Microbes in tree swallow semen

A frequently hypothesized but poorly studied cost of multiple mating in birds is that exposure to pathogenic sexually transmitted microbes (STM's) can lower reproductive success. Conversely, female birds may benefit from high frequencies of copulation and multiple copulation partners if they receive cloacal inoculations of beneficial STM's that can either protect them against future encounters with pathogens and/or serve as therapy against present infection. We examined the semen of 30 male tree swallows (Tachycineta bicolor) in 1998 to determine the presence and prevalence of potential pathogenic and beneficial STM's. Semen was collected directly from males after applying gentle pressure to the cloaca and we used standard microbiological techniques to identify microbes. We found that 19 of 30 samples contained one or more types of microbes. In these 19 positive samples, we isolated both pathogenic and beneficial microbes from 11, only pathogenic microbes from seven, and only beneficial microbes from one. This variation among males suggests that females would benefit from considering a particular male's potential as a donor of either pathogenic or beneficial STM's as a criterion for mate choice. There were few significant differences between males with pathogen-infected semen and those without pathogens in their semen in measures of size, morphology, and ectoparasite score and feather damage. Likewise, there were few significant differences between males with beneficial Lactobacilli spp. in their semen and those without Lactobacilli spp. in their semen in measures of size, morphology, and ectoparasite score and feather damage. We were unable to determine if there was a relationship between microbe presence and prevalence on reproductive performance.     

Rhesus macaque copulation calls: Re-evaluating the “honest signal” hypothesis

Male rhesus macaques sometimes give loud calls while thrusting or dismounting during multi-mount copulations.Hauser (1993) has proposed that these calls (1) impose a cost (increased risk of aggression) on calling males, and (2) increase callers' copulation frequencies, supporting the hypothesis that calls function as honest signals (handicaps) that females use to evaluate male quality during mate choice. This hypothesis was re-examined using data collected at Cayo Santiago, Puerto Rico on 40 focal females and their 56 observed copulatory partners. Although attacks by males against copulating pairs were frequent, they were usually directed only against the female of the pair. Males that called were no more likely than silent males to suffer male escalated attack during or immediately following mount series. Male-female dyads in which the male called during copulation were significantly more likely than non-calling dyads to complete the most copulations observed for any given female. Males that called at least once were significantly more likely than non-calling males to complete at least one copulation with a peri-ovulatory female. A log-linear model revealed that male rank and calling were both associated with likelihood of experiencing at least one peri-ovulatory copulation. However, calling was not associated with reception of demonstrated female mate choice behaviors. Controlling for dominance rank, callers did not experience more female proximity maintenance than non-callers. Nor were callers' hip-grasps refused less frequently than non-callers' hip-grasps. These results cast doubt on the hypothesis that rhesus macaque copulation calls are costly, honest indicators of intrinsic male quality. A contrasting alternative hypothesis, that a male's copulatory calls advertise relative immunity from attacks against his copulatory partners, was not supported either. Thus, the function of rhesus macaque copulatory calls remains unknown. The unusually high rate of copulations amongHauser's (1993) subjects may explain the discrepancy in results, but it is unclear how high copulation rates would increase the cost of copulatory calling to males.     

Genitalia‐associated microbes in insects

In sexual reproduction different types of symbiotic relationships between insects and microbes have become established. For example, some bacteria have evolved almost exclusive vertical transmission and even define the compatibility of insect mating partners. Many strictly sexually transmitted diseases have also been described in insects. Apart from such rather specific relationships the role of opportunistic infections in the reproductive process has been widely neglected. Opportunistic microbes transmitted passively during mating might impose an energetic cost, as the immune system will need to be alert and will use resources to fight potential intruders. Through mating wounds and contaminated reproductive organs opportunistic microbes might be transferred to mating partners and even enter the body cavity. Females as the “receiving” sex are particularly likely to have evolved adaptations to avoid or reduce opportunistic infections. Males of several species show highly complex seminal fluids, which as well as containing components that influence a males’ fertilization success, also possess antimicrobial substances. The role of antimicrobials in the reproductive process is not well understood. Some evidence hints at the protection of sperm against microbes, indicating a role for natural selection in shaping the evolution of reproductive traits. By highlighting the potential importance of microbes in sexual selection and their role in reproduction in general I will make a case for studies in sexual selection, especially the ones investigating postcopulatory processes, that should incorporate environmental, as well as genotypic variation, in reproductive traits.     

Why is sterility virulence most common in sexually transmitted infections? Examining the role of epidemiology

Sterility virulence, or the reduction in host fecundity due to infection, occurs in many host–pathogen systems. Notably, sterility virulence is more common for sexually transmitted infections (STIs) than for directly transmitted pathogens, while other forms of virulence tend to be limited in STIs. This has led to the suggestion that sterility virulence may have an adaptive explanation. By focusing upon finite population models, we show that the observed patterns of sterility virulence can be explained by consideration of the epidemiological differences between STIs and directly transmitted pathogens. In particular, when pathogen transmission is predominantly density invariant (as for STIs), and mortality is density dependent, sterility virulence can be favored by demographic stochasticity, whereas if pathogen transmission is predominantly density dependent, as is common for most directly transmitted pathogens, sterility virulence is disfavored. We show these conclusions can hold even if there is a weak selective advantage to sterilizing.     

Female Copulation Calls in Guinea Baboons: Evidence for Postcopulatory Female Choice?

We tested the hypothesis that primate female copulation calls are a form of postcopulatory female choice. We collected data on female sexual swellings, sexual and agonistic behavior, copulation calls and postcopulatory behavioral interactions in a multimale-multifemale captive group of Guinea baboons over a 3-mo period. Males copulated with only a few females, and females copulated with only 1 or 2 different males in the group, suggesting a harem-like mating system similar to that of hamadryas and gelada baboons. Female copulations were most likely to occur at peak sexual swellings and male copulatory success was accounted for by dominance rank and age. Variation in female tendencies to call after copulation is best explained by the copulatory success of the male with which each female copulated the most and by the number of copulating partners. The findings are consistent with predictions that calls are likely to be associated with copulation with preferred males and the risk of sperm competition. The prediction that copulation calls increased the probability of postcopulatory mate guarding is also supported. Taken together, the findings suggest that female copulation calls may play an important role in postcopulatory sexual selection and in particular in the expression of postcopulatory female choice in primate species in which females have little opportunity to choose their mates or female mate choice is costly or both.     

Indirect partner choice through manipulation of male behaviour by female fowl, Gallus gallus domesticus

The direct and indirect consequences of female copulatory behaviour for copulation success have seldom been quantified. In feral fowl, most copulations were forced by males and copulation success was determined by two factors. First, female differential resistance and solicitation directly affected copulation success and were displayed non-randomly with respect to male social status. Second, another female copulatory behaviour, the distress call, had an indirect effect on both copulation success and the quality of copulation partners. Distress calls triggered male attention to a copulation, which increased the probability of higher-ranking males than the copulating male disrupting the copulation and inseminating the calling female. Females preferentially uttered distress calls when mounted by low-ranking males. Both copulation resistance and distress calling influenced copulation success, but only distress calling increased the probability of copulation disruption by other males. Consistent with the effect of direct selection, differential distress calling indirectly biased copulation success in favour of dominant males. Female fowl may thus ameliorate the effect of male sexual coercion by manipulating male behaviour.     

Copulation exposes female Red-winged Blackbirds to bacteria in male semen

One often cited but poorly studied cost of multiple mating by female birds is the risk of acquiring sexually transmitted pathogens. We examined the ejaculates of male Red-winged Blackbirds Agelaius phoeniceus to determine if exposure to bacteria from males was a potential consequence of copulation for females. Ejaculates were collected in the field using a model female fitted with a sterile artificial cloaca. We found that 11 of 18 sampled males left ejaculates containing bacteria (compared to 3 of 18 control swabs of a sterile cloaca similarly exposed to the environment). We could identify to species or genus 13 of 26 isolates of bacteria from ejaculates, and found that each male left a unique combination of types. Only three types were found in more than one male (one additional male in each case). We found no qualitative effects of bacterial contamination on male fertility or female reproductive success, but larger sample sizes would be needed for a quantitative analysis. Little information is available on how the strains we identified might affect birds, but several types have known debilitating effects in humans or domesticated mammals. Two bacterial types isolated from blackbird semen are reported to produce chitinase, an enzyme with possibly beneficial consequences if produced by bacteria entering the gut of an insect-eating bird. These results suggest that exposure to new bacterial types is a consequence of extra-pair copulations to females. This exposure could have beneficial and/or detrimental effects on female fitness.     

Bacterial communities of the reproductive organs of virgin and mated common bedbugs,Cimex lectularius

1. Microbes associated with reproductive organs of animals are either sexually transmitted or opportunistic. Both can affect host defence, immunity, and future colonisation with other microbes. There are only few studies on the microbiota of reproductive organs in insects and how they are affected by copulation. 2. This study examines the bacterial communities associated with reproductive organs in the common bedbug Cimex lectularius, a well-established insect model for the effects of microbes on male and female reproduction. Combining a metagenomic approach with a controlled mating scheme, we found 31 sequence variants (SVs) across 55 organ samples, with on average three SVs in each sample. Male and female reproductive organs harboured distinct bacterial communities in terms of present SVs. 3. Using a community ecology approach, we found three potential indications of sexual transmission of bacteria in the common bedbug: (i) copulation increased the similarity of the communities of male and female organs; (ii) mated individuals harboured bacteria that were found in non-mated individuals of the opposite sex but not in non-mated individuals of the same sex; and (iii) bacterial communities showed a high SV turnover between non-mated and mated individuals, suggesting a mating-induced replacement of bacteria. 4. Our findings show that the community ecology approach is useful to examine the bacterial dynamics on reproductive organs, especially when combined with studies that quantify the frequency of transmission and/or estimate the effect of the transmitted microbes on the host immune system and the host endosymbionts.     

The effects of nitric oxide-cGMP pathway stimulation on dopamine in the medial preoptic area and copulation in DHT-treated castrated male rats

Dopamine (DA) in the medial preoptic area (MPOA) provides important facilitative influence on male rat copulation. We have shown that the nitric oxide-cGMP (NO-cGMP) pathway modulates MPOA DA levels and copulation. We have also shown that systemic estradiol (E(2)) maintains neuronal NO synthase (nNOS) immunoreactivity in the MPOA of castrates, as well as relatively normal DA levels. This effect of E(2) on nNOS probably accounts for at least some of the previously demonstrated behavioral facilitation by intra-MPOA E(2) administration in castrates. Therefore, we hypothesized that stimulation of the MPOA NO-cGMP pathway in dihydrotestosterone (DHT)-treated castrates should restore DA levels and copulatory behaviors. Reverse-dialysis of a NO donor, sodium nitroprusside (SNP), increased extracellular DA in the MPOA of DHT-treated castrates and restored the ability to copulate to ejaculation in half of the animals. A cGMP analog, 8-Br-cGMP, also increased extracellular DA, though not as robustly, but did not restore copulatory ability. The effectiveness of the NO donor in restoring copulation and MPOA DA levels is consistent with our hypothesis. However, the lack of behavioral effects of 8-Br-cGMP, despite its increase in MPOA DA, suggests that NO may have additional mediators in the MPOA in the regulation of copulation. Furthermore, the suboptimal copulation seen in the NO donor-treated animals suggests the importance of extra-MPOA systems in the regulation of copulation.     

Post-copulatory Mounting Behavior of the West Indian Sweetpotato Weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae)

Post‐copulatory associations between males and females have been found in a variety of insects and are often described as mate guarding. Males of the West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) mount the female's back after copulation. Two hypotheses have been advanced to explain this behavior: mate guarding to prevent future copulations by rivals (hypothesis 1), and mate guarding to gain additional copulations (hypothesis 2). We conducted three experiments to test predictions from these hypotheses. Our results disproved hypothesis 1 because the duration of the post‐copulatory association was very brief in comparison with the length of the refractory phase all females showed after copulation. When we prevented females from resisting copulations during the post‐copulatory mounted phase males copulated again, while under normal conditions, a second copulation was never observed. This result may indicate the presence of a sexual conflict over mating. However, we propose an alternative interpretation of the result, namely that after mating, males test whether the copulation has successfully reduced female receptivity by attempting to remate. If females resist the mating, males leave.     

How the length of genital parts affects copulation performance in a carabid beetle: implications for correlated genital evolution between the sexes

To identify factors leading to the correlated evolution of exaggerated male and female genitalia, we studied the effects of the variable dimensions of corresponding functional genital parts (male copulatory piece and female vaginal appendix) on copulatory performance in the polygamous carabid beetle Carabus (Ohomopterus) maiyasanus. We used mating pairs of individuals from two populations to increase the variances in genital dimensions and determined the copulation performance (insemination and spermatophore replacement, and copulation time) in single‐ and double‐mating situations. In single mating, insemination success was not affected by genital dimensions, although the copulation time was significantly shorter when the male aedeagus was longer. In the double‐mating experiment, insemination and replacement of spermatophores by the second male succeeded more frequently when the copulatory piece was shorter and the vaginal appendix was longer, and when the difference between the length of the copulatory piece and the vaginal appendix was smaller. Thus, a matching of the corresponding genital parts between the sexes increases the male's reproductive success in sperm competition, but elongation of the copulatory piece cannot be explained simply by the improvement in male reproductive success. We discuss possible factors for the elongation of genital parts in terms of sexual conflict and reproductive interference through interspecific copulation.     

Efficient copulation and the evolutionary loss of the avian intromittent organ

The absence of an intromittent organ (IO) in most species (>97%) of birds is an enigma: birds are the only terrestrial vertebrates in which insemination typically occurs without the use of an IO. In an earlier review, we evaluated six hypotheses to explain the loss of IOs among birds. We found some support for the influence of sperm competition and female choice, but other hypotheses (e.g. avoidance of sexually transmitted disease) could not be tested because of a lack of empirical data. Wesołowski (1999, J. Avian Biol. 30: 483–485) has criticised our female choice and sexually transmitted disease hypotheses as implausible and insufficient to explain the loss of the IO in birds. Instead, he proposes that IOs were lost to minimise the risk of predation (by shortening duration of copulation) and/or to increase the efficiency of sperm transfer. Here we respond to Wesołowski's (1999) criticisms and test his efficient copulation (EC) hypothesis with data on the duration of copulation in 243 species. Contrary to expectations from the EC hypothesis, copulation durations did not differ significantly between species with and without an IO. Thus we can reject the EC hypothesis as an explanation for the loss of IOs in birds.     

The copulatory plug delays ejaculation by rival males and affects sperm competition outcome in house mice

Females of many species mate with multiple males (polyandry), resulting in male–male competition extending to post‐copulation (sperm competition). Males adapt to such post‐copulatory sexual selection by altering features of their ejaculate that increase its competitiveness and/or by decreasing the risk of sperm competition through female manipulation or interference with rival male behaviour. At ejaculation, males of many species deposit copulatory plugs, which are commonly interpreted as a male adaptation to post‐copulatory competition and are thought to reduce or delay female remating. Here, we used a vertebrate model species, the house mouse, to study the consequences of copulatory plugs for post‐copulatory competition. We experimentally manipulated plugs after a female's first mating and investigated the consequences for rival male behaviour and paternity outcome. We found that even intact copulatory plugs were ineffective at preventing female remating, but that plugs influenced the rival male copulatory behaviour. Rivals facing intact copulatory plugs performed more but shorter copulations and ejaculated later than when the plug had been fully or partially removed. This suggests that the copulatory plug represents a considerable physical barrier to rival males. The paternity share of first males increased with a longer delay between the first and second males' ejaculations, indicative of fitness consequences of copulatory plugs. However, when males provided little copulatory stimulation, the incidence of pregnancy failure increased, representing a potential benefit of intense and repeated copulation besides plug removal. We discuss the potential mechanisms of how plugs influence sperm competition outcome and consequences for male copulatory behaviour.     

Copulatory Courtship in Drosophila birchii and D. serrata,Species Recognition and Sexual Selection

Two endemic Australian Drosophila species, D. birchii and D. serrata, have a copulatory courtship, i.e., the males court the female mainly during copulation. In the present study we found the males of both species to mount their prospective mating partners selectively, exhibiting both sex and species recognition. The males began to sing after mounting the female, and they often exhibited also postcopulatory displays typical to copulatory courtship. D. birchii and D. serrata females discriminated against males which did not sing during mounting/copulation, which suggests that the females utilize cryptic female choice. Our findings raise the question of how widespread a phenomenon cryptic female choice is in Drosophila species.     

Copulatory behaviors and body condition predict post-mating female hormone concentrations, fertilization success, and primary sex ratios in Japanese quail

Environmental cues and social interactions are known to influence reproductive physiology and behavior in vertebrates. In female birds, male courtship displays can result in the growth of ovarian follicles, the production of reproductive hormones, and stimulation of oviduct development, all of which have the potential to influence maternal investment. Male Japanese quail follow a typical sequence of copulatory behaviors during a mating interaction and often force copulations with unreceptive females. We hypothesized that female Japanese quail could adjust maternal investment in response to male copulatory behaviors during a single mating interaction. We investigated the relationships between 1) male copulatory behaviors and post-mating concentrations of steroids in the female, 2) female steroid concentrations and fertilization success of inseminations and 3) female steroid concentrations and the offspring sex ratio. We found that male condition and copulatory behaviors predicted female steroid concentrations and maternal investment in eggs laid after a mating trial. The body condition of one or both mates was a significant predictor of the changes in female corticosterone and testosterone concentrations after mating, whereas specific male copulatory behaviors significantly predicted changes in female progesterone concentrations. Male and female body condition, male neck grabs and post-mating concentrations of female corticosterone, progesterone, and testosterone were all significant predictors of egg fertilization rates. Female body condition, male copulation efficiency, and female testosterone concentrations were significant predictors of offspring sex ratios. Our results show that phenotypic and behavioral characteristics of male Japanese quail modulate female steroid concentrations and result in changes in maternal investment.     

Sexual ornamentation reflects antibacterial activity of ejaculates in mallards

Bacteria present in ejaculates can impair sperm function and reduce male reproductive success. Thus, selection should favour the evolution of antimicrobial defences to limit the detrimental effects of sperm-associated bacteria. Additionally, current hypotheses suggest that ornamental traits may signal information about the infection status of an individual or the ability of an individual to resist bacterial-induced sperm damage. However, despite the evolutionary implications of ejaculate antimicrobials, and the putative importance of pathogens for the evolution of male ornamentation, tests of these hypotheses are lacking. We examined the antibacterial activity of semen from mallard ducks (Anas platyrhynchos) and tested whether the bactericidal capacity of semen was associated with bill coloration, a sexually selected trait. We show that mallard semen exhibits significant antibacterial activity, as measured by the in vitro capacity to kill Escherichia coli and Staphylococcus aureus. Furthermore, we demonstrate that males with more colourful bills have semen with superior bacterial-killing ability. These results suggest that females could use male phenotypic traits to avoid sexually transmitted pathogens and acquire partners whose sperm suffer less bacteria-induced damage.     

Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

Patterns of Sperm Transfer Behavior in a Pholcid Spider with Two Distinct Copulatory Phases

Sexual selection is the responsible force for the evolution and maintenance of genital diversity and function. This is the case for example, of genital movements performed by males during mating and copulation duration. Spiders perform ritualized copulations whereby males carry out different types of movements using their pedipalps with varying duration. The function and duration of these pedipalp movements is unclear. In the pholcid spider, Holocnemus pluchei males that copulate with virgin females perform two copulatory phases: phase I in which the pedipalps move and phase II in which pedipalps remain motionless. Using H. pluchei as a study species, our study aims were: 1) to assess if sperm transfer occurs when pedipalps move or are still and quantify the number of sperm in male bulbs and in the female uterus externus after copulation; and, 2) to determine if amount of sperm transferred to females is associated with duration of each copulatory phase. Two experimental groups (i. e. complete copulation and interrupted copulation) were established in which the amount of sperm remaining in the male bulbs and the amount of sperm stored by females were determined. Our results show that sperm transfer occurs during phase I, that males transfer almost all sperm from their bulbs while the females store only 20% of that male amount. There was no relation between the amount of sperm transferred or stored and the duration of the copulatory phases. These results support the hypothesis that while both phases may serve a copulatory courtship, only phase I (when pedipalps move) serves for sperm transfer.     

The combined effects of pre‐ and post‐copulatory processes are masking sexual conflict over mating rate in Gerris buenoi

In polygynandrous animals, post‐copulatory processes likely interfere with precopulatory sexual selection. In water striders, sexual conflict over mating rate and post‐copulatory processes are well documented, but their combined effect on reproductive success has seldom been investigated. We combine genetic parentage analyses and behavioural observations conducted in a competitive reproductive environment to investigate how pre‐ and post‐copulatory processes influence reproductive success in Gerris buenoi Kirkaldy. Precopulatory struggles had antagonistic effects on male and female reproductive success: efficiently gaining copulations was beneficial for males, whereas efficiently avoiding copulations was profitable for females. Also, high mating rates and an intermediate optimal resistance level of females supported the hypothesis of convenience polyandry. Contrary to formal predictions, high mating rates (i.e. the number of copulations) did not increase reproductive success in males or decrease reproductive success in females. Instead, the reproductive success of both sexes was higher when offspring were produced with several partners and when there were few unnecessary matings. Thus, male and female G. buenoi displayed different interests in reproduction, but post‐copulatory processes were masking the effects of copulatory mating success on reproductive success. Given the high mating rates observed, sperm competition could easily counter the effect of mating rates, perhaps in interaction with cryptic female choice and/or fecundity selection. Our study presents a complex but realistic overview of sexual selection forces at work in a model organism for the study of sexual conflict, confirming that insights are gained from investigating all episodes in the reproduction cycle of polygynandrous animals.