The Evolution, Development, and Genetic Basis of Cichlid Hyoid Shape

Elaboration of the feeding apparatus is a key feature of vertebrate evolution. Differences in jaw morphology can greatly impact an organism's foraging efficiency and ecological niche. In fishes, the hyoid bone is important for feeding, but the causes and consequences of hyoid shape variation are poorly understood relative to other skull elements. We utilized the rapid adaptive radiation of East African cichlids to fill this knowledge gap. We first examined variation in the morphology of the cichlid hyoid across species with different foraging niches. Next, we used a F5 hybrid population to characterize the genetic basis of hyoid shape variation. Finally, we used a developmental series to analyze growth dynamics in the parental species of our genetic cross. In the wild-caught population, hyoid shape correlated with foraging ecology, underscoring its importance in feeding. In the hybrid cross, we found that patterns of shape variation recapitulated that observed among species. We then mapped this variation to several discrete regions of the cichlid genome and identified candidate genes known to play an important role in craniofacial development. One notable candidate, utrn, which regulates bone growth and density, was differentially expressed in the parental species of our cross. Finally, through the developmental series, parental species exhibited species-specific differences in the development of the hyoid. These results provide foundational insights into the genetic and developmental origins of adaptive shape variation in the cichlid hyoid