The complex life cycle of reef fishes and associated effects on ontogenetic variation of disparity

Most teleost fishes on coral reefs have a bipartite life cycle across two environments: (1) the pelagic zone for larval dispersal and (2) the reef for juvenile and adult stages. The transition of larvae to the reef, referred to as settlement, is accompanied by metamorphosis, a process regulated by thyroid hormones that enables physiological and morphological adaptations to the coral reef environment. While the open ocean is thought to be more homogeneous, especially regarding the diversity of habitats, intrinsic factors of coral reefs such as high spatial and ecological complexity may be involved in promoting high level of fish disparity. Overall, we aim to quantify and compare phenotypic variation in coral reef fishes at two ontogenetic stages - settling larvae and adults - across multiple biological levels. By using varied morphometric analyses, we show that the level of body shape disparity is higher at the adult stage at community and assemblage levels, supporting the hypothesis that the ecological complexity encountered in coral reefs sustains higher phenotypic variation among species. At the population level, patterns vary by species with either settling larvae or adults being the least disparate stage. These findings illustrate how reef fishes and their bipartite life cycle appear as an effective system for exploring how intrinsic and extrinsic factors operate to sustain phenotypic variation at the population, family and community levels.