GENETIC AND MORPHOLOGICAL VARIATION IN VANZOLINIUS-DISCODACTYLUS - A TEST OF THE RIVER HYPOTHESIS OF SPECIATION

Allozyme and morphological variation among populations of an Amazonian frog were analyzed to test for a riverine effect on population differ entiation. High levels of genetic diversity within populations and gen etic diversification among populations were Found. Although correlatio ns between generic and geographic distances of population pairs were p ositive, they were nor significant and indicated that sires that mere dose geographically were nor genetically more similar. Only one of the 15 polymorphic loci showed any variation in allozyme frequency attrib utable to the presence of the river, but none of the overall among-pop ulation component of allozyme frequency variation (F-ST = 0.368) can b e attributed to the river (F-RT = 0.000). Significant differences in m orphology (corrected for sire differences) were Found among the 11 pop ulations 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 a ll morphological variables failed to detect obvious groups based on ri ver bank locality. We could detect no congruence of pattern between mo rphological and generic variation among populations. These results sug gest that morphological characters may evolve at different rates than detectable allozyme differentiation.