Patterns of Genetic Population Differentiation in Four Species of Amazonian Frogs: A Test of the Riverine Barrier Hypothesis¹

Abstract

Patterns and levels of allozyme variation among populations of Amazonian frogs were used to test the riverine barrier hypothesis of species differentiation. Two frog species were sampled from each of the two main forest habitats on both banks of the Juruá River in the southwestern Brazilian Amazon Basin at various points along its course to contrast different barrier strengths. Scarthyla ostinodactyla and Scinax rubra were sampled from flooded forest (varzea), and Physalaemus petersi and Epipedobates femoralis from non‐flooded forest (terra firme). All species showed high levels of within‐population genetic variation. Average Nei's (1978) and Rogers’ (1972) genetic distances between sampled sites for all species were high indicating substantial among‐population differentiation. The observation of low gene flow between sampled sites within species was further substantiated with Slatkin's (1993) M̂ analyses. Randomization tests suggested that there was some population structure at a few assayed polymorphic loci that was consistent with the riverine barrier hypothesis. However, it was apparent from the raw allozyme frequency data that these results were largely driven by substantial differentiation at one or a few collecting localities rather than by basin‐wide patterns of riverine differentiation. Phenograms using genetic distance matrices supported this interpretation. Patterns of geographic variation are probably more consistent with the idea of this region being a zone of secondary contact.

Phylogeny and biogeography of paradoxical frogs (Anura, Hylidae, Pseudae) inferred from 12S and 16S mitochondrial DNA

“…Within the Amazon basin, sites along major tributaries have similar frog assemblages (Azevedo-Ramos and Galatti, 2001), and previous work showed that Amazonian rivers are not barriers for frog dispersal (Gascon et al, 1996(Gascon et al, , 1998. The low divergence between the geographically distant populations of L. limellum from the Amazon basin in the present study (Figs.…”

Rivers shape population genetic structure in Mauritia flexuosa (Arecaceae)

“…Rivers influence animal distributions such as birds (e.g., Fernandes, Wink, & Aleixo, 2012), frogs (Gascon, Lougheed, & Bogart, 1998), and mammals (e.g., Patton, Da Silva, & Malcolm, 2000) that disperse the seeds of palms and other plants. The impact of rivers on the genetic structure of other plants such as Myricaria laxiflora (Tamaricaceae; Liu, Wang, & Huang, 2006) has shown that water flow is a major driver of seed and propagule dispersal, and that migration patterns among populations can form along rivers, similar to what we found here in M. flexuosa .…”

Molecular systematics and phylogeography of Amazonian poison frogs of the genus Dendrobates

“…An important prediction of this hypothesis is that species or haplotype assemblages should demonstrate monophyly between arches, and arches should reflect points of ancient divergence of species (Patton and da Silva, 1998). Several authors have found evidence to support this hypothesis in rodent and marsupial species (Patton and da Silva, 1998), and frogs (Gascon et al, 1998;Lougheed et al, 1999). Haffer (1969Haffer ( , 1990 proposed that tropical forests expanded and contracted during glacial cycles (Refuge Hypothesis).…”

“…The modern formulation of this ''Riverine Barrier'' hypothesis (Sick, 1967) proposes that gene flow in Amazonia is restricted by the formation of rivers in regions where forests were previously uninterrupted. This hypothesis predicts that increased river width will result in increased divergence, that populations on each side of a river should form monophyletic groups, and that gene flow should be higher at headwater regions (Capparella, 1988;Gascon et al, 1998). Evidence for and against this hypothesis has been published (e.g., Capparella, 1988;Patton and da Silva, 1998).…”

“…Examination of genetic divergence across populations or groups from a variety of taxa is necessary to test these biogeographic hypotheses (Gascon et al, 1998). Models of vicariance predict that divergence between populations or closely related species should reflect the presence of specific biogeographic barriers within a geographic region (Patton and da Silva, 1998).…”