Not available / text

Darwin identified sexual selection as an important evolutionary process resulting from differences among males in their ability to secure mates. In the latter half of the 20th century, it became apparent that females often mate with multiple partners within the same reproductive cycle, leading to the overlap of ejaculates from multiple males and sperm competition for the fertilization of the eggs. Here, I examine how sperm competition has influenced the evolution of Xiphophorus nigrensis, an internally fertilized, livebearing fish with alternative male mating tactics that are dependent upon male size. I find that variation in male tactic is correlated with variation in traits relevant to sperm competition: small males that sneak copulations produce ejaculates with a greater proportion of fertilization-capable sperm (sperm viability) and sperm that is longer-lived following activation compared to large males that court females. Sperm morphology is also divergent between tactics and correlated with sperm performance: smaller males have larger midpieces and midpiece size is positively correlated with sperm velocity and longevity. Social environment also affects ejaculate quality, with sperm velocity rapidly increasing when a small male is exposed to another small male compared to when he is exposed to a large male. Large male ejaculates were invariant across social environments. Next, I demonstrate experimentally that the observed variation in sperm quality has important consequences for the outcome of sperm competition. Males with superior sperm viability sire more offspring, while sperm velocity is negatively associated with sperm competitive ability when sperm are stored within the female prior to fertilization. Finally, I show that sperm competition is likely to have important effects on male reproductive success in the wild by characterizing the genetic mating system of X. nigrensis. I find that 61% of females collected from the Nacimiento Río Choy produce offspring sired by 2-4 males. Paternity is strongly skewed among sires, with an average of 70% of offspring sired by one of the males represented in the brood. These studies illustrate sperm competition can have potent effects on the evolution of animals. / text

Not available / text

The evolution of adaptation depends on genetic and phenotypic variation, both of which are expected to be depleted in populations as a result of selection. Thus, understanding the maintenance of variation in fitness-related traits is of central importance in evolutionary biology as such processes can mitigate the constraining effects of adaptation on evolutionary change. Secondary sexual traits involved in attracting mates offer conspicuous examples of adaptation and are suggestive of strong directional selection, yet abundant variation is commonly observed both within and among populations. One explanation posits that variation in elaborate sexual traits might be maintained by fluctuating selection, such that episodes of intense selection are interspersed by periods in which variation is shielded from elimination, yet little is known about the processes that lead to such heterogeneity. In many cases, mate choice results from highly localized social interactions such that fine scale demographic variation may contribute to variation in patterns of sexual selection, especially when individuals' attractiveness is assessed in comparison to local conspecifics. Additionally, selection on sexual traits might fluctuate when the fitness consequences of mate choice depends on the complementarity of male and female characters, such as when offspring viability is influenced by the genetic relatedness of parents. In this dissertation, I examined demographic, behavioral, and genetic causes of variation in sexually-selected male plumage ornaments in a wild population of house finches (Carpodacus mexicanus). Over a five-year field study, I found that mate choice occurred largely within small social groups, the composition of which was influenced by active social sampling by males, suggesting that variation in male sexual traits may be maintained as a result of behaviors that enable individuals to shape their environment of selection. Additionally, using a panel of neutral molecular markers, I found that parental relatedness predicted multiple metrics of offspring fitness, and also affected the ability of neonates to buffer development from environmental variation, suggesting that inbreeding is likely to have pervasive effects on the evolution of adaptation. Taken together, these studies provide evidence of distinct processes that contribute to the maintenance of quantitative variation in sexual traits in this natural population.

Although sexual selection often explains the evolution and maintenance of a single male ornament, it is unclear how the multicomponent nature of most sexual displays evolves. Theoretical models suggest that handicap signalling should converge on a single most informative quality indicator, whereas additional signals are more likely to be arbitrary Fisherian traits, amplifiers, or exploitations of receiver psychology. Despite the predictions that multiple handicap signals are unlikely to be stable, the male nuptial plumage of the highly polygynous (ca. 3, but up to 9 actively nesting females) red-collared widowbird Euplectes ardens comprises two classic quality-indicating avian ornaments (handicaps); a long graduated tail (22 cm) and a red carotenoid throat patch (collar). To investigate the evolution and maintenance of these handicaps in the red-collared widowbird, a population was studied in the Hilton district, KwaZulu-Natal, South Africa, where these small (males ca. 20 g) African weaverbirds (Ploeceidae) inhabit a grassy valley during the breeding season. Multivariate selection analyses, used to investigate net, direct and indirect female selection, demonstrated an unusually strong fitness effect of natural tail length (47%) on male reproductive success (the order and total number of nests acquired). There were no other effects of morphology, ectoparasite load, display rate, territory quality, tail asymmetry or collar measures (hue, brightness and size) on reproductive success, suggesting that females base their mate choice exclusively on only one handicap signal, extreme tail elongation. Although ignored in mate choice, there is strong evidence that the variable carotenoid collar (ranging from yellow to red) functions as a status or agonistic signal in male contest competition for territories. Compared to 'floating' males (that did not establish a territory in the area), resident males had a 60% larger and 23 nm 'redder' (longwave hue) collar. Model presentations also corroborated the status signalling function of the collar as territorial males were less aggressive towards conspecific models with intense collar displays, and males with greater carotenoid investment responded more aggressively to the models. In captive experiments, non-breeding brown males painted with red 'collars' dominated orange painted, control brown, novel blue collared and testosterone-implanted males in dyadic contests over food resources. In addition, experiments in the field demonstrated that males manipulated with larger and redder collars established and maintained territories in the area, whereas most males with small, orange or blackened collars failed to establish or retain territories. Thus the size and particularly redness of the costly carotenoid collar reliably signals male status and fighting ability in male contests. The unique negative phenotypic relationship between the expression of tail length and carotenoid pigmentation, suggests strong overlapping developmental costs (and allocation conflicts) between the two handicap ornaments. This tradeoff is predicted to be strongest between signals with the same or similar costs. Although current theory predicts that multiple handicaps should be evolutionary unstable, the coexistence of multiple costly ornaments in the red-collared widowbird is stable because of selection by different receivers, females and males (i.e., multiple receivers). / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Motor vehicle accidents are the leading cause of death and injury among teenagers. The crash risk is highest for young male drivers with young male passengers. The goal of this study is to find out why young males are at such high risk. One possible explanation could be the Sexual Selection Theory (Darwin, 1871), which emphasizes the competitive nature of young males that may determine their behaviour for future benefits. I tested if there was competition between males that made them take more risks while driving in the simulator. Various driving performance variables (speed, car following distance, standard deviation of the lateral position, hazard response times, number of vehicles passed) and individual differences variables (risky driving, risk perception, sensation seeking, competitiveness) were measured. Results provided little support for the effect of interpersonal competition and an opportunity for discussion arose. / AUTO21, Ontario Innovation Trust (OIT), Canadian Foundation for Innovation (CFI).

Male birds of many species use conspicuous song and plumage displays in both courtship and territorial interactions. In some species, one or both of these signalling traits may not reach full adult maturity until a male’s second year of life. While the prevalence of delayed plumage maturation is well documented, delayed song maturation may be more difficult to detect. As a result, there are few studies which report age-based song differences between first-year and adult males. Additionally, despite the potentially large degree of variation of each trait within yearling males, little work has examined the benefits for young males who appear or sound more adult-like. Here, I investigate variation in both song and plumage displays of yearling male American redstarts (Setophaga ruticilla) as they relate to success during the breeding and non-breeding seasons. I first demonstrate a relationship between the degree of adult-like black plumage and both non-breeding season habitat quality in Jamaica and breeding season arrival date in Ontario. Previous studies have linked breeding season arrival date with winter habitat quality in adult males using stable-carbon isotope analysis. Together, these results suggest that variation in yearling male appearance may signal an individual’s competitive ability for high-quality resources. Next, I quantified the mate-attraction songs of both adult and yearling males and demonstrate a delayed maturation in this song type. I also present evidence of the potential benefits of expressing a more adult-like song by linking song structure with reproductive success in adult males. Finally, I demonstrate a potential relationship between the degree of adult-like song and plumage expression in yearling males, but not adult males. This work demonstrates that the delayed maturation of sexual signals may play an important role in the life-history of yearling male American redstarts, and highlights the need for in-depth analyses of individual variation of multiple sexual signals in this poorly-studied age class of birds. / Thesis (Master, Biology) -- Queen's University, 2009-09-25 10:42:19.794

The human voice is a common and important part of the social environment. In addition to being the primary carrier of language, there is growing evidence that the sound of a person’s voice contains a great deal of socially relevant information. Drawing on a functional approach to perception, the current research investigated the attunement of social perceivers to the vocal specification of speaker physical properties. An initial study developed a set of vocal samples for use in subsequent perceptual studies, and conducted exploratory analyses investigating relationships between speaker vocal and physical characteristics. Significant differences in the acoustic properties of male and female voices were identified, but the relationships between acoustic properties and speaker age, body size, and body configuration were less robust. Study 2 investigated the ability of listeners to accurately perceive the physical characteristics of speakers from vocal information. Perceivers made assessments of speaker physical characteristics that were highly consensual and that accurately reflected speaker sex, age, and body size. Studies 3 and 4 investigated perceiver judgments of vocal attractiveness. In Study 3, both male and female perceivers rated the voices of male speakers with lower indices of body asymmetry (a marker of genotypic and phenotypic condition) as more attractive. However, for female perceivers it was shown that this relationship is influenced by changes in fertility levels associated with the menstrual cycle. At times of high fertility female perceivers displayed a stronger attraction to the voices of male speakers with low asymmetry than they did at times of low fertility. This finding was interpreted as a functional shift increasing attraction to males possessing phenotypic markers of high fitness when the likelihood of conception is highest. Study 4 considered the effects of menstrual cycle variation on the voices of female speakers. Both male and female perceivers rated female voices recorded during a phase of high fertility to be more attractive than the same voices recorded during a phase of low fertility. This finding extends previous research demonstrating cyclic shifts in visual and olfactory attractiveness to the auditory domain, and is discussed in terms of the vocal specificity of female fertility status. Study 5 extended the previous studies by considering how vocal cues specifying the sex and age of a social target interact with visual cues to influence social perception. Relative to concordant voice and face information, discordant information was found to facilitate social memory. This finding is discussed with regards to the integration of multiple sources of information in social perception. The results of all studies are discussed in terms of the adaptive significance of perceivers accurately detecting the physical characteristics of others that are specified vocally.

Males of many species have elaborate phenotypes that are absent in females and that are thought to be the result of sexual selection. Sexual selection requires: (i) variance in male mating success, (ii) variation in male phenotype, and (iii) covariation between male mating success and male phenotype. Environmental conditions influence these factors, and management practices that alter environmental conditions have the potential to shape mating patterns and sexual selection. I investigated the hypothesis that the frequency of fire, used to manage tallgrass prairie, affects the mating patterns and process of sexual selection in the organisms breeding in managed prairies. I studied dickcissels (Spiza americana), a small songbird resident in tallgrass prairie. I first examined mating patterns and sexual selection in dickcissels independent of burning regime. I found variation among males in the number of mates attracted, in the number of offspring sired with each mate, and the offspring sired with the mates of other males. I found a positive association between social mates and siring success, but no evidence for an effect of breeding density or synchronous nesting on mating success. Male dimorphic traits, size, song, and plumage, showed between-individual variation but selection gradients were weak and often fluctuated between the years of study. I next examined patterns of mating success in plots burned on a variable schedule. I found little evidence that burning influenced either the mean or the variance in social mating success, paternity, or male phenotype. Burning regime also had no influence on sexual selection gradients with the single exception of selection on tarsus length. Temporal variation was more important for patterns of mating success and sexual selection gradients on male traits than was burning regime. The demography of dickcissels in the breeding season suggests, however, that habitat management on a larger scale may be more influential. My findings extend our understanding of sexual selection in birds and the effects of management on the factors required for sexual selection and the magnitude of selection.

Sexual conflict occurs when individuals of one sex express traits that reduce the fitness of their mates. Males of many species harass females to gain copulations, which benefits males by increasing the number of offspring they sire but imposes energetic and opportunity costs on the females they harass. This thesis examined the fitness costs of sexual harassment to females, the energetic costs of mating to males, and the factors influencing the intensity of male competition for mates in the western mosquitofish Gambusia affinis. I quantified male and female behavior, four female fitness components (number of offspring per female, embryo number, growth, and survival), and an index of male body condition in response to changes in operational sex ratio (experiment 1) and male and female density (experiment 2). I found that a strong, negative effect of female density on female fitness overwhelmed any potential costs of male harassment, suggesting that ecological interactions between females may play a larger role in determining female fitness than conflict between the sexes. Agonistic chases and displays between males increased as the operational sex ratio increased (became male-biased), while the number of copulations males attempted decreased. This inverse relationship suggests a tradeoff between interfering with other males and attempting additional copulations with females. Increases in chases between males were largely due to changes in female density, but not male density, suggesting that the availability of females determines whether males escalate contests with other males. In contrast, the number of displays between males depended varied with male density but did not female density. This difference between chases and displays is likely due to their difference in function; chases are performed to prevent other males from mating while displays are used to assess male competitors. I did not detect any energetic cost of mating to males.