FWF-Project P20994-B03

Summary

The Great Lakes of East Africa with their species flocks of cichlid fishes provide excellent model systems for the study of adaptive radiation, an evolutionary phenomenon during which a multitude of species emerges within a short period of time. The present proposal builds on a previous grant addressing evolutionary patterns and mechanisms during speciation and adaptive radiation. Our focus turns towards the understanding a critical issue for this process, the role of natural selection as driving force of diversification. We plan to study the role of adaptive evolution in two selected sets of model species, the first at an early stage of radiation in a satellite lake of Lake Victoria, and the second at a mature stage in Lake Tanganyika. Using a combination of comparative morphological, population genetic and quantitative genetic methods we will address three major topics: (1) Do morphological differences among populations or species have an inherited basis? (2) Do the observed eco-morphological differences bear the signature of natural selection? (3) What is the relative importance of divergent and stabilizing selection, enforced by competitive interactions, in evolutionary young and mature stages of adaptive radiation? We reconstruct quantitative trait evolution in the wild, through joint analysis of relatedness and quantitative trait variation at the population level of traits critical for ecological specialization. In a first step the genetic basis of morphological differences among populations or species must be demonstrated by heritability-calculations of related versus unrelated population members, or by hybrid experiments. Then we assess the presence and direction of selection by comparing neutral genetic variation of microsatellite markers to morphological variation of ecologically relevant quantitative traits. We concentrate on characters that have been shown to be relevant for niche differentiation, such as body proportions and the shape of particular viscerocranial bones, and assess them by a combination of geometric morphometric and traditional comparative methods. To demonstrate selection-driven evolution against the null-hypothesis of evolution by random genetic drift we use a combination of GST/QST comparisons by applying the “animal model approach” to natural populations.