The riverine thruway hypothesis: rivers as a key mediator of gene flow for the aquatic paradoxical frog Pseudis tocantins (Anura, Hylidae)

Context Rivers, landscape, and climate can alter patterns of gene flow and consequently, shape intraspecific genetic variation. While rivers are predicted to halt gene flow in terrestrial species, they may facilitate migration for aquatic species. Amphibians are usually seen as water-dependent, yet multiple studies have indicated that rivers exert a barrier effect on these organisms. Objectives In this study, we investigated the effects of rivers and other abiotic factors, such as climate and geography on genetic variation of a highly aquatic frog (Pseudis tocantins) inhabiting central Brazil. Methods We sequenced fragments of one mitochondrial and two nuclear genes of 179 individuals of P. tocantins from 19 localities along the Tocantins-Araguaia Basin in Brazil and used Generalized Dissimilarity Modeling (GDM) to test the role of rivers, landscape, and climate features on its genetic differentiation. Next, we tested three scenarios of migration along the Tocantins-Araguaia Basin using approximate Bayesian computation (ABC). Results We found that genetic differentiation among localities is mostly explained by the influence of river connectivity. Conversely, elevation, slope, and past and current climate have little or no impact on genetic differentiation. Furthermore, our results show that patterns of migration took place directionally, from upstream to downstream sites. Conclusions Rivers have shaped patterns of intraspecific diversity in P. tocantins by acting as the most important facilitator of gene flow. Therefore, we suggest that future research should include the role of rivers as a facilitator of gene flow, especially for those species that are associated with aquatic environments.

Automated summary

Rivers, landscape, and climate can alter patterns of gene flow and shape intraspecific genetic variation. The study on highly aquatic frog Pseudis tocantins in central Brazil found that genetic differentiation among localities is mostly explained by river connectivity, while elevation, slope, and climate have little impact. Migration patterns took place directionally from upstream to downstream sites.