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paco.garcia[at]ebd.csic.es

Sperm competition

Publications filtered by: Sperm competition

Journal of Evolutionary Biology, in press
Firman, R. C., Garcia-Gonzalez, F., Simmons, L. W. & André, G. 2018 A competitive environment influences sperm production, but not testes tissue composition, in house mice Journal of Evolutionary Biology, 31:1647-1654
The total opportunity for sexual selection and the integration of pre- and post-mating episodes of sexual selection in a complex world
Evans, J. P. & Garcia-Gonzalez, F. 2016 The total opportunity for sexual selection and the integration of pre- and post-mating episodes of sexual selection in a complex world Journal of Evolutionary Biology, 29: 2338-2361
Abstract

It is well known that sexual selection can target reproductive traits during successive pre- and post-mating episodes of selection. A key focus of recent studies has been to understand and quantify how these episodes of sexual selection interact to determine overall variance in reproductive success. In this paper we review empirical developments in this field but also highlight the considerable variability in patterns of pre- and post-mating sexual selection, attributable to variation in patterns of resource acquisition and allocation, ecological and social factors, genotype-by-environment interaction, and possible methodological factors that might obscure such patterns. Our aim is to highlight how (co)variances in pre- and post-mating sexually selected traits can be sensitive to changes in a range of ecological and environmental variables. We argue that failure to capture this variation when quantifying the opportunity for sexual selection may lead to erroneous conclusions about the strength, direction or form of sexual selection operating on pre- and post-mating traits. Overall, we advocate for approaches that combine measures of pre- and post-mating selection across contrasting environmental or ecological gradients to better understand the dynamics of sexual selection in polyandrous species. We also discuss some directions for future research in this area.

Genetic variation but weak genetic covariation between pre- and postcopulatory episodes of sexual selection in Drosophila melanogaster
Travers, L. M., Garcia-Gonzalez, F. & Simmons, L. W. 2016 Genetic variation but weak genetic covariation between pre- and postcopulatory episodes of sexual selection in Drosophila melanogaster Journal of Evolutionary Biology, 29: 1535-1552
Additive genetic variance in polyandry enables its evolution but polyandry is unlikely to evolve through sexy or good sperm processes
Travers, L. M., Simmons, L. W. & Garcia-Gonzalez, F. 2016 Additive genetic variance in polyandry enables its evolution but polyandry is unlikely to evolve through sexy or good sperm processes Journal of Evolutionary Biology, 29: 916-928.
Abstract

Polyandry is widespread despite its costs. The sexually selected sperm hypotheses (‘sexy’ and ‘good’ sperm) posit that sperm competition plays a role in the evolution of polyandry. Two poorly studied assumptions of these hypotheses are the presence of additive genetic variance in polyandry and sperm competitiveness. Using a quantitative genetic breeding design in a natural population of Drosophila melanogaster, we first established the potential for polyandry to respond to selection. We then investigated whether polyandry can evolve through sexually selected sperm processes. We measured lifetime polyandry and offensive sperm competitiveness (P2) while controlling for sampling variance due to male x male x female interactions. We also measured additive genetic variance in egg-to-adult viability and controlled for its effect on P2 estimates. Female lifetime polyandry showed significant and substantial additive genetic variance and evolvability. In contrast, we found little genetic variance or evolvability in P2 or egg-to-adult viability. Additive genetic variance in polyandry highlights its potential to respond to selection. However, the low levels of genetic variance in sperm competitiveness suggest the evolution of polyandry may not be driven by sexy sperm or good sperm processes.

Mating portfolios: bet-hedging, sexual selection and female multiple mating
Garcia-Gonzalez, F., Yasui, Y. and Evans, J. P. 2015 Mating portfolios: bet-hedging, sexual selection and female multiple mating Proceedings of the Royal Society of London B, 282: 20141525
Abstract

Polyandry (female multiple mating) has profound evolutionary and ecological implications. Despite considerable work devoted to understanding why females mate multiply, we currently lack convincing empirical evidence to explain the adaptive value of polyandry. Here we provide a direct test of the controversial idea that bet-hedging functions as a risk-spreading strategy that yields multi-generational fitness benefits to polyandrous females. Unfortunately, testing this hypothesis is far from trivial, and the empirical comparison of the across-generations fitness payoffs of a polyandrous (bet hedger) versus a monandrous (non-bet hedger) strategy has never been accomplished because of numerous experimental constraints presented by most ‘model’ species. In the present study we take advantage of the extraordinary tractability and versatility of a marine broadcast spawning invertebrate to overcome these challenges. We are able to simulate multi-generational (geometric mean) fitness among individual females assigned simultaneously to a polyandrous and monandrous mating strategy. Our approaches, which separate and account for the effects of sexual selection and pure bet-hedging scenarios, reveal that bet-hedging, in addition to sexual selection, can enhance evolutionary fitness in multiply-mated females. In addition to offering a tractable experimental approach for addressing bet-hedging theory, our study provides key insights into the evolutionary ecology of sexual interactions.

Fertilization success and the estimation of genetic variance in sperm competitiveness
Garcia-Gonzalez, F. & Evans, J. P. 2011 Fertilization success and the estimation of genetic variance in sperm competitiveness Evolution, 65: 746-756
Abstract
A key question in sexual selection is whether the ability of males to fertilize eggs under sperm competition exhibits heritable genetic variation. Addressing this question poses a significant problem, however, because a male’s ability to win fertilizations ultimately depends on the competitive ability of rival males. Attempts to partition genetic variance in sperm competitiveness, as estimated from measures of fertilization success, must therefore account for stochastic effects due to the random sampling of rival sperm competitors. In this contribution, we suggest a practical solution to this problem. We advocate the use of simple crossclassified breeding designs for partitioning sources of genetic variance in sperm competitiveness and fertilization success and show how these designs can be used to avoid stochastic effects due to the random sampling of rival sperm competitors. We illustrate the utility of these approaches by simulating various scenarios for estimating genetic parameters in sperm competiveness, and show that the probability of detecting additive genetic variance in this trait is restored when stochastic effects due to the random sampling of rival sperm competitors are controlled. Our findings have important implications for the study of the evolutionary maintenance of polyandry.
Linking sperm length and velocity: the importance of intramale variation
Fitzpatrick, J. L., Garcia-Gonzalez, F. & Evans, J. P. 2010 Linking sperm length and velocity: the importance of intramale variation Biology Letters, 6: 797-799
Abstract
Selection imposed through sperm competition is commonly thought to promote the evolution of longer sperm, since sperm length is assumed to be positively associated with sperm swimming velocity. Yet, the basis for this assumption remains controversial, and there is surprisingly little intraspecific evidence demonstrating such a link between sperm form and function. Here, we show that sperm length and velocity are highly correlated in the sea urchin Heliocidaris erythrogramma, but importantly we report that failure to account for within-male variation in these sperm traits can obscure this relationship. These findings, in conjunction with the mounting evidence for extremely high levels of intraspecific variance in sperm traits, suggest that a functional link between sperm morphology and velocity may be more prevalent than what current evidence suggests. Our findings also suggest that selection for faster swimming sperm may promote the evolution of longer sperm, thereby supporting recent findings from macroevolutionary studies.
Evolutionary reduction in testes size and competitive fertilization success in response to the experimental removal of sexual selection in dung beetles
Simmons, L. W. & Garcia-Gonzalez, F. 2008 Evolutionary reduction in testes size and competitive fertilization success in response to the experimental removal of sexual selection in dung beetles Evolution, 62:2580-2591
Abstract
Sexual selection is thought to favor the evolution of secondary sexual traits in males that contribute to mating success. In species where females mate with more than one male, sexual selection also continues after copulation in the form of sperm competition and cryptic female choice. Theory suggests that sperm competition should favor traits such as testes size and sperm production that increase a male’s competitive fertilization success. Studies of experimental evolution offer a powerful approach for assessing evolutionary responses to variation in sexual selection pressures. Here we removed sexual selection by enforcing monogamy on replicate lines of a naturally polygamous horned beetle, Onthophagus taurus, and monitoring male investment in their testes for 21 generations. Testes size decreased in monogamous lines relative to lines in which sexual selection was allowed to continue. Differences in testes size were dependent on selection history and not breeding regime. Males from polygamous lines also had a competitive fertilization advantage when in sperm competition with males from monogamous lines. Females from polygamous lines produced sons in better condition, and those from monogamous lines increased their sons condition by mating polygamously. Rather than being costly for females, multiple mating appears to provide females with direct and/or indirect benefits. Neither body size nor horn size diverged between our monogamous and polygamous lines. Our data show that sperm competition does drive the evolution of testes size in onthophagine beetles, and provide general support for sperm competition theory.
The relative nature of fertilization success: implications for the study of post-copulatory sexual selection
Garcia-Gonzalez, F. 2008 The relative nature of fertilization success: implications for the study of post-copulatory sexual selection BMC Evolutionary Biology, 8:140
Abstract
Background: The determination of genetic variation in sperm competitive ability is fundamental to distinguish between post-copulatory sexual selection models based on good-genes vs compatible genes. The sexy-sperm and the good-sperm hypotheses for the evolution of polyandry require additive (intrinsic) effects of genes influencing sperm competitiveness, whereas the genetic incompatibility hypothesis invokes non-additive genetic effects. A male's sperm competitive ability is typically estimated from his fertilization success, a measure that is dependent on the ability of rival sperm competitors to fertilize the ova. It is well known that fertilization success may be conditional to genotypic interactions among males as well as between males and females. However, the consequences of effects arising from the random sampling of sperm competitors upon the estimation of genetic variance in sperm competitiveness have been overlooked. Here I perform simulations of mating trials performed in the context of sibling analysis to investigate whether the ability to detect additive genetic variance underlying the sperm competitiveness phenotype is hindered by the relative nature of fertilization success measurements. Results: Fertilization success values render biased sperm competitive ability values. Furthermore, asymmetries among males in the errors committed when estimating sperm competitive abilities are likely to exist as long as males exhibit variation in sperm competitiveness. Critically, random effects arising from the relative nature of fertilization success lead to an underestimation of underlying additive genetic variance in sperm competitive ability. Conclusion: The results show that, regardless of the existence of genotypic interactions affecting the output of sperm competition, fertilization success is not a perfect predictor of sperm competitive ability because of the stochasticity of the background used to obtain fertilization success measures. Random effects need to be considered in the debate over the maintenance of genetic variation in sperm competitiveness, and when testing good-genes and compatible-genes processes as explanations of polyandrous behaviour using repeatability/heritability data in sperm competitive ability. These findings support the notion that the genetic incompatibility hypothesis needs to be treated as an alternative hypothesis, rather than a null hypothesis, in studies that fail to detect intrinsic sire effects on the sperm competitiveness phenotype.
Garcia-Gonzalez, F. 2008 Male genetic quality and the inequality between paternity success and fertilization success: consequences for studies of sperm competition and the evolution of polyandry Evolution, 62:1653-1665
Abstract
Studies of postcopulatory sexual selection typically estimate a male’s fertilization success from his paternity success (P2) calculated at hatching or birth. However, P2 may be affected by differential embryo viability, thereby confounding estimations of true fertilization success (F2). This study examines the effects of variation in the ability of males to influence embryo viability upon the inequality between P2 and F2. It also investigates the consequences of this inequality for testing the hypothesis that polyandrous females accrue viability benefits for their offspring through facilitation of sperm competition (good-sperm model). Simulations of competitive mating trials show that although relative measures of male reproductive success tend to underestimate the strength of underlying good-sperm processes, good-sperm processes can be seriously overestimated using P2 values if males influence the viability of the embryos they sire. This study cautions the interpretation of P2 values as a proxy for fertilization success or sperm competitiveness in studies of postcopulatory sexual selection, and highlights that the good-sperm hypothesis needs empirical support from studies able to identify and separate unequivocally the males’ ability to win fertilizations from their ability to influence the development of embryos.

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