Functional novelties and behavioural flexibility underpin diversification of the surgeonfish feeding mechanism

Turfs and macroalgae are prevalent benthic resources on coral reefs, and central to the biology of herbivorous fishes. However, the mechanics of how algae are detached has only sparsely been studied, raising questions about the nature of diversification across herbivorous species. Surgeonfishes (Acanthuridae) represent one of the most abundant and speciose lineages of herbivorous coral reef fishes. Using high-speed filming of 15 surgeonfish species feeding on filamentous algae in the laboratory, we reveal a major axis of diversity based on the frequency of use of six distinct biting behaviours; High interspecific variance in the extent these behaviours are used revealed that flexibility of the feeding mechanism is a major axis of diversity. Behavioural extremes are characterized by three main regimes: lateral biting, ventral biting and brushing. The prevalence of these bite types is strongly correlated with upper jaw tooth shape, which we use to reconstruct the phylogenetic history of the bite types across 38 surgeonfish species. Phylogenetic reconstructions uncover a dynamic evolutionary history between lateral and ventral biting, with six independent origins of ventral biting from a more widespread lateral biting, emphasizing a major role for transitions in feeding kinematics in the ecological diversification of this group.