Cichlid jaw mechanics:: linking morphology to feeding specialization

1. The utility of the anterior jaw four-bar linkage model and the trophic consequences of jaw protrusion were investigated in Heroine cichlids by examining the evolutionary relationships among maxillary kinematic transmission (KT), maximum jaw protrusion and dietary specialization on evasive prey. 2. In 31 species of Heroine cichlids, a four-bar linkage model was used to generate kinematic predictions of maxillary KT, the angular amount of maxilla rotation per unit lower jaw rotation, expected during mouth opening. Maxillary KT averaged 0.79 and ranged from 0.58 in Herichthys tamasopoensis to 1.06 in Petenia splendida. 3. Because the maxilla pushes the toothed premaxilla out during jaw protrusion, we predicted higher maxillary KT should characterize species with greater maximum jaw protrusion. Maximum jaw protrusion ranged from 1.5 to 14.2% of cichlid standard length and was highly correlated with greater maxillary KT. 4. The proportion of fish and crustaceans in the diet of these cichlids was correlated with maximum protrusion, suggesting jaw protrusion may aid in the capture of evasive prey. 5. Phylogenetic independent contrasts indicate changes in anterior jaw mechanics may be necessary for diversification of cichlid jaw protrusion abilities, and the labile evolution of jaw protrusion in Heroine cichlids likely facilitated the repeated specialization on evasive prey during their diversification.