Ontogenetic shifts in natural diet, chelae, and mandibles of the omnivorous freshwater crab Aegla uruguayana: linking morphology and function

Abstract

We analyze whether ontogenetic diet change in Aegla uruguayana Schmitt, 1942 is related to the morphological changes in chelae and mandibles. We use a combination of scanning electron microscope (SEM) observation, dietary composition analysis (stomach observation, trophic niche amplitude, trophic overlap, and feeding strategy), and geometric morphometric tools (discriminant analysis and two-block partial least squares analysis). The two structures analyzed by SEM show differences between juvenile and adult specimens, both in their cuticle and morphology specializations. In juveniles, the absence of the lobular tooth is the notable feature. However, in adult sizes, it is marked development. Both groups have simple setae with infracuticular articulation and denticles with different arrangements between groups. In the incisive mandible process, the teeth and spines present sharper points in juveniles and considerable wear in adults. Aegla uruguayana presented two trophic strategies: a profile of more predatory traits when younger and mostly detritivorous when adults. The analysis of geometric morphometry substantiates the patterns observed in SEM and stomach contents analysis. The morphology of smaller specimens is associated with the consumption of animal items (ephemeropteran larvae and cladocerans), while the morphology of larger specimens is related to the consumption of plant remains.