Sexual size dimorphism (SSD), or the difference in body size between males and females, is common in almost all taxa of animals and is usually assumed to be adaptive. Darwin's two main mechanisms for the evolution of SSD, sexual selection for larger males and fecundity selection for larger females, have often been demonstrated. However, males and females frequently share both genes and environment and more recent papers have noted that males and females must experience differences in lifetime selection on body size for SSD to be maintained. Over two generations I examined lifetime selection acting on adult body size (total length) in a common insect where females are larger than males, the waterstrider Aquarius remigis. Both fecundity selection for larger females and sexual selection for larger males are occurring in this species and both selective forces appear to target specific components of body size rather than total length; sexual selection targeting male genital length and fecundity selection targeting female abdomen length. While body size did not appear to influence adult prereproductive survival, longevity during the reproductive season was negatively related to body size for both sexes. When the opposing selection of reproductive success and reproductive longevity are combined, both males and females have an intermediate optimum body size. A remarkable result of this stabilizing selection was that the optimum size of males was smaller than that of females. I also examined the repeatability of reproductive success in both sexes and the trade-off between egg size and egg number. Finally, estimates of the quantitative genetic basis of the traits examined indicate that both male and female body size, and components of body size, are heritable and can respond to the selection detected. Components of body size in A. remigis are variable in both the degree and direction of sexual dimorphism and the genetic analysis indicates partial isolation of dimorphic and

Successional changes in a habitat may result in bottlenecks where few individuals in a population survive. During such events, changes in the genetic architecture of traits are predicted to occur as is subsequent inbreeding depression. In two literature reviews, I document that, (1) dominance variance increases in traits that are subject to strong selection and, (2) inbreeding depression is substantially higher in the wild as compared to captive populations. In addition to these changes, successional pressures may also result in the evolution of morphologies that allow organisms to avoid unfavourable conditions. A common dimorphism in insects is wing dimorphism, in which the macropterous morph is long-winged (LW), has functional flight muscles and is flight-capable while the micropterous morph (SW) has reduced wings and cannot fly. Due to the energy required to maintain the flight apparatus, macropterous individuals are predicted to have less energy available for reproduction. Trade-offs to macroptery have been documented in female insects. Gryllus firmus is a wing-dimorphic cricket of the southeastern USA. Although there are well established trade-offs between macroptery and reproduction in female crickets, no trade-offs have been demonstrated in male crickets. The prediction is that LW males, because they have to expend energy to maintain the flight apparatus, will call less and therefore attract fewer females than SW males. To be evolutionarily important, the traits involved in the trade-off; call duration, wing morph, wing muscle condition and lipid weight should have significant heritabilities and be genetically correlated. I found that SW males attracted significantly more females than LW males (mean % = 70% (SW) 30% (LW)). A significant difference in time spent calling was found between SW and LW males and as the difference in calling time between males increased, the likelihood of a female choosing the longer-calling male also increased. All the traits ha

Thesis (Ph.D.) - University of St Andrews, May 2007.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [76]-86).

Thesis (M.S.)--Ohio State University, 2005. / Includes bibliographical references (leaves 86-98). Available online via OhioLINK's ETD Center

Thesis--Groningen. / Summary in English and Dutch. "Stellingen" inserted. Bibliography: p. 120-129.

No description available.

No description available.

The advent of sexual reproduction in early evolutionary history had profound effects on the evolution of animals. In most sexually reproducing species, males and females have distinct morphological and behavioral differences that are shaped by the evolutionary imperatives of each sex. Underlying the behavioral differences between males and females are distinct and measurable dimorphisms in the nervous system. These dimorphisms can arise in the form of connectivity, neurotransmitter usage, gene expression or combinations of all three. The androdioecious nematode Caenorhabditis elegans, with its stereotyped development and simple nervous system, offers a remarkably powerful system for studying the conserved mechanisms of sex determination that shape neural development. In this thesis, I present my work on the characterization of several genes that regulate the development of sexual dimorphisms in the nervous system. The first part of the thesis concerns the characterization of the gene ham-3, which codes for a subunit of the C. elegans ortholog of the SWI/SNF chromatin remodeling complex. ham-3 is required for the proper terminal differentiation of the HSN, a serotonergic neuron of the sex-specific nervous system, which it manages by regulating the expression of transcription factors required for crucial steps of migration, axon guidance and serotonergic fate adoption. The second part of the thesis concerns the investigation of sexually dimorphic pruning mechanisms. I show that unc-6/Netrin is subject to direct transcriptional repression in hermaphrodites by tra-1, the master transcriptional regulator of sexual fate determination in C. elegans. This regulation is required for the proper timing of the sexually dimorphic pruning of synapses in the tail region in hermaprhodites. In males, where unc-6 is not repressed by tra-1, unc-6 expression perdures into adulthood and the synapse is maintained. Together, these data provide insight into the ways in which conserved genetic and developmental mechanisms manage the generation differentiation, connectivity, and maintenance of sexually dimorphic nervous systems.

The purpose of this study was to determine how two morphs of the acorn barnacle, Chthamalus anisopoma, coexist on rocky intertidal shores in the northern Gulf of California. The test of one of these forms (here called "typical") has the conical, volcano shape which is characteristic of acorn barnacles while the test of the atypical form (here called "bent") grows bent-over so that the plane of the aperture's rim is perpendicular to the substrate. I tested the hypotheses that bents are more resistant than typicals to: (1) desiccation during low tides and (2) attack by a carnivorous snail (Acanthina angelica) involving the use of a labial spine. These two hypotheses (which were suggested from analysis of the distribution patterns of the two morphs) were tested in conjunction with experiments designed to determine whether the bent form is genetically controlled or environmentally induced. The results indicated that the bent-over morph is a developmental response to the presence of A. angelica and that it is more resistant than the typical form to specialized predation by this gastropod. I also tested the hypotheses that: (1) bents are inferior competitors for primary rock space, and (2) the bent-over morphology places constraints on growth and reproduction. I found no evidence to suggest that bents are inferior competitors for space. They were, however, found to grow more slowly than typicals and to brood fewer eggs per unit body size. In summary, the bent-over form of C. anisopoma is a conditional response to the presence of a predator and both the conditional strategy and the dimorphism appear to be maintained by a trade-off between resistance to predation and the ability to convert resources into offspring.