Morphological And Molecular Evolution And Biogeography Of Butterflies PDF Download

Gene flow and hybridization among species dramatically affect our understanding of the species as a biological unit, species relationships, and species adaptations. Hybridization has been shown to lead to adaptive radiation in some systems, and decreased hybrid fitness and an evolutionary dead-end in others. In North American Colias eurytheme and Colias eriphyle, there has been historical debate over the extent of hybridization occurring and the identity of phenotypically intermediate individuals as genetic hybrids. My dissertation assesses the population structure of these two species to measure the extent of hybridization, the identity of phenotypic intermediates as hybrids, and the presence of divergence within species.The first chapter takes a morphological approach to the question of hybridization between C. eurytheme and C. eriphyle. I collected 249 specimens that were identified visually as C. eurytheme, C. eriphyle, or putative hybrids from sites spanning the California Central Valley, Sierra Nevada mountain range, western Great Basin, and southern Cascade Mountains. For each specimen, I measured five wing morphology traits: forewing area, forewing aspect ratio, black border width, ground color, and ultraviolet reflectance. A multivariate analysis of variance provided variable support for the presence of hybridization between the two species and little support for phenotypic intermediates as hybrids. A principal components analysis provided stronger, but still not definitive, support for hybridization and intermediates as hybrids. The second chapter investigates the same question of hybridization as Chapter 1, but using a molecular genetics approach. I collected 378 specimens, some of which were the same specimens used in Chapter 1, from the same sites as in Chapter 1. Following a DNA extraction, I performed an amplified fragment length polymorphism marker analysis to determine the population structure among all individuals. A Bayesian/Markov Chain Monte Carlo method was used to probabilistically assign individuals to genetic clusters. Three genetic clusters provided the best fit for the data. C. eurytheme individuals were primarily assigned to two closely related clusters and C. eriphyle individuals were mostly assigned to a third, more distantly related cluster. There appeared to be significant hybridization between the two species. Individuals of intermediate phenotype (putative hybrids) were found to be genetically indistinguishable from C. eriphyle, indicating that previous work based on the assumption that these intermediate forms are hybrids may warrant reconsideration. The third chapter takes both a morphological and genetic approach to measuring the extent of divergence present within C. eurytheme and C. eriphyle. The same morphological data used in Chapter 1 and the same genetic data used in Chapter 2 were used to compare populations within each of the species. Within C. eurytheme, a comparison of the California Central Valley, eastern Sierra Nevada, and southern Cascade Mountains revealed genetic divergence between the Central Valley and the other two regions. Multivariate analyses suggested the presence of morphological divergence between the Central Valley and eastern Sierra Nevada, but evidence for divergence of these two regions from the Cascades was inconclusive. Within the Sierra Nevada, both genetic and morphological data indicated that C. eurytheme specimens from a western slope site originated from the Central Valley rather than the eastern side of the Sierra Nevada. Within C. eriphyle, a comparison of the eastern Sierra Nevada and southern Cascade Mountains produced no genetic or morphological support for divergence between the two regions.