Neonatal manipulation of oxytocin alters oxytocin levels in the pituitary of adult rats.

The neuropeptide oxytocin (OT) and its OT antagonists (OTA) in infant rats affect their behavior as adults. In this study we attempted to determine whether treating rats on the day of birth (postnatal day 1) with OT or OTA would affect brain OT levels of these rats as adults. Rat pups were injected with OT (3 microg), OTA (0.3 microg) or saline vehicle ip on postnatal day 1. As 60-day-old adults, treated rats were killed, and the OT content in their medial preoptic areas (MPOAs), medial hypothalami (MH) and pituitaries were assayed. In females, treatment with OTA on postnatal day 1 significantly decreased pituitary OT levels as adults. In males, by contrast, treatment with OTA on postnatal day 1 resulted in increased pituitary OT levels when they become adults compared to male rats treated with OT on postnatal day 1. There were no significant effects of neonatal treatment on OT levels in either the MH or MPOA. Day 1 postnatal treatment with OT or OTA had a long-term sexually dimorphic effect on OT levels in the pituitary.     

Sex differences and developmental effects of oxytocin on aggression and social behavior in prairie voles (Microtus ochrogaster)

Various hormones, including sex steroids and neuropeptides, have been implicated in aggression. In this study we examined (1) sex differences in intrasexual aggression in na?ve prairie voles; (2) the effects of developmental manipulations of oxytocin on intrasexual aggression; and (3) changes in patterns of intrasexual aggression after brief exposure to an animal of the opposite sex. Within 24 h of birth, infants were randomly assigned to receive either an injection of oxytocin (OT) or oxytocin antagonist (OTA) or to one of two control (CTL) groups receiving either isotonic saline or handling without injection. As adults, animals were tested twice in a neutral arena; before (Test 1) and 24 h after (Test 2) a 4-h exposure to an animal of the opposite sex. In Test 1, CTL males were more likely to show aggressive and less likely to show social behavior than CTL females. No significant treatment differences were observed within either sex in Test 1. In Test 2, after brief exposure to a male, females treated with OT became more aggressive and less social than OTA or CTL females. Male aggressive behavior did not change after exposure to a female. An increase in aggression and decline in social behavior toward other females, seen here in OT-treated females, is typically observed only following several days of female-male cohabitation. These findings demonstrate a sex difference in intrasexual aggression and suggest that neonatal exposure to OT may facilitate the onset of the mate-guarding component of pair bonding in female prairie voles.     

Neonatal oxytocin treatment modulates oxytocin receptor, atrial natriuretic peptide, nitric oxide synthase and estrogen receptor mRNAs expression in rat heart

Oxytocin (OT) has been implicated in reproductive functions, induction of maternal behavior as well as endocrine and neuroendocrine regulation of the cardiovascular system. Here we demonstrate that neonatal manipulation of OT can modulate the mRNAs expression for OT receptor (OTR), atrial natriuretic peptide (ANP), endothelial nitric oxide synthase (eNOS) and estrogen receptor alpha (ERalpha) in the heart. On the first day of postnatal life, female and male rats were randomly assigned to receive one of the following treatments: (a) 50microl i.p. injection of 7microg OT; (b) 0.7microg of OT antagonist (OTA); or (c) isotonic saline (SAL). Hearts were collected either on postnatal day 1 or day 21 (D1 or D21) and the mRNAs expression of OTR, ANP, inducible NOS (iNOS), eNOS, ERalpha and estrogen receptor beta (ERbeta) were compared by age, treatment, and sex utilizing real time PCR. OT treatment significantly increased heart OTR, ANP and eNOS mRNAs expression on D1 in both males and females, ERalpha increased only in females. While there were significant changes in the relative expression of all types of mRNA between D1 and D21, there were no significant treatment effects observed in D21 animals. OTA treatment significantly decreased basal ANP and eNOS mRNAs expression on D1 in both sexes. The results indicate that during the early postnatal period OT can have an immediate effect on the expression OTR, ANP, eNOS, and ERalpha mRNAs and that these effects are mitigated by D21. Also with the exception of ERalpha mRNA, the effects are the same in both sexes.     

Endogenous oxytocin is necessary for preferential Fos expression to male odors in the bed nucleus of the stria terminalis in female Syrian hamsters

Successful reproduction in mammals depends on proceptive or solicitational behaviors that enhance the probability of encountering potential mates. In female Syrian hamsters, one such behavior is vaginal scent marking. Recent evidence suggests that the neuropeptide oxytocin (OT) may be critical for regulating this behavior. Blockade of OT receptors in the bed nucleus of the stria terminalis (BNST) or the medial preoptic area (MPOA) decreases vaginal marking responses to male odors; lesion data suggest that BNST, rather than MPOA, mediates this effect. However, how OT interacts with sexual odor processing to drive preferential solicitation is not known. To address this issue, intact female Syrian hamsters were exposed to male or female odors and their brains processed for immunohistochemistry for Fos, a marker of recent neuronal activation, and OT. Additional females were injected intracerebroventricularly (ICV) with an oxytocin receptor antagonist (OTA) or vehicle, and then tested for vaginal marking and Fos responses to sexual odors. Colocalization of OT and Fos in the paraventricular nucleus of the hypothalamus was unchanged following exposure to male odors, but decreased following exposure to female odors. Following injections of OTA, Fos expression to male odors was decreased in BNST, but not in MPOA or the medial amygdala (MA). Fos expression in BNST may be functionally relevant for vaginal marking, given that there was a positive correlation between Fos expression and vaginal marking for BNST, but not MPOA or MA. Together, these data suggest that OT facilitation of neuronal activity in BNST underlies the facilitative effects of OT on solicitational responses to male odors.     

Yes, I am ready now: differential effects of paced versus unpaced mating on anxiety and central oxytocin release in female rats

Sexual activity and partner intimacy results in several positive consequences in the context of stress-coping, both in males and females, such as reduced state anxiety in male rats after successful mating. However, in female rats, mating is a rewarding experience only when the estrous female is able to control sexual interactions, i.e., under paced-mating conditions. Here, we demonstrate that sex-steroid priming required for female mating is anxiolytic; subsequent sexual activity under paced mating conditions did not disrupt this anxiolytic priming effect, whereas mating under unpaced conditions increased anxiety-related behavior. In primed females, the release of the neuropeptide oxytocin (OT) within the hypothalamic paraventricular nucleus was found to be elevated and to further increase during paced, but not unpaced mating. Central administration of an OT receptor antagonist partly prevented priming/mating-induced anxiolysis indicating the involvement of brain OT in the anxiolysis triggered by priming and/or sexual activity.These findings reveal that the positive consequences of mating in females are dependent on her ability to control sexual interactions, and that brain OT release is at least in part the underlying neurobiological correlate.     

Oxytocin has dose-dependent developmental effects on pair-bonding and alloparental care in female prairie voles

The present study examines the developmental consequences of neonatal exposure to oxytocin on adult social behaviors in female prairie voles (Microtus ochrogaster). Female neonates were injected within 24 h of birth with isotonic saline or one of four dosages of oxytocin (OT). As adults, females were tested in an elevated plus-maze paradigm (a measure of anxiety and exploratory behavior), and for alloparental behavior and partner preferences. At 2 mg/kg OT, females took longer to approach pups, but were the only group to form a statistically significant within-group partner preference. At 4 mg/kg OT, females retrieved pups significantly more frequently but no longer displayed a partner preference; while females treated developmentally with 8 mg/kg spent significantly more time in side-to-side contact with a male stranger than any other treatment group. OT may have broad developmental consequences, but these effects are not linear and may both increase and decrease the propensity to display behaviors such as pair-bonding.     

Peripherally administered non-peptide oxytocin antagonist, L368,899, accumulates in limbic brain areas: a new pharmacological tool for the study of social motivation in non-human primates

Central administration of oxytocin (OT) antagonists inhibits maternal and sexual behavior in non-primates, providing the strongest experimental evidence that endogenous OT facilitates these behaviors. While there have been a few reports that ICV administration of OT increases social behaviors in monkeys, no studies to date have assessed the effects of OT antagonists. Therefore, we studied in rhesus monkeys whether L368,899, a non-peptide antagonist produced by Merck that selectively blocks the human uterine OT receptor, penetrates the CNS after peripheral administration and alters female maternal and sexual behavior. In two studies in four male monkeys, L368,899 was injected iv (1 mg/kg) after which (1) CSF samples were collected at intervals over 4 h and (2) brains were collected at 60 min. Assay of samples confirmed that iv-administered L368,899 entered CSF and accumulated in the hypothalamus, septum, orbitofrontal cortex, amygdala and hippocampus, but not other areas. An adult female monkey was tested for interest in either an infant or sexual behavior, receiving a different iv treatment prior to each test (1 or 3 mg/kg of L368,899 or saline). OT antagonist treatment reduced or eliminated interest in the infant and sexual behavior. These results, although preliminary, are the first to directly implicate endogenous OT in activation of primate maternal interest and sexual behavior. While it remains to be empirically demonstrated that peripherally administered L368,899 blocks central OT receptors, our behavioral findings suggest that this non-peptide antagonist may facilitate testing OT involvement in a variety of social and other behaviors in primates.     

Oxytocin in the medial preoptic area facilitates male sexual behavior in the rat

Oxytocin (OT) is a versatile neuropeptide that is involved in a variety of mammalian behaviors, and its role in reproductive function and behavior has been well established. The majority of pharmacological studies of the effects of OT on male sexual behavior have focused on the paraventricular nucleus (PVN), ventral tegmental area (VTA), hippocampus, and amygdala. Less attention has been given to the medial preoptic area (MPOA), a major integrative site for male sexual behavior. The present study investigated the effects of intra-MPOA administration of OT and (d(CH2)51, Tyr(Me)2, Thr4, Orn8, Tyr-NH29)-vasotocin, an OT antagonist (OTA), on copulation in the male rat. The relationship between OT receptor (OTR) binding levels in the MPOA and sexual efficiency was also explored. Microinjection of OT into the MPOA facilitated copulation in sexually experienced male rats, whereas similar injections of an OTA inhibited certain aspects of copulation but had no significant effect on locomotor activity in an open field. Contrary to expectation, sexually efficient males had lower levels of OTR binding in the rostral MPOA compared to inefficient animals. The present data suggest that OT activity in the MPOA is not necessary for the expression of male sexual behavior but is sufficient to facilitate copulatory behaviors and improve sexual efficiency in sexually experienced male rats. These data also suggest that OTR activity in the MPOA stimulates anogenital investigation, facilitates the initiation of copulation, and plays a role in the sensitization effect of the first ejaculation on subsequent ejaculations.     

Both oxytocin and vasopressin may influence alloparental behavior in male prairie voles

Neuropeptides, especially oxytocin (OT) and arginine vasopressin (AVP), have been implicated in several features of monogamy including alloparenting. The purpose of the present study was to examine the role of OT and AVP in alloparental behavior in reproductively na?ve male prairie voles. Males received intracerebroventricular (ICV) injections of artificial cerebrospinal fluid (aCSF), OT, an OT receptor antagonist (OTA), AVP, an AVP receptor antagonist (AVPA), or combinations of OTA and AVPA and were subsequently tested for parental behavior. Approximately 45 min after treatment, animals were tested for behavioral responses to stimulus pups. In a 10-min test, spontaneous alloparental behavior was high in control animals. OT and AVP did not significantly increase the number of males that showed parental behavior, although more subtle behavioral changes were observed. Combined treatment with AVPA and OTA (10 ng each) significantly reduced male parental behavior and increased attacks; following a lower dose (1 ng OTA/1 ng AVPA), males were less likely to display kyphosis and tended to be slower to approach pups than controls. Since treatment with only one antagonist did not interfere with the expression of alloparenting, these results suggest that access to either OT or AVP receptors may be sufficient for the expression of alloparenting.     

Attenuation of the neuronal stress responsiveness and corticotrophin releasing hormone synthesis after sexual activity in male rats

Beneficial effects of sexual activity and mating on the responsiveness to environmental stress can be observed in humans and other mammalian species alike, but the underlying neurobiological mechanisms are largely unknown. Sexual activity and mating with a receptive female has recently been shown to reduce the subsequent emotional stress response via activation of the brain oxytocin system. Therefore, we investigated the neuronal and hormonal responses to an acute stressor (forced swimming) after mating in male rats.Attenuation of the stress-induced increase of c-fos and CRH mRNA expression within the hypothalamic paraventricular nucleus 4 h after mating revealed that sexual activity reduced neuronal reactivity in this region. However, this effect was independent of oxytocin as oxytocin receptor blockade, by central administration of an oxytocin receptor antagonist, after mating did not prevent the reduced expression of c-fos mRNA in response to stressor exposure. Mating itself stimulated corticotrophin (ACTH) and corticosterone secretion, which was absent in males after contact with an unreceptive female (non-mated group). However, ACTH and corticosterone responses to forced swimming applied either 45 min or 4 h after female contact were similar between mated and non-mated males. These findings provide evidence for a stress-protective effect of sexual activity and mating in male rats and for dissociation between neuronal and neuroendocrine stress responses.     

Peripheral oxytocin in female baboons relates to estrous state and maintenance of sexual consortships

The neuro-hypophysial hormone oxytocin (OT) has been implicated in female reproductive and maternal behaviors and in the formation of pair bonds in monogamous species. Here we measure variation in urinary OT concentrations in relation to reproductive biology and socio-sexual behavior in a promiscuously breeding species, the chacma baboon (Papio hamadryas ursinus). Subjects were members of a habituated group of baboons in the Okavango Delta, Botswana. We collected behavioral data and urine samples from n = 13 cycling females across their estrous cycles and during and outside short-term, exclusive sexual consortships. Samples were analyzed via enzyme immunoassay (EIA) and we used linear mixed models (LMM) to explore the relationship between peripheral OT and a female's estrous stage and consortship status, her previous reproductive experience and fertility. We also used a Pearson's correlation to examine the relationship between OT concentrations of consorting females and their extent of behavioral coordination with their consort partners. The results of the LMM indicate that only estrous stage had a significant influence on OT levels. Females had higher OT levels during their periovulatory period than during other stages of their estrous cycle. There were no differences in the OT levels between consorting and non-consorting periovulatory females. However, among consorting females, there was a significant positive relationship between urinary OT levels and the maintenance of close proximity between consort partners. Our results suggest that physiological and behavioral changes associated with the initiation and maintenance of short-term inter-sexual relationships in baboons correspond with changes in peripheral OT.     

Neonatal immune challenge alters reproductive development in the female rat

This article is part of a Special Issue "Neuroendocrine-Immune Axis in Health and Disease." Neonatal lipopolysaccharide (LPS) exposure alters neuroendocrine, immune and behavioural responses in adult rats. Recent findings indicate that neonatal LPS treatment may have a more pronounced effect on the mating behaviours of females compared to males. The current study further explored the impact of neonatal inflammation on reproductive development in the female rat. Wistar rats were administered LPS (0.05mg/kg, i.p.) or saline (equivolume) on postnatal days (PNDs) 3 and 5. The immediate effect of treatment was assessed on plasma corticosterone and tyrosine hydroxylase (TH) phosphorylation in the adrenal medulla. Weight gain and vaginal opening were recorded, and oestrous cyclicity was monitored post-puberty and in late adulthood. Blood and ovaries were collected throughout development to assess HPA and HPG hormones and to examine ovarian morphology. Reproductive success in the first (F1) generation and reproductive development in the second (F2) generation were also assessed. Neonatal LPS exposure resulted in increased TH phosphorylation in the neonatal adrenals. LPS treatment increased the corticosterone concentrations of females as juveniles, adolescents and adults, and reduced FSH in adolescence. Increased catch-up growth was evident in LPS-treated females, prompting earlier onset of puberty. Diminished follicular reserve was observed in neonatally LPS-treated females along with the advanced reproductive senescence. While fertility rates were not compromised, higher mortality and morbidity were observed in litters born to LPS-treated mothers. Female offspring of LPS-treated mothers displayed increased corticosterone on PND 14, increased catch-up growth and delayed emergence of the first oestrous cycle. No differences in any of the parameters assessed were observed in F2 males. These data suggest that neonatal immunological challenge has a profound impact on the female reproductive development, via the alteration of metabolic and neuroendocrine factors which regulate sexual maturation. Evidence of altered development in the female, but not male offspring of LPS-treated dams suggests increased susceptibility of females to the deleterious effects of neonatal immunological stress and its possible transferability to a subsequent generation.     

Polyandry as a mediator of sexual selection before and after mating

The Darwin–Bateman paradigm recognizes competition among males for access to multiple mates as the main driver of sexual selection. Increasingly, however, females are also being found to benefit from multiple mating so that polyandry can generate competition among females for access to multiple males, and impose sexual selection on female traits that influence their mating success. Polyandry can reduce a male''s ability to monopolize females, and thus weaken male focused sexual selection. Perhaps the most important effect of polyandry on males arises because of sperm competition and cryptic female choice. Polyandry favours increased male ejaculate expenditure that can affect sexual selection on males by reducing their potential reproductive rate. Moreover, sexual selection after mating can ameliorate or exaggerate sexual selection before mating. Currently, estimates of sexual selection intensity rely heavily on measures of male mating success, but polyandry now raises serious questions over the validity of such approaches. Future work must take into account both pre- and post-copulatory episodes of selection. A change in focus from the products of sexual selection expected in males, to less obvious traits in females, such as sensory perception, is likely to reveal a greater role of sexual selection in female evolution.     

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.     

Oxytocin maintains as well as initiates female sexual behavior: effects of a highly selective oxytocin antagonist

In previous studies, central administration of the oxytocin (OT) antagonist d(CH2)5[Tyr(Me)2, Thr4, Tyr-NH(9)2]OVT (OTA1) blocked receptive and proceptive components of female sexual behavior (FSB) and increased male-directed agonistic behavior when given before progesterone (P) treatment in estradiol-primed female rats but not when given shortly before behavioral testing 4-6 h after P. Because the considerable V(1a) antagonist potency of OTA1 may have contributed to these results, we tested the effects of the far more selective OT antagonist desGly-NH2, d(CH2)5[d-Tyr2, Thr4]OVT (OTA2). In ovariectomized, estradiol benzoate-primed (1 microg x 2 days sc) rats, icv infusion of OTA2 (1 microg) prior to P injection (250 microg sc) significantly suppressed lordosis and hops and darts and trended toward significantly increasing male-directed kicks during testing at 4 and 6 h. Infusion of OTA2 3 h and 40 min after P did not alter behavior at 4 and 6 h after P but significantly decreased lordosis as well as hops and darts and increased male-directed kicks 8-12 h after P. These results provide further evidence that central OT receptor activation shortly after P treatment contributes to the subsequent onset and early expression of FSB and demonstrate, for the first time, that OT receptor activation at later time points also contributes to maintaining FSB. The FSB-stimulating effect of central OT appears to persist for several hours.     

Dual reproductive cost of aging in male Medflies: dramatic decrease in mating competitiveness and gradual reduction in mating performance

Although age-based effects on the reproductive success of males have been reported in several animal taxa the cost of aging on male mating success in lekking species has not been fully explored. We used the Mediterranean fruit fly, a lekking species, to investigate possible cost of aging on male reproductive success. We performed no choice and choice mating tests to test the hypothesis that aging does not affect the mating performance (mating success in conditions lacking competition) or the mating competitiveness (mating success against younger rivals) of males. The mating probability of older males decreased significantly when competing with younger males. Aging gradually reduced the mating performance of males but older males were still accepted as mating partners in conditions lacking competition. Therefore, older males are capable of performing the complete repertoire of sexual performance but fail to be chosen by females in the presence of young rivals. Older males achieved shorter copulations than younger ones, and female readiness to mate was negatively affected by male age. Older and younger males transferred similar amount of spermatozoids to female spermathecae. Females stored spermatozoids asymmetrically in the two spermathecae regardless the age of their mating partner. Aging positively affected the amount of spermatozoids in testes of both mated and nonmated males. No significant differences were observed on the amount of spermatozoids between mated and nonmated males.     

Paternity analyses in wild‐caught and laboratory‐reared Caribbean cricket females reveal the influence of mating environment on post‐copulatory sexual selection

Polyandry is ubiquitous in insects and provides the conditions necessary for male‐ and female‐driven forms of post‐copulatory sexual selection to arise. Populations of Amphiacusta sanctaecrucis exhibit significant divergence in portions of the male genitalia that are inserted directly into the female reproductive tract, suggesting that males may exercise some post‐copulatory control over fertilization success. We examine the potential for male–male and male–female post‐copulatory interactions to influence paternity in wild‐caught females of A. sanctaecrucis and contrast our findings with those obtained from females reared in a high‐density laboratory environment. We find that female A. sanctaecrucis exercise control by mating multiple times (females mount males), but that male–male post‐copulatory interactions may influence paternity success. Moreover, post‐copulatory interactions that affect reproductive success of males are not independent of mating environment: clutches of wild‐caught females exhibit higher sire diversity and lower paternity skew than clutches of laboratory‐reared females. There was no strong evidence for last male precedence in either case. Most attempts at disentangling the contributions of male–male and male–female interactions towards post‐copulatory sexual selection have been undertaken in a laboratory setting and may not capture the full context in which they take place – such as the relationship between premating and post‐mating interactions. Our results reinforce the importance of designing studies that can capture the multifaceted nature of sexual selection for elucidating the role of post‐copulatory sexual selection in driving the evolution of male and female reproductive traits, especially when different components (e.g. precopulatory and post‐copulatory interactions) do not exert independent effects on reproductive outcomes.     

Hormonal regulation of agonistic and affiliative behavior in female mongolian gerbils (Meriones unguiculatus)

Ovarian steroids and oxytocin (OT) have been implicated in the regulation of social behaviors. The purpose of the present study was to examine hormonal substrates of aggression and affiliation in the female Mongolian gerbil (Meriones unguiculatus), a highly social, monogamous rodent. Sexually naive adult females were paired with sexually experienced males for 48 h and their interactions videotaped. Females were gonadally intact and tested during vaginal estrus (INT) or ovariectomized and observed after the following treatments, administered by means of sc injections: EBEB (7 days of estradiol-benzoate); EBP (2 days of EB followed by progesterone), SALEB (saline, days 1-5 then 2 days of EB), OTEB (OT for days 1-5 then 2 days of EB); OTOIL (OT for days 1-5 then 2 days of OIL); or SALOIL (saline days 1-5 then 2 days of OIL). During the first hour of pairing INT females displayed higher levels of affiliation and lower levels of sniffing and agonistic behavior than SALOIL females. All hormonal treatments reduced agonistic behaviors when compared to SALOIL, although none of the hormonal treatments restored affiliation to INT levels. During the 48-h test overt aggression varied by treatment with INT, EBEB, EBP, and OTEB females displaying lower levels than SALOIL, while all groups displayed similar levels of affiliation. The results indicate that OT and E play a significant role in regulating male-directed aggressive behavior in females and that the presence of ovarian hormones as well as OT can increase affiliation during initial contact. Over a sustained period of cohabitation social cues appear to be more important in regulating affiliation than gonadal hormones.     

Sex peptide causes mating costs in female Drosophila melanogaster

Conflicts between females and males over reproductive decisions are common . In Drosophila, as in many other organisms, there is often a conflict over how often to mate. The mating frequency that maximizes male reproductive success is higher than that which maximizes female reproductive success . In addition, frequent mating reduces female lifespan and reproductive success , a cost that is mediated by male ejaculate accessory gland proteins (Acps) . We demonstrate here that a single Acp, the sex peptide (SP or Acp70A), which decreases female receptivity and stimulates egg production in the first matings of virgin females , is a major contributor to Acp-mediated mating costs in females. Females continuously exposed to SP-deficient males (which produce no detectable SP ) had significantly higher fitness and higher lifetime reproductive success than control females. Hence, rather than benefiting both sexes, receipt of SP decreases female fitness, making SP the first identified gene that is likely to play a central role in sexual conflict.     

No reduction of female sexual receptivity following mating in a stalk‐eyed fly,Cyrtodiopsis dalmanni (Diptera: Diopsidae)

The level of female sexual receptivity is an important component of male and female reproductive success. In many insects, mating itself causes a sharp decline in female receptivity. This can be a direct result of the physical act of mating, or because of actions of sperm or seminal fluid proteins. The degree to which males can decrease female receptivity will directly affect their reproductive success, by altering the chance that their sperm will be used in fertilizations in the interval before the female mates again. In this study, we investigated the effect of mating on female receptivity in the sexually dimorphic stalk‐eyed fly, Cyrtodiopsis dalmanni. Our results showed no evidence for mating‐induced reductions in female receptivity. In addition, we found that matings with males that differed in eyespan did not cause differences in the level of female receptivity. There was also no evidence that females remated sooner when presented with large eyespan males. These results are surprising, given the indirect benefits that females gain from matings with large eyespan males. Finally we demonstrate that males do not appear to discriminate between females on the basis of female mating status.