Historical connections between Atlantic Forest and Amazonia drove genetic and ecological diversity in Lithobates palmipes (Anura, Ranidae)

The Atlantic and Amazon rainforests have a shared but unclear past, with
intermittent connections resulting from historical climate change. We
investigate these connections by studying the phylogeography and climatic
niche of the disjunct distributed frog Lithobates palmipes. We sequenced
two fragments of mitochondrial DNA from Atlantic Forest (AtF) and Amazonia
(AmF) individuals and evaluated how genetic diversity is distributed in
space and whether past demographic changes occurred. Also, we evaluated
the existence of past suitable connections between biomes for L. palmipes
through ecological niche models (ENM) and tested for niche divergence. The
AtF group is nested within the AmF group and closely related to
individuals from eastern Amazonia, a pattern recovered in many species
that used northeast connection routes. We found evidence of recurrent use
of connections in different directions and time during the Pleistocene,
resulting in genetic structure between biomes, with no signal of
demographic change and evidence of niche divergence across both genetic
groups. ENMs indicated suitable areas connecting forests throughout
northeastern Brazil during the Pleistocene. Mitochondrial lineages do not
match biomes exactly. One lineage is composed of AtF populations and
eastern Amazonia individuals. The other is composed of western Amazonia
individuals, suggesting an effect of past climatic heterogeneity within
the Amazonia forest. This is the first evidence that this route drove
genetic and ecological diversity for amphibians recently, a group with
habits and ecological requirements different from other vertebrates that
have been shown to use this putative corridor.