Pleistocene climate changes affected species ranges and evolutionary processes in the Atlantic Forest

Abstract

The effects of global glaciations on the distribution of organisms are an essential element of many diversification models. However, the empirical evidences supporting this idea are mixed, in particular to explain tropical forest evolution. In this study, we evaluated the impacts of range shifts associated to Pleistocene global glacial cycles on the evolution of tropical forests. In particular, we tested the following predictions: 1) that population genetic structure increases with fragmentation variation between the present and the LGM, and also 2) with geographic range instability; 3) that genetic diversity increases with range stability, and 4) decreases with fragmentation variation between periods. In order to address our predictions, we studied population genetic structures and modelled present and past distributions of 15 Atlantic Forest (AF) endemic birds. Afterwards, we evaluated the relationship of population genetic parameters with metrics of species range shifts between the present and the last glacial maxima. We found that geographic ranges of AF birds changed in concert with Pleistocene glacial cycles, but unexpectedly, our findings suggests the novel idea that ranges during glacial maxima were in average slightly larger, equally fragmented and displaced from the interglacial ranges. Our findings support that range shifts over the late Pleistocene impacted diversification of forest organisms, although, they did not show that those range shifts have a strong effect. We found that a combination of fragmentation variation across time, small current range size and range stability increased population genetic structure. However, neither fragmentation nor range stability affected genetic diversity. Our study showed that evolutionary response to range shifts across AF birds have a high variance, which could explain the mixed support given by single-species studies to the action of Pleistocene range shifts on population evolution.