Dissertation Research: Phenotypic Plasticity of Jaw and Skull Morphology in the Cichlid Fishes, Geophagus braziliensis and G. steindachneri

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Phenotypic plasticity is the modification of some trait of an organism in response to environmental change. Often this plasticity has a genetic basis and as a result can influence the rate and direction of evolution. Morphological plasticity is little known among vertebrates. Increasing evidence indicates braziliensis and G.steindachneri, which represent the extremes of cichlid developmental modes. Our research aims to answer the following questions: (1) What effect does the size at which feeding commences have on the amount of morphological plasticity that is expressed? (2) Are there age-related differences in the amount of plasticity that can be induced? (3) Do induced morphological differences affect feeding efficiency on diets that are associated with different feeding modes? (4) Is there genetic variation for the plasticity of jaw and skull bones? This study will go beyond a description of morphological plasticity; it will examine plasticity in a developmental, genetic, functional, and ecological context. Only through such an interdisciplinary approach can the effect of plasticity on evolution, and the evolution of plasticity, itself, be understood. 8700940 McCume Phenotypic plasticity is the modification of some trait of an organism in response to environmental change. Often this plasticity has a genetic basis and as a result can influence the rate and direction of evolution. Morphological plasticity is little known among vertebrates. Increasing evidence indicates that jaw and skull morphology of cichlid fishes, Geophagus braziliensis and G.steindachneri, which represent the extremes of cichlid developmental modes. Our research aims to answer the following questions: (1) What effect does the size at which feeding commences have on the amount of morphological plasticity that is expressed? (2) Are there age-related differences in the amount of plasticity that can be induced? (3) Do induced morphological differences affect feeding efficiency on diets that are associated with different feeding modes? (4) Is there genetic variation for the plasticity of jaw and skull bones? This study will go beyond a description of morphological plasticity; it will examine plasticity in a developmental, genetic, functional, and ecological context. Only through such an interdisciplinary approach can the effect of plasticity on evolution, and the evolution of plasticity, itself, be understood. 8700999 Johnson Vocal behavior is important in evolutionary processes in songbirds, yet few studies have attempted to explain morphological and genetic diversification in light of vocal information. This research will integrate vocal, morphological, and genetic data in the highly polytypic North American red crossbill (Loxia curvirostra) complex. This group presents an unsolved evolutionary paradox: the birds are nomadic, suggesting a high rate of gene flow, yet there is extreme diversity in bill size, body size, and plumage coloration within the group. Several testable alternative hypotheses regarding the nature