INTERPOPULATION VARIATION IN PREY USE AND FEEDING BIOMECHANICS IN CARIBBEAN TRIGGERFISHES

The relationships between prey utilization and jaw biomechanics were e xplored in two Caribbean populations (La Parguera and Mona Island) of four trigger-fishes. The volumetric contribution of major prey types a nd six biomechanical features of the jaws that characterize biting str ength were contrasted between populations. At Mona, Xanthichthys ringe ns ate 45% benthic organisms, whereas conspecifics at La Parguera fed exclusively on plankton. Balistes vetula at Mona consumed 63% soft and nonelusive invertebrates, in contrast to their La Parguera conspecifi cs, which consumed 62% hard prey. Differences in diet between populati ons were associated with differences in jaw biomechanics. Xanthichthys al Mona had jaw muscles, bones, and closing-lever ratios larger than those of fish at La Parguera, indicating a stronger bite. Balistes at Mona had 50% smaller jaw bones, muscles, and closing-lever ratios than their La Parguera conspecifics, indicating a weaker but swifter bite. Melichthys niger and Cantherhines macrocerus ate similar prey at the two locations and showed little difference in trophic anatomy. We hypo thesize that the interpopulation differences in morphology are induced by the activities of feeding on different prey and enhance the feedin g ability of fishes for locally dominant prey. Plasticity of the feedi ng mechanism may be a widespread attribute of fish feeding systems tha t promotes the ability of species to occupy multiple habitat types suc cessfully.