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Search Results: 1 - 10 of 85575 matches for " Leigh W Simmons "
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Seminal Fluid Affects Sperm Viability in a Cricket
Leigh W. Simmons,Maxine Beveridge
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0017975
Abstract: Recent studies have suggested that males may vary the quality of their ejaculates in response to sperm competition, although the mechanisms by which they do so remain unclear. The viability of sperm is an important aspect of ejaculate quality that determines competitive fertilization success in the field cricket Teleogryllus oceanicus. Using in vitro mixtures of sperm and seminal fluid from pairs of male crickets, we show that seminal fluid can affect the viability of sperm in this species. We found that males who invest greatly in the viability of their own sperm can enhance the viability of rival sperm, providing the opportunity for males to exploit the investments in sperm competition made by their rivals. Transitive effects of seminal fluids across the ejaculates of different males are expected to have important implications for the dynamics of male investments in sperm competition.
Preferences across the Menstrual Cycle for Masculinity and Symmetry in Photographs of Male Faces and Bodies
Marianne Peters, Leigh W. Simmons, Gillian Rhodes
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0004138
Abstract: Background Previous studies have shown that women increase their preference for masculinity during the fertile phase of the menstrual cycle. Evidence for a similar preference shift for symmetry is equivocal. These studies have required participants to choose between subtle variations in computer-generated stimuli, and preferences for more natural stimuli have not been investigated. Methodology/Principal Findings Our study employed photographs of individual males to investigate women's preferences for face and body masculinity and symmetry across the menstrual cycle. We collected attractiveness ratings from 25 normally cycling women at high- and low-fertility days of the menstrual cycle. Attractiveness ratings made by these women were correlated with independent ratings of masculinity and symmetry provided by different sets of raters. We found no evidence for any cyclic shift in female preferences. Correlations between attractiveness and masculinity, and attractiveness and symmetry did not differ significantly between high- and low-fertility test sessions. Furthermore, there was no significant difference between high- and low-fertility ratings of attractiveness. Conclusions These results suggest that a menstrual cycle shift in visual preferences for masculinity and symmetry may be too subtle to influence responses to real faces and bodies, and subsequent mate-choice decisions.
Rival Male Relatedness Does Not Affect Ejaculate Allocation as Predicted by Sperm Competition Theory
Melissa L. Thomas, Leigh W. Simmons
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002151
Abstract: When females are sexually promiscuous, the intensity of sperm competition for males depends on how many partners females mate with. To maximize fitness, males should adjust their copulatory investment in relation to this intensity. However, fitness costs associated with sperm competition may not only depend on how many males a female has mated with, but also how related rival males are. According to theoretical predictions, males should adjust their copulatory investment in response to the relatedness of their male rival, and transfer more sperm to females that have first mated with a non-sibling male than females that have mated to a related male. Here, for the first time, we empirically test this theory using the Australian field cricket Teleogryllus oceanicus. We expose male crickets to sperm competition from either a full sibling or non-sibling male, by using both the presence of a rival male and the rival male's actual competing ejaculate as cues. Contrary to predictions, we find that males do not adjust ejaculates in response to the relatedness of their male rival. Instead, males with both full-sibling and non-sibling rivals allocate sperm of similar quality to females. This lack of kin biased behaviour is independent of any potentially confounding effect of strong competition between close relatives; kin biased behaviour was absent irrespective of whether males were raised in full sibling or mixed relatedness groups.
Good Genes and Sexual Selection in Dung Beetles (Onthophagus taurus): Genetic Variance in Egg-to-Adult and Adult Viability
Francisco Garcia-Gonzalez,Leigh W. Simmons
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016233
Abstract: Whether species exhibit significant heritable variation in fitness is central for sexual selection. According to good genes models there must be genetic variation in males leading to variation in offspring fitness if females are to obtain genetic benefits from exercising mate preferences, or by mating multiply. However, sexual selection based on genetic benefits is controversial, and there is limited unambiguous support for the notion that choosy or polyandrous females can increase the chances of producing offspring with high viability. Here we examine the levels of additive genetic variance in two fitness components in the dung beetle Onthophagus taurus. We found significant sire effects on egg-to-adult viability and on son, but not daughter, survival to sexual maturity, as well as moderate coefficients of additive variance in these traits. Moreover, we do not find evidence for sexual antagonism influencing genetic variation for fitness. Our results are consistent with good genes sexual selection, and suggest that both pre- and postcopulatory mate choice, and male competition could provide indirect benefits to females.
Low Pitched Voices Are Perceived as Masculine and Attractive but Do They Predict Semen Quality in Men?
Leigh W. Simmons, Marianne Peters, Gillian Rhodes
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0029271
Abstract: Women find masculinity in men's faces, bodies, and voices attractive, and women's preferences for men's masculine features are thought to be biological adaptations for finding a high quality mate. Fertility is an important aspect of mate quality. Here we test the phenotype-linked fertility hypothesis, which proposes that male secondary sexual characters are positively related to semen quality, allowing females to obtain direct benefits from mate choice. Specifically, we examined women's preferences for men's voice pitch, and its relationship with men's semen quality. Consistent with previous voice research, women judged lower pitched voices as more masculine and more attractive. However men with lower pitched voices did not have better semen quality. On the contrary, men whose voices were rated as more attractive tended to have lower concentrations of sperm in their ejaculate. These data are more consistent with a trade off between sperm production and male investment in competing for and attracting females, than with the phenotype-linked fertility hypothesis.
Ejaculate Economics: Testing the Effects of Male Sexual History on the Trade-Off between Sperm and Immune Function in Australian Crickets
Damian K. Dowling, Leigh W. Simmons
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0030172
Abstract: Trade-offs between investment into male sexual traits and immune function provide the foundation for some of the most prominent models of sexual selection. Post-copulatory sexual selection on the male ejaculate is intense, and therefore trade-offs should occur between investment into the ejaculate and the immune system. Examples of such trade-offs exist, including that between sperm quality and immunity in the Australian cricket, Teleogryllus oceanicus. Here, we explore the dynamics of this trade-off, examining the effects that increased levels of sexual interaction have on the viability of a male's sperm across time, and the concomitant effects on immune function. Males were assigned to a treatment, whereby they cohabited with females that were sexually immature, sexually mature but incapable of copulation, or sexually mature and capable of copulation. Sperm viability of each male was then assessed at two time points: six and 13 days into the treatment, and immune function at day 13. Sperm viability decreased across the time points, but only for males exposed to treatment classes involving sexually mature females. This decrease was similar in magnitude across both sexually mature classes, indicating that costs to the expression of high sperm viability are incurred largely through levels of pre-copulatory investment. Males exposed to immature females produced sperm of low viability at both time points. Although we confirmed a weak negative association between sperm viability and lytic activity (a measure of immune response to bacterial infection) at day 13, this relationship was not altered across the mating treatment. Our results highlight that sperm viability is a labile trait, costly to produce, and subject to strategic allocation in these crickets.
Sexual selection on cuticular hydrocarbons in the Australian field cricket, Teleogryllus oceanicus
Melissa L Thomas, Leigh W Simmons
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-162
Abstract: We found that all three measures of male attractiveness generated sexual selection on male cuticular hydrocarbons, however there were differences in the form and intensity of selection among these three measures. Mating success was the only measure of attractiveness that imposed both univariate linear and quadratic selection on cuticular hydrocarbons. Although we found that all three attractiveness measures generated nonlinear selection, again only mating success was found to exert statistically significant stabilizing selection.This study shows that sexual selection plays an important role in the evolution of male cuticular hydrocarbon signals.It is common in natural populations for individuals of one sex, usually the female, to prefer certain phenotypic trait values over others in their choice of mates. Female preferences for male sexual signals are responsible for a spectacular array of phenotypic diversity found in the natural world, driving the evolution of exaggerated traits such as colouration [1], conspicuous ornaments [2,3], and song [4,5]. Females have also been found to base their choice of mate on pheromone signals. Although less well studied, pheromone signals are subject to the same kinds of natural and sexual selective forces that shape visual and auditory signals [6]. However, our understanding of the processes driving the evolution of pheromones is significantly less well developed.Cuticular hydrocarbons are chemical compounds found on the cuticle of most terrestrial arthropods. These compounds have been studied extensively for their role as signals in mate and species recognition, and ecology [7,8]. Cuticular hydrocarbons are highly sexually dimorphic in a range of species, with many of the compounds present in one sex but absent in the other, while shared compounds often differ quantitatively between the sexes [see [9] for review]. Such sexual dimorphism is expected to result from sex-specific selection. Despite the large number of species that di
Experimental evolution of sperm competitiveness in a mammal
Renée C Firman, Leigh W Simmons
BMC Evolutionary Biology , 2011, DOI: 10.1186/1471-2148-11-19
Abstract: Adopting the naturally polygamous house mouse (Mus domesticus) as our vertebrate model, we performed an experimental evolution study and observed genetic divergence in sperm quality; males from the polygamous selection lines produced ejaculates with increased sperm numbers and greater sperm motility compared to males from the monogamous lines. Here, after 12 generations of experimental evolution, we conducted competitive matings between males from lineages evolving under sperm competition and males from lineages subject to relaxed selection. We reduced variation in paternity arising from embryo mortality by genotyping embryos in utero at 14 days gestation. Our microsatellite data revealed a significant paternity bias toward males that evolved under the selective regime of sperm competition.We provide evidence that the sperm competitiveness phenotype can respond to selection, and show that improved sperm quality translates to greater competitive fertilisation success in house mice.When females mate with multiple partners, sperm from rival males compete to fertilise the ova [1]. Sperm competition has been shown to influence the evolution of testes size and efficiency [2-5], and sperm form and function [6-11]. Studies of experimental evolution have shown that male reproductive traits can evolve in response to sperm competition [12-17]. However, this does not prove that sperm competitive ability responds to selection or how different genotypes contribute to future generations. The assumption that divergence in sperm number and/or quality translates to competitive ability has been demonstrated in only two cases [15,17], and never before in a vertebrate.It is now recognised that the sperm competitiveness phenotype is a multifarious, transitional trait that can be influenced by genetic interactions between females and/or rival males. In some species, the female genotype plays a major role in determining the outcome of sperm competition [18-20]. Additionally, it seems that
Nuptial gifts fail to resolve a sexual conflict in an insect
Nina Wedell, Tom Tregenza, Leigh W Simmons
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-204
Abstract: We show that receiving multiple ejaculates reduces longevity in female R. verticalis, indicating a cost of male derived receptivity-suppressing compounds. Consumption of male nutrient donations does not appear to ameliorate this longevity cost, and there was no effect of nutrient provisioning on female lifetime fecundity.These results indicate that nutrient provisioning does not provide a resolution to sexual conflict over female receptivity in this bushcricket species.The reproductive interests of mates rarely coincide, resulting in sexual conflict over most aspects of reproduction [1,2]. There is frequent conflict over female remating, as males will have to endure sperm competition and reduced fertilization success when females mate again [3]. The risk of sperm competition has promoted a variety of male adaptations, often associated with female costs [4]. Males frequently transfer compounds in the ejaculate that manipulate female reproductive physiology to increase male reproductive success. For example, Drosophila melanogaster males transfer a cocktail of >80 different proteins in the ejaculate that (amongst other things) stimulate oviposition and reduce female receptivity, thereby increasing male fertilization success [5,6]. However, these male-derived molecules have a negative effect on female fitness by reducing lifespan [7]. It has even been suggested that male harm could evolve as a means to manipulate females to increase their terminal investment in immediate reproductive output, due to reduced residual reproductive value, which then results in higher male reproductive success [8,9].Not all compounds transferred to the female at mating have a negative effect on female fitness. Males of several insects transfer nutrients at mating, either in the ejaculate or together with the sperm packet, that increase female reproductive success by enhancing fecundity and/or offspring survival [10-13]. As a consequence, male nutrient donations create an additional conflict
Does Genetic Diversity Predict Health in Humans?
Hanne C. Lie, Leigh W. Simmons, Gillian Rhodes
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006391
Abstract: Genetic diversity, especially at genes important for immune functioning within the Major Histocompatibility Complex (MHC), has been associated with fitness-related traits, including disease resistance, in many species. Recently, genetic diversity has been associated with mate preferences in humans. Here we asked whether these preferences are adaptive in terms of obtaining healthier mates. We investigated whether genetic diversity (heterozygosity and standardized mean d2) at MHC and nonMHC microsatellite loci, predicted health in 153 individuals. Individuals with greater allelic diversity (d2) at nonMHC loci and at one MHC locus, linked to HLA-DRB1, reported fewer symptoms over a four-month period than individuals with lower d2. In contrast, there were no associations between MHC or nonMHC heterozygosity and health. NonMHC-d2 has previously been found to predict male preferences for female faces. Thus, the current findings suggest that nonMHC diversity may play a role in both natural and sexual selection acting on human populations.
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