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Leigh W. Simmons - One of the best experts on this subject based on the ideXlab platform.
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socially cued seminal fluid gene expression mediates responses in ejaculate quality to Sperm Competition risk
Proceedings of The Royal Society B: Biological Sciences, 2017Co-Authors: Leigh W. Simmons, Maxine LovegroveAbstract:There is considerable evidence that males will increase the number of Sperm ejaculated in response to Sperm Competition risk. However, whether they have the capacity to adjust seminal fluid components of the ejaculate has received less attention. Male crickets ( Teleogryllus oceanicus ) have been shown to adjust the viability of Sperm in their ejaculate in response to Sperm Competition risk. Here we show that socially mediated plasticity in Sperm viability is probably due, at least in part, to male adjustments in the protein composition of the seminal fluid. Seven seminal fluid protein genes were found to have an increased expression in males exposed to rival calls. Increased expression of these genes was correlated with increased Sperm viability in whole ejaculates, and gene knockdown confirmed that at least one of these proteins promotes Sperm viability. Our results lend support for recent theoretical models that predict complex responses in male allocation to seminal fluid composition in response to Sperm Competition risk.
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Sperm Competition and the evolution of precopulatory weapons increasing male density promotes Sperm Competition and reduces selection on arm strength in a chorusing frog
Evolution, 2015Co-Authors: Bruno A Buzatto, Dale J Roberts, Leigh W. SimmonsAbstract:Sperm Competition theory assumes a trade-off between precopulatory traits that increase mating success and postcopulatory traits that increase fertilization success. Predictions for how Sperm Competition might affect male expenditure on these traits depend on the number of competing males, the advantage gained from expenditure on weapons, and the level of Sperm Competition. However, empirical tests of Sperm Competition theory rarely examine precopulatory male expenditure. We investigated how variation in male density affects precopulatory sexual selection on male weaponry and the level of Sperm Competition in the chorusing frog Crinia georgiana, where males use their arms as weapons in male-male combat. We measured body size and arm girth of 439 males, and recorded their mating success in the field. We found density-dependent selection acting on arm girth. Arm girth was positively associated with mating success, but only at low population densities. Increased male density was associated with higher risk and intensity of Sperm Competition arising from multimale amplexus, and a reversal in the direction of selection on arm girth. Opposing patterns of pre- and postcopulatory selection may account for the negative covariation between arm girth and testes across populations of this species.
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acoustic cues alter perceived Sperm Competition risk in the field cricket teleogryllus oceanicus
Behavioral Ecology, 2013Co-Authors: Brian Gray, Leigh W. SimmonsAbstract:Sperm Competition game theory predicts that males should respond to increasing Sperm Competition risk by increasing ejaculate expenditure. There is considerable support for this prediction from a diverse range of taxa. However, the cues males use to assess risk and the fitness returns for strategic ejaculation are less well understood. We explored the role of acoustic cues in the assessment of Sperm Competition risk by manipulating male experience of acoustically signaling conspecifics in the field cricket Teleogryllus oceanicus. Compared with males reared in acoustic isolation, males reared in song-dense environments mimicking a high Sperm Competition risk produced ejaculates with a greater percentage of viable Sperm. However, acoustic experience had only a weak and nonsignificant effect on competitive fertilization success. We argue that female influences on paternity are likely to have a strong moderating effect on male fitness returns from prudent allocation and call for more studies that address the consequences of strategic ejaculation for male fitness.
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male derived cuticular hydrocarbons signal Sperm Competition intensity and affect ejaculate expenditure in crickets
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Melissa L Thomas, Leigh W. SimmonsAbstract:Female sexual promiscuity can have significant effects on male mating decisions because it increases the intensity of Competition between ejaculates for fertilization. Because Sperm production is costly, males that can detect multiple matings by females and allocate Sperm strategically will have an obvious fitness advantage. The presence of rival males is widely recognized as a cue used by males to assess Sperm Competition. However, for species in which males neither congregate around nor guard females, other more cryptic cues might be involved. Here, we demonstrate unprecedented levels of Sperm Competition assessment by males, which is mediated via the use of chemical cues. Using the cricket Teleogryllus oceanicus, we manipulated male perception of Sperm Competition by experimentally coating live unmated females with cuticular compounds extracted from males. We found that males adjusted their ejaculate allocation in response to these compounds: the viability of Sperm contained within a male's ejaculate decreased as the number of male extracts applied to his virgin female partner was increased. We further show that males do not respond to the relative concentration of male compounds present on females, but rather to the number of distinct signature odours of individual males. Our results conform to Sperm Competition theory, and show for the first time, to our knowledge, that males can detect different intensities of Sperm Competition by using distinct chemical cues of individual males present on females.
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Sperm Competition linking form to function
BMC Evolutionary Biology, 2008Co-Authors: Stuart Humphries, Jonathan P Evans, Leigh W. SimmonsAbstract:Background Using information from physics, biomechanics and evolutionary biology, we explore the implications of physical constraints on Sperm performance, and review empirical evidence for links between Sperm length and Sperm Competition (where two or more males compete to fertilise a female's eggs). A common theme in the literature on Sperm Competition is that selection for increased Sperm performance in polyandrous species will favour the evolution of longer, and therefore faster swimming, Sperm. This argument is based on the common assumption that Sperm swimming velocity is directly related to Sperm length, due to the increased thrust produced by longer flagella.
Eduardo R S Roldan - One of the best experts on this subject based on the ideXlab platform.
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Sperm Competition and the evolution of Sperm design in mammals
2020Co-Authors: Maximiliano Tourmente, Montserrat Gomendio, Eduardo R S RoldanAbstract:Abstract Background: The influence of Sperm Competition upon Sperm size has been a controversial issue during the last 20 years which remains unresolved for mammals. The hypothesis that, when ejaculates compete with rival males, an increase in Sperm size would make Sperm more competitive because it would increase Sperm swimming speed, has generated contradictory results from both theoretical and empirical studies. In addition, the debate has extended to which Sperm components should increase in size: the midpiece to accommodate more mitochondria and produce more energy to fuel motility, or the principal piece to generate greater propulsion forces. Results: In this study we examined the influence of Sperm Competition upon Sperm design in mammals using a much larger data set (226 species) than in previous analyses, and we corrected for phylogenetic effects by using a more complete and resolved phylogeny, and more robust phylogenetic control methods. Our results show that, as Sperm Competition increases, all Sperm components increase in an integrated manner and Sperm heads become more elongated. The increase in Sperm length was found to be associated with enhanced swimming velocity, an adaptive trait under Sperm Competition. Conclusions: We conclude that Sperm Competition has played an important role in the evolution of Sperm design in mammals, and discuss why previous studies have failed to detect it
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faster and more efficient swimming energy consumption of murine Spermatozoa under Sperm Competition
Biology of Reproduction, 2019Co-Authors: Maximiliano Tourmente, Maria Vareasanchez, Eduardo R S RoldanAbstract:ATP supply is essential for Sperm performance and increases in ATP content coevolve with enhanced Sperm swimming velocity as a response to Sperm Competition in rodents. ATP content is the balance between production and consumption but, although ATP production has received much attention, little is known about ATP consumption. The rate of ATP consumption is crucial for the propagation of the flagellar wave, becoming a main determinant of the time and distance Sperm could move before exhausting their reserves. A high yield in distance per unit of ATP consumed (efficiency) could provide advantages in Sperm Competition. We characterized Sperm ATP consumption rate in a group of mouse species with different Sperm Competition levels to understand its impact on swimming velocity, duration, and yield of Sperm ATP reserves. Interspecific comparisons revealed that Sperm of species with higher Sperm Competition levels had high ATP consumption rates and faster swimming velocity. Moreover, Sperm that consumed ATP at a faster rate swam more efficiently, since they were able to cover more distance per unit of ATP consumed. Our results suggest that by coupling the advantages of higher ATP turnover rates to increased efficiency of ATP expenditure, Sperm would respond to increasingly competitive environments while maintaining a positive ATP balance.
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Sperm Competition Sperm numbers and Sperm quality in muroid rodents
PLOS ONE, 2011Co-Authors: Laura Gomez Montoto, Concepcion Magana, Maximiliano Tourmente, Juan Martincoello, C Crespo, Juan Jose Luquelarena, Montserrat Gomendio, Eduardo R S RoldanAbstract:Sperm Competition favors increases in relative testes mass and production efficiency, and changes in Sperm phenotype that result in faster swimming speeds. However, little is known about its effects on traits that contribute to determine the quality of a whole ejaculate (i.e., proportion of motile, viable, morphologically normal and acrosome intact Sperm) and that are key determinants of fertilization success. Two competing hypotheses lead to alternative predictions: (a) Sperm quantity and quality traits co-evolve under Sperm Competition because they play complementary roles in determining ejaculate's competitive ability, or (b) energetic constraints force trade-offs between traits depending on their relevance in providing a competitive advantage. We examined relationships between Sperm Competition levels, Sperm quantity, and traits that determine ejaculate quality, in a comparative study of 18 rodent species using phylogenetically controlled analyses. Total Sperm numbers were positively correlated to proportions of normal Sperm, acrosome integrity and motile Sperm; the latter three were also significantly related among themselves, suggesting no trade-offs between traits. In addition, testes mass corrected for body mass (i.e., relative testes mass), showed a strong association with Sperm numbers, and positive significant associations with all Sperm traits that determine ejaculate quality with the exception of live Sperm. An "overall Sperm quality" parameter obtained by principal component analysis (which explained 85% of the variance) was more strongly associated with relative testes mass than any individual quality trait. Overall Sperm quality was as strongly associated with relative testes mass as Sperm numbers. Thus, Sperm quality traits improve under Sperm Competition in an integrated manner suggesting that a combination of all traits is what makes ejaculates more competitive. In evolutionary terms this implies that a complex network of genetic and developmental pathways underlying processes of Sperm formation, maturation, transport in the female reproductive tract, and preparation for fertilization must all evolve in concert.
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Sperm Competition and the evolution of Sperm design in mammals
BMC Evolutionary Biology, 2011Co-Authors: Maximiliano Tourmente, Montserrat Gomendio, Eduardo R S RoldanAbstract:The influence of Sperm Competition upon Sperm size has been a controversial issue during the last 20 years which remains unresolved for mammals. The hypothesis that, when ejaculates compete with rival males, an increase in Sperm size would make Sperm more competitive because it would increase Sperm swimming speed, has generated contradictory results from both theoretical and empirical studies. In addition, the debate has extended to which Sperm components should increase in size: the midpiece to accommodate more mitochondria and produce more energy to fuel motility, or the principal piece to generate greater propulsion forces. In this study we examined the influence of Sperm Competition upon Sperm design in mammals using a much larger data set (226 species) than in previous analyses, and we corrected for phylogenetic effects by using a more complete and resolved phylogeny, and more robust phylogenetic control methods. Our results show that, as Sperm Competition increases, all Sperm components increase in an integrated manner and Sperm heads become more elongated. The increase in Sperm length was found to be associated with enhanced swimming velocity, an adaptive trait under Sperm Competition. We conclude that Sperm Competition has played an important role in the evolution of Sperm design in mammals, and discuss why previous studies have failed to detect it.
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Sperm Competition promotes asymmetries in reproductive barriers between closely related species
Evolution, 2009Co-Authors: Juan Martincoello, Montserrat Gomendio, Eduardo R S Roldan, Jose BenaventcoraiAbstract:Reproductive barriers between closely related species are often incomplete and asymmetric, but the evolutionary significance of these well-known phenomena remains unsolved. We test the hypothesis that the degree of gametic incompatibility in reciprocal crosses is associated to levels of Sperm Competition because this selective force favors both increased Sperm competitiveness and ovum defensiveness. Using three species of Mus with high, intermediate, and low levels of Sperm Competition, we examined fertilization rates in competitive and noncompetitive contexts. We found that the influence of Sperm Competition upon Sperm competitiveness is as strong as it is upon ovum defensiveness, revealing an effect upon female gametes so far overlooked. As a result, fertilization success was strongly related to differences in Sperm Competition levels between species providing Sperm and ova, thus generating major asymmetries in reciprocal crosses. When placed in Competition, conspecific Sperm maintained levels of fertilization success similar to those found in noncompetitive contexts, at the expense of the success of heterospecific Sperm. When only heterospecific Sperm competed, species with highest levels of Sperm Competition outcompeted others and asymmetries were exacerbated. We conclude that Sperm Competition explains both the degree of gametic isolation and the degree of asymmetries between closely related species.
Paula Stockley - One of the best experts on this subject based on the ideXlab platform.
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Sperm Competition risk drives plasticity in seminal fluid composition
BMC Biology, 2015Co-Authors: Steven A. Ramm, Dominic A Edward, Amy J Claydon, Dean E Hammond, Philip Brownridge, Jane L Hurst, Robert J Beynon, Paula StockleyAbstract:Ejaculates contain a diverse mixture of Sperm and seminal fluid proteins, the combination of which is crucial to male reproductive success under competitive conditions. Males should therefore tailor the production of different ejaculate components according to their social environment, with particular sensitivity to cues of Sperm Competition risk (i.e. how likely it is that females will mate promiscuously). Here we test this hypothesis using an established vertebrate model system, the house mouse (Mus musculus domesticus), combining experimental data with a quantitative proteomics analysis of seminal fluid composition. Our study tests for the first time how both Sperm and seminal fluid components of the ejaculate are tailored to the social environment. Our quantitative proteomics analysis reveals that the relative production of different proteins found in seminal fluid – i.e. seminal fluid proteome composition – differs significantly according to cues of Sperm Competition risk. Using a conservative analytical approach to identify differential expression of individual seminal fluid components, at least seven of 31 secreted seminal fluid proteins examined showed consistent differences in relative abundance under high versus low Sperm Competition conditions. Notably three important proteins with potential roles in Sperm Competition – SVS 6, SVS 5 and CEACAM 10 – were more abundant in the high Competition treatment groups. Total investment in both Sperm and seminal fluid production also increased with cues of heightened Sperm Competition risk in the social environment. By contrast, relative investment in different ejaculate components was unaffected by cues of mating opportunities. Our study reveals significant plasticity in different ejaculate components, with the production of both Sperm and non-Sperm fractions of the ejaculate strongly influenced by the social environment. Sperm Competition risk is thus shown to be a key factor in male ejaculate production decisions, including driving plasticity in seminal fluid composition.
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Sperm Competition and Sperm length influence the rate of mammalian Spermatogenesis
Biology Letters, 2010Co-Authors: Steven A. Ramm, Paula StockleyAbstract:Sperm Competition typically favours an increased investment in testes, because larger testes can produce more Sperm to provide a numerical advantage in Competition with rival ejaculates. However, interspecific variation in testis size cannot be equated directly with variation in Sperm production rate—which is the trait ultimately selected under Sperm Competition—because there are also differences between species in the proportion of Spermatogenic tissue contained within the testis and in the time it takes to produce each Sperm. Focusing on the latter source of variation, we provide phylogenetically controlled evidence for mammals that species with relatively large testes (and hence a high level of Sperm Competition) have a shorter duration of the cycle of the seminiferous epithelium and consequently a faster rate of Spermatogenesis, enabling males to produce more Sperm per unit testis per unit time. Moreover, we identify an independent negative relationship between Sperm length and the rate of Spermatogenesis, such that Spermatogenesis takes longer in species with longer Sperm. We conclude that Sperm Competition selects for both larger testes and a faster rate of Spermatogenesis to increase overall Sperm production, and that an evolutionary trade-off between Sperm size and numbers may be mediated via constraints on the rate of Spermatogenesis imposed by selection for longer Sperm.
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Sperm Competition and the evolution of male reproductive anatomy in rodents
Proceedings of The Royal Society B: Biological Sciences, 2005Co-Authors: Steven A. Ramm, Geoffrey Parker, Paula StockleyAbstract:Sperm Competition is a pervasive selective force in evolution, shaping reproductive anatomy, physiology and behaviour. Here, we present comparative evidence that varying Sperm Competition levels account for variation in the male reproductive anatomy of rodents, the largest and most diverse mammalian order. We focus on the Sperm-producing testes and the accessory reproductive glands, which produce the seminal fluid fraction of the ejaculate. We demonstrate a positive association between relative testis size and the prevalence of within-litter multiple paternity, consistent with previous analyses in which relative testis size has been found to correlate with Sperm Competition levels inferred from social organization and mating systems. We further demonstrate an association between Sperm Competition level and the relative size of at least two accessory reproductive glands: the seminal vesicles and anterior prostate. The size of the major product of these glands—the copulatory plug—is also found to vary with Sperm Competition level. Our findings thus suggest that selection for larger plugs under Sperm Competition may explain variation in accessory gland size, and highlight the need to consider both Sperm and non-Sperm components of the male ejaculate in the context of post-copulatory sexual selection.
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Sperm Competition in fishes the evolution of testis size and ejaculate characteristics
The American Naturalist, 1997Co-Authors: Paula Stockley, Matthew J G Gage, G A Parker, Anders Pape MollerAbstract:Fishes show one of the widest ranges of Sperm Competition intensity of any animal group. Here we present a comparative study whose aim is to investigate the effect of relative intensity of Sperm Competition on investment in Spermatogenesis and the number and size of Sperm produced. We find that both the gonadosomatic index (GSI5 (gonad weight/body weight) 3 100) and Sperm numbers increase with intensity of Sperm Competition across species but that Sperm length decreases. These new findings are consistent with a raffle-based mode of Sperm Competition in fishes. Most of these results (positive correlation of the GSI and Sperm number with Sperm Competition intensity) concur with the predictions of current Sperm Competition the- ory. However, we also find that Sperm longevity decreases with Sperm length across species. Cur- rent models for continuous fertilization suggest that if length increases a Sperm's speed but de- creases its longevity, Sperm length should increase with Sperm Competition intensity, whereas models for instant fertilization suggest that Sperm length should remain constant. The negative relationship found between Sperm Competition and Sperm length therefore does not fit predictions of either model.
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sexual conflict resulting from adaptations to Sperm Competition
Trends in Ecology and Evolution, 1997Co-Authors: Paula StockleyAbstract:Abstract Recent research on diverse animal taxa has revealed that male adaptations to Sperm Competition often lead to a conflict with female interests. That is, male attempts to increase their own fertilization success can result in a reduction of female fitness. This sexual conflict has led to selection for a variety of female adaptations that apparently reduce male-imposed costs. Understanding the causes and consequences of sexual conflict arising from adaptations to Sperm Competition offers much potential for new insight into the coevolution of male and female sexual strategies.
Montserrat Gomendio - One of the best experts on this subject based on the ideXlab platform.
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Sperm Competition and the evolution of Sperm design in mammals
2020Co-Authors: Maximiliano Tourmente, Montserrat Gomendio, Eduardo R S RoldanAbstract:Abstract Background: The influence of Sperm Competition upon Sperm size has been a controversial issue during the last 20 years which remains unresolved for mammals. The hypothesis that, when ejaculates compete with rival males, an increase in Sperm size would make Sperm more competitive because it would increase Sperm swimming speed, has generated contradictory results from both theoretical and empirical studies. In addition, the debate has extended to which Sperm components should increase in size: the midpiece to accommodate more mitochondria and produce more energy to fuel motility, or the principal piece to generate greater propulsion forces. Results: In this study we examined the influence of Sperm Competition upon Sperm design in mammals using a much larger data set (226 species) than in previous analyses, and we corrected for phylogenetic effects by using a more complete and resolved phylogeny, and more robust phylogenetic control methods. Our results show that, as Sperm Competition increases, all Sperm components increase in an integrated manner and Sperm heads become more elongated. The increase in Sperm length was found to be associated with enhanced swimming velocity, an adaptive trait under Sperm Competition. Conclusions: We conclude that Sperm Competition has played an important role in the evolution of Sperm design in mammals, and discuss why previous studies have failed to detect it
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Sperm Competition Sperm numbers and Sperm quality in muroid rodents
PLOS ONE, 2011Co-Authors: Laura Gomez Montoto, Concepcion Magana, Maximiliano Tourmente, Juan Martincoello, C Crespo, Juan Jose Luquelarena, Montserrat Gomendio, Eduardo R S RoldanAbstract:Sperm Competition favors increases in relative testes mass and production efficiency, and changes in Sperm phenotype that result in faster swimming speeds. However, little is known about its effects on traits that contribute to determine the quality of a whole ejaculate (i.e., proportion of motile, viable, morphologically normal and acrosome intact Sperm) and that are key determinants of fertilization success. Two competing hypotheses lead to alternative predictions: (a) Sperm quantity and quality traits co-evolve under Sperm Competition because they play complementary roles in determining ejaculate's competitive ability, or (b) energetic constraints force trade-offs between traits depending on their relevance in providing a competitive advantage. We examined relationships between Sperm Competition levels, Sperm quantity, and traits that determine ejaculate quality, in a comparative study of 18 rodent species using phylogenetically controlled analyses. Total Sperm numbers were positively correlated to proportions of normal Sperm, acrosome integrity and motile Sperm; the latter three were also significantly related among themselves, suggesting no trade-offs between traits. In addition, testes mass corrected for body mass (i.e., relative testes mass), showed a strong association with Sperm numbers, and positive significant associations with all Sperm traits that determine ejaculate quality with the exception of live Sperm. An "overall Sperm quality" parameter obtained by principal component analysis (which explained 85% of the variance) was more strongly associated with relative testes mass than any individual quality trait. Overall Sperm quality was as strongly associated with relative testes mass as Sperm numbers. Thus, Sperm quality traits improve under Sperm Competition in an integrated manner suggesting that a combination of all traits is what makes ejaculates more competitive. In evolutionary terms this implies that a complex network of genetic and developmental pathways underlying processes of Sperm formation, maturation, transport in the female reproductive tract, and preparation for fertilization must all evolve in concert.
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Sperm Competition and the evolution of Sperm design in mammals
BMC Evolutionary Biology, 2011Co-Authors: Maximiliano Tourmente, Montserrat Gomendio, Eduardo R S RoldanAbstract:The influence of Sperm Competition upon Sperm size has been a controversial issue during the last 20 years which remains unresolved for mammals. The hypothesis that, when ejaculates compete with rival males, an increase in Sperm size would make Sperm more competitive because it would increase Sperm swimming speed, has generated contradictory results from both theoretical and empirical studies. In addition, the debate has extended to which Sperm components should increase in size: the midpiece to accommodate more mitochondria and produce more energy to fuel motility, or the principal piece to generate greater propulsion forces. In this study we examined the influence of Sperm Competition upon Sperm design in mammals using a much larger data set (226 species) than in previous analyses, and we corrected for phylogenetic effects by using a more complete and resolved phylogeny, and more robust phylogenetic control methods. Our results show that, as Sperm Competition increases, all Sperm components increase in an integrated manner and Sperm heads become more elongated. The increase in Sperm length was found to be associated with enhanced swimming velocity, an adaptive trait under Sperm Competition. We conclude that Sperm Competition has played an important role in the evolution of Sperm design in mammals, and discuss why previous studies have failed to detect it.
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Sperm Competition promotes asymmetries in reproductive barriers between closely related species
Evolution, 2009Co-Authors: Juan Martincoello, Montserrat Gomendio, Eduardo R S Roldan, Jose BenaventcoraiAbstract:Reproductive barriers between closely related species are often incomplete and asymmetric, but the evolutionary significance of these well-known phenomena remains unsolved. We test the hypothesis that the degree of gametic incompatibility in reciprocal crosses is associated to levels of Sperm Competition because this selective force favors both increased Sperm competitiveness and ovum defensiveness. Using three species of Mus with high, intermediate, and low levels of Sperm Competition, we examined fertilization rates in competitive and noncompetitive contexts. We found that the influence of Sperm Competition upon Sperm competitiveness is as strong as it is upon ovum defensiveness, revealing an effect upon female gametes so far overlooked. As a result, fertilization success was strongly related to differences in Sperm Competition levels between species providing Sperm and ova, thus generating major asymmetries in reciprocal crosses. When placed in Competition, conspecific Sperm maintained levels of fertilization success similar to those found in noncompetitive contexts, at the expense of the success of heterospecific Sperm. When only heterospecific Sperm competed, species with highest levels of Sperm Competition outcompeted others and asymmetries were exacerbated. We conclude that Sperm Competition explains both the degree of gametic isolation and the degree of asymmetries between closely related species.
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implications of diversity in Sperm size and function for Sperm Competition and fertility
The International Journal of Developmental Biology, 2008Co-Authors: Montserrat Gomendio, Eduardo R S RoldanAbstract:Sperm Competition is now recognised as a potent selective force shaping many male reproductive traits. While the influence of Sperm Competition on Sperm number is widely accepted, its effects upon Sperm size remain controversial. It had been traditionally assumed that there is a trade-off between Sperm number and Sperm size, so that an increase in Sperm number would result in a decrease in Sperm size, under conditions of Sperm Competition. Contrary to this prediction, we proposed some time ago that Sperm Competition favours an increase in Sperm size, because longer Sperm swim faster and are more likely to win the race to fertilize ova. Comparative studies between species show that in many taxa such a relationship exists, but the consequences of an increase in Sperm size may vary between taxa depending on the environment in which Spermatozoa have to compete. We present new evidence showing that in mammals longer Sperm swim at higher speeds. We also show that mean swimming speed is highly correlated with maximum swimming speed, so even if the fastest swimming Sperm are more likely to fertilize, both measures are informative. When individuals of the same species are compared, ratios between the dimensions of different Sperm components, as well as the shape of the head, seem better at explaining Sperm swimming velocity. Finally, we show that mean and maximum Sperm swimming speed determine male fertility. Other studies have shown that in competitive contexts, males with faster swimming Sperm have higher fertilization success. We conclude that the available evidence supports our original hypothesis.
Andrea Pilastro - One of the best experts on this subject based on the ideXlab platform.
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Sperm number and velocity affect Sperm Competition success in the guppy poecilia reticulata
Behavioral Ecology and Sociobiology, 2011Co-Authors: Chiara Boschetto, Clelia Gasparini, Andrea PilastroAbstract:While both Sperm number and quality are now recognized to be important in determining the outcome of Sperm Competition, very few studies have experimentally assessed the influence of these two parameters simultaneously. We studied the effect of Sperm quality and number on competitive fertilization success in an internal-fertilizing fish, the guppy (Poecilia reticulata), which is characterized by high levels of Sperm Competition. We artificially inseminated virgin females with varying proportion of Sperm from two competing males, while holding constant the total number of Sperm transferred to the female. Sperm morphology and Sperm swimming velocity were also determined prior to insemination. The paternity outcome of Sperm Competition trials was assessed through molecular analyses of the resulting offspring using polymorphic microsatellite loci. We found that both Sperm number and Sperm velocity affected the outcome of Sperm Competition, with males that contributed more and faster Sperm achieving a greater paternity share.
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effect of male age on Sperm traits and Sperm Competition success in the guppy poecilia reticulata
Journal of Evolutionary Biology, 2010Co-Authors: Clelia Gasparini, Chiara Boschetto, Ilaria A M Marino, Andrea PilastroAbstract:Deleterious mutations can accumulate in the germline with age, decreasing the genetic quality of Sperm and imposing a cost on female fitness. If these mutations also affect Sperm Competition ability or Sperm production, then females will benefit from polyandry as it incites Sperm Competition and, consequently, minimizes the mutational load in the offspring. We tested this hypothesis in the guppy (Poecilia reticulata), a species characterized by polyandry and intense Sperm Competition, by investigating whether age affects post-copulatory male traits and Sperm Competition success. Females did not discriminate between old and young males in a mate choice experiment. While old males produced longer and slower Sperm with larger reserves of strippable Sperm, compared to young males, artificial insemination did not reveal any effect of age on Sperm Competition success. Altogether, these results do not support the hypothesis that polyandry evolved in response to costs associated with mating with old males in the guppy.
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individual adjustment of Sperm expenditure accords with Sperm Competition theory
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Andrea Pilastro, Marta Scaggiante, Maria B RasottoAbstract:Sperm Competition theory predicts that males should strategically allocate their Sperm reserves according to the level of Sperm Competition, defined as the probability that the Sperm of two males compete for fertilizing a given set of ova. Substantial evidence from numerous animal taxa suggests that, at the individual level, Sperm expenditure increases when the risk of Sperm Competition is greater. In contrast, according to the “intensity model” of Sperm Competition [Parker, G. A., Ball, M. A., Stockley, P. & Gage, M. J. G. (1996) Proc. R. Soc. London Ser. B 263, 1291–1297], when more than two ejaculates compete during a given mating event, Sperm expenditure should decrease as the number of competing males increases. Empirical evidence supporting this prediction, however, is still lacking. Here we measured Sperm expenditure in two gobiid fishes, the grass (Zosterisessor ophiocephalus) and black goby (Gobius niger), in which up to six sneakers can congregate around the nest of territorial males and release their Sperm when females spawn. We show that, in accordance with theory, sneaker males of both species release fewer Sperm as the number of competitors increases.
