Unprecedented biting performance in herbivorous fish: how the complex biting system of Pomacentridae circumvents performance trade-offs

It is well accepted that the complexity of functional systems may mitigate performance trade-offs. However, data supporting this theory is hard to find because it needs to be based on a functional system with different complexity levels in closely-related species. The Pomacentridae (damselfishes) provide an excellent opportunity to test the hypothesis because most of the species have two mouth-closing systems: the first using the adductor mandibulae, as in all teleost fishes, and a second one relying on the cerato-mandibular ligament (cmd), a synapomorphic trait of the family. Interestingly, some pomacentrids have secondarily lost the cmd ligament during evolution and therefore have a less complex mouth-closing system. Using dissection, kinematic analysis, and mathematical modeling, we demonstrated that the possession of two mouth-closing systems enabled grazing damselfishes to have a forceful and extremely fast bite. This combination challenges a major functional trade-off in fish jaw ...