Caviomorph Research Articles

Human and hutia (Isolobodon portoricensis) interactions in pre-Columbian Hispaniola: The isotopic and morphological evidence

There are certain animal candidates for which researchers have long speculated as having been managed, or possibly domesticated, by indigenous peoples in the pre-Columbian Caribbean, the primary candidate being some members of a group of caviomorph rodents known as hutia (Capromyinae). This study comprises an isotopic and morphological investigation of the potential management of an extinct species endemic to Hispaniola, the Puerto Rican hutia (Isolobodon portoricensis). For comparisons, isotopic analysis was conducted of bone collagen samples examining carbon (∂13Cco) and nitrogen (∂15N) values of I. portoricensis with two other species of endemic hutia, guinea pig (Cavia porcellus), Antillean slider (Trachemys stejnegeri), rhinoceros iguana (Cyclura cornuta) and edible rat (Brotomys sp.) from four sites in the Dominican Republic: El Flaco, El Carril, El Cabo and La Entrada. This data was compared to human and dog collagen values available from El Flaco to assess similarities between these groups. Osteometric data was recorded for hutia mandibles, allowing for body mass estimations (n = 230). The findings suggest that some Isolobodon portoricensis specimens possessed carbon (δ13Cco) values similar to humans and dogs at El Flaco, possibly associated with the consumption of agriculturally produced maize. This research does not indicate whether domestication or management of this species was occurring, at least not in a systematic way. Concurrence with palaeoenvironmental and zooarchaeological data from the region in which El Flaco and El Carril are located indicate that indigenous agricultural practices may have affected populations of hutia, perhaps by attracting them and supporting them within anthropogenic mosaic landscapes. The data also suggests that some degree of either purposeful feeding or scavenging from human agricultural plots was occurring and supports some degree of commensalism between humans and Puerto Rican hutia at these sites.

Comprehensive total evidence phylogeny of chinchillids (Rodentia, Caviomorpha): Cheek teeth anatomy and evolution.

Rodents are the most diverse order of extant mammals, and caviomorph rodents, or New World hystricognaths, have a remarkable morphological disparity and a long fossil record that begins in the Eocene. Chinchilloidea is a poorly understood clade within Caviomorpha, from an evolutionary and phylogenetic perspective. It includes the extant families Chinchillidae and Dinomyidae, the extinct Neoepiblemidae and Cephalomyidae, and several extinct chinchilloids without a clear phylogenetic position, like Eoincamys, Borikenomys, Chambiramys, Ucayalimys, Incamys, Saremmys, Garridomys and Scotamys. The family Chinchillidae includes the extant Chinchilla and Lagidium, grouped in Chinchillinae, and the only living Lagostominae, Lagostomus maximus. Among extinct chinchillids, Eoviscaccia (early Oligocene-early Miocene of Argentina, Bolivia and Chile), Prolagostomus (early-middle Miocene of Argentina, Bolivia and Chile) and Pliolagostomus (early-middle Miocene of Argentina) are the only genera originally described as members of the family. Based on the study of specimens with unworn or little-worn cheek teeth, belonging to extinct and extant taxa, we propose homologies of the cheek teeth structures and perform a combined molecular and morphological phylogenetic analysis including extinct and extant taxa of all families of Chinchilloidea and all genera of Chinchillidae. Our phylogenetic analysis recovered three major lineages in the evolutionary history of Chinchilloidea. The first major lineage is composed of the extant taxa Chinchilla, Lagidium and Lagostomus, and the extinct genera Eoviscaccia, Prolagostomus, Pliolagostomus, Garridomys, Incamys, Loncolicu and Saremmys. Cephalomyid (Banderomys, Cephalomys, Litodontomys, Soriamys) and neoepiblemid (Neoepiblema, Perimys, Phoberomys, Scotamys) genera are part of the second major lineage, while dinomyids such as Dinomys, Drytomomys, Scleromys, 'Scleromys' and Tetrastylus constitute the third major lineage within Chinchilloidea. The phylogenetic position of some taxa previously considered as incertae sedis chinchilloids or without a clear suprageneric group (i.e. Incamys, Saremmys, Garridomys and Loncolicu) show that they belong to pan-Chinchillidae and conform the stem Chinchillidae along with Eoviscaccia. The euhypsodont crown Chinchillidae includes the living subfamilies Chinchillinae and Lagostominae. Dinomyidae and Eoincamys pascuali are recovered as the sisters of a major clade composed by 'Cephalomyidae'+Neopiblemidae and pan-Chinchillidae, and Chambiramys sylvaticus occupies a basal position to the same clade. Four major radiation events are identified in the evolutionary history of Chinchilloidea. The analysis of new morphological characters linked with molecular evidence as well as the addition of taxa of uncertain or unstable phylogenetic position or not considered in previous studies allowed us resolve part of the relationships within Chinchilloidea, particularly that of Chinchillidae, supporting preceding morphological hypotheses.

New late Oligocene caviomorph rodents from Mendoza Province, central-western Argentina

ABSTRACT Late Oligocene caviomorphs represent one of the most important early adaptive radiations of this group of rodents. They show a high taxonomic diversity and a wide geographic distribution, with those found in the upper Oligocene of Salla (Bolivia) and Patagonia (Argentina) being particularly diverse. However, caviomorphs from the Deseadan South American Land Mammal Age in other latitudes are still scarcely known. In this contribution, we describe new caviomorph rodents from the Deseadan levels of Quebrada Fiera locality (Mendoza Province; central-western Argentina) and evaluate their systematic and paleobiogeographic significance. The taxonomic composition of the caviomorphs from Quebrada Fiera reveals a complex biogeographic history, as we recognize one endemic Cavioidea (Asteromys puelche sp. nov.) and two Chinchilloidea: one with Patagonian affinities (Cephalomys sp.) and another with a wide distribution in South America (Incamys bolivianus). Asteromys puelche sp. nov., shows closer phylogenetic affinities with the Bolivian A. bolivianus than with the Patagonian A. punctus. These rodents, in common with the whole mammalian association from Quebrada Fiera, show a mix of endemic taxa and others shared with higher and lower latitudes.

Historical, allometric and ecological effects on the shape of the lumbar vertebrae of spiny rats (Rodentia: Echimyidae)

AbstractIn mammals, the lumbar vertebrae are important for sustaining the trunk, for allowing the trunk to flex and extend, and, during locomotion, for transferring forces from the sacroiliac region to the anterior region of the body. The Echimyidae is a group that comprises spiny rats, the coypu and hutias. It is the caviomorph rodent family with the greatest ecological diversity and species richness, as well as having a wide variation in body mass. Thus, echimyid rodents provide a promising model for understanding how phylogenetic, allometric and ecological factors associated with locomotion affect the evolution of the post-cranial skeleton. To assess the effect of these three factors on the morphology of the lumbar vertebrae, the penultimate lumbar vertebra of 26 echimyid species was photographed under five views and submitted to phylogenetically informed comparative analysis using 2D geometric morphometrics. Vertebral shape variation showed a low correlation with body mass and vertebral size, and a low to moderate phylogenetic signal. Remarkably, locomotory habit had a strong influence on lumbar morphology, particularly when analysed in lateral view. Our results indicate that the echimyid penultimate lumbar vertebra is potentially useful for future ecomorphological studies on living and fossil small mammals.

Temperament, Plasticity, and Emotions in Defensive Behaviour of Paca (Mammalia, Hystricognatha).

Simple SummaryThe paca (Cuniculus paca), a Neotropical caviomorph rodent, provides the most sought-after game meat in all its range, and it therefore faces high hunting pressure and consequent poor welfare. The species is categorised as having a conservation status of “least concern” and appears resilient to over-hunting by humans, which may be related to individuals’ behavioural characteristics. To investigate this, we submitted captive pacas to temperament (personality) tests designed to assess individual responses to short challenges and to evaluate individuals’ emotional states. Our results showed that paca with a “restless” temperament performed more abnormal behaviour and less exploratory behaviour in a test of defensive behaviour, which elevations in faecal glucocorticoid metabolites indicated to be stressful. Plasticity in defensive behaviour was inferred from changes in behavioural responses and apparently rapid adaptation to different levels of risk. Our results suggest that individual differences and consistency of behavioural responses displayed by paca toward challenges may reflect a generally flexible and successful defensive behavioural response that underpins the paca’s survival, despite the threat of overhunting throughout its range.Within a species, some individuals are better able to cope with threatening environments than others. Paca (Cuniculus paca) appear resilient to over-hunting by humans, which may be related to the behavioural plasticity shown by this species. To investigate this, we submitted captive pacas to temperament tests designed to assess individual responses to short challenges and judgement bias tests (JBT) to evaluate individuals’ affective states. Results indicated across-time and context stability in closely correlated “agitated”, “fearful” and “tense” responses; this temperament dimension was labelled “restless”. Individual “restless” scores predicted responses to novelty, although not to simulated chasing and capture by humans in a separate modified defence test battery (MDTB). Restless animals were more likely to show a greater proportion of positive responses to an ambiguous cue during JBT after the MDTB. Plasticity in defensive behaviour was inferred from changes in behavioural responses and apparently rapid adaptation to challenge in the different phases of the MDTB. The results indicate that both temperament and behavioural plasticity may play a role in influencing paca responses to risky situations. Therefore, our study highlights the importance of understanding the role of individual temperament traits and behavioural plasticity in order to better interpret the animals’ conservation status and vulnerabilities.

Conservation status of the order Rodentia of Brazil: taxonomic and biogeographical patterns

The Global Mammal Assessment (GMA) evaluates the risk of extinction for all species of mammals, providing important data on their status to national and global conservation agencies and conventions. We assessed all of the species of Brazilian rodents as part of the GMA activities of the International Union for the Conservation of Nature Species Survival Commission (IUCN SSC) Small Mammal Specialist Group. A total of 234 species were evaluated against the IUCN Red List Criteria and placed into one of eight categories. Although rodents do not have elevated extinction risk compared to mammals as a whole, several families of caviomorph rodents have high levels of either threat, data deficiency, or both. The family Echimyidae has a large number of species and one-third of those either are species of conservation concern or data deficient. The family Ctenomyidae also is of concern in this regard. There are also strong geographic patterns to threat and poor knowledge. The focal areas for conservation effort are the Atlantic Forest and the Cerrado, and for Data Deficient species Atlantic Forest, Cerrado, and Amazonia, in particular the eastern Amazon. The results highlight the need for targeted field research and the application of ecological and spatial data to the development of conservation actions.

Adaptive evolution of β-globin gene in subterranean in South America octodontid rodents.

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.

Overlooked diversity in Argentine caviomorph rodents: the need to increase field efforts

Abstract Based on a variety of evidence (photographs, feces, specimens), three previously unsuspected caviomorph rodents are reported from Argentina: (1) a spiny rat (Echimyidae) probably belonging to the genus Phyllomys, in northern Misiones Province near Iguazú National Park; (2) an undetermined octodontid (Octodontidae) in western Chacoan Córdoba Province; and (3) the octodontid Spalacopus (Octodontidae), in high-Andean ranges of San Juan Province. The latter constitutes the first record of the genus for Argentina, and all the three findings highlight the necessity to increase collecting efforts in the country.

Brachiocephalic Muscular Arrangements in Cavioid Rodents (Caviomorpha): a Functional, Anatomical, and Evolutionary Study

In cursorial mammals, reduction or loss of the clavicle is usually associated with the constitution of the m. brachiocephalicus, a continuous muscle that extends from head and neck regions to the forelimb, protracting it during locomotion. Among caviomorph rodents, the Cavioidea are characterized by many adaptations that improve running performance, such as the presence of a brachiocephalic configuration of the mm. cleidomastoideus, cleido-occipitalis, and deltoideus pars clavicularis, a feature that was interpreted as one of the main modifications for speed in running. However, a comprehensive analysis of this muscular configuration in the Cavioidea is not yet available. In this study, we analyze the morphological diversity, homologies, functions, and evolutionary changes of those shoulder muscles in cavioids that constitute the m. brachiocephalicus in cursorial mammals. We hypothesize that a brachiocephalic muscular arrangement of these muscles has evolved in this group in relation to a swift mode of locomotion. Muscular dissections on seven species of cavioids were performed while myological data on three other species were taken from the literature. Our results indicate that all cavioids have a brachiocephalic arrangement of the mm. cleidomastoideus, cleido-occipitalis, and deltoideus pars clavicularis, whereas a second brachiocephalic arrangement constituted by the mm. omotransversarius and trapezius pars cervicalis is present only in the larger cavioids. Both muscular configurations act in protracting the forelimb during the gait, but we also hypothesize that the particular disposition of the m. omotransversarius around the shoulder joint of larger cavioids could also assist in the stabilization of this joint during fast half-bounding locomotion.

Nutritional ecology and ecological immunology in degus: Does early nutrition affect the postnatal development of the immune function?

Environmental conditions experienced by developing animals have an impact on the development and maturity of the immune system. Specifically, the diet experienced during early development influences the maintenance and function of the immune system in young and adult animals. It is well known that exposure to low-protein diets during early development are related to an attenuation of immunocompetence in adulthood. While this functional linkage has been widely studied in altricial models' mammals, it has been little explored how the nutritional history modulates the immune function in precocial animals. We evaluated the effect of dietary protein consumed during early development on the immune function and the oxidative costs in the precocial Caviomorph rodent Octodon degus, or degu. We evaluated components of the acute phase response (APR) and oxidative parameters before and after immune challenge. We found that after the immune challenge, the juveniles on the low-protein dietary treatment exhibited an attenuation of body temperature but showed higher levels of lipid peroxidation than juvenile degus on the high-protein diet. We did not find a significant effect of the interaction between diet and immune challenge on body mass, levels of inflammatory proteins, nor in the total antioxidant capacity. Our results suggest that some components of the immune function and the oxidative status in the degu can be modulated by diet during development. However, the modulation would depend on the immune variables analyzed, and the characteristics of the immune system of precocial rodents.

Ancient DNA Suggests Single Colonization and Within-Archipelago Diversification of Caribbean Caviomorph Rodents.

Reconstructing the evolutionary history of island biotas is complicated by unusual morphological evolution in insular environments. However, past human-caused extinctions limit the use of molecular analyses to determine origins and affinities of enigmatic island taxa. The Caribbean formerly contained a morphologically diverse assemblage of caviomorph rodents (33 species in 19 genera), ranging from ∼0.1 to 200 kg and traditionally classified into three higher-order taxa (Capromyidae/Capromyinae, Heteropsomyinae, and Heptaxodontidae). Few species survive today, and the evolutionary affinities of living and extinct Caribbean caviomorphs to each other and to mainland taxa are unclear: Are they monophyletic, polyphyletic, or paraphyletic? We use ancient DNA techniques to present the first genetic data for extinct heteropsomyines and heptaxodontids, as well as for several extinct capromyids, and demonstrate through analysis of mitogenomic and nuclear data sets that all sampled Caribbean caviomorphs represent a well-supported monophyletic group. The remarkable morphological and ecological variation observed across living and extinct caviomorphs from Cuba, Hispaniola, Jamaica, Puerto Rico, and other islands was generated through within-archipelago evolutionary radiation following a single Early Miocene overwater colonization. This evolutionary pattern contrasts with the origination of diversity in many other Caribbean groups. All living and extinct Caribbean caviomorphs comprise a single biologically remarkable subfamily (Capromyinae) within the morphologically conservative living Neotropical family Echimyidae. Caribbean caviomorphs represent an important new example of insular mammalian adaptive radiation, where taxa retaining “ancestral-type” characteristics coexisted alongside taxa occupying novel island niches. Diversification was associated with the greatest insular body mass increase recorded in rodents and possibly the greatest for any mammal lineage.

3D models related to the publication: Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies

This contribution contains the 3D models of the fossil teeth of two chinchilloid caviomorph rodents (Borikenomys praecursor and Chinchilloidea gen. et sp. indet.) discovered from lower Oligocene deposits of Puerto Rico, San Sebastian Formation (locality LACM Loc. 8060). These fossils were described and figured in the following publication: Marivaux et al. (2020), Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies. Proceedings of the Royal Society B. http://dx.doi.org/10.1098/rspb.2019.2806

New remains of Cephalomys arcidens (Rodentia, Caviomorpha) and a redefinition of the enigmatic Cephalomyidae

Cephalomys is the best-known cephalomyid, recorded in five localities in Argentina and known from well-preserved mandibles, fragments of skull, and a large number of isolated teeth, from both juveniles and adults. Despite this, a modern description is lacking and the validity of some species of Cephalomys has been questioned in the last few years. New material from the Deseadan locality of Cabeza Blanca (Chubut, Argentina), including skull fragments unknown for the species thus far, and well-preserved juvenile teeth, along with a large number of specimens from collections in Argentina, allow us to propose a more complete description of the genus and a new taxonomic arrangement for the Cephalomys species. We also analysed some dubious records of Cephalomys from Quebrada Honda and Pico Truncado and confirm that they are not part of this genus. We consider C. plexus to be a synonym of C. arcidens, we consider the combination previously proposed for C. bolivianus (as a species of Asteromys) to be valid, and we consider C. ceciae also to be a valid species. We performed a phylogenetic analysis including for the first time all cephalomyids (Cephalomys, Litodontomys, Cephalomyopsis, Soriamys and Banderomys) and possibly related genera (Perimys, Scotamys, Asteromys) to test the position of the family Cephalomyidae among the other caviomorph rodents, as well as its validity and internal relationships. The results recovered Cephalomyidae as a clade, including Cephalomys, Cephalomyopsis and Litodontomys. The monophyly of Cephalomys could not be confirmed. Soriamys and Banderomys were recovered within Cavioidea. Perimys, Scotamys and Asteromys were recovered within Chinchilloidea, and we analysed the implications of their positions within the group. The implications in terms of the biochron, distribution and evolutionary history of the Cephalomyidae, considering the new definition for the family proposed herein (including only Cephalomys, Cephalomyopsis and Litodontomys), are discussed, as well as inferences regarding caviomorph evolution at the scale of the entire group.

Biomarkers as a tool for assessing diffuse contamination of coastal wetland

Playa Penino is a natural reserve located on the south coast of Uruguay. It hosts 244 species of birds (more than 50% of the bird biodiversity recorded for Uruguay). The area is included in the International BirdLife Program for biodiversity preservation. Urbanization and pollution generally have affected the quality of the water and biodiversity in wetlands. The analysis of the major wetland of Playa Penino revealed high levels of organic compounds. The biomonitoring was done using the caviomorph rodent Ctenomys pearsoni (commonly known as tuco tuco) as an indicator species because they inhabit burrows around the wetland. Genetic effects were determined using the comet assay and micronucleus test. The significant correlations between chemical and microbiological parameters and genetic damage might indicate that macronutrients from sewage could be one of the causes of the genetic damage. There is an urgent need to conserve the biodiversity of this natural area by introducing sewage treatment, cesspool control and by controlling settlement in the area etc.

Evolutionary Patterns of Mandible Shape Diversification of Caviomorph Rodents

Caviomorphs are a mainly South American rodent clade with high taxonomic and ecomorphological diversity. In this study, we combine geometric morphometric, functional, ancestral reconstruction, and macroevolutionary analyses to quantify the magnitude, direction, and rates of shape diversification of the caviomorph mandible, and to explore the morpho-functional implications and potential ecological catalysts of the observed shape changes. The mandible shape was significantly related to habits and size, and had a better fit with an evolutionary model where the main clades occupy distinct adaptive peaks. The morphological evolution of octodontoids is characterized by pulses of rate acceleration, but without reaching high disparity. Such pulses are mainly linked to the acquisition of fossorial specializations, including short and robust mandibles, and the increasement of forces at incisors. Conversely, derived cavioids show slower but continuous shape changes that allowed them to reach the most divergent, grazing morphologies in which slender mandibles with more marked antero-posterior movements for grinding action are favored. Interestingly, the major morphological changes occurred mainly during the early Oligocene and lower late Miocene, two time periods that involved global climatic events and strong changes in the vegetational structure of South America. The evolution of octodontoid and cavioid mandibles seems to be related to the occupation of subterranean and epigean niches, respectively, in the progressively expanded Cenozoic open landscapes of southern South America.

Late early Miocene caviomorph rodents from Laguna del Laja (~37° S), Cura-Mallín Formation, south-central Chile

Despite recent efforts, the paleodiversity of the Neogene mammals in Chile remains poorly known, with several putative new species awaiting description. For example, previous studies suggest that the early to late Miocene mammalian assemblages from the Laguna del Laja fossiliferous locality (Cura-Mallín and Trapa-Trapa formations), which crop out in the Andean Cordillera of Chile (~37°), comprise dozens of undescribed taxa. A better understanding of the taxonomic affinities of the Laguna del Laja faunas is needed, as it represents one of the few faunas known from the early to late? Miocene of the south-central Andean main range. Several specimens of caviomorphs recently recovered in late early Miocene beds of the Cura-Mallín Formation at Laguna del Laja are here described in detail, and a brief discussion of their chronological, biogeographical, and paleoenvironmental significance is also provided. Based on fragments of mandible, maxilla and isolated teeth five taxa were recognized, Phanomys mixtus Ameghino, Prolagostomus sp., Neoreomys sp., Maruchito nov. sp.?, and Luantus sompallwei nov. sp. The radiometric ages of the fossil-bearing horizons, constrained between 17.7 and 16.4 Ma, as well as the common species (P. mixtus) and genera (Prolagostomus and Neoreomys) indicate that the fauna here reported belongs to the Santacrucian SALMA. Finally, our finding preliminary suggests the predominance of rather open habitats in the Cura-Mallín Formation during this time, but also a widely distributed late Early Miocene caviomorph fauna along the southern Andes, in both intra-arc and foreland basins.

Uncovering the species diversity of subterranean rodents at the end of the World: three new species of Patagonian tuco-tucos (Rodentia, Hystricomorpha, Ctenomys).

Ctenomys Blainville 1826 is one of the most diverse genera of South American caviomorph rodents. Currently, six species of this genus are reported from Patagonia, south of 42°S. In this contribution, we assessed the taxonomic status of several populations from eastern and central Chubut province, northern Patagonia. Based on phylogenetic analyses of DNA sequences, morphology assessment (qualitative and quantitative), and previously published karyological data, we describe three new species of this genus, one formed by two subspecies, endemic to northern Patagonia. In addition, we include C. coyhaiquensis Kelt and Gallardo 1994 into the synonymy of C. sericeus J.A. Allen 1903. Finally, we discussed the need for additional integrative approaches, including field collection of specimens, to better understand the diversity of this highly speciose rodent genus.

Spatial and temporal taphonomic study of bone accumulations of the burrowing owl (Athene cunicularia) in central Argentina

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.

Female degus show high sociality but no preference for familiar peers

Group-living animals vary in social behavior across multiple dimensions, including in the selectivity of social interactions with familiar versus unfamiliar peers. Standardized behavioral tests can be used to tease apart different dimensions of behavior. These serve a dual function—on one hand, helping to isolate behavioral factors that may support collective behavior in natural habitats, and, on another, providing a basis for comparative approaches to understanding physiological mechanisms of behavior. Degus (Octodon degus) are South American caviomorph rodents that nest and forage in groups with relatively low genetic relatedness. Flexibility in group membership is likely supported by gregariousness toward strangers, but the relative preference for strangers compared with familiar individuals has not been systematically tested. We assessed the specificity of social preferences in female degus using a same-sex partner preference test. Degus huddled extensively with both familiar and unfamiliar peers, with no average preference for one over the other. Detailed analysis of social interactions demonstrated an effect of familiarity on social investigation and aggressive behaviors, indicating that degus distinguished between familiar and unfamiliar conspecifics, even though it did not impact huddling. This behavioral profile is thus far unique to degus; in similar tests, meadow and prairie voles exhibit strong partner preferences for known peers, while mice exhibit low social huddling and spend relatively less time in social chambers. Understanding how group-living species differ in specific aspects of social behavior such as familiarity/novelty preference and propensity for social contact will offer a foundation to interpret differences in neural systems supporting sociality.

The auditory region of a caviomorph rodent (Hystricognathi) from the early Miocene of Patagonia (South America) and evolutionary considerations

ABSTRACT Caviomorphs, the ctenohystrican rodents endemic to the Neotropics, have a long evolutionary history during the Cenozoic, and is one of the more abundant mammalian groups with striking morphological disparity. Several living taxa have auditory regions adapted to hearing low-frequency sounds, yet almost nothing is known about the basicranium in fossil taxa. The octodontoid Prospaniomys priscus from the lower Miocene of Patagonia, Argentina, exhibits a skull with a curious combination of generalized dental characters and supposed derived tympanic cavity. Owing to the basal phylogenetic position of P. priscus, the study of its basicranium based on high resolution X-ray computed tomography represents an excellent opportunity to study an ancestral morphological pattern. Comparisons with living octodontoids permit the evaluation of the auditory region in an evolutionary context. Our results identified that at least since the early Miocene octodontoids, and certainly caviomorphs, have specializations to enhance low-frequency hearing: highly coiled cochlea, small secondary bony laminae, well-developed tympanic cavity, and reduced or absent stapedius muscle, characters that seem not to be directly related to the environment. Possible generalized or specialized states for the latter features are discussed. The significance of this work lies in the fact that it is the first detailed anatomical description of the auditory regions of a fossil caviomorph, providing a new framework with regards to this region of the skull.