SYSTEMATICS AND HISTORICAL BIOGEOGRAPHY OF Phyllotis xanthopygus (RODENTIA: SIGMODONTINAE)
Phyllotis xanthopygus is currently understood to be a widespread species, inhabiting regions of Peru, Bolivia, Chile and Argentina. This vast geographic distribution is complemented by an extensive altitudinal gradient, occupying areas at sea level up to 5570m in the central Andes cordillera. This e...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2020 |
| País: | Chile |
| OAI Identifier: | oai:repositorio.anid.cl:10533/253013 |
| Acceso en línea: | https://hdl.handle.net/10533/253013 |
| Access Level: | acceso abierto |
| Palabra clave: | Ciencias Naturales Ciencias de la Tierra y del Medio Ambiente Biología Molecular |
| Sumario: | Phyllotis xanthopygus is currently understood to be a widespread species, inhabiting regions of Peru, Bolivia, Chile and Argentina. This vast geographic distribution is complemented by an extensive altitudinal gradient, occupying areas at sea level up to 5570m in the central Andes cordillera. This extensive colonization area includes a broad array of environments, from lush bushland through to sparse rocky deserts. Traditionally six subspecies have been recognized in P. xanthopygus, described on the basis of morphological features, primarily differences in coat pigmentation. The northernmost distributed subspecies being P. x. posticalis, found at approximately 11 to 16º S. Further south and concentrated in the Bolivian highlands are P. x. chilensis and P. x. rupestris, for which an extensive contact zone has been reported in the Arequipa, Moquegua and Tacna areas of Peru. Relative to these subspecies, P. x. vaccarum and P. x. ricardulus are recognized further south, the latter endemic to the north-west of Argentina. Occupying the southernmost distribution, the nominotypical subspecies, P. x. xanthopygus inhabits regions at approximately 38 to 50º S. Once recognized as a subspecies of P. xanthopygus, it was thought that divergence of P. limatus, occurred during the last glaciation, as ascertained by paleoburrow analysis and phylogenetic relationship studies. Presently considered a different species, P. bonariensis has been differentiated from P. xanthopygus based on subtle morphological characters and geographical isolation to the Sierra de la Ventana, Buenos Aires, although further research was suggested. Currently, it is understood that P. limatus and P. bonariensis are included in a complex with P. xanthopygus, forming a paraphyletic group, although specific taxonomical relationships are not clear. Considering the climactic events and the limited prevalence of widespread direct (fossil) evidence in Patagonia, paleodistribution reconstruction of the xanthopygus complex was needed, including spatial geographical aspects. To attempt to solve these taxonomical and population issues, this study evaluated current phylogenetic relationships within the xanthopygus complex and tested the validity of the current taxonomical arrangement, placing emphasis on the species P. bonariensis and P. limatus. In order to unveil the biogeographic history of this taxa, ancestral distribution areas were reconstructed. Species limits were estimated through use of a lineal and a geometric morphometric approach, to test congruency based on molecular results with morphological data across the entire distribution range of the xanthopygus complex, including P. limatus and P. bonariensis. In order to ascertain potential refugia during glacial periods and recolonization routes since the Last Glacial Maximum, niche modelling was conducted. Using a genomic approach, the population structure of individuals from the xanthopygus complex in southern Patagonia was discovered, including P. x. vaccarum, P. x. xanthopygus and P. bonariensis. Phylogenetic results showed the southern clade to be composed of two distinct groups; P. x. xanthopygus forming the first group, and P. bonariensis, alongside the furthest eastern distribution of P. vaccarum forming the second. Similarly, two distinctive groups were included in the northern clade. The northern clade contained the group formed by P. limatus and the northern distribution of P. x. posticalis. A divergence was observed in the second northern clade group, consisting of the samples P. x. posticalis, P. x. chilensis, P. x. rupestris and the northern distribution range of P. x. vaccarum. Furthermore, the ancestral region of the xanthopygus complex was determined to be located in the Puna Region, at an estimated crown age of 1.925 million years ago. Morphologically, the species forming the xanthopygus complex presented sexual dimorphism, but no differentiation was noted between taxonomical groups (subspecies and species). However according to phylogenetic groups, samples of both sexes were found to be clustered primarily on the Principal Component 2 and Canonical Vector 1 axis. The phylogeographic analysis revealed two geographically differentiated clusters; north (purple and blue) and south (orange). Subsequently, the northern cluster was divided into two groups, differentiated by altitude; high (purple) and low (blue). Plio-pleistocene refugia were located in similar areas for each lineage, occupying the Patagonian distribution of P. xanthopygus. This study resolved some previous taxonomic issues surrounding the species complex, suggesting the inclusion of P. limatus as a subspecies of P. xanthopygus and situated in the northern clade. Grouped within the southern clade, P. bonariensis can also be considered a subspecies of P. xanthopygus. Therefore, this study calls for the number of subspecies within P. xanthopygus to be reduced to three, accurately reflecting the phylogenetic clades. The basal clade identified by genetic analysis were also demonstrated in skull size variation, where smaller skull size was observed in samples occupying the relatively higher area in Puna. Lastly, the impact of the glacial cycles extends to the genesis of two barriers; a geographical barrier formed by the relatively rock-free environment surrounding the Río Negro, a habitat less associated with P. xanthopygus distribution and a physiological barrier, characterized by altitude. Population genetics shows a complex population dynamic and shared refugia during glacial periods. |
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