Abstracts (first author)
Competition driven ecological speciation in Lake Tanganyika cichlids
Disruptive selection operating on different habitat use can lead to ecological speciation. However the selective forces are often unclear. In Lake Tanganyika the cichlid fish Telmatochromis temporalis has two morphs: a small-bodied "shell" breeding morph, and a large-bodied "rock" breeding morph. We first show that body size differences are heritable in laboratory-reared first generation offspring. Using mtDNA and AFLP data we then show populations are philopatic, and that these morphs have evolved repeatedly. We next tested for divergence on habitat preference using substrate choice trials on wild-caught fish. We found individual habitat preferences in the absence of other fish were tightly linked to body size with larger individuals using rock, and smaller individuals using shells, irrespective of collection habitat. However, medium-sized "shell" males also used rock when given a free choice, but the presence of large competitor "rock" males caused them to shift towards the less preferred shell habitat, and to pair assortatively. Thus, the results support competition as a crucial agent driving the dichotomous habitat use observed in nature. Ecological speciation is feasible because smaller fish are favoured on shell habitat but outcompeted on rocks, while larger fish are selected against on shell habitats by predators.