Over the last century, sexual selection has grown from a controversial theory into a vast field of theoretical and empirical research. Although Darwin outlined two major mechanisms within his theory, male-male competition and female mate choice, the latter has promoted a wealth of research by virtue of its complexity. Despite decades of research into how female preferences and sexually selected traits have evolved, there is still little consensus as to why females prefer the males they do. Preferences are thought to evolve from either direct selection on the preference, as females themselves benefit directly from mating with a preferred male, or through indirect selection on the preference via offspring fitness. In all cases however, female preferences should compensate for the costs of discriminating between potential mates, if they are to remain overall beneficial. The fitness benefits of mating with preferred males were investigated here using the fruitfly Drosophila simulans, employing a range of behavioural, phenotypic and quantitative genetic approaches. The findings presented here indicate that female Drosophila simulans do not gain directly from mating with a preferred male. Multiple mating can increase fecundity, although costs from male harassment can reduce the net benefit. They also indicate that females may benefit indirectly from mating with attractive males as attractiveness is heritable and sons of preferred males are themselves preferred. There is also evidence that attractive males are successful in both the pre- and post-copulatory sense, as preferred males are better sperm competitors than less-preferred males. However, although there appear to be benefits from preferred males via their sons, there appear to be no benefits from males via their daughters’ fitness. These findings collectively indicate that female preferences in Drosophila simulans are driven by indirectly selected benefits (via Fisherian sons), and that females benefit directly from mating multiply.

Sperm competition occurs when the sperm of multiple males concurrently occupy a female's reproductive tract and compete for fertilization. Sperm competition may have been a recurrent adaptive problem over human evolutionary history. Women's orgasm may facilitate retention of a particular man's sperm. I therefore hypothesized that men experiencing greater sperm competition risk will be particularly interested in the occurrence of their partner's copulatory orgasm. Men who are more satisfied with and invested in their relationship may experience greater costs in the event of sperm competition and potential cuckoldry. Therefore, these men may be more interested in ensuring their partner's copulatory orgasm. I hypothesized that men's relationship satisfaction and investment would predict interest in their partner's copulatory orgasm and moderate the link between sperm competition risk and interest in partner's copulatory orgasm. Using data secured from 229 men in a committed relationship, I tested and found support for these hypotheses. / by Vincent M. Bates. / Thesis (M.A.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Sexual coercion in romantic relationships is a facet of criminal behaviour requiring psychological investigation. The cuckoldry risk hypothesis, that sexual coercion is a tactic used by some males to reduce the risk of cuckoldry by engaging in sperm competition, was developed to account for such behaviour. From this hypothesis, four predictions were generated and empirically tested: (1) males should be more willing to use sexually coercive tactics when the risk of cuckoldry is high; (2) greater instances of cuckoldry risk in the past should be related to greater instances of sexual aggression; (3) cuckoldry risk and sexual jealousy should positively correlate in men; and (4) among males, rape attitudes and arousal are highest when the risk of cuckoldry is high. Theoretical considerations also suggested the following exploratory questions: (1) are factors currently known to be related to general sexual coercion also related to measures of coercion in romantic relationships; and (2) can the cuckoldry risk measures still predict coercion after controlling for psychopathy? In order to test these predictions, a sample of 82 male and 82 female undergraduate students who were sexually active in a heterosexual relationship completed a survey that collected information on demographics, relationship characteristics, arousal, antisociality, and attitudes. Results found: (1) a significant interaction between cuckoldry risk variables in predicting coercion among male participants and not among females; (2) no relationship between past instances of cuckoldry risk and instances of sexual aggression; (3) those who spend proportionally less time away from their partner were more likely to score higher on sexual jealousy; (4) significant interactions in the anticipated direction were found when predicting scores on the Rape Empathy Scale and Rape Myth Acceptance Scale, a trend in the anticipated direction was found when predicting Adversarial Sexual Beliefs, and nonsignificant results were found when predicting Attraction to Sexual Aggression. Results addressing the exploratory questions found that: (1) only psychopathy significantly predicted partner sexual coercion; and (2) cuckoldry risk variables predicted sexual coercion after controlling for psychopathy. Discussion of these results cover: the importance of finding a sex difference; understanding the interaction between variables; how cuckoldry risk impacts rape-supportive thoughts, attitudes, and arousal; the role of sexual jealousy; the function of a cuckoldry risk psychological mechanism; and lastly, the implications on dynamic risk prediction.

Sexual coercion in romantic relationships is a facet of criminal behaviour requiring psychological investigation. The cuckoldry risk hypothesis, that sexual coercion is a tactic used by some males to reduce the risk of cuckoldry by engaging in sperm competition, was developed to account for such behaviour. From this hypothesis, four predictions were generated and empirically tested: (1) males should be more willing to use sexually coercive tactics when the risk of cuckoldry is high; (2) greater instances of cuckoldry risk in the past should be related to greater instances of sexual aggression; (3) cuckoldry risk and sexual jealousy should positively correlate in men; and (4) among males, rape attitudes and arousal are highest when the risk of cuckoldry is high. Theoretical considerations also suggested the following exploratory questions: (1) are factors currently known to be related to general sexual coercion also related to measures of coercion in romantic relationships; and (2) can the cuckoldry risk measures still predict coercion after controlling for psychopathy? In order to test these predictions, a sample of 82 male and 82 female undergraduate students who were sexually active in a heterosexual relationship completed a survey that collected information on demographics, relationship characteristics, arousal, antisociality, and attitudes. Results found: (1) a significant interaction between cuckoldry risk variables in predicting coercion among male participants and not among females; (2) no relationship between past instances of cuckoldry risk and instances of sexual aggression; (3) those who spend proportionally less time away from their partner were more likely to score higher on sexual jealousy; (4) significant interactions in the anticipated direction were found when predicting scores on the Rape Empathy Scale and Rape Myth Acceptance Scale, a trend in the anticipated direction was found when predicting Adversarial Sexual Beliefs, and nonsignificant results were found when predicting Attraction to Sexual Aggression. Results addressing the exploratory questions found that: (1) only psychopathy significantly predicted partner sexual coercion; and (2) cuckoldry risk variables predicted sexual coercion after controlling for psychopathy. Discussion of these results cover: the importance of finding a sex difference; understanding the interaction between variables; how cuckoldry risk impacts rape-supportive thoughts, attitudes, and arousal; the role of sexual jealousy; the function of a cuckoldry risk psychological mechanism; and lastly, the implications on dynamic risk prediction.

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

Thesis (M.S.)--The University of North Carolina at Greensboro, 2008. / Directed by Malcolm Schug; submitted to the Dept. of Biology. Title from PDF t.p. (viewed Aug. 14, 2009). Includes bibliographical references (p. 40-47).

The European earwig exhibits a remarkable male-dimorphism in forceps morphology that is associated with alternative reproductive tactics under the control of a conditional evolutionarily stable strategy. Populations on the small, rocky islands of the Farnes off the Northumberland coast are known to sustain populations with dramatically higher morph ratios than observed on the UK mainland. A survey conducted of island and mainland sites around the UK showed that the dimorphic populations of the Farnes are similar to other islands and that mainland populations generally exhibit low morph ratios. Additionally, a correlation between morph ratio and population density was found lending support to the hypothesis that the ESS thresholds that define the morph ratios have diverged through local adaptation. A set of seven microsatellite markers are presented that were developed from a Farne island population of F. auricularia with one additional, previously published locus. These eight markers exhibit genetic variability within and between populations and as such can potentially be applied at a range of scales, from broad-scale phylogeography to within population parentage studies. A phylogeographic study of the UK populations using these markers suggests a single postglacial colonisation from mainland Europe and give further support to the local adaptation hypothesis of ESS threshold evolution. A study of ejaculate size in F. auricularia showed that the males transfer free sperm at a steady rate and that the morphs do not differ in the number of sperm per ejaculate. Measurements of change in body-mass were found to be ineffective measures of ejaculate size, but that macrolabic males lost more weight during copula than brachylabic males. This may be the result of differential investment in accessory ejaculate components between the morphs, as a result of the differing risk of sperm competition.

The mating behaviour and reproductive ecology of the big-handed crab Heterozius rotundifrons was studied at Kaikoura between November 1997 and December 1998. H. rotundifrons was found at mean densities of 7.6 per m² (± 1.4) within the middle and low shore levels and varied little between seasons. The variance! mean ratio indicated that males and females aggregated within these shore levels. The sex ratio was significantly female biased during the majority of the year. Allometric growth rates indicated that males and females reached sexual maturity at 11 mm carapace width (CW). In males, spermatozoa production occurred between 9-9.99 mm CW. Ovigerous females were present every month except February. The first broods of the year were produced in March which coincides with a decrease in the female gonado-somatic index (GSI). These broods were incubated for approximately nine months whereas broods produced in August were incubated for only five months. Female brood production appeared to be cyclical, alternating between a winter incubation period and a summer incubation period. The completed cycle takes approximately three years with two broods produced during the cycle. Fecundity increased with female size but egg mortality was quite high (19%). Instantaneous mortality rate increased with increasing brood development. Females mate when recently moulted (soft-shelled). Although females moulted through out the year, in small numbers, there was a peak in female moulting during October and November. The operational sex ratio (OSR) was male biased during all months of the year. Females released an attractant prior to moulting which initiated pre-copulatory mate guarding by the male. Once the female moulted, copulation occurred approximately 6 h later. Copulation lasted for approximately 3 h and was followed by a period of post-copulatory mate guarding. Males increased the duration of post-copulatory mate guarding if another male was present. Large males out competed small males for receptive females. Males used their large cheliped to subdue competitors and to provide protection for the soft female. Mate guarding was shown to reduce cannibalism from other females. Spermatozoa are packaged in spermatophores within the vas deferens of males but are quickly dehisced within the spermathecae (ventral-type) of newly mated females. Last male to copulate probably achieves the highest level of paternity. Postcopulatory mate guarding by the male was found and ejaculates were found in discrete packets within the spermatheca. Sperm competition appeared to be important because large males displaced small males during copulation, males left when a female was still receptive and the females could retain sperm between moults. It is concluded that H. rotundifrons probably has a polygynous mating system in which males compete for soft females (female centered competition)

Dynamics of acrosome reaction during intra-specific sperm competition in rodents Sperm acrosome integrity is disturbed in promiscuous species field mice (Apodemus) and more than half of the spermatozoa undergoing spontaneous acrosome reaction (AR) before binding to the zona pellucida. In Muridae it is documented a generally high rate of spontaneous AR, and the percentage increases in promiscuous species up to 60 % in 60 min capacitation in vitro. The acrosome integrity positively corellates with presence of CD46 protein which absence in wood mouse is fenotypicaly same as in CD46 knock-out mouse leading to accelerated spontaneous AR. It is necessary to clarify whether for mouse sperm it is essential the primary binding of intact sperm to zona pellucida of the egg or whether it is preferred secondary sperm binding after spontaneous AR. In this context, the question is whether there is a relocalization of the key fusion protein IZUMO in sperm during spontaneous AR. IZUMO relocalization was monitored by immunofluorescence at specific times of capacitation in vitro during spontaneous and induced AR. IZUMO relocalization as closely connected to actin cytoskeleton, and β1 integrins. Dynamics and localization of β1 integrin during spontaneous and induced AR was also detected by immunofluorescence. Our results...

Marine and freshwater environments support numerous species of teleost fish with a wide and diverse range of reproductive strategies. Despite the considerable interest in fish reproduction, our knowledge regarding ejaculate traits and factors affecting them is limited. Using computer-assisted sperm analysis (CASA) I measured ejaculate traits (sperm swimming speed, motility, path trajectory, longevity and concentration) from sexually mature chinook salmon (Oncorhynchus tshawytscha) activated in freshwater and ovarian fluid. I also looked at these ejaculate traits in relation to measures of male quality (body condition) and investment into reproduction (relative testes mass). Furthermore, I determined the chemical composition of seminal and ovarian fluid and looked at the effect these fluids have on sperm behaviour. A considerable amount of intraspecific variation existed in all ejaculate traits measured, and investment into reproduction (relative testes mass) was dependent on male body condition, as males in better condition had relatively larger testes. However, these males did not have superior quality ejaculates or ejaculates with a higher density of spermatozoa; hence the potential reproductive advantage of having larger relative testes in this species remains unknown and requires further investigation. In addition, a positive relation between sperm longevity and sperm swimming speed was observed defying the expected trade-off between ejaculate traits according to theory. There was also a weak negative trend in our data between body condition and sperm swimming speed, linearity, and longevity. All sperm traits measured were greatly enhanced when activated in a solution containing ovarian fluid (a viscous fluid which is excreted with the egg batch during spawning) from female chinook salmon. Interestingly, sperm swimming speed activated in fresh water only accounted for < 12% of the observed variation in mean sperm swimming speed in ovarian fluid. This result suggests the sperm traits measured in fresh water are not relevant to those same traits measured in ovarian fluid, so caution should be applied when comparing the potential for individual males to fertilize ova when sperm traits are activated in water, especially in studies of sperm competition in an externally fertilising species. Sperm competition between males is known to strongly influence sperm and ejaculate traits, but less is known about female sperm choice after copulation via a process called cryptic female choice (CFC). In CFC, females may have the ability to favour the sperm of one male over another and bias fertilisation accordingly. To test whether ovarian fluid could act as a mechanism of CFC in an externally fertilising fish species, I measured sperm traits from each male activated in the ovarian fluids from different females. I found that mean sperm swimming speed, longevity, and path trajectory differed significantly among males, but most importantly, the pattern of within-male variation in these traits also varied significantly among males in response to different females’ ovarian fluids. This result suggests that ovarian fluid may be a potential mechanism of CFC whereby females differentially enhance the swimming speed of sperm from different males. In addition, I found that sperm longevity was negatively correlated with variation in [Ca²⁺] and [Mg²⁺] concentration in the ovarian fluid, while percent motility increased with increasing concentration of [Mg²⁺]. These observations provide a possible chemical basis for cryptic female choice whereby female ovarian fluid differentially influences the behaviour of sperm from different males and thus their fertilisation success. This finding is particularly exciting, as we may have uncovered a potential mechanism of CFC in an externally fertilising species, which is poorly understood. In addition, results from this study suggest new directions for genetic studies to provide direct evidence for CFC. For example, does sperm selection via ovarian fluid promote favoured genetic combinations that enhance male reproductive success?