Abstract: Organisms consist of many anatomical systems that function together to form complex phenotypes, which are involved in tasks such as feeding, breathing, or locomotion. These phenotypes require the coordinated evolution, or coevolution, of numerous traits to maintain functionality. However, multifunctional phenotypes face trade-offs that may restrict their diversification. The skull of fishes represents a complex phenotype, containing over 100 bones, which perform multiple functions such as feeding, breathing, and brooding eggs. Neotropical cichlids represent a fruitful system to study how a complex phenotype, the feeding system, has evolved in the context of an ancient adaptive continental radiation, with repeated transitions to specialized diets, and a second jaw in their throat, which is thought to have resulted in their immense ecological and species diversity across two continents through functional decoupling. This dissertation investigates the macroevolutionary patterns in cichlid feeding morphology to better understand how complex phenotypes, which are multifunctional, have evolved in the context of constraint and adaptation. Utilizing three-dimensional geometric morphometrics and microcomputed tomography (μCT) scanning, I explore the diversity and macroevolutionary patterns of the Neotropical cichlid feeding system, including all bones in the oral and pharyngeal jaw for the first time.
In Chapter 2, I characterize the diversity and phylogenetic trajectories of pharyngeal jaws across Cichlinae. The upper pharyngeal jaw has been largely absent in studies of cichlid feeding, however, with µCT scanning, I am able to describe the diversity of the upper pharyngeal jaw and measure disparity through time, revealing unexpected patterns in phenotypic divergence. In Chapter 3, I examine the relationship between diet and feeding morphology, highlighting instances of morphological convergence and divergence among ecologically similar species. I also reconstruct the evolutionary history of dietary transitions and test for correlations between diet and previously unstudied morphological traits. Lastly, I test the hypothesis that functional decoupling has led to evolutionary decoupling between the oral and pharyngeal jaws in Chapter 4. My findings challenge traditional views on functional decoupling and suggest that evolutionary integration between the two jaws is necessary for functional decoupling to occur. The findings from this dissertation enhance our understanding of how complex phenotypes have evolved at a continental scale, and the influence diet has on shaping macroevolutionary patterns.