Evolutionary diversification of pelagic larval duration in three reef fish families

In many animal taxa, studies of trait diversification have mainly focused on adult phenotypes, while early life traits have been poorly studied from a macroevolutionary perspective. Reef fishes provide a good system for studying the evolution of animals with complex life cycles. Their biphasic life cycle – a pelagic larval stage and reef-associated juvenile/adult stages – and the fact that they are among the most diversified groups of vertebrates make them ideal candidates. This study aims to describe the patterns of diversification of an important larval trait, the pelagic larval duration (PLD), responsible for the dispersal ability of reef fishes in the ocean. Leveraging data available in the literature, we explored the diversification of PLD in three diverse families (Labridae, Pomacanthidae, and Pomacentridae). Our results show significant variation in PLD across the three fish families and across biogeographic regions, and reveal a strong phylogenetic signal in PLD. Our macroevolutionary analyses support that the tempo of PLD evolution is tightly associated with speciation events in Labridae and Pomacanthidae, sustaining the role of the pelagic larval phase in reef fish diversification. The hypothesis of a single optimal PLD value for all fishes – representing a trade-off between genetic mixing, colonisation of isolated reefs and mortality during the pelagic phase – was rejected by our comparisons of trait evolution models. Instead, we highlight multiple evolutionary shifts towards both short and long PLD durations. Finally, we reveal that PLD is linked to some adult ecological traits in Pomacanthidae but the same relationship is absent for Pomacentridae and Labridae. Our results strengthen the idea that PLD diversity is structured by phylogenetic relationships, and that the evolutionary dynamics of PLD are lineage-specific.