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 dynamics,
as systems better suited for force transmission are usually less suited
for speed transmission, and vice versa. The combination of grazing
behavior, small and robust lower jaws (conferring high biting force), and
an ultra-fast bite is unusual within actinopterygians. These attributes
and their associated performance seem to be required conditions to
colonize the ecological niche of farming, i.e., the maintenance of small
filamentous algae crops serving as both food and storage.