Caribbean reef fish assemblages are associated with more rapid and recent evolutionary rates

In the tropical marine realm, the increasing concentration of species toward the Indo-Australian Archipelago (IAA) has been extensively studied. The literature provides numerous biogeographical scenarios explaining this pronounced longitudinal diversity gradient. However, most proposed scenarios were investigated on a neutral framework and did not consider the potential influence of trait diversification and diversity-dependence processes. In this study, we use a global data set on tropical reef fish distributions, combined with species traits and a comprehensive Actinopterygii phylogeny, to address this question. We apply a statistical approach that simultaneously accounts for the potential influence of both biotic and abiotic factors on recent speciation rates and trait evolution, and ultimately, on species richness distribution. Our results reveal gradients in speciation rates and trait evolution rates that do not match the spatial distribution of species richness. The Caribbean region, while being fourfold species poor compared to the IAA, displayed the greatest rates of recent speciation. Compared to the IAA, the Caribbean also harbored species with, on average, faster recent rates of body size evolution. Finally, regardless of the biogeographic realm considered (Indo-Pacific, Atlantic, or Tropical Eastern Pacific), species richness was found to strongly constrain trait evolutionary rates related to trophic level. Overall, our findings suggest that the Caribbean region has acted as an evolutionary engine for reef fishes in the recent past, and that diversity-dependent mechanisms may have played a key role in shaping biogeographic patterns of trait evolution related to trophic level in tropical reef fishes.

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