Colour and shape evolution reflect ecological specialisation in Pomacentridae

Abstract How ecological pressures shape phenotypic traits such as colouration and morphology is a fundamental question in evolutionary biology. Colouration often mediates functions such as communication, camouflage, and species recognition, while morphological traits influence locomotion, feeding, and habitat use. In reef fishes, both traits exhibit striking diversity, frequently shaped by ecological interactions. The damselfish family (Pomacentridae) exemplifies this variation, displaying a wide range of colouration, morphology, and ecological strategies, including dietary specialisation, mutualistic behaviours, and freshwater tolerance. In this study, we examined 342 Pomacentridae species using an integrative framework that combined colouration and morphometric analyses, ancestral state reconstructions of habitat, diet, and symbiosis, and Phylogenetic Comparative Methods (PCMs). Our goal was to assess how ecological factors have influenced the evolution of phenotypic traits and to identify patterns of convergence linked to ecological specialisation. We found repeated convergent evolution in both colouration and body shape, often associated with similar ecological pressures. Species with specialised diets exhibited consistent morphological adaptations, underscoring the role of trophic ecology in shaping body form. Additionally, we observed a strong association between habitat type and dominant colouration patterns, consistent with a camouflage function. These findings clarify the evolutionary processes driving phenotypic diversity in damselfishes and highlight the importance of ecological adaptation in shaping both morphology and colouration. Our work contributes to a broader understanding of how form and function evolve in response to ecological pressures in coral reef ecosystems.