FOUGEROLLE, M.F.*; TURINGAN, R.G.: Coupled vs. decoupled feeding systems: diet-induced plasticity in the feeding mechanism of Archosargus probatocephalus

The biomechanical basis for the ability of A. probatocephalus to consume both soft and hard prey organisms within its environment was examined in an attempt to understand the mechanisms that underlie the ubiquitous distribution of this species. Most durophagous teleosts such as grunts (Haemulidae) and pumpkinseeds (Centrarchidae) decouple prey processing from prey-capture mechanism. These fishes use the oral jaws to capture prey, and subsequently use the pharyngeal jaws to process prey before swallowing. In A. probatocephalus, both prey capture and processing are accomplished by the oral jaws. Sheepsheads from the same location were reared under two diets: whole bean clams (Donax sp.) [hard prey] and Donax with shells removed (soft prey). At the end of a 70-day rearing period, fish were measured for key biomechanical features of the prey-capture (oral jaws) and processing (pharyngeal jaws) mechanisms. Biting muscles and bones of the oral jaw for fish fed hard prey were more massive than fish fed soft prey. The force generating capability of the adductor mandibulae complex was higher for fish fed hard prey. The higher mechanical advantage of the jaws in fish fed hard prey suggests that they are designed for slow, strong bite compared to fish fed soft prey. In contrast, the pharyngeal jaw-bone and muscle masses did not differ between the two treatments. It appears that the repeated use of the bone and muscle of the prey-processing mechanism subjects these elements to stress that may lead to constant remodeling. Phenotypic plasticity of the oral jaw appears to be one of the mechanisms that underlie a species ability to exploit locally available prey-resource.