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1
André, Gonçalo I., Renée C. Firman, and Leigh W. Simmons. "Phenotypic plasticity in genitalia: baculum shape responds to sperm competition risk in house mice." Proceedings of the Royal Society B: Biological Sciences 285, no. 1882 (July 11, 2018): 20181086. http://dx.doi.org/10.1098/rspb.2018.1086.
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Males are known to adjust their expenditure on testes growth and sperm production in response to sperm competition risk. Genital morphology can also contribute to competitive fertilization success but whether male genital morphology can respond plastically to the sperm competition environment has received little attention. Here, we exposed male house mice to two different sperm competition environments during their sexual development and quantified phenotypic plasticity in baculum morphology. The sperm competition environment generated plasticity in body growth. Males maturing under sperm competition risk were larger and heavier than males maturing under no sperm competition risk. We used a landmark-based geometric morphometric approach to measure baculum size and shape. Independent of variation in body size, males maintained under risk of sperm competition had a relatively thicker and more distally extended baculum bulb compared with males maintained under no sperm competition risk. Plasticity in baculum shape paralleled evolutionary responses to selection from sperm competition reported in previous studies of house mice. Our findings provide experimental evidence of socially mediated phenotypic plasticity in male genitalia.
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Lüke, Lena, Polly Campbell, María Varea Sánchez, Michael W. Nachman, and Eduardo R. S. Roldan. "Sexual selection on protamine and transition nuclear protein expression in mouse species." Proceedings of the Royal Society B: Biological Sciences 281, no. 1783 (May 22, 2014): 20133359. http://dx.doi.org/10.1098/rspb.2013.3359.
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Post-copulatory sexual selection in the form of sperm competition is known to influence the evolution of male reproductive proteins in mammals. The relationship between sperm competition and regulatory evolution, however, remains to be explored. Protamines and transition nuclear proteins are involved in the condensation of sperm chromatin and are expected to affect the shape of the sperm head. A hydrodynamically efficient head allows for fast swimming velocity and, therefore, more competitive sperm. Previous comparative studies in rodents have documented a significant association between the level of sperm competition (as measured by relative testes mass) and DNA sequence evolution in both the coding and promoter sequences of protamine 2. Here, we investigate the influence of sexual selection on protamine and transition nuclear protein mRNA expression in the testes of eight mouse species that differ widely in levels of sperm competition. We also examined the relationship between relative gene expression levels and sperm head shape, assessed using geometric morphometrics. We found that species with higher levels of sperm competition express less protamine 2 in relation to protamine 1 and transition nuclear proteins. Moreover, there was a significant association between relative protamine 2 expression and sperm head shape. Reduction in the relative abundance of protamine 2 may increase the competitive ability of sperm in mice, possibly by affecting sperm head shape. Changes in gene regulatory sequences thus seem to be the basis of the evolutionary response to sexual selection in these proteins.
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Champion de Crespigny, Fleur E., and Nina Wedell. "Wolbachia infection reduces sperm competitive ability in an insect." Proceedings of the Royal Society B: Biological Sciences 273, no. 1593 (March 21, 2006): 1455–58. http://dx.doi.org/10.1098/rspb.2006.3478.
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The maternally inherited bacterium Wolbachia pipientis imposes significant fitness costs on its hosts. One such cost is decreased sperm production resulting in reduced fertility of male Drosophila simulans infected with cytoplasmic incompatibility (CI) inducing Wolbachia . We tested the hypothesis that Wolbachia infection affects sperm competitive ability and found that Wolbachia infection is indeed associated with reduced success in sperm competition in non-virgin males. In the second male role, infected males sired 71% of the offspring whereas uninfected males sired 82% of offspring. This is the first empirical evidence indicating that Wolbachia infection deleteriously affects sperm competition and raises the possibility that polyandrous females can utilize differential sperm competitive ability to bias the paternity of broods and avoid the selfish manipulations of Wolbachia . This suggests a relationship between Wolbachia infection and host reproductive strategies. These findings also have important consequences for Wolbachia population dynamics because the transmission advantage of Wolbachia is likely to be undermined by sperm competition.
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Hoysak, Drew J., N. Robin Liley, and Eric B. Taylor. "Raffles, roles, and the outcome of sperm competition in sockeye salmon." Canadian Journal of Zoology 82, no. 7 (July 1, 2004): 1017–26. http://dx.doi.org/10.1139/z04-073.
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In species with male alternative reproductive phenotypes, one phenotype is usually disadvantaged in mating competition. In salmonid fishes, large late-maturing males pair with nesting females and maintain close contact before and during spawning. Small early-maturing males have little contact with nesting females and, during spawning, begin to release sperm after the paired male. The effects of male phenotype and timing of ejaculation on success in sperm competition are not known. In this study, we determined paternity of offspring resulting from in vitro competitive fertilizations to examine these two aspects of sperm competition in sockeye salmon, Oncorhynchus nerka (Walbaum, 1792). When we fertilized eggs with mixtures of equal numbers of sperm from each of two male age classes, we found that success in sperm competition did not depend on male age. However, success in these competitive fertilizations did not conform to the fair raffle model of sperm competition, since paternity in most of the clutches was biased in favour of one male. When we added milt from two males sequentially to a batch of eggs, we found that sperm from the second male fertilized fewer eggs than sperm from the first male, but the difference was less than expected. In addition, a male's success when his milt was added first was not correlated with his success when his milt was added second.
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Engqvist, Leif, and Klaus Reinhold. "Sperm competition games: optimal sperm allocation in response to the size of competing ejaculates." Proceedings of the Royal Society B: Biological Sciences 274, no. 1607 (November 7, 2006): 209–17. http://dx.doi.org/10.1098/rspb.2006.3722.
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Sperm competition theory predicts that when males are certain of sperm competition, they should decrease sperm investment in matings with an increasing number of competing ejaculates. How males should allocate sperm when competing with differently sized ejaculates, however, has not yet been examined. Here, we report the outcomes of two models assuming variation in males' sperm reserves and males being faced with different amounts of competing sperm. In the first ‘spawning model’, two males compete instantaneously and both are able to assess the sperm competitive ability of each other. In the second ‘sperm storage model’, males are sequentially confronted with situations involving different levels of sperm competition, for instance different amounts of sperm already stored by the female mating partner. In both of the models, we found that optimal sperm allocation will strongly depend on the size of the male's sperm reserve. Males should always invest maximally in competition with other males that are equally strong competitors. That is, for males with small sperm reserves, our model predicts a negative correlation between sperm allocation and sperm competition intensity, whereas for males with large sperm reserves, this correlation is predicted to be positive.
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Vuarin, Pauline, Yves Hingrat, Loïc Lesobre, Michel Saint Jalme, Frédéric Lacroix, and Gabriele Sorci. "Sperm competition accentuates selection on ejaculate attributes." Biology Letters 15, no. 3 (March 2019): 20180889. http://dx.doi.org/10.1098/rsbl.2018.0889.
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Ejaculate attributes are important factors driving the probability of fertilizing eggs. When females mate with several males, competition between sperm to fertilize eggs should accentuate selection on ejaculate attributes. We tested this hypothesis in the North African houbara bustard ( Chlamydotis undulata undulata ) by comparing the strength of selection acting on two ejaculate attributes when sperm from single males or sperm from different males were used for insemination. In agreement with the prediction, we found that selection on ejaculate attributes was stronger when sperm of different males competed for egg fertilization. These findings provide the first direct comparison of the strength of selection acting on ejaculate attributes under competitive and non-competitive fertilizations, confirming that sperm competition is a major selective force driving the evolution of ejaculate characteristics.
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Singson, Andrew, Katherine L. Hill, and Steven W. L’Hernault. "Sperm Competition in the Absence of Fertilization in Caenorhabditis elegans." Genetics 152, no. 1 (May 1, 1999): 201–8. http://dx.doi.org/10.1093/genetics/152.1.201.
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Abstract Hermaphrodite self-fertilization is the primary mode of reproduction in the nematode Caenorhabditis elegans. However, when a hermaphrodite is crossed with a male, nearly all of the oocytes are fertilized by male-derived sperm. This sperm precedence during reproduction is due to the competitive superiority of male-derived sperm and results in a functional suppression of hermaphrodite self-fertility. In this study, mutant males that inseminate fertilization-defective sperm were used to reveal that sperm competition within a hermaphrodite does not require successful fertilization. However, sperm competition does require normal sperm motility. Additionally, sperm competition is not an absolute process because oocytes not fertilized by male-derived sperm can sometimes be fertilized by hermaphrodite-derived sperm. These results indicate that outcrossed progeny result from a wild-type cross because male-derived sperm are competitively superior and hermaphrodite-derived sperm become unavailable to oocytes. The sperm competition assays described in this study will be useful in further classifying the large number of currently identified mutations that alter sperm function and development in C. elegans.
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Sloan, Nadia S., Maxine Lovegrove, and Leigh W. Simmons. "Social manipulation of sperm competition intensity reduces seminal fluid gene expression." Biology Letters 14, no. 1 (January 2018): 20170659. http://dx.doi.org/10.1098/rsbl.2017.0659.
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A considerable body of evidence supports the prediction that males should increase their expenditure on the ejaculate in response to sperm competition risk. The prediction that they should reduce their expenditure with increasing sperm competition intensity is less well supported. Moreover, most studies have documented plasticity in sperm numbers. Here we show that male crickets Teleogryllus oceanicus exhibit reduced seminal fluid gene expression and accessory gland mass in response to elevated sperm competition intensity. Together with previous research, our findings suggest that strategic adjustments in seminal fluid composition contribute to competitive fertilization success in this species.
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Firman, Renée C., and Leigh W. Simmons. "Sperm midpiece length predicts sperm swimming velocity in house mice." Biology Letters 6, no. 4 (February 10, 2010): 513–16. http://dx.doi.org/10.1098/rsbl.2009.1027.
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Evolutionary biologists have argued that there should be a positive relationship between sperm size and sperm velocity, and that these traits influence a male's sperm competitiveness. However, comparative analyses investigating the evolutionary associations between sperm competition risk and sperm morphology have reported inconsistent patterns of association, and in vitro sperm competition experiments have further confused the issue; in some species, males with longer sperm achieve more competitive fertilization, while in other species males with shorter sperm have greater sperm competitiveness. Few investigations have attempted to address this problem. Here, we investigated the relationship between sperm morphology and sperm velocity in house mice ( Mus domesticus ). We conducted in vitro sperm velocity assays on males from established selection lines, and found that sperm midpiece size was the only phenotypic predictor of sperm swimming velocity.
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Parker, Geoff A., and Jussi Lehtonen. "Gamete evolution and sperm numbers: sperm competition versus sperm limitation." Proceedings of the Royal Society B: Biological Sciences 281, no. 1791 (September 22, 2014): 20140836. http://dx.doi.org/10.1098/rspb.2014.0836.
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Both gamete competition and gamete limitation can generate anisogamy from ancestral isogamy, and both sperm competition (SC) and sperm limitation (SL) can increase sperm numbers. Here, we compare the marginal benefits due to these two components at any given population level of sperm production using the risk and intensity models in sperm economics. We show quite generally for the intensity model (where N males compete for each set of eggs) that however severe the degree of SL, if there is at least one competitor for fertilization ( N − 1 ≥ 1), the marginal gains through SC exceed those for SL, provided that the relationship between the probability of fertilization ( F ) and increasing sperm numbers ( x ) is a concave function. In the risk model, as fertility F increases from 0 to 1.0, the threshold SC risk (the probability q that two males compete for fertilization) for SC to be the dominant force drops from 1.0 to 0. The gamete competition and gamete limitation theories for the evolution of anisogamy rely on very similar considerations: our results imply that gamete limitation could dominate only if ancestral reproduction took place in highly isolated, small spawning groups.
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Calhim, Sara, Stephen Pruett-Jones, Michael S. Webster, and Melissah Rowe. "Asymmetries in reproductive anatomy: insights from promiscuous songbirds." Biological Journal of the Linnean Society 128, no. 3 (August 9, 2019): 569–82. http://dx.doi.org/10.1093/biolinnean/blz100.
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Abstract Directional asymmetry in gonad size is commonly observed in vertebrates and is particularly pronounced in birds, where the left testis is frequently larger than the right. The adaptive significance of directional asymmetry in testis size is poorly understood, and whether it extends beyond the testes (i.e. side-correspondent asymmetry along the reproductive tract) has rarely been considered. Using the Maluridae, a songbird family exhibiting variation in levels of sperm competition and directional testis asymmetry, yet similar in ecology and life history, we investigated the relative roles of side-correspondence and sperm competition on male reproductive tract asymmetry at both inter- and intraspecific levels. We found some evidence for side-correspondent asymmetry. Additionally, sperm competition influenced directional asymmetry at each end of the reproductive tract: species experiencing higher levels of sperm competition had a relatively larger right testis and relatively more sperm in the right seminal glomerus. Within red-backed fairy-wrens (Malurus melanocephalus), auxiliary males had relatively more sperm in the left seminal glomerus, in contrast to a right-bias asymmetry throughout the reproductive tract in breeding males. Given that the number of sperm is important for competitive fertilization success, our results suggest that sperm competition shapes reproductive asymmetries beyond testis size, with likely functional consequences for male reproductive success.
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Firman, Renée C. "Of mice and women: advances in mammalian sperm competition with a focus on the female perspective." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200082. http://dx.doi.org/10.1098/rstb.2020.0082.
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Although initially lagging behind discoveries being made in other taxa, mammalian sperm competition is now a productive and advancing field of research. Sperm competition in mammals is not merely a ‘sprint-race’ between the gametes of rival males, but rather a race over hurdles; those hurdles being the anatomical and physiological barriers provided by the female reproductive tract, as well as the egg and its vestments. With this in mind, in this review, I discuss progress in the field while focusing on the female perspective. I highlight ways by which sperm competition can have positive effects on female reproductive success and discuss how competitive outcomes are not only owing to dynamics between the ejaculates of rival males, but also attributable to mechanisms by which female mammals bias paternity toward favourable sires. Drawing on examples across different species—from mice to humans—I provide an overview of the accumulated evidence which firmly establishes that sperm competition is a key selective force in the evolution of male traits and detail how females can respond to increased sperm competitiveness with increased egg resistance to fertilization. I also discuss evidence for facultative responses to the sperm competition environment observed within mammal species. Overall, this review identifies shortcomings in our understanding of the specific mechanisms by which female mammals ‘select’ sperm. More generally, this review demonstrates how, moving forward, mammals will continue to be effective animal models for studying both evolutionary and facultative responses to sperm competition. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Castillo, Dean M., and Leonie C. Moyle. "Intraspecific sperm competition genes enforce post-mating species barriers in Drosophila." Proceedings of the Royal Society B: Biological Sciences 281, no. 1797 (December 22, 2014): 20142050. http://dx.doi.org/10.1098/rspb.2014.2050.
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Sexual selection and sexual conflict are considered important drivers of speciation, based on both theoretical models and empirical correlations between sexually selected traits and diversification. However, whether reproductive isolation between species evolves directly as a consequence of intrapopulation sexual dynamics remains empirically unresolved, in part because knowledge of the genetic mechanisms (if any) connecting these processes is limited. Here, we provide evidence of a direct mechanistic link between intraspecies sexual selection and reproductive isolation. We examined genes with known roles in intraspecific sperm competition (ISC) in D. melanogaster and assayed their impact on conspecific sperm precedence (CSP). We found that two such genes ( Acp36DE and CG9997 ) contribute to both offensive sperm competition and CSP; null/knockdown lines both had lower competitive ability against D. melanogaster conspecifics and were no longer able to displace heterospecific D. simulans sperm in competitive matings. In comparison, Sex Peptide ( Acp70A )—another locus essential for ISC—does not contribute to CSP. These data indicate that two loci important for sperm competitive interactions have an additional role in similar interactions that enforce post-mating reproductive isolation between species, and show that sexual selection and sexual isolation can act on the same molecular targets in a gene-specific manner.
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Carleial, Rômulo, Grant C. McDonald, Lewis G. Spurgin, Eleanor A. Fairfield, Yunke Wang, David S. Richardson, and Tommaso Pizzari. "Temporal dynamics of competitive fertilization in social groups of red junglefowl ( Gallus gallus ) shed new light on avian sperm competition." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200081. http://dx.doi.org/10.1098/rstb.2020.0081.
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Studies of birds have made a fundamental contribution to elucidating sperm competition processes, experimentally demonstrating the role of individual mechanisms in competitive fertilization. However, the relative importance of these mechanisms and the way in which they interact under natural conditions remain largely unexplored. Here, we conduct a detailed behavioural study of freely mating replicate groups of red junglefowl, Gallus gallus , to predict the probability that competing males fertilize individual eggs over the course of 10-day trials. Remating frequently with a female and mating last increased a male's probability of fertilization, but only for eggs ovulated in the last days of a trial. Conversely, older males, and those mating with more polyandrous females, had consistently lower fertilization success. Similarly, resistance to a male's mating attempts, particularly by younger females, reduced fertilization probability. After considering these factors, male social status, partner relatedness and the estimated state of male extragonadal sperm reserves did not predict sperm competition outcomes. These results shed new light on sperm competition dynamics in taxa such as birds, with prolonged female sperm storage and staggered fertilizations. This article is part of the theme issue ‘Fifty years of sperm competition’.
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LAWNICZAK, MARA K. N., and DAVID J. BEGUN. "A QTL analysis of female variation contributing to refractoriness and sperm competition in Drosophila melanogaster." Genetical Research 86, no. 2 (October 2005): 107–14. http://dx.doi.org/10.1017/s0016672305007755.
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Sperm competition is an important fitness component in many animal groups. Drosophila melanogaster males exhibit substantial genetic variation for sperm competitive ability and females show considerable genetic variation for first versus second male sperm use. Currently, the forces responsible for maintaining genetic variation in sperm competition related phenotypes are receiving much attention. While several candidate genes contributing to the variation seen in male competitive ability are known, genes involved in female sperm use remain largely undiscovered. Without knowledge of the underlying genes, it will be difficult to distinguish between different models of sexual selection such as cryptic female choice and sexual conflict. We used quantitative trait locus (QTL) mapping to identify regions of the genome contributing to female propensity to use first or second male sperm, female refractoriness to re-mating, and early-life fertility. The most well supported markers influencing the phenotypes include 33F/34A (P2), 57B (refractoriness) and 23F/24A (fertility). Between 10% and 15% of the phenotypic variance observed in these recombinant inbred lines was explained by these individual QTLs. More detailed investigation of the regions detected in this experiment may lead to the identification of genes responsible for the QTLs identified here.
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RADWAN, JACEK, and WOJCIECH WITALIŃSKI. "Sperm competition." Nature 352, no. 6337 (August 1991): 671–72. http://dx.doi.org/10.1038/352671b0.
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Wigby, Stuart, and Tracey Chapman. "Sperm competition." Current Biology 14, no. 3 (February 2004): R100—R103. http://dx.doi.org/10.1016/j.cub.2004.01.013.
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Hughes, A. L. "Sperm Competition." Bulletin of the Entomological Society of America 33, no. 3 (September 1, 1987): 202–3. http://dx.doi.org/10.1093/besa/33.3.202a.
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Fisher, Heidi S., Luca Giomi, Hopi E. Hoekstra, and L. Mahadevan. "The dynamics of sperm cooperation in a competitive environment." Proceedings of the Royal Society B: Biological Sciences 281, no. 1790 (September 7, 2014): 20140296. http://dx.doi.org/10.1098/rspb.2014.0296.
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Sperm cooperation has evolved in a variety of taxa and is often considered a response to sperm competition, yet the benefit of this form of collective movement remains unclear. Here, we use fine-scale imaging and a minimal mathematical model to study sperm aggregation in the rodent genus Peromyscus . We demonstrate that as the number of sperm cells in an aggregate increase, the group moves with more persistent linearity but without increasing speed. This benefit, however, is offset in larger aggregates as the geometry of the group forces sperm to swim against one another. The result is a non-monotonic relationship between aggregate size and average velocity with both a theoretically predicted and empirically observed optimum of six to seven sperm per aggregate. To understand the role of sexual selection in driving these sperm group dynamics, we compared two sister-species with divergent mating systems. We find that sperm of Peromyscus maniculatus (highly promiscuous), which have evolved under intense competition, form optimal-sized aggregates more often than sperm of Peromyscus polionotus (strictly monogamous), which lack competition. Our combined mathematical and experimental study of coordinated sperm movement reveals the importance of geometry, motion and group size on sperm velocity and suggests how these physical variables interact with evolutionary selective pressures to regulate cooperation in competitive environments.
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Smith, Chad C., and Michael J. Ryan. "Tactic-dependent plasticity in ejaculate traits in the swordtail Xiphophorus nigrensis." Biology Letters 7, no. 5 (April 20, 2011): 733–35. http://dx.doi.org/10.1098/rsbl.2011.0286.
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In species with alternative reproductive tactics, males that sneak copulations often have larger, higher quality ejaculates relative to males that defend females or nest sites. Ejaculate traits can, however, exhibit substantial phenotypic plasticity depending on a male's mating role in sperm competition, which may depend on the tactic of his competitor. We tested whether exposure to males of different tactics affected sperm number and quality in the swordtail Xipophorus nigrensis , a species with small males that sneak copulations and large males that court females. Sperm swimming speed was higher when the perceived competitor was small than when the competitor was large. Plasticity, however, was only exhibited by small males. Sperm number and viability were invariant between social environments. Our results suggest sperm quality is role-dependent and that plastic responses to the social environment can differ between male reproductive tactics.
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Alonzo, Suzanne H., and Tommaso Pizzari. "Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics." Philosophical Transactions of the Royal Society B: Biological Sciences 368, no. 1613 (March 5, 2013): 20120044. http://dx.doi.org/10.1098/rstb.2012.0044.
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Female remating rate dictates the level of sperm competition in a population, and extensive research has focused on how sperm competition generates selection on male ejaculate allocation. Yet the way ejaculate allocation strategies in turn generate selection on female remating rates, which ultimately influence levels of sperm competition, has received much less consideration despite increasing evidence that both mating itself and ejaculate traits affect multiple components of female fitness. Here, we develop theory to examine how the effects of mating on female fertility, fecundity and mortality interact to generate selection on female remating rate. When males produce more fertile ejaculates, females are selected to mate less frequently, thus decreasing levels of sperm competition. This could in turn favour decreased male ejaculate allocation, which could subsequently lead to higher female remating. When remating simultaneously increases female fecundity and mortality, females are selected to mate more frequently, thus exacerbating sperm competition and favouring male traits that convey a competitive advantage even when harmful to female survival. While intuitive when considered separately, these predictions demonstrate the potential for complex coevolutionary dynamics between male ejaculate expenditure and female remating rate, and the correlated evolution of multiple male and female reproductive traits affecting mating, fertility and fecundity.
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Firman, Renée C., Jamie N. Tedeschi, and Francisco Garcia-Gonzalez. "Sperm sex ratio adjustment in a mammal: perceived male competition leads to elevated proportions of female-producing sperm." Biology Letters 16, no. 6 (June 2020): 20190929. http://dx.doi.org/10.1098/rsbl.2019.0929.
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Mammal sex allocation research has focused almost exclusively on maternal traits, but it is now apparent that fathers can also influence offspring sex ratios. Parents that produce female offspring under conditions of intense male–male competition can benefit with greater assurance of maximized grand-parentage. Adaptive adjustment in the sperm sex ratio, for example with an increase in the production of X-chromosome bearing sperm (CBS), is one potential paternal mechanism for achieving female-biased sex ratios. Here, we tested this mechanistic hypothesis by varying the risk of male–male competition that male house mice perceived during development, and quantifying sperm sex ratios at sexual maturity. Our analyses revealed that males exposed to a competitive ‘risk’ produced lower proportions of Y-CBS compared to males that matured under ‘no risk’ of competition. We also explored whether testosterone production was linked to sperm sex ratio variation, but found no evidence to support this. We discuss our findings in relation to the adaptive value of sperm sex ratio adjustments and the role of steroid hormones in socially induced sex allocation.
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Rowe, Melissah, Annabel van Oort, Lyanne Brouwer, Jan T. Lifjeld, Michael S. Webster, Joseph F. Welklin, and Daniel T. Baldassarre. "Sperm Numbers as a Paternity Guard in a Wild Bird." Cells 11, no. 2 (January 11, 2022): 231. http://dx.doi.org/10.3390/cells11020231.
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Sperm competition is thought to impose strong selection on males to produce competitive ejaculates to outcompete rival males under competitive mating conditions. Our understanding of how different sperm traits influence fertilization success, however, remains limited, especially in wild populations. Recent literature highlights the importance of incorporating multiple ejaculate traits and pre-copulatory sexually selected traits in analyses aimed at understanding how selection acts on sperm traits. However, variation in a male’s ability to gain fertilization success may also depend upon a range of social and ecological factors that determine the opportunity for mating events both within and outside of the social pair-bond. Here, we test for an effect of sperm quantity and sperm size on male reproductive success in the red-back fairy-wren (Malurus melanocephalus) while simultaneously accounting for pre-copulatory sexual selection and potential socio-ecological correlates of male mating success. We found that sperm number (i.e., cloacal protuberance volume), but not sperm morphology, was associated with reproductive success in male red-backed fairy-wrens. Most notably, males with large numbers of sperm available for copulation achieved greater within-pair paternity success. Our results suggest that males use large sperm numbers as a defensive strategy to guard within-pair paternity success in a system where there is a high risk of sperm competition and female control of copulation. Finally, our work highlights the importance of accounting for socio-ecological factors that may influence male mating opportunities when examining the role of sperm traits in determining male reproductive success.
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Yeates, Sarah E., Sigurd Einum, Ian A. Fleming, Hendrik-Jan Megens, René J. M. Stet, Kjetil Hindar, William V. Holt, Katrien J. W. Van Look, and Matthew J. G. Gage. "Atlantic salmon eggs favour sperm in competition that have similar major histocompatibility alleles." Proceedings of the Royal Society B: Biological Sciences 276, no. 1656 (October 14, 2008): 559–66. http://dx.doi.org/10.1098/rspb.2008.1257.
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Polyandry and post-copulatory sexual selection provide opportunities for the evolution of female differential sperm selection. Here, we examined the influence of variation in major histocompatibility (MH) class I allelic composition upon sperm competition dynamics in Atlantic salmon. We ran in vitro fertilization competitions that mimicked the gametic microenvironment, and replicated a paired-male experimental design that allowed us to compare differences in sperm competition success among males when their sperm compete for eggs from females that were genetically either similar or dissimilar at the MH class I locus. Concurrently, we measured variation in spermatozoal traits that are known to influence relative fertilization success under these conditions. Contrary to the findings demonstrating mechanisms that promote MH complex heterozygosity, our results showed that males won significantly greater relative fertilization success when competing for eggs from genetically similar females at the MH class I. This result also showed covariation with the known influences of sperm velocity on relative fertilization success. We discuss these unexpected findings in relation to sperm–egg recognition and hybridization avoidance mechanisms based upon immunogenetic variation.
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Moschilla, Joe A., Joseph L. Tomkins, and Leigh W. Simmons. "Males adjust their manipulation of female remating in response to sperm competition risk." Proceedings of the Royal Society B: Biological Sciences 287, no. 1934 (September 2, 2020): 20201238. http://dx.doi.org/10.1098/rspb.2020.1238.
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To reduce the potential for sperm competition, male insects are thought to inhibit the post-mating reproductive behaviour of females through receptivity-inhibiting compounds transferred in the ejaculate. Selection is expected to favour phenotypic plasticity in male post-copulatory expenditure, with males investing strategically in response to their perceived risk of sperm competition. However, the impact that socially cued strategic allocation might have on female post-mating behaviour has rarely been assessed. Here, we varied male perception of sperm competition risk, both prior to and during mating, to determine if a male's competitive environment impacts the extent to which he manipulates female remating behaviour. We found that female Australian field crickets ( Teleogryllus oceanicus ) mated to males that were reared under sperm competition risk emerged from a shelter in search of male song sooner than did females mated to males reared without risk, but only when mating occurred in a risk-free environment. We also found that females reared in a silent environment where potential mates were scarce emerged from the shelter sooner than females exposed to male calls during development. Collectively, our findings suggest complex interacting effects of male and female sociosexual environments on female post-mating sexual receptivity.
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Gasparini, Clelia, Elizabeth M. Speechley, and Giovanni Polverino. "The bold and the sperm: positive association between boldness and sperm number in the guppy." Royal Society Open Science 6, no. 7 (July 2019): 190474. http://dx.doi.org/10.1098/rsos.190474.
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Assessing the consequences of personality traits on reproductive success is one of the most important challenges in personality studies and critical to understand the evolutionary implications of behavioural variability among animals. Personality traits are typically associated with mating acquisition in males, and, hence, linked to variation in their reproductive success. However, in most species, sexual selection continues after mating, and sperm traits (such as sperm number and quality) become very important in determining post-mating competitive success. Here, we investigate whether variation in personality traits is associated with variation in sperm traits using the guppy ( Poecilia reticulata ), a species with high levels of sperm competition. We found a positive association between boldness and sperm number but not sperm velocity, suggesting that bolder males have increased post-copulatory success than shyer individuals. No association was found between exploration and sperm traits. Our work highlights the importance of considering post-copulatory traits when investigating fitness consequences of personality traits, especially in species with high levels of female multiple matings and hence sperm competition.
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Evans, Jonathan P., Patrice Rosengrave, Clelia Gasparini, and Neil J. Gemmell. "Delineating the roles of males and females in sperm competition." Proceedings of the Royal Society B: Biological Sciences 280, no. 1772 (December 7, 2013): 20132047. http://dx.doi.org/10.1098/rspb.2013.2047.
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Disentangling the relative roles of males, females and their interactive effects on competitive fertilization success remains a challenge in sperm competition. In this study, we apply a novel experimental framework to an ideally suited externally fertilizing model system in order to delineate these roles. We focus on the chinook salmon, Oncorhynchus tshawytscha , a species in which ovarian fluid (OF) has been implicated as a potential arbiter of cryptic female choice for genetically compatible mates. We evaluated this predicted sexually selected function of OF using a series of factorial competitive fertilization trials. Our design involved a series of 10 factorial crosses, each involving two ‘focal’ rival males whose sperm competed against those from a single ‘standardized’ (non-focal) rival for a genetically uniform set of eggs in the presence of OF from two focal females. This design enabled us to attribute variation in competitive fertilization success among focal males, females (OF) and their interacting effects, while controlling for variation attributable to differences in the sperm competitive ability of rival males, and male-by-female genotypic interactions. Using this experimental framework, we found that variation in sperm competitiveness could be attributed exclusively to differences in the sperm competitive ability of focal males, a conclusion supported by subsequent analyses revealing that variation in sperm swimming velocity predicts paternity success. Together, these findings provide evidence that variation in paternity success can be attributed to intrinsic differences in the sperm competitive ability of rival males, and reveal that sperm swimming velocity is a key target of sexual selection.
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Lizé, Anne, Rowan J. Doff, Eve A. Smaller, Zenobia Lewis, and Gregory D. D. Hurst. "Perception of male–male competition influences Drosophila copulation behaviour even in species where females rarely remate." Biology Letters 8, no. 1 (July 13, 2011): 35–38. http://dx.doi.org/10.1098/rsbl.2011.0544.
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Males in many taxa are known to exhibit behavioural plasticity in response to the perceived intensity of sperm competition, reflected in Drosophila melanogaster by increased copulation duration following prior exposure to a rival. We tested the prediction that males do not adjust their copulation effort in response to the presence of a competitor in Drosophila species where there is little or no sperm competition. Contrary to expectations, male plasticity in copulation duration was found in both Drosophila subobscura and Drosophila acanthoptera , species in which females rarely remate. These results are discussed in relation to the adaptive basis of plasticity in these species.
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Zheng, W., C. Strobeck, and N. Stacey. "The steroid pheromone 4-pregnen-17,20ss-diol-3-one increases fertility and paternity in goldfish." Journal of Experimental Biology 200, no. 22 (November 1, 1997): 2833–40. http://dx.doi.org/10.1242/jeb.200.22.2833.
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Previous studies in goldfish (Carassius auratus) showed that the oocyte maturation-inducing steroid 4-pregnen-17,20ss-diol-3-one (17,20ssP) functions after release as a pheromone that increases male serum gonadotropin II (GtH II) concentration, milt (sperm and seminal fluid) volume and sexual activity, effects hypothesized to increase male reproductive success in the sperm competition of multi-male spawnings. The present study tested this hypothesis by determining whether overnight exposure to 17,20ssP increases fertility. In pair spawnings, 17,20ssP-exposed males fertilized a greater percentage of eggs than did control males, apparently because 17,20ssP-exposed males had more releasable sperm at the onset of spawning. Microsatellite DNA paternity analysis showed that 17,20ssP-exposed males also fertilized more eggs in competitive spawnings involving one control male and one 17,20ssP-exposed male. This effect of 17,20ssP on competitive fertility could be due to demonstrated increases in spawning activity, milt volume, duration of sperm motility and proportion of motile sperm. However, it appears that a change in sperm quality is a major component of the pheromonal effect because, in competitive in vitro fertilizations, sperm from 17,20ssP-exposed males fertilized more eggs than did sperm from control males. The results indicate that the response to pheromonal 17,20ssP is a major determinant of reproductive success in male goldfish.
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Birkhead, T. R. "Enduring Sperm Competition." Journal of Avian Biology 25, no. 3 (August 1994): 167. http://dx.doi.org/10.2307/3677071.
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Sutter, Andreas, and Simone Immler. "Within-ejaculate sperm competition." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200066. http://dx.doi.org/10.1098/rstb.2020.0066.
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Sperm competition was defined by Geoff Parker 50 years ago as the competition between sperm from two or more males over the fertilization of a set of eggs. Since the publication of his seminal paper, sperm competition has developed into a large field of research, and many aspects are still being discovered. One of the relatively poorly understood aspects is the importance of selection and competition among sperm within the ejaculate of a male. The sheer number of sperm present in a male's ejaculate suggests that the competition among sibling sperm produced by the same male may be intense. In this review, we summarize Parker's theoretical models generating predictions about the evolution of sperm traits under the control of the haploid gamete as opposed to the diploid male. We review the existing evidence of within-ejaculate competition from a wide range of fields and taxa. We also discuss the conceptual and practical hurdles we have been facing to study within-ejaculate sperm competition, and how novel technologies may help in addressing some of the currently open questions. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Linhart, O., M. Rodina, D. Gela, M. Kocour, and M. Vandeputte. "Spermatozoal competition in common carp (Cyprinus carpio): what is the primary determinant of competition success?" Reproduction 130, no. 5 (November 2005): 705–11. http://dx.doi.org/10.1530/rep.1.00541.
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The percentage of sperm motility (92–100%), spermatozoan velocity (112–163 μm·s−1) and control hatching rates (83–96%) were evaluated for each of six gold and five green male common carp (Cyprinus carpio). In all 30 possible paired combinations of sperm-competition tests, hatching rates of 90–97% were achieved. The mean percentage of offspring sired was strongly influenced by the male used (P < 0.001, R 2 = 0.91). The best male sired an average of 88% of the offspring in its competition tests, and the worst male sired only 5%. Spermatozoan-quality parameters could explain only part of the variation in male competitive ability. The male effects alone explained 91.4% of the observed variance, consisting of 17.1% explained by spermatozoan motility and 32.5% by control hatching rates in single fertilizations. Undetermined male effects explained 41.8%. The velocity of spermatozoa had no effect on the outcome of sperm competition. Neither was there any link between spermatozoan velocity and hatching rate in a control hatching test, whereas there was an effect of motility on hatching rate in this same test.
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Kustra, Matthew C., and Suzanne H. Alonzo. "Sperm and alternative reproductive tactics: a review of existing theory and empirical data." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200075. http://dx.doi.org/10.1098/rstb.2020.0075.
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Males that exhibit alternative reproductive tactics (ARTs) often differ in the risk of sperm competition and the energetic trade-offs they experience. The resulting patterns of selection could lead to between-tactic differences in ejaculate traits. Despite extensive research on male ARTs, there is no comprehensive review of whether and what differences in sperm traits exist between male ARTs. We review existing theory on ejaculate evolution relevant to ARTs and then conduct a comprehensive vote-counting review of the empirical data comparing sperm traits between males adopting ARTs. Despite the general expectation that sneaker males should produce sperm that are more competitive (e.g. higher quality or performance), we find that existing theory does not predict explicitly how males adopting ARTs should differ in sperm traits. The majority of studies find no significant difference in sperm performance traits between dominant and sneaker males. However, when there is a difference, sneaker males tend to have higher sperm performance trait values than dominant males. We propose ways that future theoretical and empirical research can improve our understanding of the evolution of ejaculate traits in ARTs. We then highlight how studying ejaculate traits in species with ARTs will improve our broader knowledge of ejaculate evolution. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Hirohashi, Noritaka, Noriyosi Sato, Yoko Iwata, Satoshi Tomano, Md Nur E. Alam, Lígia Haselmann Apostólico, and José Eduardo Amoroso Rodriguez Marian. "Context-dependent behavioural plasticity compromises disruptive selection of sperm traits in squid." PLOS ONE 16, no. 8 (August 30, 2021): e0256745. http://dx.doi.org/10.1371/journal.pone.0256745.
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Sperm morphology is generally uniform within a species due to selective pressures that act to achieve better fertilization outcomes under postcopulatory competitive circumstances. Therefore, polyandry that intensifies post-mating sperm competition should constrain intraspecific sperm polymorphism. Contrary to this paradigm, we previously found that a polyandrous squid, Heterololigo bleekeri, produces dimorphic eusperm (flagellum length dimorphism; FLD), which is closely associated with alternative reproductive tactics (ARTs); large males (consorts) transfer their spermatophores inside the female’s mantle cavity, while small males (sneakers) do so outside the mantle. Thus, FLD was considered as the consequence of different insemination strategies that arise from different modes of sperm competition, sperm storage and the fertilization environment. However, in other squid species showing ARTs, the choice of mating behaviour is rather conditional (i.e., switching mating tactic between consorts and sneakers), which poses the question of whether sperm FLD could have evolved. Here, we investigated five species in the family Loliginidae that exhibit ARTs and found that all species showed sneaker-biased FLD. However, in a species with conditional ARTs, we found FLD rather ambiguous and the testicular somatic index to be nearly continuous among individuals at transitional state, suggesting that plasticity in mating behaviour compromises the disruptive selection on a sperm morphological trait.
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Civetta, Alberto, Kim R. Rosing, and Jolene H. Fisher. "Differences in sperm competition and sperm competition avoidance in Drosophila melanogaster." Animal Behaviour 75, no. 5 (May 2008): 1739–46. http://dx.doi.org/10.1016/j.anbehav.2007.10.031.
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Verspoor, Rudi L., Tom A. R. Price, and Nina Wedell. "Selfish genetic elements and male fertility." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200067. http://dx.doi.org/10.1098/rstb.2020.0067.
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Selfish genetic elements (SGEs) are diverse and near ubiquitous in Eukaryotes and can be potent drivers of evolution. Here, we discuss SGEs that specifically act on sperm to gain a transmission advantage to the next generation. The diverse SGEs that affect sperm often impose costs on carrier males, including damaging ejaculates, skewing offspring sex ratios and in particular reducing sperm-competitive success of SGE-carrying males. How males and females tolerate and mitigate against these costs is a dynamic and expanding area of research. The intense intra-genomic conflict that these selfish elements generate could also have implications for male fertility and spermatogenesis more widely. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Friesen, Christopher R., Ariel F. Kahrl, and Mats Olsson. "Sperm competition in squamate reptiles." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200079. http://dx.doi.org/10.1098/rstb.2020.0079.
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Multiple paternity is ubiquitous within the polyphyletic group called ‘reptiles', especially within the lizards and snakes. Therefore, the probability of sperm competition occurring, and being intense, is high. Squamates exhibit a diversity of tactics to ensure fertilization success in the face of sperm competition. The duration of female sperm storage, which can be many months and even years in some species, remains an enigma. Here, we emphasize some mechanisms that might affect patterns of paternity, the source and function of ejaculates and features of the female reproductive tract that may aid in long-term sperm storage. In doing so, we present a new analysis of the relationship between sperm size, the strength of sperm competition and the duration of female sperm storage. Lizards and snakes are a diverse group that has provided many excellent models for the study of an array of life-history strategies. However, when it comes to postcopulatory sexual selection, there is much left to discover. This article is part of the theme issue ‘Fifty years of sperm competition'.
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Demont, Marco, Paul I. Ward, Wolf U. Blanckenhorn, Stefan Lüpold, Oliver Y. Martin, and Luc F. Bussière. "How biases in sperm storage relate to sperm use during oviposition in female yellow dung flies." Behavioral Ecology 32, no. 4 (April 23, 2021): 756–68. http://dx.doi.org/10.1093/beheco/arab026.
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Abstract Precise mechanisms underlying sperm storage and utilization are largely unknown, and data directly linking stored sperm to paternity remain scarce. We used competitive microsatellite PCR to study the effects of female morphology, copula duration and oviposition on the proportion of stored sperm provided by the second of two copulating males (S2) in Scathophaga stercoraria (Diptera: Scathophagidae), the classic model for sperm competition studies. We genotyped all offspring from potentially mixed-paternity clutches to establish the relationship between a second male’s stored sperm (S2) and paternity success (P2). We found consistent skew in sperm storage across the three female spermathecae, with relatively more second-male sperm stored in the singlet spermatheca than in the doublet spermathecae. S2 generally decreased with increasing spermathecal size, consistent with either heightened first-male storage in larger spermathecae, or less efficient sperm displacement in them. Additionally, copula duration and several two-way interactions influenced S2, highlighting the complexity of postcopulatory processes and sperm storage. Importantly, S2 and P2 were strongly correlated. Manipulation of the timing of oviposition strongly influenced observed sperm-storage patterns, with higher S2 when females laid no eggs before being sacrificed than when they oviposited between copulations, an observation consistent with adaptive plasticity in insemination. Our results identified multiple factors influencing sperm storage, nevertheless suggesting that the proportion of stored sperm is strongly linked to paternity (i.e., a fair raffle). Even more detailed data in this vein are needed to evaluate the general importance of sperm competition relative to cryptic female choice in postcopulatory sexual selection.
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Lüpold, Stefan, Raïssa A. de Boer, Jonathan P. Evans, Joseph L. Tomkins, and John L. Fitzpatrick. "How sperm competition shapes the evolution of testes and sperm: a meta-analysis." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1813 (October 19, 2020): 20200064. http://dx.doi.org/10.1098/rstb.2020.0064.
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Females of many species mate with multiple males, thereby inciting competition among ejaculates from rival males for fertilization. In response to increasing sperm competition, males are predicted to enhance their investment in sperm production. This prediction is so widespread that testes size (correcting for body size) is commonly used as a proxy of sperm competition, even in the absence of any other information about a species' reproductive behaviour. By contrast, a debate about whether sperm competition selects for smaller or larger sperm has persisted for nearly three decades, with empirical studies demonstrating every possible response. Here, we synthesize nearly 40 years of sperm competition research in a meta-analytical framework to determine how the evolution of sperm number (i.e. testes size) and sperm size (i.e. sperm head, midpiece, flagellum and total length) is influenced by varying levels of sperm competition across species. Our findings support the long-held assumption that higher levels of sperm competition are associated with relatively larger testes. We also find clear evidence that sperm competition is associated with increases in all components of sperm length. We discuss these results in the context of different theoretical predictions and general patterns in the breeding biology and selective environment of sperm. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Birkhead, TR. "Sperm competition: evolutionary causes and consequences." Reproduction, Fertility and Development 7, no. 4 (1995): 755. http://dx.doi.org/10.1071/rd9950755.
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The interaction between functional and mechanistic approaches to sperm competition and between male and female perspectives are described and illustrated by a study of the zebra finch, Taeniopygia guttata. Sperm competition experiments in the laboratory show that last male sperm precedence occurs (as it does in many other taxa) although the mechanism is unknown (as in most other taxa). Empirically-derived values were used to construct a mathematical model of sperm competition in the zebra finch. The model indicates that precedence occurs as a consequence of: (i) the temporal pattern of pair copulations; (ii) the rate at which sperm are lost from the female tract; and (iii) more sperm being transferred during extra-pair copulations than during pair copulations. The latter effect is a consequence of males seeking extra-pair copulations after their own pair copulation period has ended. The effect of sperm numbers on the pattern of sperm precedence may be further increased by: (i) extra-pair males increasing ejaculate size (sperm numbers) (for which there is no evidence); (ii) extra-pair males being of a better quality and transferring more sperm or better quality sperm (for which there is some evidence); and (iii) cryptic female choice. Females eject over 99% of sperm following insemination; if they eject fewer sperm from males chosen as extra-pair copulation partners, the potential for cryptic female choice is considerable. However, this is still being investigated. The model also predicts the optimal time for an extra-pair copulation to occur (from either a male or female perspective). A comparison between the predicted and observed pattern suggests that the optimal timing of extra-pair copulations is constrained in both sexes.
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Magallón-Gayón, Erika, Patricia Briones-Fourzán, and Enrique Lozano-Álvarez. "Does size always matter? Mate choice and sperm allocation in Panulirus guttatus, a highly sedentary, habitat-specialist spiny lobster." Behaviour 148, no. 11-13 (2011): 1329–54. http://dx.doi.org/10.1163/000579511x605740.
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Abstract Spotted spiny lobsters, Panulirus guttatus, are small, obligate reef-dwellers that exhibit a highly sedentary lifestyle and a low tendency to aggregate with conspecifics, and that reproduce asynchronously year-round. Individual females can produce multiple clutches per year but have a short receptivity per clutch. As in most spiny lobsters, females of P. guttatus mate only once per clutch and resist further mating attempts, features that may favour development of female mate choice but limit the potential for sperm competition. We separately examined mate choice by large and small mature females through laboratory experiments that controlled for effects of male–male competition, quality of shelter, and mere social attraction. Only large females expressed preference for larger males relative to their own size, suggesting that only large females that mate with small males risk sperm limitation on fecundity success. In couples that mated, males deposited rather small, thinly spread spermatophores on the sterna of females. Spermatophore area (considered as a proxy measure of sperm content) increased with male size and showed no relationship with female size, suggesting that males of P. guttatus have a short sperm-recovery period or do not exhibit strategic sperm allocation in a non-competitive context. A comparison of average sperm allocation between P. guttatus and its sympatric species, P. argus (a much larger, highly mobile, and highly social species with more seasonal reproductive periods and a longer receptivity of females per clutch), suggests that males of P. guttatus allocate proportionally less sperm to females, on average, than males of P. argus do. According to predictions of across-species risk models, this result suggests that males of P. guttatus perceive lower average levels of sperm competition risk than males of P. argus do, implying that different Panulirus species may exhibit different mating strategies in accordance with their particular life-history and sociobiological traits.
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Devigili, Alessandro, Jonathan P. Evans, and John L. Fitzpatrick. "Predation shapes sperm performance surfaces in guppies." Proceedings of the Royal Society B: Biological Sciences 286, no. 1905 (June 26, 2019): 20190869. http://dx.doi.org/10.1098/rspb.2019.0869.
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Sperm velocity is a key determinant of competitive fertilization success in many species. Selection is therefore expected to favour the evolution of faster sperm when the level of sperm competition is high. However, several aspects can determine the direction and strength of selection acting on this key performance trait, including ecological factors that influence both sperm competition and the strength of selection acting on correlated traits that may constrain evolutionary responses in sperm velocity. Here, we determine how a key ecological variable, the level of predation, shapes sperm swimming speed across 18 Trinidadian populations of guppies ( Poecilia reticulata ). We use performance analysis, a statistical tool akin to the familiar methods of multivariate selection analyses, to determine how the level of predation influences sperm velocity (modelled as a performance trait) when accounting for correlated pre- and postcopulatory traits that are also impacted by predation. We show that predation affects the combination of pre- and postcopulatory traits that ultimately predict sperm performance. Overall, we report evidence for disruptive relationships between sperm performance and combinations of ornaments and sperm morphology, but the specific combinations of traits that predict sperm velocity depended on the level of predation. These analyses underscore the complex nonlinear interrelationships among pre- and postcopulatory traits and the importance of considering ecological factors that may ultimately change the way in which multiple traits interact to determine a trait's performance value. As such, our results are likely to be broadly applicable across systems where selection is influenced by ecological conditions.
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Simmons, Leigh W., Amy Denholm, Chantelle Jackson, Esther Levy, and Ewa Madon. "Male crickets adjust ejaculate quality with both risk and intensity of sperm competition." Biology Letters 3, no. 5 (August 7, 2007): 520–22. http://dx.doi.org/10.1098/rsbl.2007.0328.
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Sperm competition theory predicts that males should increase their expenditure on the ejaculate with increasing risk of sperm competition, but decrease their expenditure with increasing intensity. There is accumulating evidence for sperm competition theory, based on examinations of testes size and/or the numbers of sperm ejaculated. However, recent studies suggest that ejaculate quality can also be subject to selection by sperm competition. We used experimental manipulations of the risk and intensity of sperm competition in the cricket, Teleogryllus oceanicus . We found that males produced ejaculates with a greater percentage of live sperm when they had encountered a rival male prior to mating. However, when mating with a female that presented a high intensity of sperm competition, males did not respond to risk, but produced ejaculates with a reduced percentage of live sperm. Our data suggest that males exhibit a fine-tuned hierarchy of responses to these cues of sperm competition.
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Jones, Beatrix, and Andrew G. Clark. "Bayesian Sperm Competition Estimates." Genetics 163, no. 3 (March 1, 2003): 1193–99. http://dx.doi.org/10.1093/genetics/163.3.1193.
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Abstract We introduce a Bayesian method for estimating parameters for a model of multiple mating and sperm displacement from genotype counts of brood-structured data. The model is initially targeted for Drosophila melanogaster, but is easily adapted to other organisms. The method is appropriate for use with field studies where the number of mates and the genotypes of the mates cannot be controlled, but where unlinked markers have been collected for a set of females and a sample of their offspring. Advantages over previous approaches include full use of multilocus information and the ability to cope appropriately with missing data and ambiguities about which alleles are maternally vs. paternally inherited. The advantages of including X-linked markers are also demonstrated.
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Birkhead, T. "Sperm competition in birds." Reviews of Reproduction 3, no. 2 (May 1, 1998): 123–29. http://dx.doi.org/10.1530/revreprod/3.2.123.
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Birkhead, T. "Sperm competition in birds." Reviews of Reproduction 3, no. 2 (May 1, 1998): 123–29. http://dx.doi.org/10.1530/ror.0.0030123.
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Birkhead, Tim. "Distinguished sperm in competition." Nature 400, no. 6743 (July 1999): 406–7. http://dx.doi.org/10.1038/22650.
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Harcourt, A. H. "Sperm Competition in Primates." American Naturalist 149, no. 1 (January 1997): 189–94. http://dx.doi.org/10.1086/285986.
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Hosken, D. J. "Sperm competition in bats." Proceedings of the Royal Society of London. Series B: Biological Sciences 264, no. 1380 (March 22, 1997): 385–92. http://dx.doi.org/10.1098/rspb.1997.0055.
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Stockley, P. "Sperm competition in mammals." Human Fertility 7, no. 2 (June 2004): 91–97. http://dx.doi.org/10.1080/14647270410001699054.
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