Mechanisms of speciation in sympatry in polymorphic crater lake cichlid fish: the Neotropical Amphilophus citrinellus species complex

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Recently, both theoretical and empirical evidence for sympatric speciation suggested that some evolutionary conditions are conducive to speciation in sympatry. The Midas cichlid species complex (Amphilophus citrinellus) fits several of the key characteristics of these models - with strong assortative mating on the basis of a color polymorphism coupled with trophic and ecological differentiation based on a polymorphism in their pharyngeal jaws. This species complex is a young radiation in the process of speciation. We plan to use microsatellite markers and a segment of the mtDNA control region to study the population-genetics of polymorphic populations of the Midas cichlid species complex from three crater lakes and two large lakes in Nicaragua. All populations are known to be strongly genetically differentiated on the basis of geography. So far the available evidence suggests that genetic separation, even in fully sympatric conditions of the crater lakes, is more strongly based on color and we failed to find significant genetic structuring based on trophic differences and ecological niche separation between jaw morphs. Preliminary data therefore support the hypothesis that sexual selection contributes more strongly or earlier during the process of speciation than ecological separation. In this project we plan to increase the sampling and the ecological characterization of both morphs of Amphilophus citrinellus, and its closely related species, to investigate the rates of divergence (genetically and phenotypically - through morphometrics) and the mechanisms of repeated sympatric speciation in parallel ecological systems.