Meeting Abstract
Establishing patterns of morphological convergence among organisms that share similar ecologies is the first step toward understanding the interplay between adaptation and constraint. In fishes, zooplanktivory is a specialized type of foraging often associated with particular morphological traits including large eyes, an emarginate caudal fin, a slender body shape and small body size. However, the morphological trends associated with zooplanktivory have yet to be described comparatively across a broad taxonomic scale and the effects of the ancestral foraging condition on the expected trajectories of morphological change remain unknown. As a first look we focus on marine butterflyfishes (family Chaetodontidae), a group that includes species with multiple forms of benthic foraging as well as zooplanktivory. Evolutionary model-fitting indicates that zooplanktivorous butterflyfishes are converging on eye size, caudal fin shape, body depth and body size optima that are separate from benthic foraging lineages. We find that the ancestral foraging strategy impacts both the direction and magnitude of morphological changes following transitions to zooplanktivory for some, but not all of the aforementioned traits. Eye diameter and maximum body size increase when lineages transition from coral grazing but decrease with transitions from benthic hunting. In contrast, caudal fin shape and body depth change in the same direction following transitions from each form of benthic foraging, becoming more emarginate and shallow-bodied, respectively. Our results emphasize the importance of considering the effects different ancestral states may have on patterns of morphological convergence and the description of ecomorphs.
