Abstract of Doctoral Dissertation

Mitochondrial DNA (mtDNA) restriction fragment length variation was used to study the evolution of the haplochromine cichlids of Lake Malawi in East Africa. This investigation was directed at three levels of taxonomic hierarchy. First, phylogenetic relationships were examined in a broad sampling of the most ecologically and morphologically diverse of Lake Malawi's haplochromines. Second, a more detailed study was initiated to explore the phylogenetic relationships and taxonomic distribution of mtDNA haplotypes among the members of a single trophic guild, the rock-dwelling mbuna. Finally, a population study of selected mbuna species was conducted to explore the demographics of speciation in these very recently derived taxa. The first study revealed six primary mtDNA lineages, two of which included large numbers of diverse taxa, whereas each of the other four were found in single species. All the mbuna examined comprised one lineage; however, a number of other species, not previously recognized as mbuna, were also included in this group, indicating a paraphyletic relationship. Sequence divergence was found to be remarkably low, indicating unprecedented rapidity of speciation and radiation. Further examination of the mbuna revealed two mtDNA subgroupings. Interestingly, these mtDNA lineages were each found in multiple species and are interpreted as a retained ancestral polymorphism. This result has significant implications for the further use of mtDNA in phylogenetic reconstruction of this group because the mtDNA gene tree is incongruent with the mbuna species tree. The final study sought to examine the potential role of founding events in the speciation of local endemics restricted to a single group of islands. Haplotype diversity and frequency distribution indicated that one of these species did indeed experience a bottleneck during or subsequent to its isolation. For the other species, significant differences in haplotype frequency in the presence of high haplotype diversity, presents a somewhat equivocal result; several potential explanations are examined. In two species, replicate samples from different sites at single locations produced significant differences in haplotype frequency. This result suggests a fine scale of spatial structuring, resulting from extreme philopatry. Taken as a whole these results provide substantial insight into both pattern and process of speciation and radiation of this evolutionarily interesting group.