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126 results for “Sperm competition”
Data from: Sperm competition and the evolution of precopulatory weapons: testis size and amplexus position, but not arm strength, affect fertilization success in a chorusing frog
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Data from: Multivariate sexual selection on ejaculate traits under sperm competition
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Divergent natural selection alters male sperm competition success in Drosophila melanogaster
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Data from: Sperm competition risk drives rapid ejaculate adjustments mediated by seminal fluid
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Data from: Male responses to sperm competition risk associated with increased macronutrient intake and reduced lifespan
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Data from: Lack of perceived sperm competition risk increases post-copulatory song in Pacific field crickets
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Data from: Does the risk of sperm competition help explain cooperation between reproductive competitors? A study in the ocellated wrasse (Symphodus ocellatus)
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Male age alone predicts paternity success under sperm competition when effects of age and past mating effort are experimentally separated
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Data from: Extensive variation in sperm morphology in a frog with no sperm competition
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Data from: Assessing risks of invasion through gamete performance: farm Atlantic salmon sperm and eggs show equivalence in function, fertility, compatibility and competitiveness to wild Atlantic salmon
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Data from: No support for the sexy‐sperm hypothesis in the seed beetle: sons of monandrous females fare better in post‐copulatory competition
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Data from: Polyandrous females provide sons with more competitive sperm: support for the sexy-sperm hypothesis in the rattlebox moth (Utetheisa ornatrix)
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Males adjust their manipulation of female remating in response to sperm competition risk
<p>To reduce the potential for sperm competition, male insects are thought to inhibit the post-mating reproductive behaviour of females through receptivity inhibiting compounds transferred in the ejaculate. Selection is expected to favour phenotypic plasticity in male post-copulatory expenditure, with males investing strategically in response to their perceived risk of sperm competition. However, the impact that socially cued strategic allocation might have on female post-mating behaviour has rarely been assessed. Here, we varied male perception of sperm competition risk, both prior to and during mating, to determine if a male's competitive environment impacts the extent to which he manipulates female remating behaviour. We found that female Australian field crickets<i> </i>(<i>Teleogryllus oceanicus</i>) mated to males that were reared under sperm competition risk emerged from a shelter in search of male song sooner than did females mated to males reared without risk, but only when mating occured in a risk free environment. We also found that females reared in a silent environment where potential mates were scarce displayed greater post-mating mate searching behaviour than females exposed to male calls during development. Collectively, our findings suggest complex interacting effects of male and female sociosexual environments on female post-mating sexual receptivity.</p>
Data from: Sperm competition games: a general model for pre-copulatory male-male competition
Reproductive males face a trade-off between expenditure on pre-copulatory male-male competition – increasing the number of females that they secure as mates – and sperm competition – increasing their fertilisation success with those females. Previous sperm allocation models have focused on scramble competition in which males compete by searching for mates and the number of matings rises linearly with pre-copulatory expenditure. However, recent studies have emphasised contest competition involving pre-copulatory expenditure on armaments, where winning contests may be highly dependent on marginal increases in relative armament level. Here we develop a general model of sperm allocation that allows us to examine the effect of all forms of pre-copulatory competition on sperm allocation patterns. The model predicts that sperm allocation decreases if either the 'mate-competition loading', a, or the number of males competing for each mating, M, increases. Other predictions remain unchanged from previous models: (i) expenditure per ejaculate should increase and then decrease, and (ii) total post-copulatory expenditure should increase, as the level of sperm competition increases. A negative correlation between a and M is biologically plausible, and may buffer deviations from the previous models. There is some support for our predictions from comparative analyses across dung beetle species and frog populations.
Data from: Artificial selection on walking distance suggests a mobility-sperm competitiveness trade-off
Securing matings is a key determinant of fitness and in many species males are the sex that engages in mate searching. Searching for mates is often associated with increased mobility. This elevated investment in movement is predicted to trade-off with sperm competitiveness, but few studies have directly tested whether this trade-off occurs. Here, we assessed whether artificial selection on mobility affected sperm competitiveness and mating behavior, and if increased mobility was due to increased leg length in red flour beetles (Tribolium castaneum). We found that in general, males selected for decreased mobility copulated for longer, stimulated females more during mating and tended to be better sperm competitors. Surprisingly, they also had longer legs. However, how well males performed in sperm competition depended on females. Males with reduced mobility always copulated for longer than males with high mobility, but this only translated into greater fertilization success in females from control populations and not the selection populations (treatment females). These results are consistent with a mate-searching/mating-duration trade-off and broadly support a trade-off between mobility and sperm competiveness.
Data from: No association between sperm competition and sperm length variation across dung flies (Scathophagidae)
Sperm length is extremely variable across species, but a general explanation for this variation is lacking. However, when the risk of sperm competition is high, sperm length is predicted to be less variable within species, and there is some evidence for this in birds and social insects. Here, we examined intraspecific variation in sperm length, both within and between males, and its potential associations with sperm competition risk and variation in female reproductive tract morphology across dung flies. We used two measures of variation in sperm size, and testis size was employed as our index of sperm competition risk. We found no evidence of associations between sperm length variation and sperm competition or female reproductive tract variation. These results suggest that variation in sperm competition risk may not always be associated with variation in sperm morphology, and the cause(s) of sperm length variation in dung flies remains unclear.
Data from: Male responses to sperm competition risk when rivals vary in their number and familiarity
Males of many species adjust their reproductive investment to the number of rivals present simultaneously. However, few studies have investigated whether males sum previous encounters with rivals, and the total level of competition has never been explicitly separated from social familiarity. Social familiarity can be an important component of kin recognition and has been suggested as a cue that males use to avoid harming females when competing with relatives. Previous work has succeeded in independently manipulating social familiarity and relatedness among rivals, but experimental manipulations of familiarity are confounded with manipulations of the total number of rivals that males encounter. Using the seed beetle Callosobruchus maculatus we manipulated three factors: familiarity among rival males, the number of rivals encountered simultaneously, and the total number of rivals encountered over a 48-hour period. Males produced smaller ejaculates when exposed to more rivals in total, regardless of the maximum number of rivals they encountered simultaneously. Males did not respond to familiarity. Our results demonstrate that males of this species can sum the number of rivals encountered over separate days, and therefore the confounding of familiarity with the total level of competition in previous studies should not be ignored.
Data from: Feed-backs among inbreeding, inbreeding depression in sperm traits and sperm competition can drive evolution of costly polyandry
Ongoing ambitions are to understand the evolution of costly polyandry and its consequences for species ecology and evolution. Emerging patterns could stem from feed-back dynamics between the evolving mating system and its genetic environment, defined by interactions among kin including inbreeding. However, such feed-backs are rarely considered in non-selfing systems. We use a genetically-explicit model to demonstrate a mechanism by which inbreeding depression can select for polyandry to mitigate the negative consequences of mating with inbred males rather than avoiding inbreeding. Specifically, given inbreeding depression in sperm traits, costly polyandry evolved to ensure female fertility, without requiring explicit inbreeding avoidance. We show the mechanisms behind two main feed-backs. First, resulting sperm competition caused evolution of sperm traits and further mitigated the negative effect of inbreeding depression on female fertility. Second, the evolving mating system fed back to decrease population-wide homozygosity, and hence inbreeding. However, net overall reduction was small due to compound effects on the variances in sex-specific reproductive success and paternity skew. Purging of deleterious mutations did not eliminate inbreeding depression in sperm traits and hence selection for polyandry. Polyandry evolution, both directly and through sperm competition, might consequently facilitate evolutionary rescue for populations experiencing sudden increases in inbreeding.
Data from: A competitive environment influences sperm production, but not testes tissue composition, in house mice
Due to the physiological cost of sperm production, males are expected to be prudent in their expenditure and adjust their investment according to current social conditions. Strategic adjustments in sperm expenditure during development can be made via changes in testes size, sperm production rates, or testes tissue composition. Here, using house mice, we test the hypothesis that elevated sperm production is driven by a plastic response in the spatial organisation of the testes. We reared males under different social conditions (competitive vs. non-competitive) and quantified sperm number and the proportion of sperm‐producing tissue within the testes. Further, because sperm quality is a critical determinant of competitive fertilization success, we used computer-assisted sperm analysis to quantify six sperm motility traits. Our investigation revealed that males reared in an environment with a perceived risk of reproductive competition produced more sperm in the absence of changes in testes morphology. We discuss this result in relation to fixed and flexible phenotypically plastic responses to future competitive conditions, and conclude that adaptive adjustments in sperm number in response to the social environment are likely attributable to variation in sperm production rate. Further, we found no difference in in vitro sperm motility parameters among males from the different social environment regimes. Overall, this investigation improves our understanding of the mechanisms of male plastic responses to reproductive competition experienced during sexual development.
Data from: Sperm competitive ability evolves in response to experimental alteration of operational sex ratio
In naturally polygamous organisms such as Drosophila, sperm competitive ability is one of the most important components of male fitness and is expected to evolve in response to varying degrees of male–male competition. Several studies have documented the existence of ample genetic variation in sperm competitive ability of males. However, many experimental evolution studies have found sperm competitive ability to be unresponsive to selection. Even direct selection for increased sperm competitive ability has failed to yield any measurable changes. Here we report the evolution of sperm competitive ability (sperm defense-P1, offense-P2) in a set of replicate populations of Drosophila melanogaster subjected to altered levels of male–male competition (generated by varying the operational sex ratio) for 55–60 generations. Males from populations with female-biased operational sex ratio evolved reduced P1 and P2, without any measurable change in the male reproductive behavior. Males in the male-biased regime evolved increased P1, but there was no significant change in P2. Increase in P1 was associated with an increase in copulation duration, possibly indicating greater ejaculate investment by these males. This study is one of the few to provide empirical evidence for the evolution of sperm competitive ability of males under different levels of male–male competition.
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