Abstracts (first author)
Divergence between lake and stream populations in an East African cichlid fish
Integrative studies of species that occur along an environmental gradient provide important insights into ecological speciation and serve as prime examples for the presence of a speciation continuum. The cichlid species Astatotilapia burtoni occurs in lacustrine environment as well as in the surrounding rivers of Lake Tanganyika (LT), offering the possibility to study a lake-stream environmental gradient in a member of a large cichlid adaptive radiation in East Africa. We have established phylogeographic relationships and assessed the population structure in A. burtoni from the southern LT drainage using neutral nuclear (microsatellite) and mtDNA markers. We detect an unexpectedly high genetic diversity in A. burtoni, exceeding – at least in mtDNA – the diversity of the entire cichlid species flock of Lake Victoria, and a relatively complex phylogeographic pattern. Next, we have examined morphological differences among these populations by analyzing body shape. Based on these results, we focused on four lake-stream systems in detail. We here find that stream fish show a more inferior mouth, a more streamlined body, and shorter gill-rakers compared to lake fish, shifts presumably associated with differential foraging styles. Current work is now evaluating this hypothesis directly, and includes high-density SNP marker data generated by RADseq for population genomic analyses.