Further insight into the iterative ecological radiation of damselfishes (Pomacentridae)

The evolutionary history of Pomacentridae (damselfishes) is a rare example of the occurrence of an iterative ecological radiation in the ocean. Damselfishes have experienced many repeated convergences wherein subclades radiated across similar trophic strategies (i.e. pelagic foragers, benthic feeders, and an intermediate group) and similar morphologies. The presence of evolutionary convergences in damselfishes was recently highlighted by the combination of ecological and morphological data, and the use of phylogenetic comparative methods. Nevertheless, many other aspects of these replicated sets of lineages remain unexplored. For example, little is known about the functional diversity of assemblages including convergent lineages that emerged from iterative processes of ecological radiation, or which of the niche-related processes and phylogenetic conservatism are the major factors shaping these assemblages. Here, we conducted a quantitative comparison of these processes in damselfish assemblages that belong to three distinct Indo-Pacific coral reefs differing in taxonomic composition, morphology and degree of human disturbance. Using various metrics, we compared the functional diversity (based on a dataset of eight functional traits) and the isotopic diversity (a proxy of trophic diversity) among assemblages, grasping many aspects of the eco-functional diversity of Pomacentridae. We also tested whether these eco-functional traits displayed some evolutionary conservatism. Our results demonstrate that the eco-functional diversity of damselfishes follows similar patterns among Indo-Pacific coral reefs. The trophic space remains equivalent despite gradient in species richness, whereas the number of functional entities occupied by taxa dictates the size of the functional space. In each assemblage, eco-functional niches are highly differentiated and evenly distributed in spaces of similar size. The inconsistent phylogenetic structure of eco-functional traits suggests that the similarity in the diversity of damselfish assemblages is mainly driven by niche-based processes and not by phylogenetic relatedness. We suggest that a broader application of our approach will help to uncover the mechanisms of reef fish community assembly over space and time.