Predicting variation in sperm precedence
29 Jul 1997-Philosophical Transactions of the Royal Society B (The Royal Society)-Vol. 352, Iss: 1355, pp 771-780
TL;DR: This work presents a technique for analysing the variance in P2 when a given mechanism of P2 is assumed, and applies it to P2 data collected from Plodia interpunctella, assuming a 'fair raffle' mechanism of sperm competition.
Abstract: Sperm competition theory predicts that males are adapted for success in sperm competition by the production of large numbers of sperm. This is supported by both inter- and intraspecific studies showing that males mating under high sperm competition risk increase investment in sperm production. Such an increase in sperm production is an advantage if sperm mix randomly or if sperm displacement occurs. When two males mate with the same female, the measurement of the proportion of eggs fertilized by the second male to mate (termed P2) has been used to help elucidate sperm competition mechanisms. P2 is usually quoted as a mean value, with little attention being paid to its variance, although P2 estimates are notoriously variable. By predicting an expected variance for P2, additional information on sperm competition mechanisms may be obtained. Here we present a technique for analysing the variance in P2 when a given mechanism of P2 is assumed. We apply this technique to P2 data collected from Plodia interpunctella (Lepidoptera, Pyralidae), assuming a 'fair raffle' mechanism of sperm competition. We compare observed distributions of P2 with theoretical distributions generated assuming random mixing of two ejaculates drawn randomly from a population of known mean and variance in sperm numbers. Ejaculates of known size were obtained by counting the number of sperm ejaculated by males mating for the first (large ejaculate) or second (small ejaculate) time. Females either received two small or one small and one large ejaculate, and the distribution of P2 (estimated using the sterile male technique) was compared with our theoretical predictions. The observed variance in P2 was greater than our model prediction, thus we conclude that sperm from P. interpunctella do not mix randomly before fertilization.
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TL;DR: It is concluded that post‐copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice and that some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm.
Abstract: The aim of this review is to consider the potential benefits that females may gain from mating more than once in a single reproductive cycle. The relationship between non-genetic and genetic benefits is briefly explored. We suggest that multiple mating for purely non-genetic benefits is unlikely as it invariably leads to the possibility of genetic benefits as well. We begin by briefly reviewing the main models for genetic benefits to mate choice, and the supporting evidence that choice can increase offspring performance and the sexual attractiveness of sons. We then explain how multiple mating can elevate offspring fitness by increasing the number of potential sires that compete, when this occurs in conjunction with mechanisms of paternity biasing that function in copula or post-copulation. We begin by identifying cases where females use pre-copulatory cues to identify mates prior to remating. In the simplest case, females remate because they identify a superior mate and 'trade up' genetically. The main evidence for this process comes from extra-pair copulation in birds. Second, we note other cases where pre-copulatory cues may be less reliable and females mate with several males to promote post-copulatory mechanisms that bias paternity. Although a distinction is drawn between sperm competition and cryptic female choice, we point out that the genetic benefits to polyandry in terms of producing more viable or sexually attractive offspring do not depend on the exact mechanism that leads to biased paternity. Post-copulatory mechanisms of paternity biasing may: (1) reduce genetic incompatibility between male and female genetic contributions to offspring; (2) increase offspring viability if there is a positive correlation between traits favoured post-copulation and those that improve performance under natural selection; (3) increase the ability of sons to gain paternity when they mate with polyandrous females. A third possibility is that genetic diversity among offspring is directly favoured. This can be due to bet-hedging (due to mate assessment errors or temporal fluctuations in the environment), beneficial interactions between less related siblings or the opportunity to preferentially fertilise eggs with sperm of a specific genotype drawn from a range of stored sperm depending on prevailing environmental conditions. We use case studies from the social insects to provide some concrete examples of the role of genetic diversity among progeny in elevating fitness. We conclude that post-copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice. Some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm. Two future areas of research seem likely to be profitable. First, more experimental evidence is needed demonstrating that multiple mating increases offspring fitness via genetic gains. Second, the role of multiple mating in promoting assortative fertilization and increasing reproductive isolation between populations may help us to understand sympatric speciation.
1,778 citations
TL;DR: It is argued that ejaculate economic theory represents a powerful heuristic to explain the diversity in ejaculate traits at multiple levels: across species, across males and within individual males.
Abstract: Sperm competition was identified in 1970 as a pervasive selective force in post-copulatory sexual selection that occurs when the ejaculates of different males compete to fertilise a given set of ova. Since then, sperm competition has been much studied both empirically and theoretically. Because sperm competition often favours large ejaculates, an important challenge has been to understand the evolution of strategies through which males invest in sperm production and economise sperm allocation to maximise reproductive success under competitive conditions. Sperm competition mechanisms vary greatly, depending on many factors including the level of sperm competition, space constraints in the sperm competition arena, male mating roles, and female influences on sperm utilisation. Consequently, theoretical models of ejaculate economics are complex and varied, often with apparently conflicting predictions. The goal of this review is to synthesise the theoretical basis of ejaculate economics under sperm competition, aiming to provide empiricists with categorised model assumptions and predictions. We show that apparent contradictions between older and newer models can often be reconciled and there is considerable consensus in the predictions generated by different models. We also discuss qualitative empirical support for some of these predictions, and detail quantitative matches between predictions and observations that exist in the yellow dung fly. We argue that ejaculate economic theory represents a powerful heuristic to explain the diversity in ejaculate traits at multiple levels: across species, across males and within individual males. Future progress requires greater understanding of sperm competition mechanisms, quantification of trade-offs between ejaculate allocation and numbers of matings gained, further knowledge of mechanisms of female sperm selection and their associated costs, further investigation of non-sperm ejaculate effects, and theoretical integration of pre- and post-copulatory episodes of sexual selection.
517 citations
TL;DR: It is found that the estimate of relative sperm number did not account for any significant variation in paternity and the results suggest that female guppies may use pre–copulatory mechanisms to maximize the genetic quality of their offspring.
Abstract: The tradeup hypothesis outlines a behavioural strategy that females could use to maximize the genetic benefits to their offspring. The hypothesis proposes that females should be more willing to acc...
224 citations
Cites methods from "Predicting variation in sperm prece..."
...We used the sperm load estimates to construct an expected distribution of paternity for each male based on a ‘fair raffle’ model (Parker et al. 1990; see also Cook et al. 1997; Evans & Magurran 2001)....
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TL;DR: This work uses the cricket Teleogryllus oceanicus to conduct sperm competition trials involving prescreened males that differ in the viability of their sperm, and finds that paternity success is determined by the proportion of live sperm in a male's ejaculate.
223 citations
TL;DR: By analyzing shape variation in male genital morphology, it is demonstrated that the shape of male intromittent genitalia was related to relative paternity success, the first direct experimental support for the suggestion that male genitalia evolve by postmating sexual selection.
Abstract: Recent theoretical and empirical interest in postmating processes have generated a need for increasing our understanding of the sources of variance in fertilization success among males. Of particular importance is whether such postmating sexual selection merely reinforces the effects of premating sexual selection or whether other types of male traits are involved. In the current study, we document large intraspecific variation in last male sperm precedence in the water strider Gerris lateralis. Male relative paternity success was repeatable across replicate females, showing that males differ consistently in their ability to achieve fertilizations. By analyzing shape variation in male genital morphology, we were able to demonstrate that the shape of male intromittent genitalia was related to relative paternity success. This is the first direct experimental support for the suggestion that male genitalia evolve by postmating sexual selection. A detailed analysis revealed that different components of male genitalia had different effects, some affecting male ability to achieve sperm precedence and others affecting male ability to avoid sperm precedence by subsequent males. Further, the effects of the shape of the male genitalia on paternity success was in part dependent on female morphology, suggesting that selection on male genitalia will depend on the frequency distribution of female phenotypes. We failed to find any effects of other morphological traits, such as male body size or the degree of asymmetry in leg length, on fertilization success. Although males differed consistently in their copulatory behavior, copulation duration was the only behavioral trait that had any significant effect on paternity.
194 citations
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Abstract: Technique non parametrique pour la signification statistique de tables de tests utilisees dans les etudes sur l'evolution notamment
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"Predicting variation in sperm prece..." refers methods in this paper
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TL;DR: In this article, Simpson et al. describe a method to solve the problem of homonymity in Bee W l d 34, 14) and show that it works well in beekeeping.
Abstract: by M. Simpson in Bee W l d 34, 14).
3,892 citations
"Predicting variation in sperm prece..." refers methods in this paper
...the ‘ fair raffle’ principle of Parker et al. (1990). Computer simulations (using Minitab, Release 9) were carried out to generate P # distributions that would occur as a result of sperm number variation: (i) A matrix was constructed to calculate the probabilities of all the possible combinations of pairs of ejaculates from males 1 and 2....
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Book•
09 Jan 1992
TL;DR: Birds as vehicles for sperm competition avian mating systems and sperm competition male and female reproductive systems and the fertile period sperm precedence and mechanisms of sperm competition copulation behaviour - pair copulation, extra-pair copulation paternity guards.
Abstract: Birds as vehicles for sperm competition avian mating systems and sperm competition male and female reproductive systems and the fertile period sperm precedence and mechanisms of sperm competition copulation behaviour - pair copulation, extra-pair copulation paternity guards - mate guarding, frequent copulation, territoriality and other guards costs and benefits of extra-pair copulation for males costs and benefits of extra-pair copulation for females extra-pair paternity evolutionary consequences of sperm copulation in birds.
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