Date of Award
Program or Major
Doctor of Philosophy
Karen L Carleton
The cichlid fishes of East Africa are the most ecologically diverse radiation of recent vertebrates. These highly visual fish live in habitats ranging from turbid rivers to clear lakes. They have evolved to exploit an astounding array of foraging strategies. The combination of phenotypic diversity and varied environmental conditions makes the cichlid system ideal for the examination of the relationship between ecology and the evolution of visual sensitivity. In this dissertation, I explore several aspects of this relationship. In Chapter 1, I compare the opsin gene sequences from 17 African cichlid species that have evolved in either clear or turbid light environments. I identify statistical evidence of molecular adaptation. I also find evidence of differences in the relative rates of substitution across clear and turbid lineages. When patterns of amino acid substitution are compared to possible tuning sites, only the ultraviolet sensitive SWS1 class have patterns of substitution that are consistent with photic environment-driven evolution. In Chapter 2, I determine the peak absorbances of in vitro expressed pigments for all seven Nile tilapia cone opsin genes and chart opsin expression across ontogeny. Each gene is found to encode a distinct photopigment. Despite the expression of a limited subset of opsin genes in adults, each opsin was found to be expressed at some point during ontogeny. In Chapter 3, I use MSP and real-time RT-PCR to characterize the differences in visual sensitivity among one of Lake Malawi's most species rich genera, Labidochromis. This study suggests that visual sensitivity is quite labile and can change during the evolution of closely related species. In chapter 4, I examine the distribution of retained opsin gene duplicates among all fish opsins sequenced to date. Duplicates are found differentially across opsin classes. Overall, the majority of retained gene duplicates began to accumulate around the time of the radiation of higher teleosts. Finally in Chapter 5, I highlight ways in which the cichlid system might be especially useful in relating ecology and vision. This includes identifying how visual sensitivity has been shaped by specific foraging strategies and how this affects the long-term evolution of the cone opsin family.
Spady, Tyrone Clifford, "Cichlids as a model for the evolution of visual sensitivity" (2006). Doctoral Dissertations. 331.