Condition-dependent sexual selection has the potential to align natural and sexual selection and accelerate adaptation. When the expression of a sexually selected trait is constrained by the condition of the bearer, it offers a reliable signal of quality on which females can base mate choice decisions. Individuals with highly expressed sexually selected traits are therefore expected to possess advantageous genes given the prevailing environmental conditions. Such genes can then spread by their naturally selected benefits as well as their sexually selected advantages, thereby accelerating adaptation. I investigate the effect of condition-dependent traits on mating and signalling behaviour to explore the potential for alignment between natural and sexual selection in the wild. By studying a wild population of the field cricket, Gryllus campestris, I explore condition-dependent sexual selection in a natural context. This avoids some limitations of laboratory studies, which may overestimate effects in the absence of natural and environmental variation. I employ a direct experimental test of the effect of condition on sexually selected traits and mating success, finding that while male acoustic signals are condition-dependent, modest increases in calling effort do not result in increased mating success. I investigate the effect of body size on mating success and find mating success to be independent of body size. I explore the possibility of condition- and context-mediated flexibility in mate-searching tactics, finding that while population density influences tactic choice, individual condition is unlikely to predict which tactic a male will adopt. Finally, I consider the role of female condition in sexual selection and find that mating latency in females is not condition-dependent, but that mating history has an important effect on female choosiness.

While the phenotypic effects of sexual selection have been well studied, the consequences for population mean fitness remain unclear. Additionally, there is a need to more fully characterize how various forms of inter- and intrasexual selection combine to affect the evolution of traits under sexual selection. Here, I address these issues as they relate to male territoriality in Drosophila serrata, a model system for the study of female preference for male pheromones. First, I demonstrate that territoriality occurs and is a likely component of male sexual fitness. Results from a phenotypic manipulation indicate that territorial success was also condition-dependent, and that sexual selection against low condition males tended to be stronger given a high opportunity for territory defense. Territorial success depended on body size but not on pheromones. How this and other components of male mating success interact to affect trait evolution and population mean fitness remains an important area for future study.

While the phenotypic effects of sexual selection have been well studied, the consequences for population mean fitness remain unclear. Additionally, there is a need to more fully characterize how various forms of inter- and intrasexual selection combine to affect the evolution of traits under sexual selection. Here, I address these issues as they relate to male territoriality in Drosophila serrata, a model system for the study of female preference for male pheromones. First, I demonstrate that territoriality occurs and is a likely component of male sexual fitness. Results from a phenotypic manipulation indicate that territorial success was also condition-dependent, and that sexual selection against low condition males tended to be stronger given a high opportunity for territory defense. Territorial success depended on body size but not on pheromones. How this and other components of male mating success interact to affect trait evolution and population mean fitness remains an important area for future study.

Sexual conflict and condition-dependent trait expression have emerged as major themes in sexual selection. There is now considerable evidence suggesting that both conflict and condition-dependence can drive the evolution and expression of sexual traits; still, important questions remain concerning the extent to which conflict shapes sexual traits and the role of condition in mediating conflict. Here, I address these two themes in studies of a ladybird mating system. One set of studies investigates the function and economics of potentially antagonistic traits – nuptial gifts and female mating resistance – while another examines condition-dependence in mating resistance and male ejaculate composition. Nuptial gifts are often considered beneficial to females, but recent thinking suggests they may also allow males to manipulate females, raising the possibility of conflict. I demonstrate that male ladybirds benefit from nuptial feeding by their mates through reduced re-mating frequency. Benefits to female reproduction and lifespan, however, are weak or non-existent. These results show that although males gain from transferring gifts that influence female behaviour, females experience neither harm nor benefit. I next tested the hypothesis that nuptial feeding is maintained – despite an absence of benefits – because female foraging is generally elevated after mating. However, although females indeed display strongly increased foraging after mating, this response did not increase nuptial feeding. Recent studies suggest that individual condition may affect the economics of mating and extent of conflict. Female ladybirds vigorously resist mating, and I show that (1) resistance is condition-dependent, with low-condition females displaying more resistance, and (2) resistance functions to minimize superfluous matings (sexual conflict), rather than to select among males (indirectly benefiting females). Resistance generates selection favouring large males; thus, this work demonstrates that ecological circumstances, through influencing condition, affect the strength of sexual selection. Finally, male condition may influence investment in ejaculate components, but condition-dependence in ejaculate composition is currently poorly understood. I show that, in agreement with theory, males in poor condition transfer smaller ejaculates that nonetheless contain more sperm, but less seminal fluid. Taken together, this work highlights both the value of economic studies in evaluating sexual conflict, and the significance of condition-dependence for sexual selection.

Sexual conflict and condition-dependent trait expression have emerged as major themes in sexual selection. There is now considerable evidence suggesting that both conflict and condition-dependence can drive the evolution and expression of sexual traits; still, important questions remain concerning the extent to which conflict shapes sexual traits and the role of condition in mediating conflict. Here, I address these two themes in studies of a ladybird mating system. One set of studies investigates the function and economics of potentially antagonistic traits – nuptial gifts and female mating resistance – while another examines condition-dependence in mating resistance and male ejaculate composition. Nuptial gifts are often considered beneficial to females, but recent thinking suggests they may also allow males to manipulate females, raising the possibility of conflict. I demonstrate that male ladybirds benefit from nuptial feeding by their mates through reduced re-mating frequency. Benefits to female reproduction and lifespan, however, are weak or non-existent. These results show that although males gain from transferring gifts that influence female behaviour, females experience neither harm nor benefit. I next tested the hypothesis that nuptial feeding is maintained – despite an absence of benefits – because female foraging is generally elevated after mating. However, although females indeed display strongly increased foraging after mating, this response did not increase nuptial feeding. Recent studies suggest that individual condition may affect the economics of mating and extent of conflict. Female ladybirds vigorously resist mating, and I show that (1) resistance is condition-dependent, with low-condition females displaying more resistance, and (2) resistance functions to minimize superfluous matings (sexual conflict), rather than to select among males (indirectly benefiting females). Resistance generates selection favouring large males; thus, this work demonstrates that ecological circumstances, through influencing condition, affect the strength of sexual selection. Finally, male condition may influence investment in ejaculate components, but condition-dependence in ejaculate composition is currently poorly understood. I show that, in agreement with theory, males in poor condition transfer smaller ejaculates that nonetheless contain more sperm, but less seminal fluid. Taken together, this work highlights both the value of economic studies in evaluating sexual conflict, and the significance of condition-dependence for sexual selection.

Environmental variation, an important source of phenotypic variation, can influence phenotypes, fitness and even rates of evolution. My thesis explores the effects of evolutionary change on the response to different types of environmental variation. In the first study, I examined the evolution of environmental canalization in adaptively diverged populations of Drosophila melanogaster that vary in degree of genetic canalization. I use these populations to test the congruence hypothesis which predicts that genetic canalization is a co-product of the evolution of environmental canalization and thus should be correlated. My results show that, despite adaptive evolutionary changes in morphology and genetic canalization, these populations have similar degree of variability due to environmental variation. In the second study, I explore how both variation in temperature and food quality during development influence patterns of sexual dimorphism in wing morphology in adaptively diverged populations of Drosophila melanogaster. I compare the relative contributions of adaptation, food availability and temperature on sexual size and shape dimorphism of the Drosophila wing. In particular, I focus on how these factors influence size-shape allometry both in general and in a sex-specific manner. My results show that despite the large adaptive divergence and a strong influence of environmental manipulation on wing size and shape, sex-specific patterns of condition dependence remain relatively consistent between the two populations. In the third study, I explore the evolutionary patterns of condition-dependent sexual size dimorphism among 27 different species from the melanogaster species group with varying degrees of sexual size dimorphism. Using food availability manipulations during development, I examine how sexual size dimorphism changes in response to condition at both the intra-specific and the inter-specific level. The results of this study suggest that, although we see a correlation between sexual size dimorphism and condition dependence among traits within most species, sexual dimorphism and condition dependence do not seem to have a correlated evolution among species of the melanogaster species group. / Dissertation / Doctor of Philosophy (PhD)

abstract: Urbanization provides an excellent opportunity to examine the effects of human-induced rapid environmental change (HIREC) on natural ecosystems. Certain species can dominate in urban habitats at the expense of biodiversity. Phenotypic plasticity may be the mechanism by which these 'urban exploiters' flourish in urban areas. Color displays and condition-dependent phenotypes are known to be highly plastic. However, conspicuous color displays are perplexing in that they can be costly to produce and may increase detection by enemies. The Western black widow spider () is a superabundant pest species that forms dense aggregations throughout metropolitan Phoenix, Arizona, USA. Adult female display a red hourglass on their abdomen, which is speculated to function as a conspicuous warning signal to enemies. Here, I performed field studies to identify how widow morphology and hourglass color differ between urban and desert subpopulations. I also conducted laboratory experiments to examine the dietary sensitivity of hourglass coloration and to identify its functional role in the contexts of agonism, mating, and predator defense. My field data reveal significant spatial variation across urban and desert subpopulations in ecology and color. Furthermore, hourglass coloration was significantly influenced by environmental factors unique to urban habitats. Desert spiders were found to be smaller and less colorful than urban spiders. Throughout, I observed a positive correlation between body condition and hourglass size. Laboratory diet manipulations empirically confirm the condition-dependence of hourglass size. Additionally, widows with extreme body conditions exhibited condition-dependent coloration. However, hourglass obstruction and enlargement did not produce any effects on the outcome of agonistic encounters, male courtship, or predator deterrence. This work offers important insights into the effects of urbanization on the ecology and coloration of a superabundant pest species. While the function of the hourglass remains undetermined, my findings characterize the black widow's hourglass as extremely plastic. Plastic responses to novel environmental conditions can modify the targets of natural selection and subsequently influence evolutionary outcomes. Therefore, assuming a heritable component to this plasticity, the response of hourglass plasticity to the abrupt environmental changes in urban habitats may result in the rapid evolution of this phenotype. / Dissertation/Thesis / M.S. Biology 2014

No description available.

No description available.

The ultimate goal of my thesis is to develop a better understanding of the contribution of indirect benefits (i.e. good genes) to the evolution of female mate preferences. It is genetic variance in, and genetic correlations (covariances) among, male sexual displays, female preferences for them, and fitness that in part determine the degree to which females preferring certain male displays over others will gain an indirect benefit by having higher fitness offspring. Recent advances in quantitative genetic theory provide the mathematical means for quantifying the strength of indirect selection for female mate preferences (Kirkpatrick and Hall 2004), at least under certain conditions, but there are few empirical systems for which such data exist (Brooks and Endler 2001; Qvarnström et al. 2006). I have undertaken a classic half-sibling breeding design with the ultimate goal of estimating the specific parameters of this model in a population of the Australian fruit fly Drosophila serrata. The breeding design was performed across two environments - one to which the population was well adapted and a novel environment to which it was not - thereby also providing insight into genotype-by-environment interactions for this suite of traits and their effects on good genes indirect benefits in a novel environment. General insight is also gained into the genetic covariance of male and female fitness and the prevalence of intralocus sexual conflict, the quantitative genetic basis of female mate preferences for multiple male traits, the condition-dependence of these traits, and the genetic association between sexual displays and fitness when mutation-selection balance is inferred. My results advocate caution in the application of existing theory to quantify the strength of indirect selection, suggesting that a good genes process may be fundamentally different when the exaggeration of sexual displays is eventually halted and an equilibrium is reached between opposing selection.