Patterns and process during the diversification of the cichlid fishes in Lake Malawi, Africa.

摘要

The 500-1000 cichlid species endemic to Lake Malawi constitute one of the most rapid and extensive radiations of vertebrates ever discovered. The objective of this dissertation was to test the assumptions and predictions of several recently published models of cichlid speciation. First, a novel assay of female choice was used to evaluate the role of visual cues during conspecific recognition. The results of this experiment demonstrate that females are able to identify conspecific mates using only visual cues. Second, the assumptions of a recent model of speciation via intrasexual selection were tested by comparing aggressive behavior during territorial contests among five closely related cichlid species from Lake Malawi. I found that interactions between conspicuously heteromorphic males tend to be less aggressive than between those of homomorphic males. Third, I used transect data to evaluate the intrinsic and extrinsic factors that have affected the dispersal of 17 closely related cichlid species introduced to Thumbi West Island in Lake Malawi. A quarter of a century after their initial introduction, I found that the translocated cichlid community around Thumbi West Island is still in a state of flux, as many species continue to spread around the island. Next, I evaluated the patterns of divergence predicted by three competing speciation models that differ in the temporal action of natural and sexual selection by using AFLP to reconstruct the evolutionary relationships among 20 species of the ubiquitous rock dwelling subgenus Pseudotropheus tropheops. I found that cladogenesis is associated with numerous unambiguous changes in male color states. A geometric morphometric analysis of the lower jaw of these taxa revealed that the repeated differentiation of jaw morphology is associated with species habitat preference. Finally, I used AFLP data to reconstruct the evolution of species within three genera of sand dwelling cichlids that construct elaborate male display platforms. I found that sister taxa with distinct bower morphologies, and that exist in discrete leks separated by only 1-2m of depth, are divergent in both sexually selected and ecological traits. These phylogenies suggest that the forces of sexual and ecological selection have been intertwined during the speciation of these groups.