Historical biogeography of the diversification in Akodon (Rodentia: Sigmodontinae)

Date

2017-08

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Abstract

The effects of past geological and climatic events in the distribution and diversification of South American taxa have been extensively studied for various taxa. Accordingly, several hypotheses have been proposed to explain the mechanisms by which these events affected the diversification of South American biota. The genus Akodon is among the most specious groups of South American rodents and constitutes an ideal clade to study mechanisms and patterns of diversification from a macroevolutionary perspective. Previous discussions on the historical biogeography of Akodon were limited by a changing taxonomy, incomplete taxon sampling, and lack of time-calibrated trees. In the present study, phylogenetic relationships were coupled with current geographic distributions of species to estimate the relative frequency of different modes of speciation and the historical biogeography of Akodon. None of the age-range correlation analyses showed a clear evidence for any particular mode of speciation. However, some general trends (albeit not significant) indicated that sympatric speciation can be considered uncommon for the group, while parapatric speciation seems to be more common. Initial divergence within Akodon occurred c.a. 3.4 Mya during the Mid-Late Pliocene. During the Pleistocene, lineages diverged at different epochs up until the last split at 0.26 Mya. We propose the area of differentiation for the genus in the lowlands of the current biogeographic Chaco region of southeastern Bolivia, northeastern Argentina and northern Paraguay. From there, diverging lineages dispersed either north along the eastern slope of the Andes, or to the east towards the lowlands of central South America and the eastern Atlantic Forest and Cerrado biomes. The conditions that influenced the speciation events of Akodon are as diverse as the group itself. Its exceptional richness in Andean habitats can be explained by both intrinsic and extrinsic factors, while its diversity in the eastern region is likely related to vegetation shifts and the capacity of Akodon ancestors to disperse with their habitats or adapt to new environments. The overall diversity of the clade can be explained by the complex relation between the effects of orogenic events during the mid and Late-Pliocene and the environmental changes produced by climatic oscillations of the Pleistocene.


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Keywords

Akodon, South America, Ancestral Range Estimation, Habitat Heterogeneity, Climatic Oscillations

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