RESUMO
We used 16S rRNA, 12S rRNA, and cytochrome-b sequence to investigate the history of the "30-chromosome" Hyla, a diverse assemblage of neotropical treefrogs. Three aspects of these frogs were examined: (1) phylogenetic relationships among constituent species groups, among the species of one of these groups (Hyla leucophyllata group), and among populations of Hyla leucophyllata; (2) the apparent age of cladogenetic events; and (3) the phylogeography of H. leucophyllata. Mixed success in resolving the phylogeny is not because of a lack of character variation; levels of genetic divergence are high and suggest pre-Pleistocene diversification, even among populations. Close temporal proximity of ancient cladogenetic events might make resolution of the topology difficult using any character set. At the population level, current geographic proximity is a poor predictor of phylogenetic affinity. A long history of dispersal and colonization may complicate, or even preclude, the accurate recovery of the history of this species in the Amazon Basin. It remains to be seen whether the patterns found here will prove common among neotropical frogs.
Assuntos
Anuros/classificação , Anuros/genética , Mapeamento Cromossômico , Grupo dos Citocromos b/genética , Evolução Molecular , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico/genética , Animais , DNA Mitocondrial/genética , DNA Ribossômico/genética , Geografia , Funções Verossimilhança , Reação em Cadeia da Polimerase , América do Sul , TempoRESUMO
Rivers have been suggested to have played an important role in shaping present-day patterns of ecological and genetic variation among Amazonian species and communities. Recent molecular studies have provided mixed support for the hypothesis that large lowland Amazonian rivers have functioned as significant impediments to gene flow among populations of neotropical species. To date, no study has systematically evaluated the impact that riverine barriers might have on structuring whole Amazonian communities. Our analyses of the phylogeography of frogs and small mammals indicate that a putative riverine barrier (the Juruá River) does not relate to present-day patterns of community similarity and species richness. Rather, our results imply a significant impact of the Andean orogenic axis and associated thrust-and-fold lowland dynamics in shaping patterns of biotic diversity along the Juruá. Combined results of this and other studies significantly weaken the postulated role of rivers as major drivers of Amazonian diversification.
Assuntos
Especificidade da Espécie , Animais , Ecologia , Geografia , América do SulRESUMO
Mitochondrial DNA cytochrome b sequence data from a dart-poison frog, Epipedobates femoralis, were used to test two hypotheses of Amazonian diversification: the riverine barrier and the ridge hypotheses. Samples were derived from sites located on both banks of the Rio Juruá 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 differentiation between paired sites on opposite banks was not at the river mouth where the strongest barrier to gene flow 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 five 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.