Male sperm expenditure under sperm competition risk and intensity in quacking frogs

In the frog Crinia georgiana, reproductive behavior comprisesa "guarding tactic," in which males defend spawn sites and attractfemales by calling, and a "sneak tactic," in which males joinspawning pairs. The aims of the present study were to (1) relateejaculate expenditure by "guarding" and "sneak" males to theirprobability of mating with other males present (sperm-competitionrisk), and (2) determine if males adjust their ejaculate expenditureaccording to the number of males involved in a spawning (sperm-competitionintensity). Theory predicts that because sneak males alwaysmate with other males present, they will experience a highersperm-competition risk and should release larger ejaculatesrelative to that of guarding males. However, as the proportionof sneaks in a population increases so does the risk of spermcompetition to guarders, so expenditure by each tactic shouldmove toward equality. Given that the incidence of sneak behavioris high in C. georgiana, guarders and sneaks were expected toexperience similar risks of sperm competition and show similarinvestment in spermatogenesis. Comparison of testes size andejaculate size showed no difference between tactics. Modelsof sperm-competition intensity predict that males should increasetheir ejaculate size when spawning in the presence of one othermale but decrease their ejaculate size when spawning in thepresence of multiple males. Here, males maintained a constantsperm number irrespective of whether a mating involved one,two, or three males. This result suggests that male C. georgianado not facultatively adjust ejaculate investment in responseto fluctuating intensities of sperm competition.     

Comparative analysis of macaque and human sperm proteomes: Insights into sperm competition

Male macaques produce faster sperm than male humans due to a higher pressure of sperm competition in macaques. To explore the molecular basis of this biological difference, we firstly constructed macaque and human sperm proteomes using LC?MS/MS. We then detected the positively selected genes specifically on the branch of macaque based on branch‐site likelihood method. We identified 197 positively selected genes specifically on the branch of macaque that are unselected in corresponding human orthologs. These genes are highly associated with mitochondria and axoneme that directly drive sperm motility. We further compared the ultrastructural differences of the midpiece between macaque and human sperms to provide evidence for our findings using transmission electron microscopy. In conclusion, our results provide potential molecular targets for explaining the different phenotypes under sperm competition between macaques and humans, and also provide resources for the analysis of male fertility.     

Sperm competition and sperm precedence in the dragonfly Nanophya pygmaea

Abstract. The libellulid dragonfly, Nanophya pygmaea Rambur, has an average ejaculate volume of 0.16 mm³. During successive copulations the volume of sperm stored in the female's sperm storage organs increases in steps equivalent to this volume, suggesting that the sperm competition mechanism in this species is sperm repositioning, i.e. adding an ejaculate to what is already present in the female's sperm storage organ. By using sterile/normal males in double matings with females we have shown that this mechanism results in last male sperm precedence (P²= 0.979).     

Male mating behavior and ejaculate expenditure under sperm competition risk in the eastern mosquitofish

Theory predicts that males should tailor the size of their ejaculatesaccording to temporal changes in the risk of sperm competition.Specifically, males are predicted to allocate more sperm toeach mating event with increasing risk (i.e., the probabilitythat the sperm from two males will compete for fertilization).We tested this hypothesis by using the eastern mosquitofish,a freshwater species of fish exhibiting a coercive mating systemand internal fertilization. We manipulated the perception ofsperm competition risk by adjusting the sex ratio under whichmales were maintained over 8 days. Males were housed eitherwith three females and one male (simulating high sperm competitionrisk) or with four females (low risk). After the treatment,we presented each test male individually to an unfamiliar male-deprivedfemale for 30 minutes and observed his mating behavior. We thenartificially stripped the test males of sperm and recoveredthe ejaculates from the females. Our results revealed that malesin the high-risk group performed higher levels of mating activityand sperm expenditure (i.e., used up more of their sperm reserves)than did low-risk males. A control experiment, in which testmales were treated but did not participate in the mating trials,revealed no significant difference in the number of sperm strippedfrom high- and low-risk males, indicating that sperm productionwas not affected by the treatment. We did not detect a differencein the number of sperm retrieved from females among the groups,raising the possibility that some sperm are lost during matingactivity, either through ejaculation with incomplete or interruptedpenetration, or via female ejection.     

Characterisation of the Manduca sexta sperm proteome: Genetic novelty underlying sperm composition in Lepidoptera

The application of mass spectrometry based proteomics to sperm biology has greatly accelerated progress in understanding the molecular composition and function of spermatozoa. To date, these approaches have been largely restricted to model organisms, all of which produce a single sperm morph capable of oocyte fertilisation. Here we apply high-throughput mass spectrometry proteomic analysis to characterise sperm composition in Manduca sexta, the tobacco hornworm moth, which produce heteromorphic sperm, including one fertilisation competent (eupyrene) and one incompetent (apyrene) sperm type. This resulted in the high confidence identification of 896 proteins from a co-mixed sample of both sperm types, of which 167 are encoded by genes with strict one-to-one orthology in Drosophila melanogaster. Importantly, over half (55.1%) of these orthologous proteins have previously been identified in the D. melanogaster sperm proteome and exhibit significant conservation in quantitative protein abundance in sperm between the two species. Despite the complex nature of gene expression across spermatogenic stages, a significant correlation was also observed between sperm protein abundance and testis gene expression. Lepidopteran-specific sperm proteins (e.g., proteins with no homology to proteins in non-Lepidopteran taxa) were present in significantly greater abundance on average than those with homology outside the Lepidoptera. Given the disproportionate production of apyrene sperm (96% of all mature sperm in Manduca) relative to eupyrene sperm, these evolutionarily novel and highly abundant proteins are candidates for possessing apyrene-specific functions. Lastly, comparative genomic analyses of testis-expressed, ovary-expressed and sperm genes identified a concentration of novel sperm proteins shared amongst Lepidoptera of potential relevance to the evolutionary origin of heteromorphic spermatogenesis. As the first published Lepidopteran sperm proteome, this whole-cell proteomic characterisation will facilitate future evolutionary genetic and developmental studies of heteromorphic sperm production and parasperm function. Furthermore, the analyses presented here provide useful annotation information regarding sex-biased gene expression, novel Lepidopteran genes and gene function in the male gamete to complement the newly sequenced and annotated Manduca genome.     

Male parasitism and intrasexual competition in a burrowing barnacle

Summary In sexually dimorphic animals, large male body size is often associated with direct interference competition among males for access to females or resources used in reproduction. In constrast, small male body size may be associated with indirect scramble competition among males for temporal or spatial access to females. Minute, “parasitic” males of the acrothoracican barnacleTrypetesa lampas (Hancock) appear to compete with one another for permanent attachment sites on the external body of the female. Several spatial patterns suggest indirect male-male competition: 1) males were consistently aggregated on the anterior surface of the female ovarian disc; 2) the average distance from attached males to the site of insemination correlated positively with local male density; 3) average male body size on a female decreased as a function of male density; 4) the distribution of males on the left and right hand sides of the female ovarian disc was more even than expected, suggesting that males avoided crowded settlement sites. The number of males attached to a female increased with female body size and matched a null model in which males colonized female “targets” of differing areas. These results suggest that competition between males primarily affected settlement sites and male body sizes within, rather than among, females. Male parasitism may have evolved through both sexual selection for efficient access to females (Ghiselin 1974) and natural selection for reduced burrow density in a space-limited habitat (Turner and Yakovlev 1983).     

与哺乳动物精子竞争有关的两种信息输入处理模式

过去的许多研究集中在“输出”或雄性对特定的精子竞争风险(Risks of spermcompetition,RSC)的反应上,对于雄性利用何种类型的信息来估计RSC也有一些研究。相比而言,缺少对于雄性如何处理RSC信息输入从而产生RSC信息输出的研究。本文提出输入信息处理(直接处理与间接处理)的两种模型并提出了检验这两种模型的方法,以便理解雄性如何处理并储存精子竞争风险的有关信息。直接的输入信息处理模型预测,一个雄性个体可能通过生理反应如激素水平的变化来储存RSC的输入信息。只要这种反应处于活动状态,那么雄性个体将处于“精子竞争风险状态”并产生RSC输出(例如,高精子投资)而不是处于非精子竞争输出状态(例如,相对低的精子投资)。间接的输入信息处理模型预测,雄性个体可能在它的记忆中储存与RSC相关的的输入信息,并在其后使用这些信息以调节其输出(例如,精子投资或交配行为)。我们使用能吸引研究者的多学科方法以理解雄性在不同层次对精子竞争的适应,相信对本文提出假说的检验将有助于新的发现以及新假说的发展。     

Women's interest in visual sexual stimuli varies with menstrual cycle phase at first exposure and predicts later interest

This study investigated whether women's interest in visual sexual stimuli varied with their hormonal state. Viewing times of 30 women, 15 normal cycling (NC) and 15 oral contracepting (OC), to sexually explicit photos were measured at three different times. NC women were tested during their menstrual, periovulatory, and luteal phases, and OC women were tested at equivalent temporal intervals. Subjects viewed stimuli as long as desired, thus viewing time measured subject interest. Subjective ratings of stimulus sexual attractiveness were obtained on each test. There was no overall relationship between menstrual cycle phase and viewing time. However the participant's menstrual cycle phase during first exposure to sexual stimuli predicted subsequent interest in sexual stimuli during the next two tests. NC women who first viewed stimuli during their periovulatory phase looked longer at the sexual stimuli across all sessions than did women first tested in their luteal phase. OC women first exposed to the sexual stimuli during menstruation looked longer at the stimuli across all sessions than did OC women first exposed at other test phases. Neither current test phase nor initial cycle phase influenced subjective ratings. Women had increased interest in sexual stimuli across all sessions if first exposed to sexual stimuli when endogenous estrogens were most likely highest. These data suggest that women's interest in visual sexual stimuli is modulated by hormones such that the hormonal condition at first exposure possibly determines the stimuli's emotional valence, markedly affecting subsequent interest in sexual stimuli.     

The ultrastructure of the spermatozoa of Boa constrictor occidentalis, with considerations on its mating system and sperm competition theories

Sperm ultrastructure has been described for several families of Squamata in which it has been considered a valuable character source for phylogenetic studies. However, sperm competition and mating systems have been demonstrated to influence variations in the sperm morphology and dynamics. The mating system of Boa constrictor occidentalis is likely to have a high degree of sperm competition. We investigated, for the first time, the ultrastructure of the spermatozoa of B. c. occidentalis and, thus, of the family Boidae. Active mating groups were captured from the field, and the spermatozoa of the males was collected by ejaculation and processed to obtain transmission electron micrographs and fluorescence micrographs. The spermatozoa are filiform and their morphology fits the general model described for snakes, and several synapomorphies belonging to the squamates can be identified in these cells. Nevertheless, the head is 25% longer and the midpiece presents a lower frequency of mitochondrial transformations than that of other snakes. We propose that this last trait, along with the extraordinary elongation of the midpiece and the system of multilaminar membranes covering this section (both synapomorphies of the snake spermatozoa), are adaptive responses to processes of sperm competition and sperm storage.     

Contest competition and men's facial hair: beards may not provide advantages in combat

In contemporary human societies, where direct male-male competition is reduced compared to ancestral societies, sporting competitions remain an avenue for status acquisition via intra-sexual competition. Beards are the most visually salient and sexually dimorphic of men's secondary sexual traits and play a strong role in communicating masculinity, dominance and aggressiveness intra-sexually. Hypotheses have been advanced that beards provide advantages in intra-sexual combat, as protective organs and honest signals of fighting ability. Here we provide the first test of these hypotheses using data from professional mixed martial arts fighters competing in the Ultimate Fighting Championship. We explored whether secondary sexual traits (height, weight, beardedness), fighting stance (southpaw, orthodox), arm reach and past contest experiences impact on contest outcomes. If beards function as protective organs, bearded fighters should succumb to fewer knock-outs, and hence protection to injuries to the jaw, fewer abrasions and lacerations to the face and brain damage than clean-shaven fighters. Alternatively, if beards signal fighting ability then bearded fighters should win more fights. We found no evidence that beardedness was associated with fewer losses by knock-out or greater fighter ability. While fighters with longer reaches won more fights, neither stance nor past experience influenced fight outcomes. We suggest that beards represent dishonest signals of formidability that may serve to curtail the escalation of intra-sexual conflict through intimidation rather than providing advantages in direct combat.     

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

There are 2 models of male adjustment of sperm investment inthe ejaculate in relation to sperm competition. The "risk model"predicts that as "risk" of sperm competition increases, sperminvestment also increases. This prediction has been supportedin many species, including mammals. The "intensity model" involvesthe number of competing males copulating with the same femaleand predicts that males will allocate the highest sperm investmentat low sperm competition intensity (SCI) and then decreasingsperm investments as SCI increases. Two alternative outcomesare that sperm investment is unaffected by SCI and that sperminvestment increases as SCI increases. There are studies supportingall 3 possible outcomes in relation to SCI but no data on mammals.The present paper presents the first study of SCI in a mammalspecies, the meadow vole, Microtus pennsylvanicus. We used odorsof conspecific males to simulate low and high intensities ofsperm competition. We found that males allocate the highestsperm investment at low SCI and decrease significantly theirsperm investment at high SCI. We also found that males allocatethe lowest sperm investment at low sperm competition risk (SCR)and the highest sperm investment at high SCR. All these resultsagree with current theoretical models of sperm competition.     

Male and female effects on sperm precedence in the giant sperm species <Emphasis Type="Italic">Drosophila bifurca</Emphasis>

Sperm competition is expected to be a driving force in sexual selection. In internally fertilized organisms, it occurs when ejaculates from more than one male are present simultaneously within the female’s reproductive tract. It has been suggested that greater sperm size may improve the competitive ability of sperm, but studies provide contradictory results depending on the species. More recently, the role of females in the evolution of sperm morphology has been pointed out. We investigate here the male and female effects that influence sperm precedence in the giant sperm species, Drosophila bifurca Patterson & Wheeler. Females were mated with two successive males, and the paternity outcomes for both males were analyzed after determining sperm transfer and storage. We found very high values of last male sperm precedence, suggesting a strong interaction between rival sperm. However, the data also indicate high frequencies of removal of the sperm of the first male from the female reproductive tract prior to any interaction with the second male. This implies that successful paternity depends mainly on successful sperm storage. Knowing what happens to the sperm within females appears to be a prerequisite for disentangling post-copulatory sexual interactions between males and females.     

Sperm competition and female procurement of male resources

This study investigates changes in sexual motivation over the duration of a partnership in a population sample stratified by age. The results replicate and extend the findings of a previous study that was based on a sample of college students. In the samples of 30- and 45-year-olds, male sexual motivation remains constant regardless of the duration of the partnership. Female sexual motivation matches male sexual motivation in the first years of the partnership and then steadily decreases. In the sample of 60-year-olds, male sexual motivation always exceeds female sexual motivation, and both are little affected by duration of the partnership. This pattern is clearly evident for some measures of sexual motivation and less so or not at all for others. Interpretations of the current results from social constructivism or from mainstream psychology are difficult to conceive. The results seem more intelligible from an evolutionary perspective as reflections of evolved design for sexual motivation, fine-tuned to the different conditions governing the reproductive success of males and females. In this view male sexual motivation promotes a constant frequency of copulation in order to guard against cuckoldry. Female sexual motivation, in contrast, promotes copulation to solve the adaptive problem of procuring male resources by establishing and maintaining a pair bond. Dr. Dietrich Klusman is a psychologist at the Institute of Medical Psychology, University Clinic Hamburg-Eppendorf, Germany. His research focus is sexual motivation.     

Sexual selection and the evolution of sperm morphology in sharks

Post‐copulatory sexual selection, and sperm competition in particular, is a powerful selective force shaping the evolution of sperm morphology. Although mounting evidence suggests that post‐copulatory sexual selection influences the evolution of sperm morphology among species, recent evidence also suggests that sperm competition influences variation in sperm morphology at the intraspecific level. However, contradictory empirical results and limited taxonomic scope have led to difficulty in assessing the generality of sperm morphological responses to variation in the strength of sperm competition. Here, we use phylogenetically controlled analyses to explore the effects of sperm competition on sperm morphology and variance in sharks, a basal vertebrate group characterized by wide variation in rates of multiple mating by females, and consequently sperm competition risk. Our analyses reveal that shark species experiencing greater levels of sperm competition produce sperm with longer flagella and that sperm flagellum length is less variable in species under higher sperm competition risk. In contrast, neither the length of the sperm head and midpiece nor variation in sperm head and midpiece length was associated with sperm competition risk. Our findings demonstrate that selection influences both the inter‐ and intraspecific variation in sperm morphology and suggest that the flagellum is an important target of sexual selection in sharks. These findings provide important insight into patterns of selection on the ejaculate in a basal vertebrate lineage.     

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

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.     

Effect of exogenous nitric oxide on sperm motility in vitro

Background

Nitric oxide (NO) has been shown to be important in sperm function, and the concentration of NO appears to determine these effects. Studies have demonstrated both positive and negative effects of NO on sperm function, but have not been able to provide a clear link between NO concentration and the extent of exposure to NO. To study the relationship between nitric oxide and sperm capacitation in vitro, and to provide a theoretical basis for the use of NO-related preparations in improving sperm motility for in vitro fertilization, we investigated the effects of NO concentration and time duration at these concentrations on in vitro sperm capacitation in both normal and abnormal sperm groups. We manipulated NO concentrations and the time duration of these concentrations using sodium nitroprusside (an NO donor) and NG-monomethyl-L-argenine (an NO synthase inhibitor).

Results

Compared to the normal sperm group, the abnormal sperm group had a longer basal time to reach the appropriate concentration of NO (p < 0.001), and the duration of time at this concentration was longer for the abnormal sperm group (p < 0.001). Both the basal time and the duration of time were significantly correlated with sperm viability and percentage of progressive sperm (p < 0.001). The experimental group had a significantly higher percentage of progressive sperm than the control group (p < 0.001).

Conclusions

We hypothesize that there is a certain regularity to both NO concentration and its duration of time in regards to sperm capacitation, and that an adequate duration of time at the appropriate NO concentration is beneficial to sperm motility.     

Male crickets adjust ejaculate quality with both risk and intensity of sperm competition

Sperm competition theory predicts that males should increase their expenditure on the ejaculate with increasing risk of sperm competition, but decrease their expenditure with increasing intensity. There is accumulating evidence for sperm competition theory, based on examinations of testes size and/or the numbers of sperm ejaculated. However, recent studies suggest that ejaculate quality can also be subject to selection by sperm competition. We used experimental manipulations of the risk and intensity of sperm competition in the cricket, Teleogryllus oceanicus. We found that males produced ejaculates with a greater percentage of live sperm when they had encountered a rival male prior to mating. However, when mating with a female that presented a high intensity of sperm competition, males did not respond to risk, but produced ejaculates with a reduced percentage of live sperm. Our data suggest that males exhibit a fine-tuned hierarchy of responses to these cues of sperm competition.     

Sexual selection and mate choice in evolutionary psychology

The importance of mate choice and sexual selection has been emphasized by the majority of evolutionary psychologists. This paper assesses three cases of work on mate choice and sexual selection in evolutionary psychology: David Buss on cross-cultural human mate preferences, Randy Thornhill and Steve Gangestad on the link between mate preferences and fluctuating asymmetry, and Geoffrey Miller on the role of Fisher’s runaway process in human evolution. A mixture of conceptual and empirical problems in each case highlights the general weakness of work in evolutionary psychology on these issues.