Deep Genomic Divergence and Phenotypic Admixture of the Treefrog Dendropsophus elegans (Hylidae: Amphibia) Coincide With Riverine Boundaries at the Brazilian Atlantic Forest

Abstract

The Atlantic Forest (AF) domain is one of the Earth’s biodiversity hotspots, known for its high levels of species diversity and endemism. Factors related to palaeoenvironmental dynamics, such as the establishment of vegetational refugia and river basins, have different impacts on biological communities and biodiversity patterns in this domain. Here, we sample genome-wide RADseq data from a widespread treefrog (Dendropsophus elegans), inhabiting natural and human-impacted ecosystems at the Brazilian AF to test the impact of riverine boundaries and climatic refugia on population structure and diversification. We estimate divergence times and migration rate across identified genetic breaks related to the rivers Doce, Paraíba do Sul, Ribeira de Iguape, and Paraguaçu, known to represent barriers to gene flow for other AF endemic species, and test the role of climatic refugia. Finally, we investigate the impact of spatio-temporal population history on morphological variation in this species. We recovered a phylogeographic history supporting three distinct clades separated into two geographically structured populations, corresponding to the north and south of AF. In addition, we identified an admixture zone between north and south populations in the latitude close to the Doce River. Our findings support a pattern of isolation-by-distance and the existence of a secondary contact zone between populations, which might have been promoted by gene flow during population expansion. Further, we found support for models considering migration parameters for all the tested rivers with different population divergence times. Based on the species history and the AF palaeoenvironmental dynamics, we corroborate the role of forest refugia impacting population structure for this species through recent range expansion after the Last Glacial Maximum (LGM). The Doce and Paraíba do Sul Rivers coincide with the main genetic breaks, suggesting they might also have played a role in the diversification processes. Finally, despite finding subtle correlations for phenotypic data among different populations, variation is not strongly detectable and does not seem associated with speciation-level processes that could warrant taxonomic changes. Such results can be explained by phenotypic plasticity of the evaluated traits and by recent divergence times, where there has been insufficient time and weak selective pressures to accumulate enough phenotypic differences.

Diversification processes in Gerp's mouse lemur demonstrate the importance of rivers and altitude as biogeographic barriers in Madagascar's humid rainforests

“…Especially arboreal and terrestrial species are likely limited in their dispersal by similar geographic factors as mouse lemurs, potentially leading to a separation of lineages through rivers and elevation in response to varying paleoclimatic conditions. Depending on the respective time period that passed since colonization of humid lowland habitats, subsequent evolutionary dynamics may range from an initial genetic differentiation and pronounced population structure to complete allopatric speciation (e.g., Pirani et al, 2022). In fact, rivers were already shown to delimit the distributions of frogs (Gehring et al, 2012), lemurs (Goodman & Ganzhorn, 2004; Lei et al, 2017), reptiles and small mammals (Everson et al, 2020) along Madagascar's east coast.…”