Phylogeography and ecological niche modelling of the South American cricetid rodent Graomys griseoflavus , with insights into its chromosomal evolution

Abstract

Te rodent Graomys griseofavus has a wide geographical distribution in the Arid Diagonal of South America, showing variation in the diploid number (2n = 33–38) caused by three diferent Robertsonian (Rb) translocations. Two contrasting hypotheses have been proposed to explain the origin and evolution of this polymorphism: (i) unique and sequential events; or (ii) multiple and independent origins of Rb translocations. Here, we combined phylogeography and ecological niche modelling to elucidate the evolutionary history of G. griseofavus and help to contrast these hypotheses. Te results indicated a demographic increase that would have begun ~150 kya from the High Monte ecoregion. Te spatial distributions of these populations were coincident with the areas of highest habitat suitability. Te palaeoclimatic projections suggested the presence of two main glacial refugia coincident with the main genetic clusters. Graomys griseofavus underwent two pulses of southward expansionat ~220 and ~210 kya. More recently (~20 kya), there was a secondary contact between the southern populations (Low Monte ecoregion) ex-panding northwards and the northern populations (High Monte ecoregion) expanding into marginal areas of the Chaco ecoregion. Combinedwith the cytogenetic evidence, our results support the multiple and independent origins of Rb translocations.