Geographical distribution and ecological diversification of South American octodontid rodents

Following the aridity: Historical biogeography and diversification of the Philodromidae spider genus Petrichus in South America

Aridity conditions and expansion of arid biomes in South America are closely linked to the onset of Andean orogeny since at least 30 Mya. Among arid-associated taxa, spiders belonging to the genus Petrichus are found along the Andes mountains and across the diagonal of open formations of the Chaco and Cerrado domains. In this contribution, we asked whether Petrichus originated prior to the central Andean uplift and what historical processes have promoted their diversification. We time-calibrated the phylogenetic tree of Philodromidae and estimated the divergence times of Petrichus. Considering phylogenetic uncertainty, we assessed biogeographical hypotheses of the historical events associated with the diversification of these spiders in South America. Petrichus originated along the Pacific coastal deserts in the Central Andes during the Early Miocene. The species likely dispersed from the western to the eastern side of the Andes coincidently with the central Andean uplift. The diversification of these spiders is coeval with the expansion of open grassland formations during the Late Miocene and Early Pliocene. Multiple dispersal events occurred from the Monte desert to southern South America and eastward to Chaco between ∼ 8 and 2.5 Mya. The Andes might have played a role as a corridor favoring geographical range expansions and colonization of new environments. In addition, we also suggest that Philodromidae might have an Oligocene origin or earlier. Future analyses based on further evidence and larger taxon sampling should be carried out to corroborate our findings.

The forelimbs of Octodontidae (Rodentia: Mammalia): substrate use, morphology, and phylogenetic signal

Rodents of the family Octodontidae, endemic to South America, represent a group with low taxonomic richness group (six genera and 14 species) but have great ecomorphological diversity with epigean, semi-fossorial, fossorial, and subterranean forms. We analyzed morphometric variation in humerus and ulna, the possible relationship with substrate preference use, and the presence of a phylogenetic signal in the forelimbs traits (five biomechanical indices). Our results show that, in octodontids, the forelimb variation was not primarily associated with their phylogeny and some attributes are highly explanatory in terms of function, with a clear differentiation between the substrate use gradient extremes (i.e. epigean and subterranean forms). The two forelimb traits, the development of humeral epicondyles and the olecranon process of the ulna, indicative of adaptive trends found in Octodontidae are consistent with most of those described for other mammals and corroborate the relevance of forelimb characters to differentiate modes of locomotion or substrate preferences.

Influence of climate change on the predicted distributions of the genus Tympanoctomys (Rodentia, Hystricomorpha, Octodontidae), and their conservation implications

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.

Patterns in research and data sharing for the study of form and function in caviomorph rodents

The combination of morphometrics, phylogenetic comparative methods, and open data sets has renewed interest in relating morphology to adaptation and ecological opportunities. Focusing on the Caviomorpha, a well-studied mammalian group, we evaluated patterns in research and data sharing in studies relating form and function. Caviomorpha encompasses a radiation of rodents that is diverse both taxonomically and ecologically. We reviewed 41 publications investigating ecomorphology in this group. We recorded the type of data used in each study and whether these data were made available, and we re-digitized all provided data. We tracked two major lines of information: collections material examined and trait data for morphological and ecological traits. Collectively, the studies considered 63% of extant caviomorph species; all extant families and genera were represented. We found that species-level trait data rarely were provided. Specimen-level data were even less common. Morphological and ecological data were too heterogeneous and sparse to aggregate into a single data set, so we created relational tables with the data. Additionally, we concatenated all specimen lists into a single data set and standardized all relevant data for phylogenetic hypotheses and gene sequence accessions to facilitate future morphometric and phylogenetic comparative research. This work highlights the importance and ongoing use of scientific collections, and it allows for the integration of specimen information with species trait data. Recientemente ha resurgido el interés por estudiar la relación entre morfología, ecología, y adaptación. Esto se debe al desarrollo de nuevas herramientas morfométricas y filogenéticas, y al acceso a grandes bases de datos para estudios comparados. Revisamos 41 publicaciones sobre ecomorfología de roedores caviomorfos, un grupo diverso y bien estudiado, para evaluar los patrones de investigación y la transparencia para la liberación de datos. Registramos los tipos de datos que se utilizaron para cada estudio y si los datos están disponibles. Cuando estos datos se compartieron, los redigitalizamos. Nos enfocamos en los ejemplares consultados, y en datos que describen rasgos ecológicos y morfológicos para las especies estudiadas. Los estudios que revisamos abarcan el 63% de las especies de caviomorfos que actualmente existen. Encontramos que raramente fueron compartidos los datos que se tomaron para especies, y menos aún para ejemplares. Los datos morfológicos y ecológicos eran demasiado heterogéneos e exiguos para consolidar en un solo banco de datos; debido a esta circunstancia, creamos tablas relacionales con los datos. Además, enlazamos todas las listas individuales de especímenes para crear un solo banco de datos y estandarizamos todos los datos pertinentes a hipótesis filogenéticas, así como los números de acceso de secuencias genéticas, para así facilitar eventuales estudios comparados de morfometría y filogenia. Este trabajo resalta la importancia de las colecciones científicas y documenta su uso, además permitiendo la futura integración de datos derivados de ejemplares con datos sobre rasgos ecomorfológicos a nivel de especie.

Spatial relationships among free-living cururos (Spalacopus cyanus) demonstrate burrow sharing and communal nesting

Spatial relationships among conspecifics can provide insights into numerous aspects of social behavior. Spatial data may be particularly important for characterizing the behavior of difficult-to-study species such as subterranean rodents, direct observations of which are challenging. To characterize the social organization of the cururo (Spalacopus cyanus), a subterranean species in the rodent family Octodontidae, we used radiotelemetry to quantify spatial relationships within populations of this species located in Parque Nacional Bosque Fray Jorge and Santuario de la Naturaleza Yerba Loca, Chile. Specifically, we sought to determine if adults in this diurnal species share burrows and subterranean nests, the two criteria typically used to identify subterranean rodents as social. Analyses of radio fixes collected during February–March 2003 revealed that cururos at both Fray Jorge and Yerba Loca shared nighttime nest sites; cluster analyses of these data identified multiple spatially distinct subsets of adults in each population. Overlap of minimum convex polygons constructed from radio fixes collected during daylight hours suggested burrow sharing by animals in both populations. Cluster analyses of overlap values revealed the same spatially distinct groups of individuals identified from analyses of nest sharing; in addition, these analyses revealed one cluster of animals in each population that was not evident from analyses of nighttime data. Collectively, these results confirm that cururos are social, with adults in both study populations sharing burrow systems and communal nests. Our findings add to the growing understanding of social organization in octodontid rodents and reveal a new system for comparative studies of the ecology and evolution of behavioral variation in burrow-dwelling mammals.

Morphology of the limbs in the semi-fossorial desert rodent species of Tympanoctomys (Octodontidae, Rodentia)

Here, a detailed description of the forelimbs and hindlimbs of all living species of the genus Tympanoctomys are presented. These rodents, highly adapted to desert environments, are semi-fossorial with capacity to move on the surface as well as to build burrows. The shape, structure, and size of the limbs are described. Contrary to what was expected for scratch digging semi-fossorial species, Tympanoctomys have slender humerus, radius and ulna; with narrow epicondyles of the humerus and short olecranon of the ulna with poorly developed processes. Following our descriptions, no intrageneric morphological variation regarding to the configuration of the limbs was detected, probably due to phylogenetic proximity, and not related to specific variations in response to different use of substrates or habits. The obtained results constitute a source of previously unpublished information as well as an important base for future analysis in different studies, such as morphometric, morpho-functional, or phylogenetic researches.