Testing the Rio Doce as a riverine barrier in shaping the Atlantic rainforest population divergence in the rodent Akodon cursor

Akodon cursor occurs in dense rainforest from northern (8 degrees S) to southern (26 degrees S) states along the Atlantic coast of Brazil. Previous karyological and molecular data revealed two major clades, one including northern (8-15 degrees S) and the other southern (19-26 degrees S) populations. The center of geographic distribution (15-20 degrees S), which included the state of Espirito Santo, was identified as a potential vicariance region. Since river barriers are among the most discussed models in the study of Neotropical diversification, we examined whether the Rio Doce (19 degrees S) plays an important role in shaping the population genetic divergence of A. cursor by including samples from Espirito Santo in the analysis. Our results showed that the northern-southern division region in Atlantic forest was no coincidence with the presence of the Rio Doce by refuting the hypothesis that this river is an effective barrier to gene flow between populations. Instead, we found evidence that isolation by geographical distance shaped the phylogeographical structure in the southern lineage. However, there is uncertainty about effectiveness of the processes involved and further studies based on wider sampling are needed.