Graduate Thesis Or Dissertation
 

On the evolution of correlated color traits in garter snakes

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fx719r97c

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  • How complex traits evolve continues to be a major focus of evolutionary investigation. A current topic of debate is the hypothesis that the phenotypic integration of complex traits gives rise to evolutionary constraints. I studied two color traits in the common garter snake, Thamnophis sirtalis, that show a high level of integration in some populations and a lower level of integration in others. Using multiple tools of evolutionary research, including phenotypic, quantitative genetic, and phylogenetic analysis, I describe the historical background of the two traits, investigate the genetic architecture underlying the traits in extant populations, and explore the extent to which both traits have differentiated at the population level. I also describe the among-population diversification of traits as a result of selection usinf FST/QST analysis. Finally, I report the results of a study of direct selection on color traits from avian predators. My main findings are: 1. Garter snake dorsal blotches function as startle patterns in most species of garter snake and as aposematic signals in at least one species; 2. Red pigmentation is derived in the genus Thamnophis; 3. Red blotches, while appearing to be a univariate trait in western populations of Thamnophis sirtalis, can be empirically decomposed into two heritable traits, pattern and pigment; 4. Pattern and pigment are highly genetically correlated in a California population of Thamnophis sirtalis but are less tightly correlated in a Manitoba population; and 5. Population means of pattern and pigment are highly correlated among subpopulations in the California population but are not correlated among subpopulations in Manitoba. I conclude that genetic correlation imposes shortterm evolutionary constraint on the ability of pattern and pigment to evolve independently of each other as predicted by theory. I also conclude that the traits can become decoupled over many generations and can evolve along independent trajectories.
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