DIFFERENCES BETWEEN INTERSPECIFIC AND INTRASPECIFIC ARCHITECTONIC ADAPTATIONS TO PHARYNGEAL MOLLUSK CRUSHING IN CICHLID FISHES

Because fish heads are densely packed with muscles, ligaments, skeleta l elements and other structures, transformations in one structure may influence surrounding structures. Transformations occur during phyloge ny, ontogeny and as environmentally induced alterations, i.e. phenotyp ic plasticity. We describe differences in intra- and interspecific tra nsformations of the pharyngeal jaw apparatus of haplochromine cichlids . Using multivariate clustering techniques we trace possible correlati ons in transformations of anatomical characters of the pharyngeal jaws and surrounding structures. The intraspecific transformation analysis is based on two environmentally induced morphs of Astatoreochromis al luaudi: a molluscivorous morph with a hypertrophied pharyngeal jaw app aratus and an insectivorous one with a non-hypertrophied apparatus. Fo r the interspecific analysis five other haplochromine species from Lak e Victoria with diets ranging from insects to molluscs were investigat ed. Although ranges in diet are the same, the anatomical ranges differ between A. alluaudi and the species dine. Besides similarities in ana tomical changes of the pharyngeal jaw apparatus in the intra- and inte rspecific dine, differences were also observed. Apparently there are a mong haplochromines multiple pathways to achieve similar performance. In A. alluaudi architectonic and intrinsic plasticity constraints limi t the adaptability of the pharyngeal jaw apparatus. In the species din e, these constraints have been overcome by genetical adaptation. (C) 1 996 The Linnean Society of London