Variation of phenotypic disparity over the ontogeny of coral reef fish populations

Phenotypic disparity present within populations is of crucial importance for adaptation and natural selection. To date, few studies have explored how disparity levels vary during fish ontogeny. Many coral reef teleosts experience ecological shifts across life stages, making them ideal models. During the larval stage, individuals are adapted to an oceanic pelagic
environment while juveniles and adults have a morphology adapted to the benthic reef environment. We hypothesize that these two environments may exert different selective pressures. Here, we quantify the variation of body shapes over the ontogeny of eight coral reef fish species to test whether (1) the morphology of post-larvae, juveniles and adults differs due to specific habitat adaptations and (2) the level of phenotypic disparity varies among ontogenetic stages. Shape analyses reveal that, in most species, adults have a more streamlined body with proportionally shorter jaws than do post-larvae. The distribution of disparity levels throughout ontogeny does not follow a general trend. Depending on the species, shape disparity may be highest during the post larval stage or during the adult stage, or conversely, may not vary at all during ontogeny. Our results oppose two contrasting scenarios: either post-larvae exhibit reduced morphological disparity due to the homogeneity of pelagic habitats, or life stages associated with the reef environment are less disparate because they experience stronger selective pressures. Further research is certainly needed to determine whether phylogeny or ecology mainly drives ontogenetic changes in phenotypic disparity.