Data from: Ecomorphological convergence in planktivorous surgeonfishes

Morphological convergence plays a central role in the study of evolution.
Often induced by shared ecological specialization, homoplasy hints at
underlying selective pressures and adaptive constraints that
deterministically shape the diversification of life. Though midwater
zooplanktivory has arisen in adult surgeonfishes (family Acanthuridae) at
least four independent times, it represents a clearly specialized state,
requiring the capacity to swiftly swim in midwater locating and sucking
small prey items. While this diet has commonly been associated with
specific functional adaptations in fishes, acanthurids present an
interesting case study as all other species feed by grazing on benthic
algae and detritus, requiring a vastly different functional morphology
that emphasizes biting behaviors. We examined the feeding morphology in 30
acanthurid species and, combined with a pre-existing phylogenetic tree,
compared the fit of evolutionary models across two diet regimes:
zooplanktivores and non-zooplanktivorous grazers. Accounting for
phylogenetic relationships, the best-fitting model indicates that
zooplanktivorous species are converging on a separate adaptive peak from
their grazing relatives. Driving this bimodal landscape, zooplanktivorous
acanthurids tend to develop a slender body, reduced facial features,
smaller teeth, and weakened jaw adductor muscles. However, despite these
phenotypic changes, model fitting suggests that lineages have not yet
reached the adaptive peak associated with plankton feeding even though
some transitions appear to be over 10 million years old. These findings
demonstrate that the selective demands of pelagic feeding promote
repeated—albeit very gradual—ecomorphological convergence within
surgeonfishes, while allowing local divergences between closely related
species, contributing to the overall diversity of the clade.