Genetic diversity mirrors trophic ecology in coral reef fish feeding guilds

Genetic diversity is essential for species persistence because it provides the raw material for evolution. For marine organisms, short pelagic larval duration (PLD) and small population size are characteristics generally assumed to associate with low genetic diversity. The ecological diversity of organisms may also affect genetic diversity, with an expected corollary that more restricted habitat and dietary requirements could lead to a reduced genetic diversity because of pronounced genetic structuring. Here, we tested whether groups of species with narrower trophic niches displayed lower genetic diversity than those with broader niches. In order to test those predictions, we used different trophic guilds (i.e. groups of species having similar trophic habits) of coral reef damselfishes in Moorea (French Polynesia) for which we determined their genetic diversity using Restriction site−associated DNA sequencing (RADseq) and their trophic ecology with stomach contents and stable isotope data. We found that pelagic feeders, i.e. the guild picking zooplankton in the water column, exhibited the lowest genetic diversity despite having the longest PLD and the largest population size. This guild had also the lowest variation in habitat characteristics and dietary composition compared to benthic feeders (i.e. those mainly grazing on algae) and the intermediate group (i.e. those feeding on zooplankton, filamentous algae and small benthic invertebrates). Our findings highlight the association between trophic ecology and genetic diversity that should be more commonly investigated in population genetics.