Master of Science (MSc)
Faculty of Science
Tristan AF Long
One of Darwin’s greatest questions, the reason why females prefer elaborate sexually selected male traits and displays, was elucidated by the Fisherian coevolution of male traits and female preferences. While variation in male attractiveness and ornamentation has received much attention, there has been little attempt to evaluate the causes and consequences of intraspecific variation in components of female preference. Furthermore, demonstrating a genetic basis to female preference does not answer the question of how within-population genetic variation is maintained.
Understanding the sources of variation in potential mating interactions between males and females is important because this variation determines the strength and the direction that evolution via sexual selection will proceed. Using cytogenetic cloning techniques developed for Drosophila melanogaster – an important model species for sexual selection and sexual conflict research – I examined not only the contribution of genetic variation from in each sex to observed phenotypic variation in biologically important traits such as mating speed, copulation duration, and subsequent offspring production, but also quantified the magnitude of intersexual genetic correlations (Chapter 2). By decomposing the genetic components of interacting phenotypes in mating behaviours between the sexes, we identified possible mechanisms maintaining genetic variation (i.e. sexual conflict) due to the presence of a negative genetic correlation between male attractiveness and female choosiness. These results may provide a framework to improve theoretical models of sexual selection and to provide a more cohesive understanding of the coevolutionary dynamics between male attractiveness and female choosiness for future empirical studies.
Even traits that have a strong genetic basis can be profoundly influenced by environmental conditions, such that the same genotype may yield quantitatively or qualitatively different phenotypes in different environments. While Chapter 2 confirmed genetic variation for female responsiveness, whether or not components of female preference, mainly choosiness, varied with individual condition had yet to be determined. In Chapter 3 I experimentally manipulated female condition by varying the larval density for hemiclonal females (the same lines from Chapter 2) to determine if a genotype-by-environment (GxE) existed for female choosiness. The absence of a GxE interaction for female choosiness suggests that this component of female preference may not be condition dependent. Since GxE interactions may be potentially important to sexual selection, especially if both sexually selected male traits and female preferences are subject to GxEs (and genetic correlations between the two are central to many models of sexual selection), more empirical work on the condition-dependence of female choosiness is needed to strengthen predictions of GxEs for sexually selected traits.
These results demonstrate, to the best of our knowledge, findings regarding the causes and consequences of variation in female mate choice using hemiclonal analysis. Furthermore, the importance of quantifying genetic variation in female mate choice –including how it is maintained – is necessary for theoretical models of sexual selection.
Tennant, Hannah ME, "Causes and consequences of female mate choice in Drosophila melanogaster: A hemiclonal analysis" (2014). Theses and Dissertations (Comprehensive). 1645.