Study of the association among ontogenetic traits in coral reef fishes

Coral reef fish have a complex life cycle with two main stages: (1) a pelagic larval phase and (2) a benthic juvenile/adult phase. The transition of larvae to the reef, referred to as settlement, is accompanied by metamorphosis that enables phenotypic adaptations to the coral reef environment. While most research emphasizes adult traits to understand diversification, early life traits also undergo natural selection and should be studied to better explain the evolution of biodiversity. This study tested whether ontogenetic traits—specifically pelagic larval duration (PLD), size at colonization and the quantity of morphological changes associated with reef settlement—evolved non-randomly. To do so, we collected post-larvae and adult specimens from 22 coral reef fish species from Moorea Island (French Polynesia). PLD were collected via a literature review and body size at colonization was recorded on post-larvae caught with crest nets. We quantified body shape variation between larval and adult stages by using morphometric techniques. The type and the level of body shape variation occurring after reef settlement differ among species, certainly driven by various ecological niche shifts. Two key relationships emerged: longer PLD correlates with (a) larger size at colonization and (b) reduced shape variation between larval and adult stages. These findings collected in a phylogenetic framework suggest that key features of coral reef fish ontogeny are evolutionary and/or ecologically correlated. Further studies will decipher if phylogeny or ecology are the main factors driving the diversification of ontogenetic traits in coral reef fishes.