Male Ejaculate Research Articles

Polygyny in the olive fly—effects on male and female fitness

Polygynous males must balance their limited ejaculate resources between current copulations, with putative future ones. Working on olive flies (Bactrocera oleae), our objectives were to determine (a) how males budget sperm to consecutive copulations, (b) what costs consecutive copulations incur, and (c) how male mating history affects female fecundity, fertility, and longevity. We allowed males to copulate with virgin females on successive days and monitored the fertility and fecundity of these females, and the longevity of both sexes. We found that as males gained sexual experience, latency to mate declined significantly, while copula duration increased. The number of sperm stored by females declined according to the sexual history of her mate—as males gained experience, significantly fewer sperm cells were transferred. Mated males suffered a significant longevity cost compared to virgin ones, but this cost was not compounded by additional matings. Male sexual experience affected both female fecundity and fertility. Furthermore, mating with an experienced male incurred a longevity cost to females. We conclude that non-sperm components of the male ejaculate are responsible for reducing female fecundity, fertility, and longevity, and predict that females should prefer to mate with virgin males.

Dynamic digestive physiology of a female reproductive organ in a polyandrous butterfly.

Reproductive traits experience high levels of selection because of their direct ties to fitness, often resulting in rapid adaptive evolution. Much of the work in this area has focused on male reproductive traits. However, a more comprehensive understanding of female reproductive adaptations and their relationship to male characters is crucial to uncover the relative roles of sexual cooperation and conflict in driving co-evolutionary dynamics between the sexes. We focus on the physiology of a complex female reproductive adaptation in butterflies and moths: a stomach-like organ in the female reproductive tract called the bursa copulatrix that digests the male ejaculate (spermatophore). Little is known about how the bursa digests the spermatophore. We characterized bursa proteolytic capacity in relation to female state in the polyandrous butterfly Pieris rapae. We found that the virgin bursa exhibits extremely high levels of proteolytic activity. Furthermore, in virgin females, bursal proteolytic capacity increases with time since eclosion and ambient temperature, but is not sensitive to the pre-mating social environment. Post copulation, bursal proteolytic activity decreases rapidly before rebounding toward the end of a mating cycle, suggesting active female regulation of proteolysis and/or potential quenching of proteolysis by male ejaculate constituents. Using transcriptomic and proteomic approaches, we report identities for nine proteases actively transcribed by bursal tissue and/or expressed in the bursal lumen that may contribute to observed bursal proteolysis. We discuss how these dynamic physiological characteristics may function as female adaptations resulting from sexual conflict over female remating rate in this polyandrous butterfly.

Sperm Economy between Female Mating Frequency and Male Ejaculate Allocation

Why females of many species mate multiply is a major question in evolutionary biology. Furthermore, if females accept matings more than once, ejaculates from different males compete for fertilization (sperm competition), which confronts males with the decision of how to allocate their reproductive resources to each mating event. Although most existing models have examined either female mating frequency or male ejaculate allocation while assuming fixed levels of the opposite sex's strategies, these strategies are likely to coevolve. To investigate how the interaction of the two sexes' strategies is influenced by the level of sperm limitation in the population, we developed models in which females adjust their number of allowable matings and males allocate their ejaculate in each mating. Our model predicts that females mate only once or less than once at an even sex ratio or in an extremely female-biased condition, because of female resistance and sperm limitation in the population, respectively. However, in a moderately female-biased condition, males favor partitioning their reproductive budgets across many females, whereas females favor multiple matings to obtain sufficient sperm, which contradicts the predictions of most existing models. We discuss our model's predictions and relationships with the existing models and demonstrate applications for empirical findings.

Digestive Organ in the Female Reproductive Tract Borrows Genes from Multiple Organ Systems to Adopt Critical Functions

Persistent adaptive challenges are often met with the evolution of novel physiological traits. Although there are specific examples of single genes providing new physiological functions, studies on the origin of complex organ functions are lacking. One such derived set of complex functions is found in the Lepidopteran bursa copulatrix, an organ within the female reproductive tract that digests nutrients from the male ejaculate or spermatophore. Here, we characterized bursa physiology and the evolutionary mechanisms by which it was equipped with digestive and absorptive functionality. By studying the transcriptome of the bursa and eight other tissues, we revealed a suite of highly expressed and secreted gene products providing the bursa with a combination of stomach-like traits for mechanical and enzymatic digestion of the male spermatophore. By subsequently placing these bursa genes in an evolutionary framework, we found that the vast majority of their novel digestive functions were co-opted by borrowing genes that continue to be expressed in nonreproductive tissues. However, a number of bursa-specific genes have also arisen, some of which represent unique gene families restricted to Lepidoptera and may provide novel bursa-specific functions. This pattern of promiscuous gene borrowing and relatively infrequent evolution of tissue-specific duplicates stands in contrast to studies of the evolution of novelty via single gene co-option. Our results suggest that the evolution of complex organ-level phenotypes may often be enabled (and subsequently constrained) by changes in tissue specificity that allow expression of existing genes in novel contexts, such as reproduction. The extent to which the selective pressures encountered in these novel roles require resolution via duplication and sub/neofunctionalization is likely to be determined by the need for specialized reproductive functionality. Thus, complex physiological phenotypes such as that found in the bursa offer important opportunities for understanding the relative role of pleiotropy and specialization in adaptive evolution.

Long sperm fertilize more eggs in a bird.

Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the zebra finch (Taeniopygia guttata), where sperm size influences sperm swimming velocity, to determine the effect of sperm total length on fertilization success. Sperm competition experiments, in which pairs of males whose sperm differed only in length and swimming speed, revealed that males producing long sperm were more successful in terms of (i) the number of sperm reaching the ova and (ii) fertilizing those ova. Our results reveal that although sperm length is the main factor determining the outcome of sperm competition, complex interactions between male and female reproductive traits may also be important. The mechanisms underlying these interactions are poorly understood, but we suggest that differences in sperm storage and utilization by females may contribute to the outcome of sperm competition.

Variability in sperm form and function in the context of sperm competition risk in two Tupinambis lizards.

In polyandrous species, sperm morphometry and sperm velocity are under strong sexual selection. Although several hypotheses have been proposed to explain the role of sperm competition in sperm trait variation, this aspect is still poorly understood. It has been suggested that an increase in sperm competition pressure could reduce sperm size variation or produce a diversity of sperm to maximize male fertilization success. We aim at elucidating the variability of sperm morphometric traits and velocity in two Tupinambis lizards in the context of sperm competition risk. Sperm traits showed substantial variation at all levels examined: between species, among males within species, and within the ejaculate of individual males. Sperm velocity was found to be positively correlated with flagellum: midpiece ratio, with relatively longer flagella associated with faster sperm. Our results document high variability in sperm form and function in lizards.

Cadherin mutation linked to resistance to Cry1Ac affects male paternity and sperm competition in Helicoverpa armigera

Several lepidopteran pests of cotton have cadherin-based resistance to the Bacillus thuringiensis (Bt) toxin Cry1Ac. Cadherins are transmembrane proteins that mediate cell–cell adhesion and tissue morphogenesis, suggesting that fitness costs associated with cadherin mutations may be present in many aspects of life history. To evaluate whether cadherin-based resistance is associated with fitness costs reducing male paternity in Helicoverpa armigera, we examined the effects of a major cadherin resistance allele on sperm competition within and between male ejaculates. When homozygous resistant and susceptible males competed for fertilization of a homozygous resistant or susceptible female, fertilization success was high in males with a different cadherin genotype than females, and low in males with the same cadherin genotype as females. Single matings between heterozygous males and susceptible females produced offspring within typical Mendelian ratios. Heterozygous males mated to resistant females, however, resulted in a disproportionate number of heterozygous offspring. While these results show that cadherin-based resistance to Cry1Ac has significant impacts on paternity in H. armigera, there was no evidence that costs associated with resistance consistently reduced male paternity. Rather, effects of cadherin-based resistance on paternity depended on interactions between male and female genotypes and differed when males or sperm competed for fertilization of females, which complicates assessment of impacts of cadherin resistance alleles on resistance evolution.

Partner satisfaction, as opposed to condom use, predicts symptoms of depression amongst women: A failure to replicate Gallup et al. (2002)

Gallup et al. (2002) argued that women who never use condoms or less frequently receive more ejaculates which contain antidepressants such as prostaglandins, testosterone or oestrogen which enters the woman’s bloodstream several hours after intercourse. Although their study received considerable media attention, there was no attempt to replicate their findings. There is additionally a lack of theoretical assumptions which may explain the evolution of antidepressants in human male ejaculates. The original study of Gallup et al. (2002) with 261 Slovak women was replicated and found extremely inconsistent results in a comparison with their original research. In contrast to condom use, partner satisfaction was found to be a unique predictor of women’s symptoms of depression. Since no scientific theory may be built on a single research project, this study calls for replications of the original research.

Genetic variation in the effect of monoamines on female mating receptivity and oviposition in the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae).

BackgroundFemale mate choice after mating is a strong force in sexual selection and could lead to coevolution of mating traits between the sexes. How females of different genotypes respond to substances in the male ejaculate should be mediated by females’ mate choices. Monoamines regulate animal physiology and behavior, including the post-mating behavior of females of the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae). This study examined differences in females’ response to four monoamines (dopamine, octopamine, tyramine, serotonin) between strains from different populations of C. chinensis.ResultsInjection with either octopamine or tyramine, two kinds of monoamines significantly reduced female receptivity in two strains with low remating frequencies. None of the four monoamines reduced female receptivity in one strain with high remating frequencies. However, all monoamines reduced it in another strain with high remating frequencies. Oviposition was activated by tyramine on days 1–5 or by serotonin on days 4 and 5 in the two strains with low remating frequencies, but only on day 1 or day 4 in the strains with high remating frequencies.ConclusionThese differences in female response to monoamines, especially tyramine and serotonin, correspond with results of previous studies. They indicate differences in female response to male substances that reduce receptivity and activate oviposition. These findings suggest relationships between the differences in female response to male substances among populations and mutations in the pathways of monoamine biosynthesis or transmission, which in turn determine female mate choice in response to male substances.

Sociosexual environment influences patterns of ejaculate transfer and female kicking in Callosobruchus maculatus

There is growing evidence that many organisms adjust their physiology and behaviour during sexual encounters according to changes in their sociosexual situation. Selection tends to favour plasticity in males that can strategically ejaculate and females that can alter their resistance or remating behaviour adaptively. We investigated plasticity both in the ejaculate transfer patterns of males and in the pericopulatory kicking behaviour of female seed beetles, Callosobruchus maculatus . We altered the sociosexual environment of the beetles by (1) manipulating male mating history, (2) preventing females from kicking and (3) altering the risk of sperm competition. Males mating for the second time transferred half the weight of ejaculate of virgin males, but at the same rate. Males mating in the presence of rivals did not alter the weight of ejaculate, as might have been expected; however, the transfer of ejaculate began sooner. By looking at the effect of female kicking on male ejaculate transfer, we found that when females have their hindlegs ablated to prevent kicking, the rate of ejaculate transfer slows, but the weight remains the same. From the female perspective we found that the probability of females kicking was positively related to both copula duration and ejaculate weight, but also to male mating history; females were less likely to kick males that had mated more times previously even after controlling for copula duration and ejaculate weight. Finally, we found that removing a female's hindlegs increased the probability that females (attempted to) kick. Our results show that males are, to some extent, plastic in their ejaculatory responses to the sociosexual environment. More striking, however, and not previously documented, is that female kicking is affected by environmental variables, including male mating history. • Males can adjust ejaculate transfer dynamics to the sociosexual environment. • The presence of rival males did not affect the volume of ejaculate transferred. • Probability of female kicking increases with mating duration and ejaculate weight. • Probability of female kicking varies with male mating history.

A Drosophila Protease Cascade Member, Seminal Metalloprotease-1, Is Activated Stepwise by Male Factors and Requires Female Factors for Full Activity

Females and males of sexually reproducing animals must cooperate at the molecular and cellular level for fertilization to succeed, even though some aspects of reproductive molecular biology appear to involve antagonistic interactions. We previously reported the existence of a proteolytic cascade in Drosophila melanogaster seminal fluid that is initiated in the male and ends in the female. This proteolytic cascade, which processes at least two seminal fluid proteins (Sfps), is a useful model for understanding the regulation of Sfp activities, including proteolysis cascades in mammals. Here, we investigated the activation mechanism of the downstream protease in the cascade, the astacin-family metalloprotease Seminal metalloprotease-1 (Semp1, CG11864), focusing on the relative contribution of the male and female to its activation. We identified a naturally occurring semp1 null mutation within the Drosophila Genetic Reference Panel. By expressing mutant forms of Semp1 in males homozygous for the null mutation, we discovered that cleavage is required for the complete activation of Semp1, and we defined at least two sites that are essential for this activational cleavage. These amino acid residues suggest a two-step mechanism for Semp1 activation, involving the action of at least two male-derived proteases. Although the cascade's substrates potentially influence both fertility and sperm competition within the mated female, the role of female factors in the activation or activity of Semp1 is unknown. We show here that Semp1 can undergo its activational cleavage in male ejaculates, without female contributions, but that cleavage of Semp1's substrates does not proceed to completion in ejaculates, indicating an essential role for female factors in Semp1's full activity. In addition, we find that expression of Semp1 in virgin females demonstrates that females can activate this protease on their own, resulting in activity that is complete but substantially delayed.

Short independent lives and selection for maximal sperm survival make investment in immune defences unprofitable for leaf-cutting ant males

The short-lived males of ants and other highly eusocial Hymenoptera are essentially ejaculates with compound eyes, brains and wings to vector sperm to its destination. Males compete for lifetime ejaculate storage by females to produce the equivalent of somatic cells (sterile workers) and new seed-propagules (gynes; males are haploid and have no father) after the colony has become sexually mature. Hymenopteran queens never re-mate later in life, which makes partner commitment between queen and male-ejaculate analogous to a sperm and egg committing when forming a zygote that subsequently sequesters a germ line and produces somatic tissues. This semelparous commitment remains unchanged when queens store ejaculates from multiple males, and colonies become chimeras of patrilines. The soma of eusocial hymenopteran males may thus not be under selection for more than minimal independent life, but eusocial male ejaculates are unusually long-lived, and sperm cells may not be used until years after storage. Somatic repair and immune defence in males should thus be minimal, particularly in response to challenges late in adult life. We tested this idea using males of Atta and Acromyrmex leaf-cutting ants and show that lethal infections with the fungal pathogen Metarhizium brunneum affect male sperm quality, but fail to induce an encapsulation immune response. This result is consistent with expectation because fungal infections are highly unlikely to ever reach immature ant males while they are nursed by their sister workers and because males will die natural deaths after leaving their colonies to mate before new infections can kill them.

Eliminating the effect of pathomorphologically formed sperm on resulting gravidity using the intracytoplasmic sperm injection method

The aim of the present study was to test whether it is possible to eliminate a high percentage of morphologically abnormal sperm in male ejaculate by assisted reproduction using the intracytoplasmic sperm injection (ICSI) method. Treatment success was evaluated by comparing fertilization, clinical pregnancy and reproduction rates between males with heavy teratospermia (≤1% morphologically normal spermatozoa) and males with a higher percentage (>1%) of normal sperm. In total, 174 patients who had previously undergone 174 ICSI cycles (1 per each pair) were evaluated retrospectively. In the group of patients with heavily impaired sperm morphology (n=37), the percentage of normal spermatozoa was ≤1%. In the second group, males with >1% normal spermatozoa (n=137) were considered as patients with mildly impaired sperm morphology. The results of partner fertilization in these two groups were compared and a lower number of fertilized oocytes was identified in the patients with heavily impaired sperm morphology (P=0.038). However, neither the gravidity nor the take-home baby rates of the partners differed between the patients with mildly and heavily impaired sperm morphology. Trends opposite to that for fertilization were observed for gravidity and delivery [odds ratio (OR), 0.62; 95% confidence interval (CI), 0.29–1.30; OR, 0.55; 95% CI, 0.26–1.24, respectively]. This indicates that the lower number of fertilized oocytes was not associated with the overall outcome of fertilization and that patients with heavily impaired sperm morphology experience the same benefit from ICSI as patients with mildly impaired sperm morphology.

Using RNA sequencing to characterize female reproductive genes between Z and E Strains of European Corn Borer moth (Ostrinia nubilalis)

BackgroundReproductive proteins often evolve rapidly and are thought to be subject to strong sexual selection, and thus may play a key role in reproductive isolation and species divergence. However, our knowledge of reproductive proteins has been largely limited to males and model organisms with sequenced genomes. With advances in sequencing technology, Lepidoptera are emerging models for studies of sexual selection and speciation. By profiling the transcriptomes of the bursa copulatrix and bursal gland from females of two incipient species of moth, we characterize reproductive genes expressed in the primary reproductive tissues of female Lepidoptera and identify candidate genes contributing to a one-way gametic incompatibility between Z and E strains of the European corn borer (Ostrinia nubilalis).ResultsUsing RNA sequencing we identified transcripts from ~37,000 and ~36,000 loci that were expressed in the bursa copulatrix or the bursal gland respectively. Of bursa copulatrix genes, 8% were significantly differentially expressed compared to the female thorax, and those that were up-regulated or specific to the bursa copulatrix showed functional biases toward muscle activity and/or organization. In the bursal gland, 9% of genes were differentially expressed compared to the thorax, with many showing reproduction or gamete production functions. Of up-regulated bursal gland genes, 46% contained a transmembrane region and 16% possessed secretion signal peptides. Divergently expressed genes in the bursa copulatrix were exclusively biased toward protease-like functions and 51 proteases or protease inhibitors were divergently expressed overall.ConclusionsThis is the first comprehensive characterization of female reproductive genes in any lepidopteran system. The transcriptome of the bursa copulatrix supports its role as a muscular sac that is the primary site for disruption of the male ejaculate. We find that the bursal gland acts as a reproductive secretory body that might also interact with male ejaculate. In addition, differential expression of proteases between strains supports a potential role for these tissues in contributing to reproductive isolation. Our study provides new insight into how male ejaculate is processed by female Lepidoptera, and paves the way for future work on interactions between post-mating sexual selection and speciation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-189) contains supplementary material, which is available to authorized users.

An Oral Male Courtship Pheromone Terminates the Response of Nasonia vitripennis Females to the Male-Produced Sex Attractant

Sex pheromones are crucial for mate finding in many animals. Long-range attraction, mate recognition, and the elicitation of sexual receptiveness during courtship are typically mediated by different compounds. It is widely unknown, however, how the different components of a species' pheromone system influence each other. Here, we demonstrated in the parasitoid wasp Nasonia vitripennis that females quickly cease to respond to the male sex attractant after they contact a male's oral secretion during courtship. We used this behavioral switch to monitor the fractionation of head extracts from male wasps for identification of the bioactive compounds as a blend of ethyl oleate, ethyl linoleate, and ethyl α-linolenate. This is the first identification of a cephalic courtship pheromone in parasitic Hymenoptera. Plasticity in pheromone-mediated sexual behavior of female insects has hitherto been attributed to the transfer of bioactive proteinaceous molecules with the male ejaculate. The pheromone interaction reported here sheds new light on the sexual communication of insects by showing that the sex pheromone response of females can be terminated by males independent of sperm transfer.

Age-dependent female responses to a male ejaculate signal alter demographic opportunities for selection.

A central tenet of evolutionary explanations for ageing is that the strength of selection wanes with age. However, data on age-specific expression and benefits of sexually selected traits are lacking—particularly for traits subject to sexual conflict. We addressed this by using as a model the responses of Drosophila melanogaster females of different ages to receipt of sex peptide (SP), a seminal fluid protein transferred with sperm during mating. SP can mediate sexual conflict, benefitting males while causing fitness costs in females. Virgin and mated females of all ages showed significantly reduced receptivity in response to SP. However, only young virgin females also showed increased egg laying; hence, there was a narrow demographic window of maximal responses to SP. Males gained significant ‘per mating’ fitness benefits only when mating with young females. The pattern completely reversed in matings with older females, where SP transfer was costly. The overall benefits of SP transfer (hence opportunity for selection) therefore reversed with female age. The data reveal a new example of demographic variation in the strength of selection, with convergence and conflicts of interest between males and ageing females occurring over different facets of responses to a sexually antagonistic trait.

Spermatophore consumption in a cephalopod

An individual's gametes can represent a nourishing food source for a manipulative mate. Here, we provide evidence of ejaculate and sperm consumption in a cephalopod. Through labelling male spermatophores with (14)C radiolabel, we found that female squid, Sepiadarium austrinum, consumed the spermatophores of their partners and directed the nutrients received into both somatic maintenance and egg production. We further show that in this species-where fertilization occurs externally in the female's buccal cavity-sperm storage is short-term (less than 21 days). The combination of female spermatophore consumption and short-term external sperm storage has the potential to exert strong selection on male ejaculates and reproductive strategies.

Defining the Interaction of HIV-1 with the Mucosal Barriers of the Female Reproductive Tract

Worldwide, HIV-1 infects millions of people annually, the majority of whom are women. To establish infection in the female reproductive tract (FRT), HIV-1 in male ejaculate must overcome numerous innate and adaptive immune factors, traverse the genital epithelium, and establish infection in underlying CD4(+) target cells. How the virus achieves this remains poorly defined. By utilizing a new technique, we define how HIV-1 interacts with different tissues of the FRT using human cervical explants and in vivo exposure in the rhesus macaque vaginal transmission model. Despite previous claims of the squamous epithelium being an efficient barrier to virus entry, we reveal that HIV-1 can penetrate both intact columnar and squamous epithelial barriers to depths where the virus can encounter potential target cells. In the squamous epithelium, we identify virus entry occurring through diffusive percolation, penetrating areas where cell junctions are absent. In the columnar epithelium, we illustrate that virus does not transverse barriers as well as previously thought due to mucus impediment. We also show a statistically significant correlation between the viral load of inocula and the ability of HIV-1 to pervade the squamous barrier. Overall, our results suggest a diffusive percolation mechanism for the initial events of HIV-1 entry. With these data, we also mathematically extrapolate the number of HIV-1 particles that penetrate the mucosa per coital act, providing a biological description of the mechanism for HIV-1 transmission during the acute and chronic stages of infection.

RELATIONSHIPS BETWEEN SPERM LENGTH AND SPEED DIFFER AMONG THREE INTERNALLY AND THREE EXTERNALLY FERTILIZING SPECIES

It is often assumed that longer sperm, by virtue of their increased swimming speed, have a fertilization advantage over shorter sperm when in competition to fertilize eggs. However, there is surprisingly little evidence for a positive correlation between sperm length and speed. Here we use an approach that accounts for within-male variation in sperm traits to examine the relationships between sperm length and sperm speed across a broad range of species, including three internally fertilizing species and three externally fertilizing species. Our results reveal that correlations between sperm size and speed are indeed present and possibly more common than currently thought. However, the direction of the correlations between sperm length and speed, which are more prevalent within a male's ejaculate than among males, were influenced by fertilization mode in contrasting and unexpected ways. Broadly, the patterns revealed that in externally fertilizing species sperm with longer flagellum and shorter heads relative to their flagellum swam faster, whereas in internally fertilizing species sperm with shorter flagellum and longer heads relative to their flagellum swam faster. We discuss these results in light of sperm competition theory and contrast the intraspecific patterns observed in this study with macroevolutionary patterns of sperm evolution reported elsewhere.

Larval competition causes the difference in male ejaculate expenditure in Callosobruchus maculatus

AbstractThe seed beetle Callosobruchus maculatus larvae exhibit two types of resource competition: scramble, in which a resource is shared, and contest, in which the resource is monopolized. This difference in larval behavior results in different adult densities. Under contest competition, adult density remains constant regardless of larval density, but under scramble competition, adult density increases with larval density. This in turn affects mating frequency during adulthood, and thus, the intensity of sexual selection operating on males. In this study, we examined the relationship between larval competition types and male reproductive investment in mating. We assessed the male ejaculate expenditure per mating across geographic strains of C. maculatus. The male investment (ejaculate expenditure) increased with the degree of scramble competition and decreased with the degree of contest competition. We therefore suggest that males experience different selective pressures depending on the type of larval competition: scramble type males are selected for increased reproductive investment.