| Coevolution of mate preference and coloration through the built-up of genetical covariance is a crucial step towards sympatric speciation by sexual selection. That mode of speciation seems to explain much of the explosive speciation rates of haplochromine cichlids in Lake Victoria and maybe in Lake Malawi. The two goals of this project are: (1) to identify the genetical mechanism of coevolution between mate preference and colouration in Lake Victoria cichlids: linkage disequilibrium that has to be maintained by selective mating, or physical linkage which protects once evolved covariance against recombination and may lead to particularly rapid speciation; (2) to identify the selection pressures that lead to build-up and/or maintenance of covariance between polymorphic preference and polymorphic colouration. The latter means asking for the conditions under which sexual selection becomes disruptive. Although evidence for disruptive sexual selection in sympatry is present from descriptive fieldwork and behavioural experiments, too little is known about the genetics of colouration and mate preferences, and about the conditions under which sexual selection becomes disruptive, to understand whether and when such selection can cause sympatric speciation. By making in one case two, and in another three generations of crosses between preference morphs and their preferred colour morphs, and between preference morphs and the nonpreferred colour morphs, we will test whether genes for preference and those for colour segregate independently, and whether disruptive variation in preferences has fitness consequences. By measuring 5 different potential fitness consequences, we will test predictions from different fuctional models of sexual selection: "good genes" models (e.g. sex-ratio selection, selection for parasite resistance) versus nonadaptive models, such as Fisherian runaway and sensory exploitation. |
