Cryptic female choice via sperm dumping favours male copulatory courtship in a spider

Males of many animals perform ‘copulatory courtship’ during copulation, but the possible reproductive significance of this behaviour has seldom been investigated. In some animals, including the spider Physocyclus globosus (Pholcidae), the female discards sperm during or immediately following some copulations. In this study, we determined which of several variables associated with copulation correlated with paternity success in P. globosus when two males mate with a single female. Then, by determining which of these variables also correlated with sperm dumping, we inferred which variables may affect paternity via the mechanism of sperm dumping. Male abdomen vibration (a copulatory courtship behaviour) and male genitalic squeezing both correlated with both paternity and sperm dumping; so, these traits may be favoured by biased sperm dumping. Biased sperm dumping may also be the mechanism by which possible cryptic female choice favours another male trait that was the subject of a previous study, responsiveness to female stridulation.     

The risk and intensity of sperm ejection in female birds

The way females utilize the gametes of different males has important consequences for sexual selection, sexual conflict, and intersexual coevolution in natural populations. However, patterns of sperm utilization by females are difficult to demonstrate, and their functional significance remains unclear. Here, we experimentally study sperm ejection in the fowl Gallus gallus domesticus, where females eject preferentially the sperm of socially subordinate males. We study two measures of sperm ejection, (i) the probability that an ejaculate is ejected ("risk") and (ii) the proportion of semen ejected ("intensity"), and show that both measures are strongly nonrandom with respect to characteristics of the ejaculate, the male, and the female. Sperm ejection neutralized on average 80% of an ejaculate, and while larger ejaculates suffered a higher ejection risk, smaller ejaculates suffered more intense ejection. After controlling for ejaculate volume, we found socially subdominant males suffered higher ejection intensity. After controlling for male and ejaculate effects, we found ejection risk increased and intensity declined as females mated with successive males. Collectively, these results reveal that sperm ejection risk and intensity are at least partly actively caused by female behavior and generate independent selective pressures on male and ejaculate phenotypes.     

Male copulatory behavior and the induction of ovulation in female voles: a quest for species specificity.

Two experiments were conducted to investigate species specificity in the neuroendocrine responsiveness of female prairie voles to the copulatory patterns of males. In Experiment 1, prairie vole males mated for one ejaculatory series were not significantly more effective in inducing ovulation in prairie vole females than montane voles mated with prairie vole females for one series, two series, or to satiety. Mating with conspecific males did result in significantly more implanted embryos than did heterospecific matings. In Experiment 2, it was found that, when the amount of vaginal stimulation was both low and equated across groups, prairie vole males were significantly more effective in triggering ovulation in female prairie voles than were either meadow voles or montane voles. Although there appears to be some species specificity to the “vaginal codes” of these congeneric species, its biological significance is unclear.     

Artificial vaginocervical stimulation induces a conditioned place preference in female rats

Female rats express a conditioned place preference (CPP) for a context paired with mating. During a mating encounter, the female rat is exposed to several different types of stimuli, including, but not limited to, vaginocervical stimulation and social contact. The present experiment tested the hypothesis that two components of the mating interaction, vaginocervical stimulation or social contact, each induce a CPP in female rats. During conditioning rats received nonpaced mating, artificial vaginocervical stimulation, social interaction or a control treatment. Rats expressed a CPP for the context paired with nonpaced mating or artificial vaginocervical stimulation whereas social interaction and the control treatment did not induce a CPP. The present findings highlight the important role that vaginocervical stimulation plays in the reinforcing effects of mating in female rats.     

Male crickets adjust the viability of their sperm in response to female mating status

Sperm competition theory predicts that males should allocate sperm according to the number of competing ejaculates. Prudent allocation of sperm in response to different levels of sperm competition has been found across a number of taxa; however, some studies suggest that males may not always allocate sperm as expected. Here we examine sperm allocation in the Australian field cricket Teleogryllus oceanicus, using female mating status (virgin, singly mated, or multiply mated) to manipulate male perception of sperm competition risk and intensity. Consistent with theory, we found that male crickets adjust their ejaculates in response to female mating status. However, rather than altering the absolute numbers of sperm transferred to a female, males altered the quality of their sperm. Males ejaculated sperm of low viability (proportion of live vs. dead sperm) when mating with virgins, increased sperm viability when mating with singly mated females, but reduced sperm viability when mating with multiply mated females. Our results show that variation in ejaculate quality can be an important aspect of strategic ejaculation by males and suggest caution in the interpretation of studies in which males do not appear to allocate sperm according to theory.     

Male sperm storage compromises sperm motility in guppies

Sperm senescence can have important evolutionary implications due to its deleterious effects on sperm quality and offspring performance. Consequently, it has been argued that polyandry (female multiple mating) may facilitate the selection of younger, and therefore competitively superior, sperm when ejaculates from multiple males compete for fertilization. Surprisingly, however, unequivocal evidence that sperm ageing influences traits that underlie sperm competitiveness is lacking. Here, we used a paired experimental design that compares sperm quality between ‘old’ and ‘young’ ejaculates from individual male guppies (Poecilia reticulata). We show that older sperm exhibit significant reductions in sperm velocity compared with younger sperm from the same males. We found no evidence that the brightness of the male''s orange (carotenoid) spots, which are thought to signal resistance to oxidative stress (and thus age-related declines in sperm fitness), signals a male''s ability to withstand the deleterious effects of sperm ageing. Instead, polyandry may be a more effective strategy for females to minimize the likelihood of being fertilized by aged sperm.     

The female pheromone 2,5-dimethylpyrazine induces sperm head abnormalities in male CBA mice

The effect of the house mouse female pheromone 2,5-dimethylpyrazine (2,5-DMP) on sperm differentiation in male CBA mice has been studied. For this purpose, mature males were treated with a 0.01% aqueous solution of the pheromone for six days. Control mice were similarly treated with physiologic saline. The mice were sacrificed 23 days after the treatment, and material for the analysis of sperm-head abnormalities was sampled from the caudal portion of the epididymis. Analysis of the frequency of abnormal sperms has demonstrated that the pheromonal treatment significantly increases the frequencies of various sperm-head abnormalities. Apparently, this results from disturbances in sex-cell differentiation germline cells caused by the induction of genetic damage at stages immediately preceding meiosis, as well as during the first and second meiotic divisions. The relationship between the effect of 2,5-DMP and the decrease in the fertility of male CBA mice that was earlier observed after a similar treatment is discussed.     

Possible coevolution of male and female genital form and function in a calopterygid damselfly

In this paper some evolutionary changes of genitalia in the damselfly Calopteryx haemorrhoidalis are investigated by determining their current and past function. Calopteryx haemorrhoidalis males stimulate females by aedeagal frictioning on a set of vaginal sensilla. The aedeagus is considerably variable and positively correlates with volumes of ejected sperm from the spermatheca. Interestingly, females show a significantly reduced sensillum number compared with other family members. Here I explore whether there existed directional selection for aedeagal width at its evolutionary onset; and whether the sensillum reduction evolved to make sperm ejection less effective. Using C. haemorrhoidalis aedeagi in females whose species retained the ancestral conditions (no stimulatory ability and large sensillum numbers), Hetaerina cruentata and C. xanthostoma, my results corroborated these assumptions: variation in aedeagal width inversely correlated with sperm ejection rate while sperm ejection was higher in species with high sensillum numbers. A suggested coevolutionary interpretation of these results in C. haemorrhoidalis is that aedeagal width was favoured which was followed by a sensillum reduction.     

Diethylstilbestrol facilitates masculine and feminine copulatory behavior in female rats

Diethylstilbestrol (DES), which binds to estrogen receptor without crossreacting to androgen receptor, was tested for its ability to facilitate male-typical mounting behavior. The administration of either 30 or 90 μg of DES per day to adult ovariectomized female rats activated mounting behavior in 94% of the animals (last three tests). The response to the two dosages did not differ. The mount frequency response to 30 μg of DES of 6.8 (mean of last three tests) was only about half as high as the response to 100 μg of testosterone propionate. All animals receiving DES also responded with lordosis behavior when mounted. The lower dosage of DES depleted 91% of hypothalamic cytosol estrogen receptors, and the higher dosage 96%. Androgen receptors were not depleted. Thus the synthetic estrogen DES can facilitate masculine sex behavior by interacting with estrogen receptors without binding to or translocating androgen receptors.     

Male copulatory behavior triggers nightly prolactin surges resulting in successful pregnancy in rats

A positive correlation between the number of preejaculatory intromissions that a female receives during copulation and the probability of successful pregnancy has been demonstrated previously. In the present investigation the nocturnal secretion of prolactin (PRL) was followed for 4 days after mating in female rats receiving either 3–5 intromissions before ejaculation (low intromission group) or 15–18 intromissions (high intromission group). Nightly PRL surges occurred in most of the females (9/12) in the high intromission group and the same 9 females became pregnant. Only 2/9 females in the low intromission group exhibited nightly PRL surges and again only these 2 females became pregnant. This study demonstrates that the stimulation which the female receives from multiple intromissions during mating is effective in setting off nightly PRL surges. We propose that the so-called pregnancy-inducing neuroendocrine reflex which is triggered in this manner is expressed in a characteristic pattern of nightly surges of prolactin, the hormone known to be essential for the activation of the corpora lutea and their secretion of progesterone.     

Male copulatory patterns in the lesser bushbaby (Galago moholi) in captivity

I observed seven pairs of sexually mature, captiveGalago moholi during the females’ ovarian cycles to determine the pattern of male copulatory behavior and its relationship to female receptivity. In this species, a copulatory lock was not apparent, a variety of thrusting patterns was displayed, and the male was capable of ejaculating following a single mount and intromission and may have ejaculated more than once during the 30-min test. Male mating indices did not differ significantly on consecutive days of the mating period, though declines in certain mating latencies on the second and third days of mating suggested increased female receptivity. Mating indices did not differ notably between the first and the second copulation within a test, though both showed some differences compared to the third copulation. InG. moholi, male copulatory behavior is typical of a prosimian species with a dispersed — nongregarious — mating system, in which copulation has a single prolonged intromission that extends into the postejaculatory period. This is characteristic of species in which more than one male has access to an estrous female.     

Male red coloration,female mate preference,and sperm longevity in the cyprinid fish Puntius titteya

In recent decades, the link between the exaggeration of male sexual ornaments and ejaculate quality has received much attention. When males with conspicuous sexual ornaments have high-quality ejaculate, females are believed to obtain benefits, such as high fertilization success and offspring with good genes, by choosing mates on the basis of male ornamentation. In this study, we examined the relationships among male body coloration, female mate preference, and sperm longevity in the sexually dichromatic fish Puntius titteya. Males of this species assume a bright red coloration over the entire body, and neither sex invests in the parental care of eggs. In the female preference test, females preferred males with redder body coloration over their counterpart males with duller coloration. In addition, the sperm longevity test indicated that redder males had sperm with greater longevity. These results suggest that the red coloration of males in this species may signal sperm longevity and that females can mate with males with higher quality sperm by choosing redder males.     

Coevolution of non-fertile sperm and female receptivity in a butterfly

Sexual conflict can promote rapid evolution of male and female reproductive traits. Males of many polyandrous butterflies transfer nutrients at mating that enhances female fecundity, but generates sexual conflict over female remating due to sperm competition. Butterflies produce both normal fertilizing sperm and large numbers of non-fertile sperm. In the green-veined white butterfly, Pieris napi, non-fertile sperm fill the females'' sperm storage organ, switching off receptivity and thereby reducing female remating. There is genetic variation in the number of non-fertile sperm stored, which directly relates to the female''s refractory period. There is also genetic variation in males'' sperm production. Here, we show that females'' refractory period and males'' sperm production are genetically correlated using quantitative genetic and selection experiments. Thus selection on male manipulation may increase the frequency of susceptible females to such manipulations as a correlated response and vice versa.     

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.