PRF/J: Mechanisms of Speciation in an African Rift Lake and the Relationship Between Morphological Divergence and Molecular Variation

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Mitochondrial DNA sequences from four prosobranch gastropod genera (Lavigeria, Limnotrochus, Reymondia, Cleopatra) will be used to examine the effect of explosive speciation on molecular variation. This addresses a current controversy over the question of whether cladogenesis increases the rate of molecular evolution. From this data a phylogeny (to be constructed) will be used to test two competing hypotheses of allopatric speciation; the hypotheses have been proposed to explain the extreme diversity of endemic fauna in Lake Tanganyika, East Africa. One hypothesis relies on separation of the lake into distinct basins while the other maintains that existing habitat differences are sufficient to drive speciation. Sequence divergence from two genes of a highly diverse endemic clade, its nondiverse sister group, a related sympatric genus, and a fluvial outgroup. Results will show: (a) how morphological and molecular divergence are correlated with relative ages of the clades, and (b) whether morphological and molecular divergence are correlated within the diverse clade. Another goal is to compare patterns of mitochondrial sequence variation in the diverse gastropod clade with those from a diverse sympatric cichlid fish to derive a general lacustrine speciation model and to identify conservation priorities. %%% The molecular data set to be obtained will be used to test phylogenetic conclusions that emerged from previous morphometric studies of shell, soft anatomy, and electrophoretic characters. These molluscs are not particularly well known with regard to number of species, life histories, and ecology, so this study will provide the opportunity to learn details of fundamental biology. Past studies of Lake Tanganyika focussed on cichlid fish and the intended studies promise to yield a sort of comparative "yardstick" for those investigations by placing them in a broader context. In addition this will be the first molecular genetic study of Tanganyikan aquatic invertebrates, despite the fact they are major components of the benthic ecosystem.