| Although the roles of isolation and selection in driving divergence in natural populations have been studied, the relative importance of each has rarely been tested. My thesis examines the roles of these two factors, geographical isolation and divergent selection in different habitats, in differentiation of populations of the Andean treefrog, Hyla andina. The unique distribution of this species in deeply incised, geographically disjunct valleys and across a broad range of habitats provides an opportunity to test these factors. I collected morphological and genetic data for 2 populations in each of three river basins. Using genetic markers, mtDNA and DNA microsatellites, I found strong differentiation among populations, both within and among basins. The mtDNA data also suggest a possible deep division between the most southern basin and the two northern basins. Low gene flow between most sites suggests that these populations, and the basins, are indeed isolated. Differences among the basins also exist for some of the morphological characters examined (especially size). Within the two northern basins a similar (but not significant) relative relationship of the HIGH and LOW populations is evident, although the most southern basin often shows a reversed pattern. Similarity of morphological characters in similar habitats may suggest a role for selection. Overall, morphological patterns suggest that both isolation and selection may play a role in the phenotypic differences among populations. Differences in size among isolated basins, but also between habitats within each of the northern basins, may imply that initial differences were due to genetic drift in isolation, but strong selection for habitat differences may have then resulted in the reiterated pattern seen for HIGH and LOW populations. |
