Parasite escape through trophic specialization in a species flock

In adaptive radiations species diversify rapidly to occupy an array of ecological niches. In these different niches, species might be exposed to parasites through different routes and at different levels. If this is the case, adaptive radiations should be accompanied by a turnover in parasite communities. How the adaptive radiation of host species might be entangled with such a turnover of parasite communities is poorly documented in nature. In the present study, we examined the intestinal parasite faunas of eleven species belonging to the tribe Tropheini, one of several adaptive radiations of cichlid fishes in Lake Tanganyika. The most parsimonious ancestral foraging strategy among Tropheini is relatively unselective substrate ingestion by browsing of aufwuchs. Certain lineages however evolved more specialized foraging strategies, such as selective combing of microscopic diatoms or picking of macro-invertebrates. We found that representatives of such specialized lineages bear reduced infection with intestinal acanthocephalan helminths. Possibly, the evolution of selective foraging strategies entailed reduced ingestion of intermediate invertebrate hosts of these food-web transmitted parasites. In Tropheini, trophic specialization is therefore intertwined with divergence in parasite infection. We conclude that the study of parasite communities could improve our understanding of host evolution, ecological speciation and the origin of adaptive radiations.