Journal articles: 'Sperm competition'

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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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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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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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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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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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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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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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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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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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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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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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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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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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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. "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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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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Briskie, James V. "Sperm Competition and Sperm Length in Shorebirds." Condor 101, no. 4 (November 1999): 848–54. http://dx.doi.org/10.2307/1370074.

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Garcı́a-González, Francisco, and Leigh W. Simmons. "Sperm Viability Matters in Insect Sperm Competition." Current Biology 15, no. 3 (February 2005): 271–75. http://dx.doi.org/10.1016/j.cub.2005.01.032.

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Ball, M. A., and G. A. Parker. "Sperm competition games: sperm selection by females." Journal of Theoretical Biology 224, no. 1 (September 2003): 27–42. http://dx.doi.org/10.1016/s0022-5193(03)00118-8.

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Hunter, F. M., and T. R. Birkhead. "Sperm Viability and Sperm Competition in Insects." Current Biology 12, no. 2 (January 2002): 121–23. http://dx.doi.org/10.1016/s0960-9822(01)00647-9.

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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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Birkhead, Tim. "Sperm competition in birds." Trends in Ecology & Evolution 2, no. 9 (September 1987): 268–72. http://dx.doi.org/10.1016/0169-5347(87)90033-4.

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Ginsberg, J. R., and U. W. Huck. "Sperm competition in mammals." Trends in Ecology & Evolution 4, no. 3 (March 1989): 74–79. http://dx.doi.org/10.1016/0169-5347(89)90152-3.

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Birkhead, T. R., and F. M. Hunter. "Mechanisms of sperm competition." Trends in Ecology & Evolution 5, no. 2 (February 1990): 48–52. http://dx.doi.org/10.1016/0169-5347(90)90047-h.

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Gowaty, Patricia Adair. "Architects of sperm competition." Trends in Ecology & Evolution 9, no. 5 (May 1994): 160–62. http://dx.doi.org/10.1016/0169-5347(94)90076-0.

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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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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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Gómez Montoto, Laura, Concepción Magaña, Maximiliano Tourmente, Juan Martín-Coello, Cristina Crespo, Juan José Luque-Larena, Montserrat Gomendio, and Eduardo R. S. Roldan. "Sperm Competition, Sperm Numbers and Sperm Quality in Muroid Rodents." PLoS ONE 6, no. 3 (March 25, 2011): e18173. http://dx.doi.org/10.1371/journal.pone.0018173.

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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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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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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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Albrecht, Tomáš, Oddmund Kleven, Jakub Kreisinger, Terje Laskemoen, Taiwo C. Omotoriogun, Ulf Ottosson, Jiří Reif, et al. "Sperm competition in tropical versus temperate zone birds." Proceedings of the Royal Society B: Biological Sciences 280, no. 1752 (February 7, 2013): 20122434. http://dx.doi.org/10.1098/rspb.2012.2434.

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Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CV bm ) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.

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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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Wedell, Nina, Matthew J. G. Gage, and Geoffrey A. Parker. "Sperm competition, male prudence and sperm-limited females." Trends in Ecology & Evolution 17, no. 7 (July 2002): 313–20. http://dx.doi.org/10.1016/s0169-5347(02)02533-8.

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McKibbin, W. F., M. N. Pham, and T. K. Shackelford. "Human sperm competition in postindustrial ecologies: sperm competition cues predict adult DVD sales." Behavioral Ecology 24, no. 4 (April 23, 2013): 819–23. http://dx.doi.org/10.1093/beheco/art031.

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Simmons, Leigh W., and John L. Fitzpatrick. "Sperm wars and the evolution of male fertility." REPRODUCTION 144, no. 5 (November 2012): 519–34. http://dx.doi.org/10.1530/rep-12-0285.

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Females frequently mate with several males, whose sperm then compete to fertilize available ova. Sperm competition represents a potent selective force that is expected to shape male expenditure on the ejaculate. Here, we review empirical data that illustrate the evolutionary consequences of sperm competition. Sperm competition favors the evolution of increased testes size and sperm production. In some species, males appear capable of adjusting the number of sperm ejaculated, depending on the perceived levels of sperm competition. Selection is also expected to act on sperm form and function, although the evidence for this remains equivocal. Comparative studies suggest that sperm length and swimming speed may increase in response to selection from sperm competition. However, the mechanisms driving this pattern remain unclear. Evidence that sperm length influences sperm swimming speed is mixed and fertilization trials performed across a broad range of species demonstrate inconsistent relationships between sperm form and function. This ambiguity may in part reflect the important role that seminal fluid proteins (sfps) play in affecting sperm function. There is good evidence that sfps are subject to selection from sperm competition, and recent work is pointing to an ability of males to adjust their seminal fluid chemistry in response to sperm competition from rival males. We argue that future research must consider sperm and seminal fluid components of the ejaculate as a functional unity. Research at the genomic level will identify the genes that ultimately control male fertility.

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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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Fitzpatrick, J. "047. SPERM COMPETITION, INBREEDING AND THE EVOLUTION OF SUPERIOR EJACULATES." Reproduction, Fertility and Development 21, no. 9 (2009): 12. http://dx.doi.org/10.1071/srb09abs047.

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The production of viable sperm is essential for male reproductive success. However, because females in many species mate with several males during a single reproductive episode, leading to sperm competition, a male's reproductive success also depends critically on the ability of his sperm to compete efficiently with those from rival males for fertilizations. Therefore, males who regularly encounter sperm competition are expected to produce high quality ejaculates. Here, I will provide an overview of how sperm morphology and performance are influenced by sperm competition, both within and between species, using recent empirical examples. Having established the importance of producing high quality ejaculates in males experiencing sperm competition, I will then examine the reproductive consequences of producing sub-optimal sperm. Given the well known role that inbreeding plays in reducing genetic quality and reproductive success, I will focus in particular on how inbreeding acts to reduce sperm quality. Finally, I will examine the consequences of inbreeding for male reproductive success in species where sperm competition is rampant. Together, these results highlight the evolutionary importance of sperm competition and inbreeding in shaping ejaculate traits.

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Shackelford, Todd K., Nicholas Pound, and Aaron T. Goetz. "Psychological and Physiological Adaptations to Sperm Competition in Humans." Review of General Psychology 9, no. 3 (September 2005): 228–48. http://dx.doi.org/10.1037/1089-2680.9.3.228.

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Postcopulatory competition between males, in the form of sperm competition, is a widespread phenomenon in many animal species. The extent to which sperm competition has been an important selective pressure during human evolution remains controversial, however. The authors review critically the evidence that human males and females have psychological, behavioral, and physiological adaptations that evolved in response to selection pressures associated with sperm competition. The authors consider, using evidence from contemporary societies, whether sperm competition is likely to have been a significant adaptive problem for ancestral humans and examine the evidence suggesting that human males have physiological and psychological mechanisms that allow for “prudent” sperm allocation in response to variations in the risk of sperm competition.

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Firman, Renée C., and Leigh W. Simmons. "Sperm competition risk generates phenotypic plasticity in ovum fertilizability." Proceedings of the Royal Society B: Biological Sciences 280, no. 1772 (December 7, 2013): 20132097. http://dx.doi.org/10.1098/rspb.2013.2097.

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Theory predicts that sperm competition will generate sexual conflict that favours increased ovum defences against polyspermy. A recent study on house mice has shown that ovum resistance to fertilization coevolves in response to increased sperm fertilizing capacity. However, the capacity for the female gamete to adjust its fertilizability as a strategic response to sperm competition risk has never, to our knowledge, been studied. We sourced house mice ( Mus domesticus ) from natural populations that differ in the level of sperm competition and sperm fertilizing capacity, and manipulated the social experience of females during their sexual development to simulate conditions of either a future ‘risk’ or ‘no risk’ of sperm competition. Consistent with coevolutionary predictions, we found lower fertilization rates in ova produced by females from a high sperm competition population compared with ova from a low sperm competition population, indicating that these populations are divergent in the fertilizability of their ova. More importantly, females exposed to a ‘risk’ of sperm competition produced ova that had greater resistance to fertilization than ova produced by females reared in an environment with ‘no risk’. Consequently, we show that variation in sperm competition risk during development generates phenotypic plasticity in ova fertilizability, which allows females to prepare for prevailing conditions during their reproductive life.

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Hopkins, Ben R., Irem Sepil, Marie-Laëtitia Thézénas, James F. Craig, Thomas Miller, Philip D. Charles, Roman Fischer, et al. "Divergent allocation of sperm and the seminal proteome along a competition gradient in Drosophila melanogaster." Proceedings of the National Academy of Sciences 116, no. 36 (August 20, 2019): 17925–33. http://dx.doi.org/10.1073/pnas.1906149116.

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Sperm competition favors large, costly ejaculates, and theory predicts the evolution of allocation strategies that enable males to plastically tailor ejaculate expenditure to sperm competition threat. While greater sperm transfer in response to a perceived increase in the risk of sperm competition is well-supported, we have a poor understanding of whether males (i) respond to changes in perceived intensity of sperm competition, (ii) use the same allocation rules for sperm and seminal fluid, and (iii) experience changes in current and future reproductive performance as a result of ejaculate compositional changes. Combining quantitative proteomics with fluorescent sperm labeling, we show that Drosophila melanogaster males exercise independent control over the transfer of sperm and seminal fluid proteins (SFPs) under different levels of male–male competition. While sperm transfer peaks at low competition, consistent with some theoretical predictions based on sperm competition intensity, the abundance of transferred SFPs generally increases at high competition levels. However, we find that clusters of SFPs vary in the directionality and sensitivity of their response to competition, promoting compositional change in seminal fluid. By tracking the degree of decline in male mating probability and offspring production across successive matings, we provide evidence that ejaculate compositional change represents an adaptive response to current sperm competition, but one that comes at a cost to future mating performance. Our work reveals a previously unknown divergence in ejaculate component allocation rules, exposes downstream costs of elevated ejaculate investment, and ultimately suggests a central role for ejaculate compositional plasticity in sexual selection.

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LaMunyon, Craig W., and Ward Samuel. "Evolution of sperm size in nematodes: sperm competition favours larger sperm." Proceedings of the Royal Society of London. Series B: Biological Sciences 266, no. 1416 (February 7, 1999): 263–67. http://dx.doi.org/10.1098/rspb.1999.0631.

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Journal articles on the topic 'Sperm competition'

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