Ecomorphological convergence in planktivorous surgeonfishes

Area of Science:

• Evolutionary biology
• Ecomorphology
• Phylogenetics

Background:

• Morphological convergence, driven by ecological specialization, reveals adaptive constraints in evolution.
• Surgeonfishes (Acanthuridae) exhibit independent evolution of midwater zooplanktivory, contrasting with their typical benthic grazing.
• This dietary shift necessitates distinct functional morphology adaptations.

Purpose of the Study:

• To investigate ecomorphological convergence in surgeonfishes related to diet.
• To compare evolutionary models for zooplanktivorous and non-zooplanktivorous surgeonfishes.
• To understand the tempo and pattern of adaptive evolution in response to pelagic feeding.

Main Methods:

• Examined feeding morphology in 30 acanthurid species.
• Utilized a pre-existing phylogenetic tree to account for evolutionary relationships.
• Compared evolutionary model fits across zooplanktivore and grazer diet regimes.

Main Results:

• Zooplanktivorous surgeonfishes are converging on a distinct adaptive peak separate from grazers.
• Key adaptations include slender bodies, reduced facial features, smaller teeth, and weaker jaw muscles.
• Despite significant changes over millions of years, lineages may not have fully reached the plankton-feeding adaptive peak.

Conclusions:

• Selective demands of pelagic feeding promote gradual, repeated ecomorphological convergence in surgeonfishes.
• This convergence occurs alongside local divergences, contributing to the clade's overall diversity.
• The study highlights the slow pace of adaptation towards specialized feeding strategies in this group.