Genetic and Morphological Variation in Vanzolinius discodactylus: A Test of the River Hypothesis of Speciation

Abstract

Allozyme and morphological variation among populations of an Amazonian frog were analyzed to test for a riverine effect on population differentiation. High levels of genetic diversity within populations and genetic diversification among populations were found. Although correlations between genetic and geographic distances of population pairs were positive, they were not significant and indicated that sites that were close geographically were not genetically more similar. Only one of the 15 polymorphic loci showed any variation in allozyme frequency attributable to the presence of the river, but none of the overall among-population component of allozyme frequency variation (FST = 0.368) can be attributed to the river (FRT = 0.000). Significant differences in morphology (corrected for size differences) were found among the 11 populations in canonical variate space. In univariate Nested ANOVAs, five of the 12 morphological variables showed significant differences due to the presence of the river. However, cluster analysis performed on all morphological variables failed to detect obvious groups based on river bank locality. We could detect no congruence of pattern between morphological and genetic variation among populations. These results suggest that morphological characters may evolve at different rates than detectable allozyme differentiation.