Riverine barriers and the geographic distribution of Amazonian species

Abstract

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.

Geographical patterns of deep mitochondrial differentiation in widespread Malagasy reptiles

“…(4) Rivers can be important factors in shaping phylogeographic patterns of vertebrates (Capparella, 1991;Eriksson et al, 2004;Pellegrino et al, 2005;Peres et al, 1996), although some studies have failed to find support for this hypothesis (Gascon et al, 2000;Lougheed et al, 1999;Lugon-Moulin et al, 1999). In Madagascan reptiles, the plated lizards of the genus Zonosaurus are an example.…”

Historical Diversification of a Terra-Firme Forest Bird Superspecies: A Phylogeographic Perspective on the Role of Different Hypotheses of Amazonian Diversification

“…In a phylogenetic and population genetics framework, the three main predictions of the riverine barrier hypothesis are: (1) sister intraspecific clades and species will occur across major rivers rather than within major Amazonian interfluves (Moritz et al 2000); (2) phylogeographic analyses should allow the distinction between primary divergence across rivers (predicted by the riverine barrier hypothesis) from secondary contact along rivers between nonsister lineages (Moritz et al 2000); and (3) within a river basin, genetic similarity between populations separated by a river should be higher in the headwaters (where the river is narrower) than in its lower part (Gascon et al 2000).…”

“…A second prediction of the riverine barrier hypothesis comes from the observation that the upper reaches of all major Amazonian rivers are narrower than the lower reaches; therefore, a gradual reduction of the ''river-barrier effect'' is expected to take place from the lower to the upper part of the river's course (Haffer 1992). The expected outcome is a higher genetic similarity between populations from opposite banks in the headwaters than in the lower parts of rivers (Gascon et al 2000).Originally developed as a speciation model for Palearctic birds (Stresemann 1919), the refuge hypothesis was first applied to explain patterns of avian speciation in the Neotropics by Haffer (1969). This hypothesis holds that climatic and 1304 ALEXANDRE ALEIXO vegetational changes promoted cladogenesis in organisms by cyclically fragmenting and reuniting their ranges.…”

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

“…A variety of hypotheses have been proposed to explain the elevated species diversity in the Amazon Basin (Gascon et al, 2000;Moritz et al, 2000). Many of these hypotheses propose specific isolating barriers as mechanisms that generated genetic divergence (Patton et al, 1994).…”