Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xii, 138 p.; also includes graphics. Includes abstract and vita. Advisor: Richard A. Bradley, Dept. of Evolution, Ecology, and Organismal Biology. Includes bibliographical references (p. 124-138).

Thesis (M.S.)--Texas A & M University, 2003. / "Major Subject: Physiology of Reproduction." Title from author supplied metadata. Includes bibliographical references.

Thesis--Ph. D., University of Hong Kong. / Typewritten.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

This thesis examines the evolutionary divergence between northern European and Italian populations of Chorthippus parallelus. Several differing approaches were taken, which identified the inception of various components of the speciation process between these parapatric populations which meet in the Alps. Firstly, partial post-zygotic reproductive isolation was demonstrated using hybrid crosses. The male hybrid offspring of both reciprocal crosses were sterile, displaying severe testicular dysfunction, while the female hybrids showed no deleterious effects of hybridisation. In this grasshopper the males are the heterogametic sex, possessing a single X chromosome, and so this pattern of hybrid sterility conforms to Haldane's rule. Secondly, investigation of the calling song of the male grasshopper, a component of the mate recognition system, suggested the presence of pre-mating reproductive isolation. Males from the different races were found to sing calling song of a significantly different structure. Finally, examination of DNA sequence divergence in a mitochondrial DNA marker demonstrated Significant levels of genetic differentiation between the races. This population divergence and incipient reproductive isolation parallels that found between the north European and Iberian populations of this grasshopper, and provides further evidence that the divergent geographical races have resulted from allopatric divergence while in isolated refugial populations during the glacial periods of the Pleistocene Epoch. These approaches were repeated to investigate genetic divergence between localised populations within the Italian peninsula. No hybrid dysfunction was observed between these populations, suggesting that they are recently derived from one continuous population. This was probably the refugial population of the last ice-age. Additionally, investigation with the mtDNA marker gave preliminary evidence for population expansion from the south to the north of Italy. Interestingly, the male calling song was Significantly different in populations from the north and the south of Italy, suggesting that a component of pre-mating reproductive isolation may have evolved prior to post-mating isolation in allopatric populations of C. parallelus.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

No description available.

Models are developed for the evolution of outcrossing in general and the evolution of distyly in particular. Field studies of distylous Lithospermum cobrense (Boraginaceae) are reported to support and compliment theoretical work. First a method is developed to model selection against selfing which takes into account the effects of consecutive generations of selfing on loss of heterozygosity. Conditions are then derived for optimal rates of outcrossing. Intermediate rates of outcrossing are optimal under a wide range of parameter values. One assumption of this model is that seedset is not pollen-limited. I then investigate the nature of inherent constraints on whether seedset is pollen-limited or resource-limited in outcrossing animal-pollinated plants, and conclude resource limitation is likely when the per-seed cost of fruit production is greater than the per-seed cost of pollen production. The model also points to why animal-pollinated plants usually have hermaphrodite flowers. This model is followed by analyses of pathways for the evolution of self-incompatibility with two mating types such as is associated with distyly. To account for this I show it necessary to postulate a fortuitous conjunction of rare mutations, very severe selection against selfing, and/or unusual mutational effects. It is also necessary to postulate resource-limited seedset. At this point I develop models for floral differentiation of mating types, culminating in the completely distylous condition. Once self-incompatibility has evolved in plants with stigmas and anthers already spatially separated, it is possible to account for complete floral differentiation under both pollen limitation and resource limitation. Field studies of L. cobrense focus on the pattern of pollen dispersal by butterflies, the mechanism accounting for this pattern, and the extent to which this pattern leads to resource or pollen limitation of seedset. In this species and in distylous species generally, the major effect of reciprocal placement of anthers and stigmas in the two mating types is to enhance the efficiency with which pollen is transported to compatible stigmas. This enhances male fitness but for full distyly to evolve it is helpful, though not strictly necessary, for female fitness to be affected too, as under pollen limitation. Finally, I argue that sporophytically controlled multiallelic self-incompatibility may originate by pathways similar to those envisioned for distyly, and that these two kinds of breeding systems are branches with a common stem.

No description available.

No description available.