Evolution and diversity of ram-suction feeding in damselfishes (Pomacentridae)

The cerato-mandibular (c-md) ligament is a synapomorphy within Pomacentridae that creates a tight link between the lower jaws and the hyoid bars. However, this morphological trait has been secondarily lost in multiple lineages during evolution. A previous study revealed that the loss of this trait acted as a release of evolutionary constraints, leading to a cascade of morphological changes such elongated buccal jaws and a slender body. Ecomorphological interpretations suggested the loss of the c-md ligament has ultimately led to a new adaptive peak in zooplanktivory through an optimization of the ram feeding mode associated with a specialization in pelagic feeding. Here, we tested these hypotheses by comparing functional and diet diversity between damselfish species with and without the c-md ligament. Although species lacking the c-md ligament presented a conserved kinematic pattern resulting from high ram and low suction performances, our results did not support an optimization of the ram feeding mode. Indeed, some species with the c-md ligament showed the same or exceeded the ram performance of species without the c-md ligament. The species with the c-md ligament had a more diverse kinematic pattern exploring the entire ram-suction functional range in damselfishes. Finally, our results did not show any diet variations associated with the loss of the c-md ligament. Our study furthers the understanding of how a morphological trait has shaped, by its presence or absence, the ecomorpho-functional diversification of Pomacentridae.