Functional significance of variation in trophic morphology within feeding microhabitat-differentiated cichlid species in Lake Malawi

Shape variation in trophic morphology between species in two trophic guilds (zooplankton and epilithic algal feeders) was investigated using landmark-based geometric morphometrics. Three disarticulated bone elements from the head region were examined; the neurocranium, the premaxilla and lower jaw. From separate analyses of each bone element, significant shape variation was identified between species in each trophic guild. The deformation grids generated revealed that, for the zooplankton feeders, Ctenopharynx pictus has a longer neurocranium, a longer and ventrally directed vomer, a larger orbit, a shorter ascending arm, a shorter maxillad spine, and a more compressed articular bone relative to Copadichromis borleyi. In algal feeders, Labeotropheus fuelleborni has a shorter neurocranium, a smaller orbit, a ventrally directed vomer, a longer ascending arm, a shorter dentigerous arm, increased height of the articular process, and a more elongated dentary than Petrotilapia genalutea. Observed anatomical differences are discussed in terms of function, specifically with respect to the feeding microhabitat differentiation between species in each trophic guild. These differences enable us to appreciate the role that trophic morphology plays in enhancing ecological segregation, leading to coexistence of the species.

Body shape variation in relation to resource partitioning within cichlid trophic guilds coexisting along the rocky shore of Lake Malawi

To appreciate better how cichlids segregate along the trophic, spatial and temporal dimensions, it is necessary to understand the cichlids' body design, and its role in resource partitioning. We investigated body shape variation, quantified using landmark-based geometric morphometrics, among cichlid species belonging to algal and zooplankton feeders coexisting along the rocky shores of Lake Malawi, in order to elucidate the adaptive significance of body shape. Significant differences were found within zooplankton feeders in which Copadichromis borleyi had a shorter gape, smaller eyes and shorter caudal peduncle relative to Ctenopharynx pictus and, within algal feeders, Labeotropheus fuelleborni had a shorter and inferior subterminal gape, and shorter head relative to Petrotilapia genalutea. Variation among species is discussed with reference to trophic and feeding microhabitat differentiation which enables us to appreciate the role of body shape in enhancing ecological separation, and thus leads to coexistence among cichlid species.