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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.

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.

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

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.

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.

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.

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.

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.

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.

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).

The middle ear of the solitary subterranean rodent Ctenomys talarum was studied. The most significant features observed were the enlarged middle-ear cavity, a round and larger eardrum without pars flaccida, no connection between malleus and the tympanic bone, partial fusion of malleus with incus, a nearly flat stapedial footplate, absence of stapedial artery, reduced tensor tympani, and absence of stapedial muscle. Some of these features are shared with unrelated subterranean rodents like Spalax ehrenbergi and geomyids, possibly as adaptations for low-frequency hearing.

Sperm quantity and quality were examined in 2 populations (from Mar de Cobo and Necochea, Argentina) of the subterranean rodent Ctenomys talarum (tuco-tuco) for which polygyny was confirmed as their mating system. Nonetheless, differential population attributes allow us to propose that polygyny may be exerted at different levels. Mean epididymal sperm counts were not different, but the Necochea population was characterized by higher variance in sperm counts. Low sperm production, with little variance, in the Mar de Cobo population is consistent with a more extreme polygyny, with aggression playing an important role in the males securing monopolization of females. In the Necochea population, where males were less likely to maintain female exclusivity, subordinant males are not driven away and may invest more in sperm production than in male-male interactions. However, C. talarum males from both populations produce high-quality sperm cells, based on their motility, percentage of live sperm cells, and morphology.

The red viscacha rat, Tympanoctomys barrerae , is an octodontid rodent endemic to the Monte and Patagonian deserts of Argentina. It lives in burrows with numerous portals facing different directions. We studied climatic factors as possible determinants of burrow architecture and portal orientation, in 2 populations. Climatic factors examined were sunlight, direction of sun’s rays, and wind frequency and intensity. Variables analyzed for burrow architecture were portal orientation, slope, and depth at the 1st turn. Mean number of portals per burrow was significantly different between populations. Burrows had few portals oriented toward predominantly cold and intense winds. More portals faced direct solar light in winter. Burrows are so constructed as to allow openings to receive direct sunlight in winter and indirect sunlight in summer.

We analysed the physical structure and functional interpretation of juvenile vocalizations ofCtenomys talarum Thomas, 1898. Two sounds, one true vocalization (care-elicitation call) and one mechanical sound (nursing sound) were recorded during the nestling period. Care-elicitation calls were emitted by isolated pups and caused the mother to respond by immediately approaching the pups to take care of them. This maternal response to the care-elicitation calls ofC. talarum pups, together with the production of these vocalizations during the first weeks after birth, when pups depend exclusively on their mother to obtain food and maintain their body temperature, give preliminary support for the recent theory that care-elicitation cries are honest advertisements of offspring need.

We studied morphological and functional variations in jaws of coastal and mountain populations of subterranean Spalacopus cyanus inhabiting soils with contrasting hardness. We found almost no morphological differentiation between populations in the variables we measured. However, there were clear differences in incisor resistance between them. Apparently, soil hardness did not represent a selective pressure on cururos' digging apparatus. An Andean origin of this genus could explain our results.

Daily patterns of activity were studied under laboratory conditions in 12 coruros, Spalacopus cyanus, subterranean social rodents originally from Chile. When able to burrow, coruros spent 90% of the total time underground, and surface activity occurred during the 1st hours of darkness. When prevented from burrowing, locomotory activity of coruro groups peaked near the onset of darkness but also occurred during episodes of light. Individually housed coruros displayed a clear nocturnal activity pattern. Coruros exhibited endogenous circadian rhythms entrained by a light–dark cycle.

Octodontoidea is the most diverse caviomorph clade presently represented in South America by Octodontidae, Echimyidae, and Abrocomidae. Some evidence suggests that in the past they were taxonomically even more diverse, including several independent lineages with no modern representatives, sometimes considered as families. One of them is Acaremyidae, known until now from the Colhuehuapian–Colloncuran (early to early–middle Miocene) of Patagonia. Here we describe a new octodontoid rodent from the Deseadan (late Oligocene) of Scarritt Pocket (Patagonia): Changquin woodi, gen. et sp. nov. Cladistic analysis indicates that the new species is an acaremyid related to the Santacrucian (early Miocene) Sciamys. Acaremyidae was recovered as a monophyletic group. C. woodi, gen. et sp. nov., the oldest representative of Acaremyidae, extends the family biochron back to the late Oligocene, and indicates that acaremyids differentiated before the Deseadan. C. woodi represents the first Deseadan octodontoid displaying protohypsodont cheek teeth, showing that the Deseadan was a period of important diversification for octodontoids, as it was for the cavioids. C. woodi adds a new element to the faunal differences observed between Patagonian and Bolivian Deseadan faunas. A new U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) date (27.17 ± 0.54 Ma) for Scarritt Pocket is provided., Facultad de Ciencias Naturales y Museo

The behavior of male and female Octodon degus (Hystricognathi; Octodontidae) was studied in captivity to examine the occurrence of non-parental infanticide, which involves the killing of immature infants by adult conspecifics other than the genetic parents. Sexually inexperienced male and female, and lactating female degus were tested for their behavior toward genetically unrelated, and socially unfamiliar, degu pups in a neutral arena. No male or female degu showed any sign of aggression toward the pups. Lactating females tended to exhibit the shortest latency to first behavioral interaction with the pup and the highest rate of social interactions with the pup, and they spent a relatively high proportion of their time in proximity with the pup. In contrast, males tended to show the longest latency to first pup contact and a reduced rate of interactions with the pup, and they spent a relatively small fraction of their time with the pup. The behavior of non-breeding females seemed intermediate between that of males and lactating females. Given that social and ecological conditions posed to promote non-parental infanticide in other rodents seemed not particularly different from what is known of degu biology, ecology, and social behavior, lack of degu infanticide may reflect phylogenetic inertia instead of an absence of conditions favoring infanticide.

The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae) were investigated and compared with that of more specialized fossorial rodents. An open-flow respirometry system was used to record energy expenditure of single degus inside respirometers partially filled with soft (moist) or hard (dry) soil. In addition, digging behaviour was recorded in groups of three animals inside a large terrarium under controlled conditions of food, photoperiod and temperature. In the field, the digging activity of degus was monitored, along with seasonal variations in rainfall, content of soil moisture and soil hardness. Mass-specific metabolic rate during digging was found to be higher in animals burrowing in soft soils compared to hard soil. However, animals burrowing in soft soil removed more soil per min than animals in hard soil. Thus, gram per gram, excavating in hard soil was energetically more expensive. The digging cost of semifossorial degus tends to be either similar to or above those of similarly sized, but more fossorial, rodents. In the field, heightened digging activity coincided with the occurrence of rainfall, greater content of soil moisture and relatively soft soil conditions. Degus generally use their front feet and teeth to shear the soil; disposal of accumulated debris being carried out by moving their front and hind feet backwards. We also observed the establishment of digging chains when two or three individuals burrowed at the same site. As far as digging is concerned, the behaviour of degus is similar to that of other fossorial rodents, such as African bathyergids and the more closely related South American ctenomyids.

We examined the hypothesis that a main benefit of group-living in the semifossorial rodent, Octodon degus (Rodentia: Octodontidae), is to decrease individual cost of burrow construction. We contrasted the digging behavior of groups of three same-sex, adult-sized individuals with that of solitary degus. The behavior of singles and trios was recorded inside a large terrarium partially filled with natural soil and under controlled conditions of food, light, and temperature. The observation that degus in groups do not decrease their burrowing time or frequency of digging compared with solitary diggers does not support the hypothesis that communal burrowing is a primary cause of degu sociality. On the other hand, the observation that degus in groups removed significantly more soil per capita than solitary digging degus, and that grouped individuals coordinated their digging – group members burrowed mostly in the same sites and formed digging chains –, suggests that social burrowing may potentially reduce the cost of burrow construction in the long term. We suggest that such long-term benefits will be a consequence rather than a cause of degu group-living.

Octodontid rodents have a long evolutionary history in arid landscapes of South America. The red vizcacha rat, Tympanoctomys barrerae, is a monotypic, micro-endemic species that inhabits salt pan-sand dune habitats in west-central Argentina. Its natural history is almost unknown. We present an analysis of the ecology, morphology, behavior, and physiology of the red vizcacha rat and assess the overall degree of convergence of this species with rodents that inhabit similar habitats in different deserts. Our results show that Tympanoctomys barrerae is highly adapted to salt flat basin habitats. Its diet of halophytic vegetation with a high salt content, and physiological and anatomical traits related to salt consumption, are similar to those found in some members of the families Heteromyidae (Dipodomys microps) of North America, and Muridae (Psammomys obesus and Rhombomys opimus) of Africa and Asia. Similarities include feeding behavior, diet composition, kidney morphology, and urine concentration, among other traits. Tympanoctomys barrerae is more similar to these desert rodents than it is to confamilials that do not feed on halophytes.

Two large groups of rodents inhabit South America: the hystricognaths and the murids. It has been postulated that while the former show a high degree of specialization to desert habitats, the murids are not well adapted to xeric conditions. We studied the renal structure and function of selected desertdwelling murid and octodontid (hystricognath) rodents from Argentina to evaluate levels of adaptation to aridity. Our results show that the murids Salinomys, Andalgalomys, Calomys and Eligmodontia have the highest renal indices and urine concentration among Argentine desert rodents. The octodontid Tympanoctomys barrerae shows higher renal indices and urine osmolarity than those of its close relatives Octomys mimax and Octodontomys gliroides. We compare the renal traits of the Argentine desert murids with those of other world-desert rodents such as North American heteromyid rodents. The results show that these Argentine murid rodents posses renal adaptations to conditions which are as impressive as those of both octodontids and the classic desert-adapted heteromyids.

Subterranean rodents are interesting organisms for communication studies because of their fossorial way of life. Acoustic communication in the South American genus Ctenomys has not yet been studied even though this species is geographically widespread. This paper represents a preliminary survey of Ctenomys vocalizations. Three types of vocal signals were identified: S-, C- and G-signals. Using field, laboratory and literature data, we provide interpretations on the possible functions of these signals. S-signals are harsh and low-pitched putative spatial localization signals that may also encode for sexual identification. C-signals are relatively high-pitched and narrow-banded FM vocalizations that are sexual signals used by females in a copulatory context. Finally, G-signals are harsh and patternless sounds that are aggressive signals used in direct encounters with con- or hetero- specific individuals.

Five captive adult female degus ( Octodon degus ) were offered leaves and twigs to eat from three woody ( Adesmia bedwellii , Porlieria chilensis and Proustia pungens ) and two suffruticose ( Baccharis paniculata and Chenopodium petiolase ) shrubs that provide cover in their natural habitat. The degus discriminated among the plant species, consuming lower amounts of P. chilensis . Daily body mass losses of degus were significantly higher when they were fed upon P. pungens and P. chilensis . The nutritional value of plants, concomitant with degu nutritional requirements, may explain changes in shrub cover previously found to follow removal of degus from experimental plots.

As part of a study on the ecological strategies related to adaptation to the subterranean habitat of genus Ctenomys (tuco-tucos), a natural population of C. talarum was live-trapped at Necochea (Buenos Aires Province, Argentina) with the aim of providing information on its population ecology. Population size was consistently low throughout the study and was related to the low habitat productivity. Mortality rates were low, although for juveniles the estimations were higher than for adults. Individuals have an average life expectancy of 22-25 months, but some individuals lived at least three years. Reproductive activity started by July and ended by March, when last known pregnancies were recorded. This long reproductive season allowed a gradual incorporation of young over an extended period of time, with a restricted period of recruitment lacking. Sex ratio did not depart from 1:1 and appears to be density dependent. The spatial distribution of individuals was clumped and corresponded to the patchy distribution of suitable habitats. The results are compared and contrasted with those from previous demographic studies performed in other conspecifics as well as in other subterranean rodents.

Two species of tuco-tucos, Ctenomys talarum and C. australis, overlap geographically in south-eastern Buenos Aires Province, Argentina. C. talarum (100-180 g) occupies habitats with clayey and harder soils, while the larger C. australis (300-600 g) occupies sandy and quite friable soils. This study compares the digging apparatus and digging performance of both species, and also provides additional ecological data to describe the adaptations of both species. When confronted with sandy, friable soils, both tuco-tucos exclusively use their forelimbs (‘scratch digging’ mode) to break the soil. When confronted with harder and clayey soils, C. australis used its forelimbs and, less frequently, its incisors, but no appreciable effectiveness was observed in breaking the soil. On the other hand, C. talarum behaved as a ‘scratch’ and ‘chisel-tooth digger’ species, using both forelimbs and incisors to dig tunnels in extremely hard soils. C. talarum showed relatively larger forelimb extensors than C. australis. Moreover, I hypothesize that the structure of the ulna in C. talarum may increase the effective forces of the digital and carpal flexors, thus accounting for the enhanced digging ability in this species. Outward forces exerted by the distal elements (claws-digits-carpals) when forelimbs impact the soil appear to be a critical factor in loosening soil fragments. In addition, the increased upper incisor procumbency of C. talarum correlated with an effective chisel-tooth digging behaviour. Finally, I briefly examine phylogenetic and biogeographical factors that may account for some C. australis morphological and physiological traits. It is suggested that the digging ability of C. australis could be a by-product of its larger size, a likely adaptation to evade predation.

A new living species of the desert-adapted tetraploid rodent Tympanoctomys (Caviomorpha, Octodontidae) is described. The new form is restricted to the type locality in Chubut Province, central Patagonia, Argentina, although is known from at least 4 additional Holocene-aged localities along the middle and lower valley of the Chubut River. Tympanoctomys sp. nov. is smaller than the living T. barrerae, its general coloration is yellowish (reddish in T. barrerae ) and its tail is equal to ~ 43–50% of head and body length (~49–53% in T. barrerae). Its skull and dentition are characterized by a unique combination of morphological traits, including narrow and posteriorly acuminate nasals (broad and barrel-shaped in T. barrerae ), supraoccipital not laterally expanded (expanded in T. barrerae), and 8-shaped lower 3rd molar (comma-shaped in T. barrerae and † T. cordubensis). Morphometric and genetic evidence supports the specific distinction of this Patagonian endemic Tympanoctomys, also characterized by smaller sperm than T. barrerae . The reduced range of the new species, coupled with its recent extinction from the Chubut River valley and the potential impact of large uranium mining projects in central Patagonia, suggest that this species faces a severe extinction risk in the short term. Fil: Teta, Pablo Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Pardiñas, Ulises Francisco J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Udrizar Sauthier, Daniel Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina Fil: Gallardo, Milton H.. Instituto de Ciencias Marinas y Limnológicas. Universidad Austral de Chile; Chile

Multiple ecological factors are known to drive variation in social behavior. However, group-living in some species appears to be highly conserved, suggesting a phylogenetic influence. In this study, we evaluated both scenarios using intraspecific and interspecific comparisons across octodontid rodents. We first examined 2 different populations of Andean degu (Octodontomys gliroides), representing 2 extremes of a climate vegetation gradient across the Andes range. We evaluated how ecological variation in terms of abundance and distribution of food resources, predation risk, and burrowing costs predicted interpopulation variation in group size and range-area overlap (2 proxies of sociality). We estimated these measures of sociality from livetrapping and radiotelemetry. We then used phylogenetic methods to determine whether sociality exhibits a phylogenetic signal and reconstructed the ancestral state of sociality across the family Octodontidae. Overall activity of females and males of O. gliroides ...

The degu, Octodon degus (Rodentia, Octodontidae) is a diurnal herbivore inhabiting the semiarid and mediterranean environments of northern and central Chile. In the field, degus are constrained to specific foraging areas, mainly by their limited thermal tolerance and by environmental food quality. Consequently, we hypothesized that degus must balance their diet selection by maximizing nutrients/digestible energy intake, in the face of their time and digestive constraints and seasonal/spatial changes in food quality; and by minimizing thermoregulatory risk, in the face of their low evaporative water loss and seasonal/spatial changes in environmental temperatures among foraging areas. This hypothesis was tested in a series of diet selection experiments conducted in an experimental arena, as well as in nutritional trials, involving synthetic diets with different fiber content and thermal patches. As predicted, results of the arena food selection experiments, as well as the nutritional trials, demonstrated that O. degus prefers items of low-fiber composition. However, food selection is compromised by seasonal and spatial changes in food quality and environmental temperatures, coupled with feeding time and digestive and thermoregulatory constraints.

The paper describes the breeding biology of the South American herbivorous fossorial rodent Ctenomys talarum (tuco-tuco), covering the following aspects: length of breeding season, prenatal mortality, mean litter size and its correlates, sex ratio and its density-dependence, and late sexual maturity of both sexes. These parameters are compared and contrasted with those of other conspecifics and other subterranean rodents.

We report the southernmost record for the octodontid rodent T. barrerae, which is also the second recording locality for this species in Patagonia. The new locality is placed in S Neuquén province (39º12´37.5"S, 70º3´32.9"W), extending the known range of the species about 150 km SW from the nearest previous record. Although T. barrerae is considered a highly specialized rodent of salar flats in Monte desert, the record reported here came from an arbustive rocky environment belonging to the Monte-Patagonia ecotone. Fil: Bernardis, Adela María. Universidad Nacional del Comahue; Argentina Fil: Formoso, Anahí Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Pardiñas, Ulises Francisco J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

The viscacha rat Octomys mimax is endemic to western Argentina; it inhabits lowland deserts and uses rocky crevices as resting sites. The aim of this study was to assess macrohabitat selection relative to the occurrence of rocky crevices and to evaluate seasonal variations in macrohabitats selected by this rodent in Ischigualasto Provincial Park, San Juan, Argentina. Random locations were classified as used or available based on signs recorded in rocky crevices. We confirmed the absence of the viscacha rat in macrohabitats with sandy or silty substrates. We provide new records of viscacha rat in creosote bush scrub, the most abundant macrohabitat of the Monte Desert. This result extends the known range of macrohabitat use for this species. The viscacha rat increased the number of rocky crevices used in the dry season, probably because the species increased its foraging area due to the low food resource abundance. Another possible reason is an increase in density due to new births and dispersal of young in this season. The present study highlights the importance of considering signs of presence for species with low capturability as well as of collecting data throughout multiple seasons for a better understanding of habitat selection and species distribution. Fil: Campos, Valeria Evelin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; Argentina Fil: Giannoni, Stella Maris. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Caviomorph rodents represent one of the most distinctive groups of mammals in southern South America drylands; they colonized South America from Africa via trans-oceanic dispersions in the Eocene (40-50 Ma) and underwent an extraordinary ecological radiation after their arrival, thus making this group of great interest for biogeographic and evolutionary studies. The aim of this article was to provide a working hypothesis regarding the biogeographical history and ecological diversification of one of its conspicuous families, the Octodontidae. We reconstruct the evolutionary theater where their ecological diversification took place, and potential events of dispersal, vicariance and extinctions. We analyzed the historical biogeography of the Octodontidae across the eight ecoregions where they occur, based on species phylogeny and divergence times. Four approaches were used to reconstruct ancestral area: (1) Statistical Dispersal-Vicariance Snalysis (S-DIVA); (2) Bayesian binary Markov chain Monte Carlo (MCMC) analysis implemented in Reconstruct Ancestral State in Phylogenies (RASP); (3) Fitch optimization method; and (d) weighted ancestral area analysis (WAAA). Parsimony ancestral state reconstructions were implemented in order to explore the evolutionary history of an ecological character, mode of life. We propose the northern portion of the Monte desert ecoregion as the ancestral area in the evolution of the Octodontidae, with subsequent dispersal and enlargement of the family geographic range. The evolution of their ecological specialization (i.e. modes of life) suggests an ambiguous ancestral condition (saxicolous, generalist terrestrial, semifossorial) linked to species adaptation to arid environments, with fossoriality appearing later in octodontid evolution. The evolution of the Octodontidae is associated with contrasting environmental conditions (i.e. climate and vegetation) produced by the Andean Uplift between eastern and western sides. Fil: Ojeda, Agustina Alejandra. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg de Invest. de Las Zonas Aridas; Argentina; Fil: Novillo, Agustina. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg de Invest. de Las Zonas Aridas; Argentina; Fil: Ojeda, Ricardo Alberto. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - Mendoza. Instituto Arg de Invest. de Las Zonas Aridas; Argentina; Fil: Roig Junent, Fidel Alejandro. Consejo Nacional de Invest.cientif.y Tecnicas. Instituto Arg.de Nivologia,glaciologia y Cs.ambient.; Argentina

Predation by owls upon two sympatric species of subterranean rodents of the genus Ctenomys was studied by comparing characteristics of individuals that were field-trapped and preyed upon. Predators took a greater proportion of the smaller C. talarum than of the larger C. australis in comparison to that estimated from their respective field densities. Only subadult individuals of C. australis were found among pellets. For C. talarum , a greater proportion of subadults than of adults was observed in pellets. We suggest that this pattern is determined both by constraints imposed by size of prey on the ability of a predator to handle large prey and by greater exposure of dispersing subadults to predation. Differential predation possibly maintains the habitat segregation observed between C. talarum and C. australis .

Members of the genus Ctenomys (tuco-tuco; Rodentia: Caviomorpha: Octodontidae) are considered scratch diggers. We compared the forelimbs of adult C. azarae with those of 13 species within other genera of caviomorph rodents to identify morphofunctional variation in osseous elements related to fossorial habits. Eight measurements of the humerus and ulna were used to construct five functional indices that were subjected to principal components analysis and simple comparisons among means. Ctenomys has a general morphology similar to that of terrestrial caviomorph rodents but exhibits some features that reflect its specialized fossorial condition, such as its comparatively large epicondyles. These features indicate greater muscular development and capacity for force production in the pronators and supinators of the forelimb and manus and flexors of the manus. The deltoid complex is well developed, indicating a large moment arm for the deltoid and latissimus dorsi muscles, which increases the capacity for force production on humeral flexion. Humeral indices are the best for differentiating fossorial forms from diggers, occasional diggers, generalized, and cursorial forms. Limb bone segments are used differently by highly fossorial and scratch-digging forms., Facultad de Ciencias Naturales y Museo

The rodent superfamily Octodontoidea comprises 6 families, 38 genera, and 193 living species of spiny rats, tuco-tucos, degus, hutias, and their relatives. All are endemic to the Neotropical Region where they represent roughly three-quarters of extant caviomorphs. Although caviomorph monophyly is well established and phylogenetic hypotheses exist for several families, understanding of octodontoid relationships is clouded by sparse taxon sampling and single-gene analyses. We examined sequence variation in one mitochondrial (12S rRNA) and three nuclear genes (vWF, GHR, and RAG1) across all caviomorph families (including 47 octodontoid species), all phiomorph families, and the sole remaining hystricognath family, using the gundi ( Ctenodactylus ) and springhaas ( Pedetes ) as outgroups. Our analyses support the monophyly of Phiomorpha, Caviomorpha, and the caviomorph superfamilies Cavioidea (Dasyproctidae, Cuniculidae, and Caviidae, the latter including Hydrochoerus ), Erethizontoidea, Chinchilloidea (including Dinomyidae), and Octodontoidea. Cavioids and erethizontoids are strongly supported as sisters, whereas chinchilloids appear to be sister to octodontoids. Among octodontoids, Abrocomidae is consistently recovered as the basal element, sister to a pair of strongly supported clades; one includes Octodontidae and Ctenomyidae as reciprocally monophyletic lineages, whereas the other includes taxa currently allocated to Echimyidae, Capromyidae and Myocastoridae. Capromys appears near the base of this clade, in keeping with current classification, but Myocastor is nested securely inside a clade of Echimyidae that also contains eumysopines, echimyines and dactylomyines. Another, more weakly supported clade of Echimyidae contains fossorial and scansorial taxa from the Chaco–Cerrado–Caatinga and the Atlantic Forest. Biogeographic analyses robustly recover the Patagonia–Southern Andes complex as ancestral for the Octodontoidea, with three component lineages emerging by the Oligocene–Miocene boundary (∼23 Ma): (1) stem abrocomids in the Central and Southern Andes; (2) a lineage leading to octodontids plus ctenomyids in Patagonia, later dispersing into the Chaco–Cerrado–Caatinga; and (3) a lineage leading to echimyids, capromyids, and myocastorids that subsequently radiated in more mesic biomes, including Amazonia, Atlantic Forest, and the Antilles. This reconstruction refutes earlier ideas that the diverse, generalized, mainly lowland family Echimyidae, which appears early in the fossil record, gave rise to the Andean lineages of octodontoids—instead, the reverse derivation appears to be true. We recommend formal synonymy of Myocastoridae with Echimyidae but defer a similar treatment of Capromyidae until additional hutia taxa and sequences can be analyzed.

Morphological variation in the glans penis of the six genera and most species of octodontid rodents was studied and compared to members of the Abrocomidae and Ctenomyidae. Most specimens of Octodon degus, O. lunatus, O. bridgesi, Octodontomys gliroides, Aconaemys fuscus , and A. sagei presented two spikes on each side at the bottom of the intromitent sac (2–2 pattern), although the number of spikes varies from 1–2 to 4–5. The largest variability in number of spikes was shown by Spalacopus cyanus , ranging from 1–1 to 4–5; although they were rather short. The 1–1 pattern characterized Tympanoctomys barrerae and Octomys mimax . This pattern was found in the species of the genera Abrocoma and Ctenomys , which belong to the related families Abrocomidae and Ctenomyidae. Our results support the view that the 1–1 pattern is ancestral and that other patterns are derived states. Within the octodontids, only Tympanoctomys barrerae and Octomys mimax showed the ancestral condition shared with Ctenomyidae and Abrocomidae. All other octodontid genera share the derived state 2–2 or modifications of it.

A removal trapping experiment was conducted in the field to investigate if microhabitat choice and population characteristics of Ctenomys talarum are affected by the bigger, dominant Ctenomys australis, in a zone where these subterranean rodent species are geographically sympatric. As reported previously by other authors, the species were distributed in a habitat segregation pattern which characterized the initial state, prior to C. australis removal. I detected a significant habitat shift-that is, changes in microhabitat choice by C. talarum individuals- in response to C. australis removal. However, it is remarkable that this only occurred after one year of continuous removal of C. australis, and was restricted to a very small expansion by C. talarum into the fringe of the area previously occupied by the dominant species. In addition, a slight increase of the C. talarum population density took place which was possibly due to the absence of the other species. It is suggested that the microhabitat typical of C. australis (with deeper, more friable soil and less vegetation) could be suboptimal and thus unpreferred for C. talarum. If the pre-experimental C. talarum population was satiated to its carrying capacity, it is possible that the small number of C. talarum individuals-mostly subadults-had invaded areas previously occupied by C. australis because they had no other choice than a suboptimal habitat. No substantial changes were detected in other population characteristics (sex ratio, age structure, distance between individuals) which were very similar to that in a control area. Interspecific interactions and displacement by the bigger C. australis could be significant but nonetheless marginal in sustaining the pattern of microhabitat segregation between the species. Difference in habitat preference, linked with species differences in body size and colour, are probably of much greater importance.

Octomys mimax O. Thomas, 1920, the viscacha rat, is a surface-dwelling rodent, endemic to the Monte biome of western Argentina. The genus Octomys is monotypic and represents a basal clade within the family Octodontidae. O. mimax is strictly herbivorous and is found in low-elevation arid environments characterized by galleries or rock formations. In these environments, O. mimax nests within rock crevices located inside ravines with relatively low vegetation cover. O. mimax is solitary and mostly nocturnal. Nocturnal activity coupled with a basal metabolic rate and thermal conductance lower than expected for body mass of O. mimax probably represent strategies for water conservation in this species. DOI: 10.1644/853.1.

The red viscacha rat, Tympanoctomys barrerae, is an octodontid rodent endemic to the arid west-central and southern regions of Argentina. It is solitary, lives in complex burrows built in soft soil, and occurs at low population densities in patches associated with salt basins and sand dunes in lowland habitats of the Monte and Patagonia deserts. The purpose of this study was to investigate the genetic structure and biogeography of this desert specialist. To assess genetic variation an 800-base pair fragment of the mitochondrial control region was sequenced for 60 individuals from 8 localities across the species’ range. Relationships among haplotypes were inferred from phylogenetic analyses (maximum parsimony, Bayesian, and networks). Genetic structure and demographic history were analyzed with descriptive statistics, mismatch distributions, neutrality tests (Tajima’s and Fu’s), and analyses of molecular variance (AMOVAs). In total, 26 haplotypes were found, most restricted to single populations. The presence of unshared haplotypes was consistent with low migration rates. Within the distribution (between 29uS and 39uS) southern and northern populations showed higher genetic diversity values than central populations. Populations of T. barrerae showed moderate to high genetic differentiation on the basis of haplotypes of central populations. AMOVA analyses indicated a moderate level of geographic structure for all populations. Low haplotype and nucleotide diversities in central populations suggest a possible bottleneck associated with Pleistocene glaciations or volcanic activity in this part of the range of the viscacha rat. Phylogeographic structure was moderate, and the analyses recovered 2 principal clades: A (with central and a part of the southern distribution) and B (with northern and another part of the southern distribution). Most populations were polyphyletic, indicating that they have not been isolated long enough to reach reciprocal monophyly. Demographic analyses conducted for clades A and B suggest a recent history of population expansion. DOI: 10.1644/09-MAMM-A-177.1.

Six geographic samples of the fossorial genus Aconaemys were studied to determine differences in cranial morphometrics, pelage coloration, and karyotype. Results showed variation that departs significantly from previous works. Distinct karyotypes were found for each nominal form. Using cluster analysis and discriminant-function analysis, contrasting patterns of cranial morphology are demonstrated that show A. fuscus to be as distinct from A. sagei as is A. porteri . Despite a certain degree of overlap in qualitative cranial characters and pelage coloration, three monotypic species of Aconaemys are recognized.

To identify wild hosts of Trypanosoma cruzi, surveys were conducted in the subandean valleys of Jujuy Province, Argentina, between June 1986 and March 1987. Seventy two mammals from 13 different species were examined by xenodiagnosis. Fifty two of them were mostly rodents trapped at the localities of Maimará, León and Tilcara, and the remainder had been kept in captivity at the Estación Biológica Experimental, in Jujuy. Trypanosoma cruzi infection was detected only in 2 Octodontomys gliroides (2 pos./8 exam. 25%) from all 72 examined mammals. Isolates were called Octodontomys Argentina 1 and 2 (OA1 and OA2). Both infected animals were caught at the archaelogical ruin of Pucará, at Tilcara. Repeated searches for triatomines in the ruin itself and in neighbour houses rendered negative results. Groups of mice inoculated with either OA1 or OA2 isolates became infected between 7 (OA1) to 12 days (OA2) postinoculation PI. Parasitemia peaks were observed between day 12th-14th PI. Scarce amastigote nests were found in myocardium and skeletal muscle. Mortality was observed only for mice inoculated with OA1. Isoenzyme patterns of OA1 and OA2 were identical to one found in dogs and slightly different from that of human parasites in Argentina. Bones from Octodontomys sp., were recently found in a cave, dated 10200-8600 BC, in Pumamarca, near Tilcara, Jujuy. There are evidences that O. gliroides cohabited with man in ancient times and was associated to the domestic cycle of T. cruzi transmission, playing a role like that of domestic caves in Bolivia. Fil:Schweigmann, N.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Pietrokovsky, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Wisnivesky-Colli, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Karyotypic evolution in the Octodontidae and Abrocomidae is examined by use of C-bands. Karyotypic pathways illustrate chromosomal rearrangements that are more varied than previously thought. A superimposition of tandem fusions and non-Robertsonian mechanisms involving euchromatic segments accounts for the pattern of variation observed. Hetero-chromatic short arms, although present, do not explain the general biarmed karyotypic condition observed across the genera. Evolution of heterochromatin has proceeded through whole-arm additions and euchromatin transformation, and has been independent of the bidirectional changes in diploid number. The magnitude of the karyotypic differences within the Octodontidae reflects its extensive adaptive radiation in the past, although the family is now represented by relatively few species.