Hyoid barbels as a key innovation triggering goatfish adaptive radiation

Abstract

Key innovations can unlock ecological opportunities and redirect the evolutionary trajectory of entire lineages, yet few traits have been shown to trigger both hallmarks of a genuine adaptive radiation, rapid speciation and pronounced ecomorphological divergence, within a single lineage. This is especially true among coral reef fishes, where trophic novelties are routinely proposed as drivers of diversity but rarely tested against both criteria. Here, we show that goatfishes (Mullidae), a reef fish family having chemosensory hyoid barbels, meet this standard. First, macroevolutionary analyses of speciation dynamics reveal that goatfishes diversified at a markedly elevated rate relative to other Syngnathiformes. Using the most comprehensive phylogeny of the family to date, combining ultraconserved elements and mitochondrial data for 76 of the 103 recognized species, alongside the largest phenotypic dataset assembled for the group, we find that this elevated rate has been sustained since the family's origin roughly 25 million years ago, rather than declining as ecological opportunity became filled. Head shape, the trait most closely tied to the foraging strategy enabled by hyoid barbels, diverged rapidly among genera early in the family's history and has remained conserved ever since, while body shape and barbel microstructure evolved conservatively and pigmentation diversified later through repeated convergence. By opening access to previously untapped benthic prey resources and triggering a lasting burst of diversification, hyoid barbels emerge as a key innovation that reshaped the evolutionary trajectory of an entire reef fish lineage.