Ridges and rivers: a test of competing hypotheses of Amazonian diversification using a dart-poison frog (Epipedobates femoralis)

Abstract

Mitochondrial DNA cytochrome b sequence data from a dart-poison frog, Epipedobates femoralis, were used to test two hypotheses of Amazonian diversi¢cation: the riverine barrier and the ridge hypotheses. Samples were derived from sites located on both banks of the Rio Jurua¨and on both sides of the Iquitos Arch in western Amazonia. The phylogeographic structure was inconsistent with predictions of the riverine barrier hypothesis. Haplotypes from opposite river banks did not form monophyletic clades in any of our phylogenetic analyses, nor was the topology within major clades consistent with the riverine hypothesis. Further, the greatest di¡erentiation between paired sites on opposite banks was not at the river mouth where the strongest barrier to gene £ow was predicted to occur. The results instead were consistent with the hypothesis that ancient ridges (arches), no longer evident on the landscape, have shaped the phylogeographic relationships of Amazonian taxa. Two robustly supported clades map onto opposite sides of the Iquitos Arch. The mean haplotypic divergence between the two clades, in excess of 12%, suggests that this cladogenic event dates to between ¢ve and 15 million years ago. These estimates span a period of major orogenesis in western South America and presumably the formation of these ancient ridges.

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

“…Gascon et al (1998) found patterns of allozyme divergence in several frog species that were consistent with the hypothesis that the Iquitos Arch has had a significant impact on interpopulation divergence. Finally, a study of mtDNA divergence among populations of the poison frog Epipedobates femoralis (currently named Allobates femoralis) revealed patterns consistent with the hypothesis that the Iquitos Arch has influenced population genetic differentiation along the Jurua a river (Lougheed et al, 1999).…”

“…Time of divergence was calculated using an approximate rate of substitution for cytochrome b (0.8-2.5% divergence per million years) (Lougheed et al, 1999) in combination with genetic distances between cytochrome b sequences (using the Kimura 2-parameter model to correct for multiple substitution). The range of average divergence times estimated between species from western Amazonia and D. quinquevittatus and D. castaneoticus was 10-31 million years.…”

“…Gascon et al (1998) provided evidence that rivers do not constitute effective barriers to gene flow in the Brazilian lowlands for several different frog species. Lougheed et al (1999) tested the Riverine Barrier Hypothesis for divergence among populations of the poison frog A. femoralis. They found that populations on opposite sides of the Jurua a River are not monophyletic, nor is divergence highest at the junction of the Jurua a and Amazon Rivers, in contrast to the predictions of the Riverine Barrier Hypothesis.…”

“…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).…”

Syntopic frogs reveal different patterns of interaction with the landscape: A comparative landscape genetic study of Pelophylax nigromaculatus and Fejervarya limnocharis from central China

“…The AMOVA for P. nigromaculatus was likely confounded by the shared genetic composition of site 1 with sites 6, 7, and 8 (see further discussion below). Indeed, it is not surprising that the Yangtze River imposes a significant barrier effect on both species as such water bodies are well documented to impede amphibian movement (Lampert, Rand, Mueller, & Ryan, 2003; Lougheed et al., 1999). Finally, IBR analyses also revealed differences in causal landscape features resisting the movement and dispersal of each species, elevation for P. nigromaculatus and road and land cover for F. limnocharis (Table 5, Figure 2b,c).…”