US-Tanzania Dissertation Enhancement: Diversification in Lake Tanganyika Endemics: Gastropods and Cichlid Fishes Compared

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Since their discovery, the cichlid fish faunas of the East African rift lakes have drawn attention as remarkable cases of within-lake speciation and adaptive divergence. Among these lakes, however, Lake Tanganyika is distinctive in the extent to which its other taxa have also diversified: over 350 unique non-cichlid species are found within this lake. Tanganyika is therefore a unique ecosystem for studying processes of endemic diversification: how is it that some taxa have diversified so dramatically within this single lake? One hypothesis is that substrate heterogeneity in the littoral zone allows taxa to ecologically specialize on specific substrates, and isolation between subpopulations in this heterogeneous environment creates the potential for speciation. Although this hypothesis for within-lake allopatric speciation was first proposed over 25 years ago, its role in creating patterns of species diversity within the East African rift lakes remains largely untested. If isolation of populations through substrate specificity and limited dispersal among habitat patches has driven diversification, it is hypothesized that species from groups with high endemic diversity will show evidence of restricted gene flow between populations. This research will investigate this hypothesis in two unrelated groups that have produced substantial endemic radiations in Lake Tanganyika: Lavigeria gastropods, and cichlid fishes of the tribe Tropheini. Study species of cichlid fishes and snails are all benthic herbivores restricted to rocky substrates. This obligate habitat association, coupled with their notably high lake-wide species diversity, suggests that ecological specialization on rocky substrate has promoted speciation in both snail and cichlid groups. Therefore, ecological specialization may drive parallel genetic subdivision of populations and diversification in multiple unrelated taxonomic groups. To test these hypotheses, both mitochondrial DNA sequence and microsatellite data will be used to analyze comparative patterns of population genetic structuring in cichlids and snails along the heterogeneous shoreline bordering Kigoma, Tanzania. Understanding the impact that ecological specialization has on gene flow dynamics and patterns of diversity across these taxa will allow the testing of important, long-standing questions about the processes of diversification among Lake Tanganyika's exceptionally diverse faunas.