Testing main Amazonian rivers as barriers across time and space within widespread taxa

Abstract

Aim Present Amazonian diversity patterns can result from many different mechanisms and, consequently, the factors contributing to divergence across regions and/or taxa may differ. Nevertheless, the river‐barrier hypothesis is still widely invoked as a causal process in divergence of Amazonian species. Here we use model‐based phylogeographic analyses to test the extent to which major Amazonian rivers act similarly as barriers across time and space in two broadly distributed Amazonian taxa. Local Amazon rain forest. Taxon The lizard Gonatodes humeralis (Sphaerodactylidae) and the tree frog Dendropsophus leucophyllatus (Hylidae). Methods We obtained RADseq data for samples distributed across main river barriers, representing main Areas of Endemism previously proposed for the region. We conduct model‐based phylogeographic and genetic differentiation analyses across each population pair. Results Measures of genetic differentiation (based on FST calculated from genomic data) show that all rivers are associated with significant genetic differentiation. Parameters estimated under investigated divergence models showed that divergence times for populations separated by each of the 11 bordering rivers were all fairly recent. The degree of differentiation consistently varied between taxa and among rivers, which is not an artifact of any corresponding difference in the genetic diversities of the respective taxa, or to amounts of migration based on analyses of the site‐frequency spectrum. Main conclusions Taken together, our results support a dispersal (rather than vicariance) history, without strong evidence of congruence between these species and rivers. However, once a species crossed a river, populations separated by each and every river have remained isolated—in this sense, rivers act similarly as barriers to any further gene flow. This result suggests differing degrees of persistence and gives rise to the seeming contradiction that the divergence process indeed varies across time, space and species, even though major Amazonian rivers have acted as secondary barriers to gene flow in the focal taxa.

Historical biogeography identifies a possible role of Miocene wetlands in the diversification of the Amazonian rocket frogs (Aromobatidae: Allobates)

“…Quaternary events of river avulsions and captures in the Amazon drainage may help explain part of the dispersal and species accumulation in particular interfluves (Pupim et al., 2019; Rosseti et al, 2015). Overall, the major Amazonian rivers seem to have acted as semi‐permeable barriers for Allobates , allowing dispersal and isolation among neighbouring interfluves, as reported for other taxa (Naka & Brumfield, 2018; Pirani et al., 2019).…”

Systematics and biogeography of theBoana albopunctataspecies group (Anura, Hylidae), with the description of two new species from Amazonia

“…However, smaller and highly dynamic meandering rivers probably represent more permeable barriers. Therefore, we assume that successive dispersals across major Amazonian rivers (parapatric speciation) (Pirani et al, 2019), as well as hydrological changes (vicariant speciation) (Naka et al, 2018), could have been major processes of diversification in these frogs.…”

Pseudocongruent phylogeography reflects unique responses to environmental perturbations in a biodiversity hotspot

“…They associate diversification with uplift of the Great Escarpment, Plio-Pleistocene climatic cycles, and note multiple eastward flowing rivers that may have acted as additional barriers between coastal lineages. Pirani et al (2019) indicated that divergence-time across river basins varies, suggesting that river barriers can be dynamic considering connection and isolation induced by climatic ameliorations. By contrast, forest-living snakes in the Congo River basin exhibit divergence across the river independent of isolation by climatic ameliorations (Allen et al, 2021).…”