Feeding innovations and the first coral-feeding fishes

Tubelip wrasses were probably the first modern fish group to feed on corals, an ability that has been linked to their unusual lips. However, the only detailed account of these lips is based on a qualitative description of one tubelip wrasse species. Here, we provide the first quantitative evaluation of the lips of a broad range of wrasses and offer insights into the functional role of lips in coral-feeding fishes. A phylogenetic principal components analysis of 27 morphological traits revealed a clear differentiation between the lips of three coral-feeding tubelip wrasse genera (Labrichthys, Labropsis, and Diproctacanthus) and 12 non-corallivorous genera. This separation among taxa was based primarily on the presence of a glandular lip epithelium in tubelip wrasses. Our findings support the hypothesis that mucus secretion in the lips of tubelip wrasses plays a key role in their coral-feeding ecology, and highlight the value of soft anatomy in enabling fishes to exploit novel trophic resources.