Adrenal contribution to the induction of sexual behavior in the female musk shrew.

Sexually experienced female musk shrews (Suncus murinus) lack an ovarian, vaginal, and behavioral estrous cycle. Females, once induced by their initial contact with a male, are able to display copulatory behavior whenever a male is present (Rissman, Silveira, and Bronson, 1988). Based on plasma levels of steroids, and on hormone replacement studies conducted after ovariectomy (OVX), we have shown that testosterone (T) plays an essential role in the regulation of female sexual behavior (Rissman and Crews, 1988; Rissman, Clendenon, and Krohmer, 1990a; Rissman, 1991). To date we have only examined the potential contribution of adrenal steroids to female sexual behavior in a preliminary manner. After adrenalectomy, gonadally intact females display significantly lower levels of sexual behavior than controls (Rissman and Bronson, 1987). The following experiments were conducted to examine the role the adrenal steroids (in contrast to the medullary hormones) play in the induction of female sexual behavior in the musk shrew. In the first experiment gonadally intact females were treated with dexamethasone (DEX) to reduce the secretion of adrenal steroids. Significantly fewer females receiving DEX demonstrated sexual behavior as compared with controls. In the second study, OVX females received T-filled Silastic implants. When DEX was administered to OVX + T females at a dose that dropped circulating T levels to those found in ovary and adrenal intact females, no effect on sexual behavior was noted. The data show that the adrenals are a behaviorally important source of T and contribute toward the hormonal control of sexual behavior in these female mammals.     

Neonatal Androgen Affects Copulatory Behavior in the Female Musk Shrew

The role of neonatal testosterone in the development of copulatory behavior was examined in an insectivore, the musk shrew (Suncus murinus). Female musk shrews were treated with testosterone propionate (TP) for the first 5 days of life and then tested in adulthood for either female or male-like copulatory behavior. Early TP had a masculinizing effect; neonatally treated animals mounted a stimulus female more frequently, and with shorter latencies, in response to adult testosterone treatment than did control females. Neonatally androgenized females also showed deficits in female sexual behavior; few received ejaculations from stud males. This difference was likely caused by increased aggression exhibited by the neonatally TP-treated females toward males. In turn, female aggression decreased efficiency of male partners' intromission attempts. Early TP treatments also caused structural abnormalities in the ovaries, but did not effect their capacity to ovulate in response to either gonadotropin-releasing hormone or human chorionic gonadotropin injection. In sum, exposure to TP during development augmented display of male-like behavior in females and had subtle deleterious effects on expression of feminine behavior.     

外源性皮质酮对雄性根田鼠交配行为的作用

本文研究了皮质酮对雄性根田鼠交配行为的作用。实验个体分别注射0.10 ug/ g体重、0. 60 ug / g体重和1.00 ug/ g体重剂量的皮质酮,1 h后测定每只雄性根田鼠的交配行为。结果显示,3 个处理组动物具有射精能力的个体比率及其爬跨、抽动和射精潜伏期与对照组动物相比均无显著差异,爬跨和抽动频次也无显著变化。不同处理组个体的血浆睾酮含量无显著差异。因此,皮质酮没有影响雄性根田鼠的交配行为和性激素的分泌。该结果提示,哺乳动物在急性应激条件下所分泌的皮质酮可能不参与对性行为的调控。     

Brief refeeding restores reproductive readiness in food-restricted female musk shrews (Suncus murinus)

Food deprivation blocks sexual behavior and disrupts estrous cycles in mammals. We asked whether reduced copulatory behavior, produced by limited food intake, could be reversed by brief refeeding intervals in the female musk shrew. In Experiment 1, animals were food restricted to 60% of ad lib (FR), and an additional group of FR females were refed for 90 min prior to testing (RF). Refed and ad lib (AL) fed females were significantly more likely to mate than FR females. To test the hypothesis that food-induced restoration of copulatory behavior is not the result of changes in peripheral steroids, we repeated Experiment 1 using ovariectomized and testosterone-implanted females. The results from Experiment 2 were similar to those found in the first study. Next, a more severe refeeding schedule was employed; females were restricted to 50% of ad lib intake. Females in the RF and FR groups were significantly less likely than the AL animals to mate. In the last experiment, females were food restricted to 50% and longer refeeding intervals were employed. Four and one-half hours of food intake did not reinstate sexual behavior, but females refed for 12 h were as likely to mate as ad lib fed controls. We also did not detect any differences in plasma concentrations of testosterone and cortisol in AL, FR, and RF ovary-intact animals. These results define a nutritional threshold for copulatory behavior in the musk shrew. Since this species is highly sensitive to small alterations in food intake, it is a useful model for studies of interactions between metabolic fuels and behavior.     

Silent or Vocalizing Rats Copulate in a Similar Manner

Both male and female rats produce 50 kHz ultrasonic vocalizations (USVs) in the presence of a sexual partner and during copulation. Previous studies showed that USVs have no incentive value for rats. In this study, we evaluated the role of USVs in behavior during copulation. Three groups of rats were used: sham males paired with sham females, devocalized females paired with sham males, and sham females paired with devocalized males. During the copulation test, the USVs emitted by the sham rat were recorded and the sexual behavior of both the male and the female were observed. The results revealed that devocalized and sham females showed similar patterns of sexual behavior and no difference was found in the copulatory behavior of devocalized and sham males. Also the behavior of the partner of a sham rat was comparable to the partner of a devocalized rat. In addition, almost no changes in USVs emission were found in the 5 seconds before and/or after a copulatory behavior. It can be concluded that USVs play no important role in rat copulatory behavior at least in sexually naïve rats.     

Sexual behavior of male rats: influence of short- and long-term adrenalectomy

Adult male rats (3 months old) were tested for their copulatory behavior: those satisfying the criterion of sexual vigor in the last three out of five weekly tests were randomly divided into two groups and adrenalectomized or sham operated, and their copulatory activity was retested 35 and 420 days after surgery. Short-term adrenalectomy did not modify any of the parameters of sexual behavior. On the other hand, a higher percentage of adrenalectomized than of sham-operated rats still had successful sexual performance when 18 months old (420 days after surgery); moreover, blood levels of testosterone were higher in adrenalectomized than in sham-operated old rats. The possibility that adrenal steroids may play a role in the age-linked decline in male sexual activity in mammals is discussed.     

EVIDENCE FOR WIDESPREAD COURTSHIP DURING COPULATION IN 131 SPECIES OF INSECTS AND SPIDERS,AND IMPLICATIONS FOR CRYPTIC FEMALE CHOICE

Male courtship behavior is generally thought to function prior to copulation, as an inducement to the female to allow the male to copulate with her; this study indicates however, that male courtship during and following copulation (“copulatory courtship”) is common in insects and spiders (81% of 131 species in 102 genera and 49 families, mostly Coleoptera, Hemiptera, Diptera, and Araneioidea). Copulatory courtship is apparently evolutionarily labile, as expected if it is under sexual selection; intrageneric variation occurred in all 17 genera in which more than one species was observed. In 81% of 94 species with copulatory courtship, the male abandoned the female soon after copulation ended; thus, copulatory courtship appears not to function generally to induce acceptance of further copulatory attempts. The most likely explanation for copulatory courtship is that it represents attempts by males to influence cryptic female choice. This suggests that an aspect of sexual selection by female choice not considered by Darwin may be more important than previously appreciated and that the common practice in evolutionary studies of measuring male reproductive success by counting numbers of copulations may sometimes be misleading because of cryptic female choice during and after copulation.     

The inhibitory actions of progesterone: effects on male and female sexual behavior of the hamster

A series of three experiments compared the inhibitory effects of progesterone on estrogen- or androgen-induced sexual behavior in male and female hamsters. In the first experiment chronic progesterone treatment was found to have no effect on male copulatory behavior maintained after castration with testosterone propionate or estradiol benzoate. However, testosterone propionate was more effective at maintaining male behavior than estradiol benzoate. In the second experiment progesterone was found to have a slight inhibitory effect on the rate of the restoration of the intromission response after androgen treatment in males which had been castrated for 8 weeks. In the final experiment, chronic progesterone treatment markedly inhibited sexual receptivity in male and female hamsters which had been given 4 weeks of androgen or estrogen treatment and a single pretest injection of progesterone. Thus, progesterone was shown to be a potent inhibitor of androgen- or estrogen-induced estrus in both male and female hamsters. Due to the large difference in effectiveness on these two behavioral systems, we suggest that progesterone affects steroid-induced male copulatory behavior and female receptivity by different mechanisms of action.     

Decline of sexual behavior in castrated male rats: Effects of female precopulatory behavior

From the population of 89 adult sexually inexperienced Wistar male rats 20 animals that initiated copulatory behavior with females exhibiting low intensity of precopulatory behavior (presenting females) were preselected. Prior to castration all 20 males had the same sexual experience: three ejaculatory series in four weekly sessions with females exhibiting high intensity of precopulatory behavior (darting females). Following castration, the decline of copulatory behavior was much slower for the nine males tested with darting females as compared to the 11 males tested with presenting females. Male precopulatory behaviors (anogenital sniffing, touching flanks, etc) outlasted the loss of copulatory behavior and seem to be less dependent on both external and internal determinants. It is concluded that intensive external sexual stimuli can function to compensate, and therefore mask, the subnormal operation of androgen-dependent mechanisms in initiating the copulatory behavior.     

Does neonatal gonadectomy affect the sexual differentiation of quail?

This experiment was designed to determine the contribution, if any, of posthatching gonadal hormones to sexual differentiation of behavior in Japanese quail (Coturnix coturnix japonica). Males and females were gonadectomized or sham-operated (controls) prior to age 7 days posthatching. At age 4-9 weeks controls were gonadectomized. All birds were then given 2 weeks of testosterone propionate injections and tested for sexual behavior with female partners. Neonatally gonadectomized females exhibited more male-typical copulatory behavior than control females, but this effect was not statistically significant. Neonatal gonadectomy had no effect on males, and neonatally gonadectomized males exhibited significantly more male-typical copulatory behavior than neonatally gonadectomized females. Although the process of sexual differentiation may extend to a minor degree into the posthatching period in females, nonetheless it is largely complete at hatching in this species.     

Issues in Bonobo (Pan paniscus) Sexual Behavior

Sexual behavior is one of the reported similarities between Pan paniscus and Homo sapiens that has stimulated recent interest in the phylogeny of the Pan and the Australopithecus/Homo genera. Similarities do exist, but an understanding of the forms and functions of Van paniscus sexual behavior is best achieved through a comparison to Pan troglodytes. Pan paniscus shows increased female receptivity, variability in copulatory position, male or female initiation of sexual behavior, differential male and female preferences for copulatory position, and association of food sharing and sexual behavior. Their sexual behavior appears to function in proximate terms as a tension-reduction mechanism. Lowered tension, in turn, facilitates multi-male, multi-female social groups. Lowered levels of aggression and increased sexual activity appear to be associated with paedomorphism, and the behavioral and anatomical/physiological characteristics of the species appear to be a consequence of a feeding ecology that promotes large groupings of the animals at preferential and comparatively rich feeding sites.     

Himalayan musk deer (Moshcus leucogaster) behavior at latrine sites and their implications in conservation

Elusive species often use latrines which also serves as communication and information hubs. Thus, studying behavior at latrines may provide critical insights into the species’ ecology and behavior. While it is established that musk deer use latrines for defecating, very little is known about the endangered Himalayan musk deer (Moschus leucogaster) and their latrines. We examined musk deer behavior from the various video clips lasting 238 min altogether, captured at latrine sites during both breeding and non‐breeding seasons in the Annapurna Conservation Area of Nepal. A total of 428 visits by musk deer and 479 behavioral events by them were captured. We constructed an ethogram to describe musk deer behavior and compared behavior across individuals and sex using parametric and non‐parametric tests. We found that musk deer are crepuscular and nocturnal animals. Both male and female musk deer repeatedly and independently visited shared latrine sites as well as exclusively used latrine sites. The proportion of male musk deer visited latrine sites were significantly higher than that of female musk deer. Hence, male musk deer were found more active (>2 times) than females during both seasons. The most frequently observed behavioral activities at the latrine sites were defecating, sniffing and browsing, followed by scrapping and covering, and ignoring the latrine sites. The defecating and sniffing activity were performed throughout breeding and non‐breeding seasons to establish communication among peers and to claim territory. Based on the behaviors observed at the latrine sites, we can presume that Himalayan musk deer likely use latrines to convey various messages, including personality, maturity, sexual status, and territory marking among conspecifics. These findings of this study can be used for the conservation of musk deer in its natural habitat and replicated in captivity to enhance breeding performance that improves long‐term conservation prospects for this species.     

Relationship between pre‐ and post‐copulatory traits in Salvator rufescens (Squamata: Teiidae)

Understanding pre‐ and post‐copulatory mechanisms of sexual selection can provide insights into the evolution of male reproductive strategies. The phenotype‐linked fertility hypothesis postulates that male sperm quality and secondary sexual characteristics will positively co‐vary, whereas the sperm competition hypothesis predicts a negative association between those traits. Male reproductive traits often show variation throughout the reproductive period, suggesting that the relationship between pre‐ and post‐copulatory sexual selection may vary temporally. Here, we evaluated the relationship between secondary sexual character and sperm traits and its temporal variation in Salvator rufescens, a south American lizard. We observed a negative relationship between jaw muscle and principal piece length of sperm and a variation in the relationship between pre‐ and post‐copulatory traits throughout the reproductive period. Collectively, our results evidenced a trade‐off between pre‐ and post‐copulatory traits and a strong seasonal flexibility of male reproductive strategies in this lizard species.     

Behavioral endocrinology of male rats with periodic sexual contacts with exclusive or varied females

Sexual contact keys a profound series of acute and chronic changes in males that, presumably, are orchestrated by acute pulsatile release of hormones. An experimental paradigm is reported in which male rats were paired periodically with either the same or different estrous females to receive identical amounts of copulatory experiences. Results confirmed the hypothesis that exposure to an unfamiliar female would induce a different endocrine response which would be reflected in various androgen-sensitive systems. The "successively polygynous" males showed more sexual behavior than "monogamous" males, and their respective females solicited the males differently, as well. Circulating levels of testosterone were higher immediately after sexual contact with an unfamiliar than with a familiar female partner. There were no differences in testosterone titers among the groups when the animals were killed at either 2 or 7 weeks after the final copulatory experiences. Yet, necropsies at 2 weeks postcopulation revealed that primary and secondary sex structures from polygynous males clearly were larger. Differences between the two experimental groups were reduced after 7 weeks of sexual rest, yet, polygnous males continued to show a different structural profile than the other groups. Conclusions were that males may experience greater activation of androgen-sensitive behavior and physiology following qualitatively different sexual contacts.     

Differential effect of testosterone and dihydrotestosterone on the sexual behavior of prepuberally castrated male rabbits

The effect of testosterone propionate (Tp) and dihydrotestosterone propionate (DHTp) at doses of 1, 3 and 9 mg daily for 30 days on the copulatory behavior of prepuberally castrated male New Zealand white rabbits was studied. Tp was significantly more effective than DHTp in eliciting copulatory behavior at each dose level tested. Three milligrams Tp was the minimal dose required to elicit mounting consistently. DHTp at the high dose level (9 mg) only elicited sexual activity comparable to that observed with the low dose of Tp (1 mg). The results suggest that T does not need to be reduced to DHT to stimulate sexual behavior in the male rabbit.     

Steroid regulation of sexual behavior.

A review of experimental data on the steroid regulation of sexual behavior in the rat suggests that estrogen is involved in the control of both male and female sexual behavior. Female sexual behavior is stimulated by estrogen alone or in combination with progesterone and by aromatizable androgens. In the male, testosterone, androstenediol, and androstenedione were effective in the control of male sexual behavior. Estrogen alone may initiate and restore full masculine copulatory behavior in sexually castrated males. Estrogen may also synergize with nonaromatizable androgens and control behavior. While antiestrogens are ineffective in inhibiting sexual behavior, aromatization blockers (primarily aminoglutethimide) can block sexual response in the presence of aromatizable androgens.     

Evolution of sexual size monomorphism: the influence of passive mate guarding

Some species have potential for intense mate competition yet exhibit little or no sexual size dimorphism, despite predictions from sexual selection theory. Using a conceptual model, we show the conditions for which passive mate guarding with copulatory plugs can be an alternative and more successful strategy to active (direct) guarding, reducing selection pressure on large male size. The model predicts that copulatory plugs in mammals should be favoured in species for which females have short sexual receptivity periods. Using data on 62 primate species and a phylogenetic regression approach, we show that, as predicted, copulatory plugs are negatively associated with degree of sexual dimorphism and females’ sexual receptivity length. Penile spines are also significantly associated with plug use and short receptivity periods suggesting a possible offensive role in sperm competition. Results highlight that life‐history characteristics, such as sexual receptivity lengths, may alter the costs and benefits of alternative male strategies and thus alter the strength of sexual selection.     

The effects of progesterone on sexual behavior in male green anole lizards (Anolis carolinensis).

It is well known that androgen-dependent sexual behaviors in male mammals and birds are inhibited by exogenous progesterone (P). However, recent research on male whiptail lizards (Cnemidophorus inornatus) indicates that P can stimulate sexual and copulatory behavior. We report here both antiandrogenic and synandrogenic actions of P on sexual behavior in males of another reptile, the green anole lizard (Anolis carolinensis). Earlier reports on birds and mammals are reviewed and discussed in relation to a possible physiological role of P in influencing sexual behavior in male vertebrates.     

Supraspinal influences on the penile reflexes of the male rat: a comparison of the effects of copulation, spinal transection, and cortical spreading depression.

The penile reflexes of the rat were observed on interruption of the copulatory behavior sequence after intromission and ejaculation in the initial ejaculatory series, after the penultimate series, during sexual exhaustion, and during recovery from sexual exhaustion 24 and 72 hr later. These were compared to the reflexes of the normal rat in control conditions, to those of the male rat after spinal transection, and to those of the sexually rested and sexually exhausted male rat under cortical spreading depression (CSD). It was concluded that (1) the stimuli associated with copulation evoke disinhibition of the penile reflexes, these showing the short reflex latencies observed in the spinal animal. The release of the spinal mechanisms is lost within 30 min of the last copulatory event. CSD further inhibits reflex responsivity. (2) Stimuli associated with intromission provoke acceleration of the normal rhythmic presentation of reflexes seen in the normal and spinal rat, resulting in a decrease in the duration of intervals between reflex clusters and an increase in reflex number. This excitation decays within about 15 min after intromission. (3) The increase in degree of penile extension and percentage of penile flips after spinal transection suggests tonic inhibition of reflex intensity in the normal rat. The decrease in capacity to attain full erection with the approach of sexual exhaustion suggests an increase in this inhibition. This does not recover during a rest period but instead intensifies. CSD effects did not mimic the effects of spinal transection but instead depressed reflex excitability. The relationship of these changes to the copulatory behavior pattern is discussed.     

Deterioration of male sexual behavior in rats by the new prolactin-secreting tumor 7315b

The effects of hyperprolactinemia on male copulatory behavior in adult male and female rats were studied. Hyperprolactinemia was induced by the transplantable purely prolactin-secreting tumor 7315b. Male rats were castrated and received testosterone-filled capsules of different sizes which induced normal and subnormal testosterone levels. After sexual training the rats of the experimental groups were inoculated with tumor 7315b. Three weeks after tumor-inoculation high prolactin levels (2000-30000 ng/ml) were found. During this hyperprolactinemia ejaculation latency increased significantly, while the mount frequency and intromission frequency remained unchanged. Only 9 out of 22 rats ejaculated 19 days after inoculation. Moreover, it appeared that the inhibitory effect of the tumor was as strong in the presence of normal (2.33 +/- 0.07 ng/ml) as in the presence of low (0.35 +/- 0.01 ng/ml) testosterone levels. The inhibitory effect of tumor 7315b on copulatory behavior was not influenced by adrenalectomy. In gonadectomized female rats bearing testosterone-filled capsules tumor 7315b induced prolactin levels of about 2000 ng/ml and an almost complete cessation of mounts and intromission patterns 4 weeks after tumor-inoculation. It was concluded that tumor 7315b causes a strong inhibitory effect on male copulatory behavior in male and female rats and that this effect is not influenced by the presence of normal or low testosterone levels or removal of the adrenals, suggesting a direct effect of prolactin on brain functions.