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<p>Previous research indicates that vocal and facial masculinity and femininity influence perceptions of attractiveness. Men generally perceive women with feminine traits as more attractive than less feminine women. This may be because women who possess more feminine traits are likely to be healthier and more fertile mates than are less feminine women. Masculine male traits also influence women’s perceptions of attractiveness. Although women do not always prefer masculine male traits, preferences for masculinity are observed under circumstances where women may gain the fitness benefits of heritable health and dominance. Masculine traits in men and feminine traits in women are further associated with the potential fitness risks of infidelity and reduced investment in mates. Here I address three previously unanswered questions concerning the influence of masculinity and femininity on social perceptions. First, how do male vocal and facial masculinity influence perceptions of attractiveness when these two traits are presented simultaneously? Second, does vocal masculinity influence perceptions of the potential fitness risks of infidelity and reduced relationship investment in mates? Third, do male masculinity and female femininity influence perceptions of potential same-sex rivals? In this dissertation I demonstrate that simultaneously presented male vocal and facial masculinity influence women’s perceptions of men’s attractiveness, that perceivers are somewhat aware of the potential fitness risks associated with preferring high quality mates, and that vocal and facial masculinity influence mate choice and intrasexual competition in similar ways. Overall, these studies demonstrate the pervasive influence of masculinity and femininity on mate-choice relevant social perceptions.</p> / Doctor of Philosophy (PhD)

Animals display considerable phenotypic variation in their mating traits, and this variation can have important consequences for the evolution of dimorphic traits between the males and females within a species. In chapter 1, I outline the current state of our understanding of plasticity in reproductive phenotypes, and argue that more work needs to be done to connect the gap between plasticity in mating traits and the outcomes of sexual conflict. Across my four data chapters, I used the fruit fly as a model organism in series of experiments that attempt to better understand how plasticity in mating traits influences the fitness outcomes of both males and females. In chapter 2, I experimentally manipulated the outcome of a fighting experience, and found that males who win a previous fight have higher precopulatory reproductive success, but losers perform better in post-copulatory areas. In chapter 3, I manipulated the amount of competition that a male experiences and found that females mated to males who experience competition produce more early-life offspring but live shorter lives compared to females mated to males that experience no competition. In chapter 4, I manipulated the intensity of sexual conflict that a female experiences and found that males mated to females who experience high conflict have lower pre- and post-copulatory reproductive success compared to males mated to females who experience low conflict. In chapter 5. I manipulated the degree of sexual aggression that a female experiences, and found that females that experience harassment and mating from a male that displays high sexual aggression is subsequently less choosy compared to females that experience a less aggressive male. Finally, in chapter 6, I discuss the significance of my results as they relate to the evolution of reproductive traits in males and females. / Dissertation / Doctor of Science (PhD) / Considerable phenotypic variation exists both within and across species. Within species, one source of this variation is phenotypic plasticity, the ability for an individual to alter its phenotype based on environmental influences. When it comes to sex, both males and females in many species exhibit striking variation in their reproductive behaviour as a result of plasticity. However, the causes and consequences of this variation are not well understood. Throughout my doctoral dissertation, I used the fruit fly as a model to explore how various social experiences such as fighting, competition, sexual harassment, and mating shape the subsequent reproductive behaviour of males and females, and quantified the evolutionary consequences of this variation. The results of my studies have important implications for understanding the evolution of various behavioural strategies such as aggression and mate choice.

The number of African American women who have never married has increased significantly. This is an ethnographic study of eight Young High Functioning (YHF) African American women from the Washington, D.C. and New York City metropolitan areas. Six of the women participated in focus groups and two were individually interviewed to understand how they perceive marriage and their thoughts about being single. YHF is defined as women who are 25-35 years old, have at least a bachelor's degree and make at least $35,000. All of the eight women had never married. The six major themes that emerged in the course of the study were: perceptions of marriage, expectations for balancing work and family, criteria for a perfect mate, dating experiences, the African American family and spirituality. While much of the literature on the decline in marriage among African Americans focuses on the sex ratio of males to females, these YHF African American women were much more concerned about the eligibility of the men in the dating pool than the ratio of males to females. They are looking for mates who share their core values of spirituality, goal oriented, family oriented and they are looking for supportive partners. / Master of Science

Humor is likely to serve as signals of fitness in potential partners. Less is known about how different styles of humor affect partner attractiveness. This study aimed to test the attractiveness of the four different humor styles proposed by Martin et al. (2003) categorized according to being benign (affiliate, self-enhancing) or detrimental (aggressive, self-defeating). Participants were presented with a series of potential partners, much like on a dating site. Each partner was described by a portrait picture and a vignette, which included examples of one of the four humor styles. The participants’ task was to rate a number of items about partner preference (date, intercourse, shortand long-term relationships) and mate value (intelligence, health, social status and parenting skill). A total of 170 women and 81 men between 18-40 years of age completed the experiment. The results showed significant effects on all measurements of partner interest and mate value for women with the aggressive humor style being rated as less attractive and lower in mate value than the other humor styles. For men there was a significant effect on two measurements on mate value (social status, parenting skill), showing that the self-defeating style was rated less attractive. The results support the notion that humor is used as a fitness signal, that this is used to a substantially greater extent by women, and that women find the aggressive humor style to be particularly unattractive in potential partners.

In economic games the facial attributes of counterparts bias decisions to trust and decisions to enter play. We report research supporting hypotheses that trust and reciprocation decisions in trust games are biased by mechanisms of sexual selection. Hypotheses that trust game behaviour is modulated by inter-sexual competition were supported. 1) Attractive individuals elicit more cooperation. 2) Male participants display trust and reciprocation toward attractive female counterparts in excess of perceived trustworthiness (and this display is modulated by male self-reported physical dominance). 3) Female participants appear to respond to male trust as a signal of sexual interest and are therefore more likely to exploit the trust of attractive males. 4) In explicitly dating contexts females are more likely to prefer attractive males to pay for the meal. These results indicate that participants are biased by mate choice and mating display considerations while playing economic games in the lab. Hypotheses that trust game behaviour is modulated by intra-sexual competition for resources were also somewhat supported. 1) Male participants reporting an ability to win fights with same-sex peers are more exploitative of other males. 2) Cues to current circulating testosterone level in counterpart’s faces are less trusted but elicit more reciprocation. 3) The male sexually dimorphic trait facial width-to-height ratio (a trait which is related to both aggression and dominance) is related to an increased proportion of decisions to exploit others in the trust game while also being used by others as a cue to untrustworthiness. We conclude that trusting and trustworthy behaviour in both sexes is biased by mating market considerations predicted by intra- and inter-sexual selection.

Le choix de partenaire est souvent considéré comme étant le résultat d’une simple interaction, mais, en nature, l’environnement social dans lequel les animaux communiquent correspond généralement à un réseau d’émetteurs et de récepteurs. La présence de congénères, de rivaux, et même de prédateurs durant le choix de partenaire peut avoir plusieurs répercussions sur ce choix. Être observé par une audience composée de congénères de même sexe peut pousser certaines espèces à modifier le niveau d’expression de leurs préférences, et même à modifier ces préférences pour réduire la compétition ou éviter d’être imitées. La préférence de plusieurs femelles diamant mandarin pour deux mâles a été mesurée en absence et en présence d’une audience femelle pour déterminer si la présence de rivales a des effets sur le choix de partenaire des femelles. De plus, afin de déterminer si ces effets varient en fonction de la qualité des femelles focales et audience, la condition de plusieurs femelles a été altérée en diminuant leur capacité à voler. Selon les résultats, les femelles diminuent leur niveau de sélectivité suite à l’ajout d’une audience femelle, et l’intensité des interactions mâle-femelle dépend de la condition des femelles focales. Les femelles ajustent leur comportement surtout pour éviter d’être imitées et non en fonction de leur condition. Cependant, ces deux mécanismes peuvent affecter les femelles simultanément. / Mate choice is often considered as the result of a simple interaction, but, in the wild, the social environment in which animals communicate generally corresponds to a network of several signallers and receivers. The presence of conspecifics, rivals, and even predators during mate choice can have many repercussions on that choice. Being observed by an audience of same-sex conspecifics can drive some species to alter the level of expression of their preferences, and even to modify those preferences to reduce competition or avoid being copied. The preference of several zebra finch females for two males was measured without and with a female audience to determine if the presence of an audience alters female mate choice. Moreover, to determine if these effects vary according to focal and audience females’ condition, the condition of several females was altered by diminishing their flying ability. According to the results, females lower their level of selectivity following the addition of an audience, and the intensity of male-female interactions depends on the focal females’ condition. Our findings suggest that females mainly adjust their behavior to avoid being copied and not according to their condition. However, these two mechanisms might have affected the females’ mating preferences simultaneously.