COOPER, W. J.; WESTNEAT, M. W.; University of Chicago; Field Museum of Natural History: Damselfish jaws: comparative and functional morphometrics in labroid fishes

Damselfishes (Labroidei, Pomacentridae) constitute a diverse group (> 340 sp.) of marine fishes that have been thought to exhibit little trophic diversity. Despite widespread interest in labroid feeding, the morphological and functional variation of pomacentrid jaws has not been quantified. We combined morphometric analyses of the oral jaws of damselfishes with biomechanical models of jaw function in order to measure the functional diversity of pomacentrid jaws. Biomechanical modeling generated estimates of jaw functional parameters that are strongly associated with trophic habitats. Results show that accounting for muscle morphology and physiology yield different estimates of jaw mechanics than bone lever ratios alone. We compared the functional diversity of damselfish oral jaws to those of wrasses (Labridae), another species rich lineage of marine fishes. Results show that the morphological and functional diversity of damselfish oral jaws was greater than expected. The hypervolume of shape space occupied by damselfishes is similar to that occupied by wrasses although the two groups have different functional specializations. The lower jaw lever of many pomacentrids confers a high mechanical advantage (0.15-0.70) and is extreme in the coral eating species Cheloprion labiatus. Surprisingly, the bite of C. Labiatus is estimated to have a mechanical advantage (0.70) greater than those predicted for parrotfishes (0.50). A significant finding of this study was that the hypervolumes of shape space occupied by wrasses and damselfishes are completely independent. We reject the hypothesis that the low degree of trophic diversity reported for damselfishes is associated with low functional and morphological diversity of their oral jaws relative to other fish clades.