Genetic basis of adaptive shape differences in the cichlid head.

East African cichlids exhibit an extraordinary level of morphological diversity. Key to their success has been a dramatic radiation in trophic biology, which has occurred rapidly and repeatedly in different lakes. In this report we take the first step in understanding the genetic basis of differences in cichlid oral jaw design. We estimate the effective number of genetic factors that control differences in the cichlid head through a comprehensive morphological assessment of two Lake Malawi cichlid species and their F(1) and F(2) hybrid progeny. We estimate that between one and 11 factors underlie shape difference of individual bony elements. We show that many of the skeletal differences in the head and oral jaw apparatus are inherited together, suggesting a degree of pleiotropy in the genetic architecture of this character complex. Moreover, we find that cosegregation of shape differences in different elements corresponds to developmental, rather than functional, units.