• Levels of Selection in a Polymorphic Species

      Korody, Marisa L. (2013-09-05)
      Phenotype is affected by many factors, including but not limited to environment, conspecifics, and genetics. Evidence of phenotypic variation is everywhere, some of which is controlled solely by environment, and others that are fixed by genetics. Genetic polymorphisms are rare, but very useful for the study of selection and genetics. These genetic polymorphisms provide a phenotypic link to the underlying genetics and are even more useful when there are associated behavioral differences. I examine multiple levels of selection that are acting upon a polymorphic passerine, the white-throated sparrow (Zonotrichia albicollis). Males and females of this species occur in two morphs, white or tan, based upon the color of their crown strips. This plumage polymorphism is absolutely correlated with a complex chromosomal rearrangement on the second largest autosome. Within this dissertation I explore how climate needs to be addressed in ecological studies to fully understand the mechanisms behind variation. I explore whether sexual selection is acting within this species and the differences between the morphs through the use of Bateman Gradients. Darwin suggested that sex ratios influence sexual selection, but what about morph ratios? I examine the frequency variation of morphs within this species. Variation in morph production may be favored by a potential tradeoff between the number of males and the number of white offspring produced in a clutch that suggests greater costs associated with producing white morph individuals. Mendelian segregation is inconsistent in this species, and transmission distortion may contribute to morph ratio variation. I show that white male sperm varies in production from 0% - 100% white sperm/individual consistent with transmission distortion. Finally, candidate gene mapping was used to identify the genes sequestered in this rearrangement that may be responsible for the polymorphism and the evolution behind the rearrangement.