Specialized morphology for a non-specialized diet: Liem’s paradox in an African cichlid fish

Abstract

Cichlid fishes of the East African Great Lakes represent some of the most diverse vertebrate faunas in the world, and trophic specialization, the specific adaptation of feeding structures to one type of prey, is often used to explain the coexistence of these closely related species. However, Liem’s Paradox suggests that organisms with specialized phenotypes may act primarily as generalist feeders in nature, which can create a mismatch between diet and morphology. Our goal was to study the diet of a widespread African cichlid, Astatoreochromis alluaudi, over the course of 1 year to test the hypothesis that the molluskvore-like morphology of this species is not an appropriate indicator of diet choice. Lake Saka, in Uganda, was sampled monthly throughout 2006, and stomach content analyses were performed on preserved specimens using established techniques to identify the relative importance of various prey items in the diet of A. alluaudi. Stomach content analyses indicated an omnivorous diet in all months, consisting mostly of insects, fish, and plant matter, whereas snails accounted for only a small portion of their overall diet. Although trophic morphology in this species is a plastic trait, specimens from Lake Saka exhibit a molluscivore-like morphology. Our data suggests that the morphology of this generalist feeder may have developed to exploit non-favoured resources, a clear example of Liem’s Paradox. This study emphasizes the importance of examining both stomach contents and trophic morphology before inferring the feeding ecology of a species.