C. Gascon et al., PATTERNS OF GENETIC POPULATION DIFFERENTIATION IN 4 SPECIES OF AMAZONIAN FROGS - A TEST OF THE RIVERINE BARRIER HYPOTHESIS, Biotropica, 30(1), 1998, pp. 104-119
Patterns and levels of allozyme variation among populations of Amazoni
an frogs were used to test the riverine barrier hypothesis of species
differentiation. Two frog species were sampled from each of the two ma
in forest habitats on both banks of the Jurua River in the southwester
n Brazilian Amazon Basin at various points along its course to contras
t different barrier strengths. Scarthyla ostinodactyla and Scinax rubr
a were sampled from flooded forest (varzea), and Physalaemus petersi a
nd Epipedobates femoralis from non-flooded forest (terra firme). All s
pecies showed high levels of within-population genetic variation. Aver
age Nei's (1978) and Rogers' (1972) genetic distances between sampled
sites for all species were high indicating substantial among-populatio
n differentiation. The observation of low gene flow between sampled si
res within species was further substantiated with Slatkin's (1993) M a
nalyses. Randomization tests suggested that there was some population
structure at a few assayed polymorphic loci that was consistent with t
he riverine barrier hypothesis. However, it was apparent from the raw
allozyme frequency data that these results were largely driven by subs
tantial differentiation al one or a few collecting localities rather t
han by basin-wide patterns of riverine differentiation. Phenograms usi
ng genetic distance matrices supported this interpretation. Patterns o
f geographic variation are probably more consistent with the idea of t
his region being a zone of secondary contact.