The farmer fish
By slamming their oral jaws shut, damselfishes produce noise and use it to defend their territory or to attract partners during courtship displays. For most of these species, the mechanics of this action are linked to the cerato-mandibular ligament. Located in the mouth, it enables the jaws to slam shut rapidly thereby producing sound. This ligament does not only have an acoustic function. It enables the fish to select algae with surgical precision and to feed on the cultivated algae. Some species have therefore been able to adopt “farming” behavior and occupy a unique position in coral ecosystems and reefs throughout the world. This morphological particularity is therefore directly behind this ecological behavior that is unique in fishes. Two studies conducted at the Functional and Evolutionary Morphology Laboratory of the University of Liege have just revealed how a morphological trait was able to shape the evolution of damselfishes.
The ligament that has been known for thirty years
The presence of this ligament in damselfishes has been known since 1981. But at that time, nobody really knew what it was used for. In 2007, Eric Parmentier, a researcher at the Functional Evolutionary Morphology Laboratory of the University of Liege, discovered its function in the production of clownfish (these belong to the family of damselfishes) and had an intuition that this slamming noise was initially the result of a mechanism at work during feeding. Following these observations, Damien Olivier, a PhD student in the same laboratory, supervised by Bruno Frédérich, a postdoctoral researcher at the F.R.S.-FNRS, extended the research to the entire family of damselfishes (Pomacentridae). He attempted to understand how the biomechanics of this oral ligament could influence their feeding, their diet and therefore their ecological role within coral reefs.
(1) Damien Olivier, Bruno Frédérich, Milton Spanopoulos-Zarco, Eduardo F Balart and Eric Parmentier (2014) The cerato-mandibular ligament: a key functional trait for grazing in damselfishes (Pomacentridae). Frontiers in Zoology, 11: 63.