Abstracts (first author)


Divergence between lake and stream populations in an East African cichlid fish

Author(s): Egger B, Theis A, Ronco F, Indermaur A, Roesti M, Berner D, Salzburger W


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.

Abstracts (coauthor)


Divergent selection due to differences between environments often triggers ecological speciation. The cichlid species Astatotilapia burtoni occurs in the lacustrine environment as well as in the surrounding rivers of Lake Tanganyika. In this setting of replicated lake-stream populations, ecologically relevant traits such as gill rakers and the pharyngeal jaw apparatus (important for food uptake) are supposed to be under divergent selection as a consequence of different resource availabilities and utilization. Here, we study traits related to gill raker morphology (gill arch length, gill raker length and raker number), apply geometric morphometrics on pharyngeal jaws and analyse gut and stomach contents of four lake-stream systems in order to tests for shifts associated with differential foraging modes in A. burtoni.


Color and pigmentation patterns seem to play a central role in the explosive radiations of cichlid fish species in the East African Great Lakes. The majority of African cichlid species are members of a single tribe, the Haplochromini. A characteristic feature and possibly a key-innovation of haplochromine cichlids are the so-called egg-spots in form of ovoid markings on the anal fins, made up of carotenoid based pigment cells. Egg-spots show a tremendous variability among different haplochromine species with regard to number, size, intensity, coloration and position on the fin. In this study we investigate the differentiation of egg-spots within a single species, Astatotilapia burtoni, which inhabits lacustrine and riverine environments of the Lake Tanganyika drainage. This phylogeographic setting enables us to study egg-spots in different habitats under divergent selection regimes. Four lake-stream population groups were analyzed and differences between stream and lake populations as well as between sexes were detected, indicating that natural and sexual selection influence the egg-spot phenotype in this species.


Chairman: Octávio S. Paulo
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XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon


Computational Biology & Population Genomics Group