Sperm Competition

Froman, D. P., Pizarri, T., Feltmann, A. J., Castillo-Juárez, H., and Birkhead, T. (2002). Sperm mobility: mechanisms of fertilizing efficiency, genetic variation, and phenotypic relationship with male status in the domestic fowl, Gallus gallus domesticus. Proceedings of the Royal Society of London B. 69 (1491): 607-612.

by Héctor Castillo-Juárez

Who's your daddy? Paternity testing reveals promiscuity and multiple paternity in the carnivorous marsupial Dasyurus maculatus (Marsupialia: Dasyuridae)

by Al Glen

Glen, AS, Cardoso, MJ, Dickman, CR and Firestone, KB (2009). Biological Journal of the Linnean Society 96: 1-7.

Female promiscuity is common among mammals but its advantages, particularly for marsupials, remain unclear. Using... more Female promiscuity is common among mammals but its advantages, particularly for marsupials, remain unclear. Using microsatellite DNA from pouch young of known mothers, we identified the most likely fathers of 25 wild spotted-tailed quolls (Dasyurus maculatus) from six litters. We aimed to determine whether young within the same litter had different fathers, and whether breeding success of males was associated with large body mass (consistent with inter-male competition) or scrotal width (consistent with sperm competition). We also explored the possible influence of promiscuity on relatedness within litters. Finally, we used data on paternity and relatedness to make inferences regarding movement and dispersal.

Four litters were sired by more than one male, and three males sired offspring in more than one litter. Known fathers had higher body mass, but not scrotal width, than males of unknown paternity status, suggesting that males may compete for access to females. Sires were less related to dams than expected by chance, and litters with multiple paternity had lower relatedness than litters sired by a single male.

Competencia de esperma en humanos: Contexto y mecanismos.

by German Gutierrez

Gutiérrez, G. & Ortiz, J. (2002).  Sperm competition in humans: Context and mechanisms.  Suma Psicológica, 9, 81-106.

Aspectos conductuales de la competencia de esperma en aves.

by German Gutierrez

Gutiérrez, G. & Riveros, J.C. (2003).  Revista Latinoamericana de Psicología, 35, 67-76.

Two modes of input processing in relation to sperm competition in mammals

by Javier delBarco-Trillo

2. delBarco-Trillo J, Ferkin MH. 2005. Two modes of input processing in relation to sperm competition in mammals. Acta Zool Sin. 51:1122-1129.

Much research has been focused on the ‘output’ or response of males to particular risks of sperm competition (RSC).... more Much research has been focused on the ‘output’ or response of males to particular risks of sperm competition (RSC). Lately, there has also been some interest on the types of information that males may use to assess RSC (RSC inputs). In contrast, there is a lack of studies on how males may process RSC inputs to generate such RSC outputs. Here we propose two modes of input processing (direct and indirect) and ways to test them in order to understand how a male may process and store RSC information. The direct mode of input processing predicts that a male may store RSC inputs through a physiological response, e.g., through a change in hormonal levels. As long as this response is active, the male will stay in a ‘RSC state’ and will produce an RSC output (e.g. high sperm investment) instead of a non-RSC output (e.g. relatively lower sperm investment) when he encounters a female. The indirect mode of input processing predicts that a male may store RSC inputs in his memory and retrieve such information later on to modify his output (e.g. sperm investment or copulatory behavior) accordingly. We use a multidisciplinary approach that should appeal to those researchers that seek to understand male’s adaptations to sperm competition at different levels. We believe that the testing of the hypotheses developed in this paper will lead to interesting findings and the development of new hypotheses

Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males

by Javier delBarco-Trillo

1. delBarco-Trillo J, Ferkin MH. 2004. Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males. Nature. 431:446-449.

Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within... more Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.

Adjustment of sperm allocation under high risk of sperm competition across taxa: a meta-analysis

by Javier delBarco-Trillo

28. delBarco-Trillo, J. (In press) Adjustment of sperm allocation under high risk of sperm competition across taxa: a meta-analysis. Journal of Evolutionary Biology. doi:10.1111/j.1420-9101.2011.02293.x

Sperm competition theory predicts that under high risk of sperm competition, males will increase the number of sperm... more Sperm competition theory predicts that under high risk of sperm competition, males will increase the number of sperm that they allocate to a female. This prediction has been supported by some experimental studies but not by others. Here, I conducted a meta-analysis to determine whether the increase in sperm allocation under high risk of sperm competition is a generalized response across taxa. I collected data from 39 studies and 37 species. Across taxa, males under a high risk of sperm competition respond by increasing their sperm allocation (mean effect size = 0.32). Number of offspring did not explain a significant portion of the variation in effect sizes. A traditional meta-analysis (i.e. without phylogenetic information) described the variation among effect sizes better than a meta-analysis that incorporates the phylogenetic relationships among species, suggesting that the increase in sperm allocation under high risk of sperm competition is similarly prevalent across taxa.

Self-grooming by male meadow voles differs across copulation but is not affected by the risk and intensity of sperm competition

by Javier delBarco-Trillo

20. Vaughn AA, delBarco-Trillo J, Ferkin MH. 2010. Self-grooming by male meadow voles differs across copulation but is not affected by the risk and intensity of sperm competition. Behaviour. 147:259-274.

Meadow voles, Microtus pennsylvanicus, self-groom before, during and after copulation, which may convey olfactory... more Meadow voles, Microtus pennsylvanicus, self-groom before, during and after copulation, which may convey olfactory information to nearby conspecifics. Since males who self-groom at high rates were found to be attractive to females, it is possible that the copulating male may attempt to increase his attractiveness over that of other males who are present or nearby. In that the presence of other males affects sperm investment and can be used by males as an indicator of sperm competition, we tested the hypothesis that the presence of scent marks of other males near a sexually receptive female affects the self-grooming behaviour of males that encounter them. We did so by pairing a male and a female vole in the presence of the odours of one male conspecific, five male conspecifics, or no male conspecifics. The amount of time male voles self-groomed was not affected by the risk or intensity of sperm competition. We also tested the hypothesis that self-grooming behaviour of males differed depending on whether it was performed before, during, or after copulation. Male voles differed in the amount of time and the location on their body that they self-groomed before, during, and after copulation.

Sperm investment in male meadow voles is affected by the condition of the nearby male conspecifics

by Javier delBarco-Trillo

12. Vaughn AA, delBarco-Trillo J, Ferkin MH. 2008. Sperm investment in male meadow voles is affected by the condition of the nearby male conspecifics. Behav Ecol. 19:1159-1164.

Sperm competition occurs when 2 or more males copulate with a particular female during the same reproductive cycle,... more Sperm competition occurs when 2 or more males copulate with a particular female during the same reproductive cycle, and their sperm compete to fertilize the female's available eggs. One strategy that male voles use to assess the risk and intensity of sperm competition involves responding to the presence of scent marks of conspecific males found near a sexually receptive female. Previously, we have shown that if a male vole copulated with a female while he was in the presence of the odors of another male he increased his sperm investment relative to his investment if another male's odors were not present. The aim of the present study was to test the hypothesis that males assess differences in the relative quality of competing males and adjust their sperm investment accordingly. We did so by allowing males to copulate when they were exposed to the scent mark of a 24-h food-deprived male (low-quality male) or the scent mark of a male that was not food deprived (high-quality male). The data indicate that male meadow voles did not increase their sperm investment during copulation when exposed to the scent mark of a food-deprived male but did so when they were exposed to the scent mark of a male that was not food deprived. The results support the hypothesis that male voles are able to adjust sperm investment when they encounter the scent marks of males that differ in quality.

Increased sperm numbers in the vas deferens of meadow voles, Microtus pennsylvanicus, in response to odors of conspecific males

by Javier delBarco-Trillo

9. delBarco-Trillo J, Ferkin MH. 2007. Increased sperm numbers in the vas deferens of meadow voles, Microtus pennsylvanicus, in response to odors of conspecific males. Behav Ecol Sociobiol. 61:1759-1764.

Sperm competition occurs when the sperm of two or more males compete to fertilize the egg/s of a particular female.... more Sperm competition occurs when the sperm of two or more males compete to fertilize the egg/s of a particular female. Males of some species respond to a high risk of sperm competition by increasing the number of sperm in their ejaculates. Males may accomplish such a response by increasing the intensity or duration of contraction of the cauda epididymidis and vas deferens. During emission (first phase of the ejaculatory process), the vas deferens receives sperm from the cauda epididymidis and propels the sperm to the urethra. In this paper, we tested the hypothesis that males exposed to a high risk of sperm competition mobilize larger numbers of sperm from the cauda epididymidis to the vas deferens before initiation of copulatory behavior. This accumulation of sperm in the vas deferens would result in a larger number of sperm in the ejaculate. To test this hypothesis, we exposed male meadow voles, Microtus pennsylvanicus, to either low or high risks of sperm competition using soiled bedding of conspecific individuals. At three different times after this exposure (15, 30, or 60 min), we removed both vasa deferentia and counted the sperm within them. We found a significant increase in sperm numbers in the vas deferens of males after 30 min of being exposed to a high risk of sperm competition. The lower sperm numbers after 15 and 60 min of exposure suggest that the observed response is relatively slow and that sperm mobilized to the vasa deferentia may return to the cauda epididymides if ejaculation does not occur some time after the observed response. Our results indicate that the physiological response that may result in high sperm numbers in the ejaculate in relation to high risk of sperm competition can occur before initiation of copulatory behavior.

Risk of sperm competition does not influence copulatory behavior in the promiscuous meadow vole (Microtus pennsylvanicus)

by Javier delBarco-Trillo

7. delBarco-Trillo J, Ferkin MH. 2007. Risk of sperm competition does not influence copulatory behavior in the promiscuous meadow vole (Microtus pennsylvanicus). Journal of Ethology. 25:139-145.

It is not clear whether males in all mammalian species adjust their copulatory behavior when faced with risk of sperm... more It is not clear whether males in all mammalian species adjust their copulatory behavior when faced with risk of sperm competition (RSC). Previous work on meadow voles, Microtus pennsylvanicus, indicated that males increase their sperm expenditure but not the number of ejaculations in the presence of odors of a conspecific male. The present study follows up on this work and asks whether male meadow voles modify any aspect of their copulatory behavior when they face a RSC. We examined 46 variables of copulatory behavior and found that the presence of odors from a conspecific male did not affect any of these variables. Thus, male meadow voles, unlike some other species of mammals, do not adjust their copulatory behavior when exposed to cues associated with an elevated RSC.

Male meadow voles respond differently to risk and intensity of sperm competition

by Javier delBarco-Trillo

5. delBarco-Trillo J, Ferkin MH. 2006. Male meadow voles respond differently to risk and intensity of sperm competition. Behav Ecol. 17:581-585.

In many species of small mammals, females undergo post-partum oestrus soon after delivering a litter, becoming... more In many species of small mammals, females undergo post-partum oestrus soon after delivering a litter, becoming pregnant while suckling the previous litter. Females raising two concurrent litters need to allocate many more resources to reproduction than females raising only one litter. Consequently, there may be differences between litters raised concurrently or singly.We investigated this issue in the meadow vole, Microtus pennsylvanicus, a species in which most females in the wild reproduce during post-partum oestrus. Specifically, we tested the hypothesis that the development of pups in two concurrent litters differs from that of pups in a single litter. To test this hypothesis, we measured the following variables for concurrent and singly reared litters: gestation length; litter size; sex ratio; bodyweight of males and females at different ages; total litter weight at weaning; growth rates; and intra-litter variation in body mass. Except for bodyweight of males at 60 days of age, which was higher in the first of the concurrent litters, none of the variables differed among the litters. These results indicate that females are able to adjust to differing loads of maternal care to provide equivalent resources to concurrent litters and singly reared litters.

Evolution of sexual size-monomorphism; the influence of passive mate-guarding

by Amy Dunham

Iossa, G., Soulsbury, C.D., Baker, P.J. & Harris, S. (2008) Sperm competition and the evolution of testes size in terrestrial mammalian carnivores. Functional Ecology, 22: 655-662.

by Carl Soulsbury

1. Understanding the factors influencing variation in the degree of sperm competition is a key question underlying the... more 1. Understanding the factors influencing variation in the degree of sperm competition is a key question underlying the mechanisms driving sexual conflict.
2. Previous behavioural and comparative studies have indicated that carnivores appear to have evolved under sperm competition but an analysis of the predictors of the level of sperm competition is missing.
3. In this study, we use phylogenetic comparative methods to investigate life-history parameters predicted to affect the degree of sperm competition in terrestrial carnivores using variation in relative testes size (RTS, after controlling for body size allometry) as a measure of the level of sperm competition. Due to a paucity of consistent data across taxa, we used three measures of RTS: testes mass (n = 40 species), testes and epididymes mass combined (n = 38), and testes volume (n = 48). We also created a derived data set (n = 79) with testes mass estimated from regression analyses on the other measures of testes size.
4. Carnivores with shorter mating seasons had relatively larger testes, consistent with the hypothesis that sperm competition is greater when the degree of female oestrous synchrony is high. This relationship was stronger in spontaneous versus induced ovulators, suggesting higher sperm competition levels in spontaneous ovulators. This is the first comparative study to show this within mammalian taxa. Neither social mating system nor reproductive lifespan were significantly associated with variation in RTS and hence are poor predictors of sperm competition levels.
5. None of the above relationships were found to be significant for the testes and epididymes mass combined data set, but our understanding of the role of the epididymis in sperm competition is too limited to draw any conclusions.
6. Finally, we consistently found a significant phylogenetic signal in all analyses, indicating that phylogeny has played a significant role in the evolution of carnivore testes size and, therefore, in shaping levels of sperm competition.
7. Our results shed new light into the factors affecting levels of sperm competition in terrestrial carnivores by showing that the degree of oestrous synchrony and ovulation type interact to predict variation in RTS.

Soulsbury, C.D. (2010) Genetic patterns of paternity and testes size in mammals. PLoS ONE, 5: e9581.

by Carl Soulsbury

Background

Testes size is used as a proxy of male intrasexual competition, with larger testes indicative of... more Background

Testes size is used as a proxy of male intrasexual competition, with larger testes indicative of greater competition. It has been shown that in some taxa, social mating systems reflect variance in testes size, but results are not consistent, and instead it has been suggested that genetic patterns of mating may reflect testes size. However, there are different measures of genetic patterns of mating. Multiple paternity rates are the most widely used measure but are limited to species that produce multi-offspring litters, so, at least for group living species, other measures such as loss of paternity to males outside the social group (extra group paternity) or the proportion of offspring sired by the dominant male (alpha paternity) might be appropriate. This study examines the relationship between testes size and three genetic patterns of mating: multiple paternity, extragroup paternity and alpha paternity.

Methodology/Principal Findings

Using data from mammals, phylogenetically corrected general linear models demonstrate that both multiple paternity and alpha paternity, but not extra group paternity, relate to testes size. Testes size is greater in species with high multiple paternity rates, whereas the converse is found for alpha paternity. Additionally, length of mating season, ovulation mode and litter size significantly influenced testes size in one model.

Conclusions/Significance

These results demonstrate that patterns of mating (multiple paternity and alpha paternity rates) determined by genetic analysis can provide reliable indicators of male postcopulatory intrasexual competition (testes size), and that other variables (length of mating season, ovulation mode, litter size) may also be important.

Soulsbury, C.D. (2010) Ovulation mode modifies paternity monopolization in mammals. Biology Letters, 6: 39-41.

by Carl Soulsbury

There are two forms of ovulation: spontaneous and induced. As copulation triggers ovulation for induced ovulators,... more There are two forms of ovulation: spontaneous and induced. As copulation triggers ovulation for induced ovulators, males can predict the timing of ovulation and may have greater paternity monopolization than spontaneous ovulators. However, this prediction has never, to my knowledge, been tested. Using a cross-species comparison I examined the percentage of offspring sired within a litter (single paternity) and in social species the percentage of offspring sired by the dominant male (alpha paternity). My results indicate that ovulation mode alters the ability of males to monopolize paternity, with males of induced ovulators having higher single paternity and greater alpha paternity where male–female association is intermittent.

Soulsbury, C.D. & Iossa, G. (2010) The impact of ovulation mode on sperm quantity and quality In mammals. Evolutiary Ecology, 24: 879-889.

by Carl Soulsbury

Ovulation generally takes two forms: spontaneous and induced. These two ovulatory modes are predicted to cause... more Ovulation generally takes two forms: spontaneous and induced. These two ovulatory modes are predicted to cause different levels of male–male competition due to differences in males’ ability to predict the timing of ovulation of females that use each mode. Ovulation mode has been shown to be correlated with differences in testis size, but it is not known whether ovulation type influences ejaculate traits, specifically sperm quantity (sperm concentration, ejaculate volume, total motile sperm per ejaculate) and/or sperm quality (% sperm motility, % normal sperm). Using a cross-species comparative analysis of 130 mammals, we found that sperm concentration and total motile sperm per ejaculate were significantly greater in spontaneous ovulators. In contrast, ejaculate volume, % sperm motility and % normal sperm were unrelated to ovulation type. These data show that ovulation alters sperm quantity by increasing sperm concentration but not ejaculate volume, and that sperm quality does not vary with ovulation mode.