Taxonomic revision of the populations assigned to Octodon degus (Hystricomorpha: Octodontidae): With the designation of a neotype for Sciurus degus G. I. Molina, 1782 and the description of a new subspecies

Species limits and hybridization in Andean leaf-eared mice (Phyllotis)

Leaf-eared mice (genus Phyllotis) are among the most widespread and abundant small mammals in the Andean Altiplano, but species boundaries and distributional limits are often poorly delineated due to sparse survey data from remote mountains and high-elevation deserts. Here we report a combined analysis of mitochondrial DNA variation and whole-genome sequence (WGS) variation in Phyllotis mice to delimit species boundaries, to assess the timescale of diversification of the group, and to examine evidence for interspecific hybridization. Estimates of divergence dates suggest that most diversification of Phyllotis occurred during the past 3 million years. Consistent with the Pleistocene Aridification hypothesis, our results suggest that diversification of Phyllotis largely coincided with climatically induced environmental changes in the mid- to late Pleistocene. Contrary to the Montane Uplift hypothesis, most diversification in the group occurred well after the major phase of uplift of the Central Andean Plateau. Species delimitation analyses revealed surprising patterns of cryptic diversity within several nominal forms, suggesting the presence of much undescribed alpha diversity in the genus. Results of genomic analyses revealed evidence of ongoing hybridization between the sister species Phyllotis limatus and P. vaccarum and suggest that the contemporary zone of range overlap between the two species represents an active hybrid zone.

The skull variation of the olive field mouse Abrothrix olivacea (Cricetidae: Abrotrichini) is localized and correlated to the ecogeographic features of its geographic distribution

The relationship between phenotypic variation and landscape heterogeneity has been extensively studied to understand how the environment influences patterns of morphological variation and differentiation of populations. Several studies had partially addressed intraspecific variation in the sigmodontine rodent Abrothrix olivacea, focusing on the characterization of physiological aspects and cranial variation. However, these had been conducted based on geographically restricted populational samples, and in most cases, the aspects characterized were not explicitly contextualized with the environmental configurations in which the populations occurred. Here, the cranial variation of A. olivacea was characterized by recording twenty cranial measurements in 235 individuals from 64 localities in Argentina and Chile, which widely cover the geographic and environmental distribution of this species. The morphological variation was analyzed and ecogeographically contextualized using multivariate statistical analyses, which also included climatic and ecological variation at the localities where the individuals were sampled. Results indicate that the cranial variation of this species is mostly clustered in localized patterns associated to the types of environments, and that the levels of cranial differentiation are higher among the populations from arid and treeless zones. Additionally, the ecogeographical association of cranial size variation indicate that this species does not follow Bergmann's rule and that island populations exhibit larger cranial sizes compared to their continental counterparts distributed at the same latitudes. These results suggest that cranial differentiation among the populations of this species is not homogeneous throughout its geographic distribution, and that the patterns of morphological differentiation are also not completely consistent with the patterns of genetic structuring that have been described recently. Finally, the analyses performed to ponder morphological differentiation among populations suggest that the contribution of genetic drift in the formation of these patterns can be ruled out among Patagonian populations, and that the selective effect imposed by the environment could better explain them.

Morphological redescription, phylogenetic position, and distribution of the near threatened cavy Microcavia shiptoni (Thomas, 1925), with a key for the living species of Microcavia

The genus Microcavia includes six species of terrestrial, medium-sized, living cavies that occupy arid to semiarid environments at both high and low elevations in western and southern South America. Among these, Microcavia shiptoni is one of the least known species, being recorded only at two isolated localities from northwestern Argentina. Genetic information and a detailed morphological characterization are lacking for this elusive species. In this work, we start filling these gaps by including M. shiptoni in a phylogenetic analysis based on mitochondrial DNA sequences that includes five of the six currently recognized species and place M. shiptoni as sister to M. niata in a clade of highland species. In addition, using both qualitative and quantitative morphological traits, we provided an emended diagnosis for this taxon and a key for the living species of the genus. Finally, we present, the first notes on the natural history of this species.

A comprehensive overview of the genetic diversity in Thylamys elegans (Didelphimorphia: Didelphidae): establishing the phylogeographic determinants

Background

For the genus Thylamys, the rivers have been reported as barriers to dispersal, limiting current and historical distribution of its lineages. We hypothesized that the Maipo river has affected the genetic structure of northern and southern lineages of Thylamys elegans, recovering a phylogenetic relationships with reciprocally monophyletic sister groups on opposite river banks. We evaluated the role of other rivers in the Mediterranean zone of Chile as historical and recent modulators of the biogeographic processes of this species.

Methods

We applied a phylogeographic approach, using the cytochrome-b mitochondrial gene for 93 individuals of T. elegans, from 37 localities in a latitudinal gradient between 21°25’ and 35˚56’S, encompassing a geographic area between the Atacama Desert and most of the Mediterranean Chilean zone.

Results

The phylogenetics results recovered six lineages within T. elegans: Thylamys elegans elegans, Thylamys elegans coquimbensis, the Loa lineage and three other lineages not described previously (Aconcagua, South 1 and South 2). We suggest that following rivers play a role like primary barrier: the Maipo river in the genetic differentiation of northern and southern ancestral lineages, and the Mataquito river and its tributary Teno river for the South 1 and South 2 lineages. On the other hand, the Quilimarí river preserve the genetic divergence in T. e. coquimbensis and Aconcagua lineage and the Aconcagua river in Aconcagua lineage and T. e. elegans acting like secondary barriers.

Conclusions

We concluded that the genetic diversity and biogeographic history of T. elegans was shaped by mountain glaciers, changes in river water levels during the Pleistocene glaciations and hyperaridity, promoting the differentiation and persistance of the T. elegans lineages.