Specialized morphology for a generalist diet: Spatial and seasonal surveys reveal Liem's Paradox in an African cichlid fish

Ecomorphology is founded on the premise that ecological interactions are reflected in adaptive morphological change across individuals, populations, and communities. Specialization in feeding structures is often used to describe and classify species and is believed to be an important mechanism driving speciation in a number of taxa including Darwin's finches, Caribbean labrid fishes, and African cichlid fishes. However, morphology and ecology are not always tightly linked, and a number of studies have shown species with specialized morphologies consuming primarily generalist diets, a phenomenon known as Liem's Paradox. In this thesis, I use both spatial (interdemic) and seasonal studies to explore Liem's Paradox in natural populations of the specialized "molluscivorous" African cichlid, Astatoreochromis alluaudi. In an interdemic study, I quantified relationships among diet, morphology and the environment in A. alluaudi from six sites in Uganda. Pharyngeal jaw and muscle morphology differed among populations, with jaw traits explaining most of the variation. Similarly, I found differences in diets among sites; mollusks were rare, found in the stomachs of only two populations sampled. Trophic morphology did match the observed diet in two sites, but diet did not correlate with either morphology or environmental variables across the six sites. The absence of tight links among morphology, diet, and prey abundance among populations of A. alluaudi is consistent with Liem's Paradox. To examine whether a mismatch between diet and morphology occurs seasonally or chronically in populations of A. alluaudi, I used a seasonal survey of diet at Lake Saka, a site where A. alluaudi exhibits a molluscivorous morphology, but an omnivorous diet. Using stomach content and isotope analysis, I found that mollusks form only a small proportion of the overall diet of A. alluaudi, and fish and insects are the most important prey items consumed. Rainfall was strongly related to the percentage of fish prey consumed. Consistent with Liem's Paradox, A. alluaudi feeds mostly on a general prey source, fish, during the rainy season when this resource is abundant, and switches its diet to feed on snails and insects when fish prey are potentially less available. This thesis provides evidence to support Liem's Paradox across a spatial and seasonal scale, and suggests that the ecology of a species should not be inferred by its morphology alone.