modern samples leads to the incorporation of molariforms of Octodontidae (Rodentia) and teeth of Chiroptera in the categories of modifications by digestion. Fil: Montalvo, Claudia I.. Universidad Nacional de La Pampa; Argentina Fil: Fernández, Fernando Julián. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tomassini, Rodrigo Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina Fil: Mignino, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Antropología de Córdoba. Universidad Nacional de Córdoba. Facultad de Filosofía y Humanidades. Instituto de Antropología de Córdoba; Argentina Fil: Kin, Marta Susana. Universidad Nacional de Córdoba; Argentina Fil: Santillán, Miguel Ángel. Universidad Nacional de La Pampa; Argentina

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

Here, a detailed description of the forelimbs and hindlimbs of all living species of the genus Tympanoctomys are presented. These rodents, highly adapted to desert environments, are semi-fossorial with capacity to move on the surface as well as to build burrows. The shape, structure, and size of the limbs are described. Contrary to what was expected for scratch digging semi-fossorial species, Tympanoctomys have slender humerus, radius and ulna; with narrow epicondyles of the humerus and short olecranon of the ulna with poorly developed processes. Following our descriptions, no intrageneric morphological variation regarding to the configuration of the limbs was detected, probably due to phylogenetic proximity, and not related to specific variations in response to different use of substrates or habits. The obtained results constitute a source of previously unpublished information as well as an important base for future analysis in different studies, such as morphometric, morpho-functional, or phylogenetic researches. Fil: Pérez, María Julieta. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Investigación de Biodiversidad Argentina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Barquez, Ruben Marcos. 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 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

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.

The genus Octodontomys contains only a single species, Octodontomys gliroides (P. Gervais and d'Orbigny, 1844), the mountain degu, found in Andean and Sub-Andean regions of 3 countries, Argentina, Bolivia, and Chile, from elevations of about 1,200'4,400 m. This fossorial octodontid is typical of dry areas, inhabits rocky zones, and is active during the day and the first few hours of night. It is not of special conservation status, being common throughout its distribution, and is considered a species of "Least Concern." Fil: Pérez, María Julieta. Universidad Nacional de Tucumán/facultad de Ciencias Naturales E Instituto Miguel Lillo/instituto de Ecología Regional; Argentina. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; Argentina Fil: Díaz, María Mónica. Fundación Miguel Lillo; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Programa de Investigación de Biodiversidad Argentina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; 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

The genome of the red vizcacha rat (Rodentia, Octodontidae, Tympanoctomys barrerae) is the largest of all mammals, and about double the size of their close relative, the mountain vizcacha rat Octomys mimax, even though the lineages that gave rise to these species diverged from each other only about five million years ago. The mechanism for this rapid genome expansion is controversial, and hypothesized to be a consequence of whole genome duplication or accumulation of repetitive elements. To test these alternative but nonexclusive hypotheses, we gathered and evaluated evidence from whole transcriptome and whole genome sequences of T. barrerae and O. mimax. We recovered support for genome expansion due to accumulation of a diverse assemblage of repetitive elements, which represent about one half and one fifth of the genomes of T. barrarae and O. mimax, respectively, but we found no strong signal of whole genome duplication. In both species, repetitive sequences were rare in transcribed regions as compared to the rest of the genome, and mostly had no close match to annotated repetitive sequences from other rodents. These findings raise new questions about the genomic dynamics of these repetitive elements, their connection to widespread chromosomal fissions that occurred in the T. barrerae ancestor, and their fitness effects ? including during the evolution of hypersaline dietary tolerance in T. barrerae. Fil: Evans, Ben J.. Mc Master University; Canadá Fil: Upham, Nathan S.. Mc Master University; Canadá. Field Museum of Natural History; Estados Unidos. University of Yale; Estados Unidos Fil: Golding, G. Brian. Mc Master University; Canadá Fil: Ojeda, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina Fil: Ojeda, Agustina Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; 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.

Systematics of fossil octodontoids (Rodentia, Caviomorpha) is in great part based on insights into the knowledge of teeth, making the step of dental characterization certainly relevant for the evolutionary reconstruction of these rodents. Different homology hypotheses were proposed for the same tooth structures, a fact that indicates the importance of knowing on which criteria the dental characters supporting the classifications were based. In this line, I evaluate the step of characterization of certain conflictive molar characters previously used, and their impact on phylogeny of octodontoids. I explore which the criteria followed to propose the hypotheses of correspondences for these characters are in light of the anatomical evidence. Based on the outcome of phylogenetic trees obtained previously, I analyze if the evolutionary transformations are compatible with character states observed in the terminals. New cladistic analyses based on recoded molar characters indicate that, unlike results recently obtained, the unorthodox position of Sallamys, Protadelphomys, and Willidewu as basal ctenomyines is not recovered. The position of Caviocricetus, Acarechimys-Neophanomysas as Octodontinae is not maintained. These results indicate that reanalyses of conflictive dental characters, scrutinizing data matrices, are particularly necessary to evaluate the current controversy on the phylogeny of octodontoids. Lower molar character definition and character states delimitation in octodontoids, being relevant to phylogenetic reconstruction, should be founded on anatomical examination, following explicit criteria of homology. Alternative hypotheses of "primary homology" proposed for the same molar traits in octodontoids indicate that each main group of caviomorphs requires its own anatomical study., Facultad de Ciencias Naturales y Museo, Consejo Nacional de Investigaciones Científicas y Técnicas

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.

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.

Endemic to South America, octodontid rodents are remarkable by being the only mammal taxa where allotetraploidy has been documented. The taxon's extensive morpho-physiological radiation associated to niche shifts has allowed testing phylogeographic hypotheses. Using maximum likelihood and Bayesian inference analyses, applied to all nominal species of octodontids, phylogenetic reconstructions based on sequences of 12S rRNA and growth hormone receptor gene are presented. Species boundaries were determined by coalescent analyses and divergence times among taxa were estimated based on mutation rates. Two main clades associated to the Andean orogenesis were recognized. The essentially western clade comprises genera Aconaemys, Octodon, Spalacopus, and Octodontomys whereas the eastern one included genera Octomys, Pipanacoctomys, Salinoctomys, and Tympanoctomys. Genetic relationships, coalescent analyses, and genetic distance supported the specific status given to Octodon pacificus and that given to Pipanacoctomys aureus as a species of Tympanoctomys. However, these analyses failed to recognize Salinoctomys loschalchalerosorum as a valid taxon considering its position within the diversity of Tympanoctomys barrerae. Although the origin of genome duplication remains contentious, the coincidence of the basal clade split with distinctive modes of karyotypic evolution across the Andes emphasizes the role of physiographic barriers and westerlies in shaping different edaphological conditions, selective grounds, and concomitantly distinct adaptations within the octodontids.

Sequence variability of RPCS (repetitive PuvII Ctenomys sequence), the major satellite DNA of octodontid Ctenomys rodents, was analysed in species belonging to three groups of species representing the two patterns of karyotypic evolution in the genus: stable and dynamic karyotypes among closely related species. The studied species represent the overall range of RPCS copy number (2000—6.6 × 10 6 copies per haploid genome) in the genus. RPCS sequence was characterised by PCR amplification of the genomic consensus sequence and cloned monomers. Our results suggest that RPCS genomic consensus sequence variability correlates with RPCS copy number stability and karyotypic stastis, but not with high or low RPCS copy number values. In contrast, the RPCS gcs shows a mutational profile that is similar across all analysed species. Our data suggest that an RPCS ancestral library of variants was maintained through the cladogenesis of the genus. There is also evidence pointing to the simultaneous contribution of processes of concerted evolution that resulted in a reduced representation of some ancestral variants and their partial replacement for new ones. In addition, analysis of distribution of the variability along the monomer suggests that subsequences of the RPCS are subject to some degree of constraint, probably driven by the recent replicative activity of RPCS in species with high copy number.

A total of 138 nematodes were found in the small intestine of Ctenomys talarum (Octodontidae) from Mar de Cobo, Argentina. A new nematode species, Pudica ctenomydis n. sp., is described. The new species more closely resembles P. pujoli Durette-Desset, 1990, parasite of Microcavia niata Thomas, from Bolivia. It can be distinguished from P. pujoli by the number of ridges and characteristics of the synlophe, the spicular morphology, differences in length between rays 9 and 10, and by the presence of a symmetrical caudal bursa and a cuticular expansion surrounding the body between vulva and anus in females.

Several factors capable of affecting the amount of resources available to an individual parasite, such as the number of other parasites in the host or host quality, may cause variability in reproductive success among parasites. Variation in egg output and mean egg volume was investigated among adult females of the nematode Graphidioides subterraneus, parasitic in the herbivorous subterranean rodent Ctenomys talarum (Octodontidae). Female nematode body size correlated strongly with the number of eggs produced. However, neither host body mass nor the number of other nematodes per host had any influence on the number or volume of eggs produced by the parasites. There was also no evidence for a trade-off between the number of eggs produced and mean egg volume among female nematodes. All these results suggest that resource supply to individual worms is not limited by host size or by the number of conspecific parasites vying for the same resources, despite the 30-fold variation in intensity of infection and the twofold variation in host body mass observed in the present study. Instead, resource availability does not appear to constrain reproduction in G. subterraneus, with its host providing a stable, predictable environment.

We present new cytogenetic, morphometric, and sperm morphology data of eight populations belonging to the C. pundti complex from Southern Córdoba and Eastern La Pampa Provinces in Argentina. The diploid numbers ranged from 2n = 44 to 2n = 50, and C- bands revealed a pattern of centromeric and pericentromeric heterochromatin. Comparisons of G-banded karyotypes revealed that the 2n = 44 (Holmberg, Santa Catalina, Sampacho), 2n = 46 (Realicó), 2n = 48 (El Guanaco, Guatraché), 2n = 46-48 (Vicuña Mackenna), and 2n = 50 (Puente Olmos) karyotypes, are closely related. In addition, these karyotypes show a high degree of homology (95%) with C. talarum talarum, despite the fact that five chromosomal rearrangements differentiate both taxa. Discriminant Function Analysis of morphometric data allows to distinguish three clusters: i) the C. mendocinus species group, ii) C. t. talarum, and iii) populations of the C. pundti complex proposed herein. The close phylogenetic relationship between C. talarum and the C. pundti complex, which undoubtedly belong to the same evolutionary lineage, is well supported by two different kinds of evidence: the extensive chromosomal homology and the same symmetric type of sperm. The morphological and chromosomal differences show that these two forms have diverged recently.

The caviomorph rodents from the San Andres Formation are revisited. The fossiliferous stratigraphic unit outcrops in the coastal cliffs of the Chapadmalal area (east-central Argentina), and represents the Late Pliocene (Upper Marplatan Stage, Sanandresian Substage). A new species of Cavia (Caviidae) and unpublished materials of Dolichotis salinicola (Caviidae) and Abrocoma (Abrocomidae) are described, and the taxonomic status of the previously described taxa is briefly discussed. The living taxa Cavia, D. salinicola and Abrocoma are first recorded in the San Andres Formation, and the extinct Abalosia (Octodontidae) is exclusive of this formation. The specimens of Abrocoma represent the single undoubted record of the living genus. The record of D. salinicola, Abalosia, Abrocoma and the octodontid Ctenomys represents an immigration event to east-central Argentina. This fauna from San Andres is the extinct caviomorph assemblage most clearly indicative of arid environments so far recorded. Its episodic character and composition, and the available palaeomagnetic data, reinforce the hypothesis that it is probably coeval with the profound Late Pliocene cooling and drying pulse detected worldwide around 2.5 Ma. The Sanandresian immigrant taxa would have inhabited the emergent semi-deserts of western Argentina, and may have reached the more eastern Chapadmalal area during an expansion of such arid environments triggered by this Late Pliocene cooling and drying pulse.

Trichuris pampeana Suriano and Navone, 1994 (Nematoda: Trichuridae) is redescribed from voucher specimens from the type host Ctenomys azarae Thomas, 1903 (Rodentia: Octodontidae) and from parasites collected from 2 populations of the subterranean rodent C. talarum Thomas, 1898 from Mar de Cobo and Necochea, Buenos Aires Province, Argentina. After a revision of these nematodes, it was confirmed that the following characters were not considered in the original description: bacillary band, cells from the esophagointestinal junction, ejaculatory duct, vas deferens, adanal papillae, vagina, oviduct, and rectum. Additional information about the spicular sheath, vulva, uteri, and ovary is provided. The morphological features given in this redescription allow to confirm the identity of T. pampeana as a valid species and also to distinguish it more clearly from other species of the genus.

Asample of 208 specimens from Ctenomys mendocinus-group species (106 females and 102 males) was studied. Five species were included in a comparative cytogenetic and morphometric analysis: Ctenomys ...

Rodents of the subfamily Ctenomyinae differentiated during the Late Miocene in relation to the development of open biomes in southern South America. This subfamily displays a peculiar and derived dental morphology characterized by euhypsodont molars with simplified occlusal figure. We analyze both adaptive and evolutionary significance of the gross molar morphology and the enamel microstructure of ctenomyines. In accordance with the basal position of the Xenodontomys lineage, dental changes experimented by this lineage illustrate a probable evolutionary pattern of acquisition of molar design for the subfamily. We propose that morphological trends in the lower molars of the Xenodontomys lineage would include changes arisen as a by-product from hypsodonty, and other adaptive ones. These latter comprise the acquisition of a crescent-shaped occlusal morphology, and the secondary acquisition of an external layer of radial enamel in the leading edge, which would favor the development of cutting edges. Such a secondary acquisition of radial enamel had not been found so far in other rodents. The evolutionary pattern of the dental changes in Xenodontomys reinforces the idea that anagenesis is frequent in the adaptive evolution of rodents.

The systematics and the geographic and stratigraphic distribution of a large and peculiar Pleistocene Ctenomys (Rodentia, Octodontidae) of Argentina are revisited. Based on the geological range of this species, and paleomagnetic and biochronological data of the bearing units, the stratigraphy and chronology of the Bonaerian Stage (Middle Pleistocene) is refined and a new biozone is proposed for the Argentine pampean region. Morphological features of this species and its association with other caviomorph taxa of Brazilian origin suggest that this rodent fauna represents an immigration event triggered by an important warm climatic pulse. We suggest that this warm pulse, the most important so far recorded for southern South America, may be correlated to the Middle Pleistocene OIS 11 recorded worldwide.

The discovery of tetraploidy in the red viscacha rat, Tympanoctomys barrerae (4 n = 102) has emphasized the evolutionary role of genome duplication in mammals. The tetraploid status of this species is corroborated here by in situ PCR and Southern blot analysis of a single-copy gene. The species meiotic configuration strongly suggests a hybrid derivation. To investigate the origin of T. barrerae further, the recently described Pipanacoctomys aureus was studied. This 92-chromosome species also has a duplicated genome size, redundant gene copy number and diploid-like meiotic pairing, consistent with an event of allotetraploidization. Phylogenetic analysis of mitochondrial sequences indicates sister-group relationships between these two tetraploid rodents. The new karyotypic data and the phylogenetic relationships suggest the participation of the ancestral lineages of Octomys mimax in the genesis of P. aureus . The high overall DNA similarity and shared band homology revealed by genomic Southern hybridization as well as matching chromosome numbers between O. mimax and the descendant tetraploid species support the notion of introgressive hybridization between these taxa. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 443‐451. ADDITIONAL KEYWORDS: allotetraploidy ‐ genome size ‐ hybridization ‐ octodontids ‐ polyploidy ‐ Tympanoctomys barrerae .

To test for the hypothesis that Ctenomys talarum can use the earth's magnetic field for spatial orientation, we carried out field and laboratory experiments to analyse if C. talarum burrows present any geomagnetic orientation in their natural habitat, if C. talarum show any spontaneous directional preference when starting to excavate their burrows and if this subterranean rodent is capable to use the earth's magnetic field to orient towards a goal in a complex maze. No correlation between the burrowing direction and the earth's magnetic field was found. We could not find any evidence for any spontaneous directional preference when starting to excavate the burrows in C. talarum. The change of the horizontal vector of the geomagnetic field did not affect the ability of this rodent to orient towards a goal in an artificial labyrinth. Explanations for these results and other possible mechanisms of orientation that could be used by C. talarum are discussed.

This work is the first report of subterranean rodent Ctenomys talarum (Rodentia: Octodontidae) as intermediate host of Taenia taeniaeformis in urban areas of Mar de Cobo (Buenos Aires Province, Argentina) and to experimentally reproduce in domestic dogs the adult stage of this parasite. Prevalence, mean abundance and mean intensity of infection with T. taeniaeformis larvae in the liver and peritoneal cavity of C. talarum were 64%, 15.3 and 9.8, respectively. Ten adults of T. taeniaeformis were obtained from experimentally infected dogs. Information about the role of subterranean rodents in the life cycle of this parasite is also given. The above mentioned data indicate that T. taeniaeformis is a frequent parasite of this species of rodents, at least within the study area. Also explanations for the high prevalence of larval forms of this parasite in C. talarum populations are given.

Molecular phylogenetic relationships were investigated in 6 species of Chinchillidae (Chinchilla lanigera, C. brevicaudata, Lagidium peruanum, L. viscacia, L. wolffsohni, and Lagostomus maximus), 1 species of Dinomyidae (Dinomys branickii), 1 of Abrocomidae (Abrocoma cinerea), and 1 of Octodontidae (Octodon degus) using the first 548 base pairs of the mitochondrial cytochrome-b gene. Maximum-parsimony and maximumlikelihood analyses consistently showed Chinchillidae as a robust clade and confirmed a close relationship with Dinomyidae. Both Chinchilla species differed at 22 sites, and 3 were nonsilent; average genetic distances were approximately 6%. Sequences from domestic C. lanigeraand wild C. brevicaudatashowed low levels of variation. Although all topologies obtained were congruent with current taxonomy, Lagidium exhibited large genetic distances (range 5.9‐8.9%), suggesting the existence of more than the 3 species currently recognized. Chinchillids are endemic South American rodents (Rodentia, Hystricognathi, Chinchillidae) and occur along the Andes. They include chinchillas (Chinchilla), mountain viscachas (Lagidium), and pampas viscachas (Lagostomus).