Sexual stimulation does not affect plasma LH nor testosterone levels in New-Zealand male rabbits

Young sexually naive (3-4 months) and sexually experienced (2-3 years) male rabbits were subjected to various sexual stimulation procedures. Blood samples were taken just before and 30 min after mounting (unreceptive females) or coitus (receptive females). Testosterone and luteinizing hormone were assayed using specific radioimmunoassays. Sexual stimulation did not affect postcoital testosterone and LH levels in naive and experienced males while in females LH levels were significantly increased. We may conclude that the postcoital neuroendocrine reflex which causes a massive release of pituitary LH in female rabbit does not exist in males.     

Sexual deprivation and its influence on testosterone levels and sexual behavior of old and middle-aged rhesus males

After approximately 6 mo without access to a receptive female, eight old (19 to 25 yr) and eight middle-aged (9 to 15 yr) males were given nine daily 10-min tests of sexual behavior with receptive females. Three ovariectomized, estrogen-primed females served as partners. Blood samples were taken from the males at 0900 and 2100 h on 2 consecutive days before and after the series of nine behavioral tests. Serum levels of testosterone (T) were measured by means of radioimmunoassay. There were no significant differences between serum T levels after 6 mo of sexual deprivation and after the nine tests of sexual behavior, nor did serum T levels differ between middle-aged and old males. Serum T levels were significantly higher in the 2100-h samples than in the 0900-h samples for both groups. The nocturnal increases in serum T, both absolute amounts and percentages of increase, did not differ between middle-aged and old males. Repeated daily testing had little effect on the major components of male sexual behavior. Middle-aged males outperformed old males; middle-aged males had higher rates of contracting the female, mounting and intromitting. They ejaculated earlier and had a greater percentage of tests with ejaculations than did old males.     

Female sexual behavior displayed by androgenized female rhesus macaques

Adult, prenatally androgenized female rhesus macaques (female pseudohermaphrodites) that had been ovariectomized were treated with estradiol benzoate (20 micrograms/day) and paired with males at weekly intervals for 4 weeks beginning on Day 12 of injection. Their sexual behavior was compared to that of a control group of females. The sexual behavior of the males toward the two groups of genetic females (control females with normal female genitalia and hermaphrodites with well-formed male genitalia) was also observed. Females and hermaphrodites were equally receptive to male invitations to copulate. Although there were some differences in the specific components of proceptive behavior displayed by the two groups, the overall differences were negligible. Earlier studies had shown that infant and juvenile hermaphrodites resemble males in patterns of play and sexual behavior. When treated with testosterone as adults and paired with receptive females, they displayed mounting patterns typical of males--one of seven hermaphrodites achieved intromission and ejaculated. It has now been demonstrated that when treated with estrogen and paired with males, they responded as females. Hence, the capacity to behave sexually as males is not incompatible with the capacity to respond sexually as females under certain hormonal and environmental conditions.     

Evidence for androgen independence of male mounting behavior in white-crowned sparrows (Zonotrichia leucophrys gambelii)

Previous experiments have shown that expression of mounting behavior in sexually inexperienced, adult male white-crowned sparrows does not require elevated plasma levels of androgen; adult males maintained on nonstimulatory short days mount sexually receptive females. The experiments reported here demonstrate that (1) sexually inexperienced, prepubertal males maintained on nonstimulatory short days show very low mounting rates in response to female sexual displays; (2) these males exhibit high mounting rates when exposed to stimulatory long days but androgen treatment on short days is ineffective in stimulating high mounting rates; and (3) prepubertal castration has no effect on the expression of mounting behavior by photostimulated adult males. Thus, there is no evidence that mounting behavior of adult male white-crowned sparrows depends on androgen.     

Male Age and Experience Increases Mating Success but Not Female Fitness in the Mexican Fruit Fly

Male age and sexual experience are important condition parameters that can influence mate choice and female fitness, yet they are seldom studied simultaneously. Here, we investigated the effect of male age and previous sexual experience on mating success and female fitness in the Mexican fruit fly, Anastrepha ludens (Diptera: Tephritidae). Males were either young or old, sexually experienced or naïve. Older and sexually experienced males obtained more copulations. However, females did not receive benefits in terms of lifetime fecundity, fertility, or longevity from mating with these males. Results suggest that males become more competitive as they age and gain sexual experience and may be able to maintain a high quality ejaculate compared to young males. Older experienced males may be manipulating females into preferentially mating with them at no benefit to females. Alternatively, females may prefer mating with older more experienced males and possibly receive other indirect benefits, but this remains to be tested.     

Gonadal hormones and sexual behavior in groups of adult talapoin monkeys (Miopithecus talapoin).

Three heterosexual groups of six to eight monkeys were studied; all females were ovariectomized, whereas males were either intact or castrated. Aggressive hierarchies were evident in all groups, with females generally outranking males. When females were treated with estradiol, all males looked more frequently at the latters' sexual skin swellings, but only one male who was both dominant and intact copulated with them. Thus, either castration or low rank resulted in decreased levels of sexual behavior in male talapoins. The sexual behavior of dominant castrated males was restored by testosterone therapy, whereas subordinate castrates never copulated, even after large doses of testosterone, though penile erections and ejaculatory reflex (during masturbation) were restored. Following removal of a dominant male, the sexual behavior of the next male in rank was restored, provided he was not castrated and untreated. In contrast to males, female talapoins showed no consistent correlation between their rank and sexual activity. Estradiol therapy was without overall effect upon the frequency of female mounting behavior, though some females mounted and presented to one another more often. Estradiol treatment also caused females to present to males more frequently, but only to those that were sexually active (i.e., who mounted females).     

The postnatal demasculinization of sexual behavior in the Japanese quail (Coturnix coturnix japonica)

Three experiments were performed to analyze the time course of demasculinization in the Japanese quail and to test the activating and organizing effects of estradiol (E2) in adult sexually active birds. In Experiment 1, males and females were castrated at the age of 1 day or 1, 2, 4, and 6 weeks and treated as adults with testosterone (T). The age of castration had no effect on behavior and morphology in males. Plasma gonadotrophins (LH and FSH) were, however, higher in males castrated at or before than in those castrated after 2 weeks of age. This suggests that postnatal testicular secretions have organizing effects on the pituitary activity. Females which were castrated before 1 week of age were less sensitive to the activating effects of T than males, but were not fully demasculinized. The demasculinization of different reproductive characteristics such as male sexual behavior, cloacal gland size, and weight of the syringeal muscles is achieved in females at different times posthatching. In Experiment 2, castration of male and female quail at the ages of 4 days or 4 weeks confirmed that postnatal ovarian secretions contribute to the full behavioral and morphological demasculinization of females. It is easier to elicit mounting in T-treated females when they are tested in their home cage instead of a test arena. This difference was not observed in males. During Experiment 3, it was impossible to demasculinize sexually active adult males or females by treatment with Silastic implants of E2. E2 did not maintain sexual behavior in ovariectomized females showing male sexual behavior when treated with T but maintained the behavior in males.     

Demasculinization of male Japanese quail by prenatal estrogen treatment

Genetic male Japanese quail were administered sex hormones or the oil vehicle on Day 10 of incubation and were caponized 3 weeks after hatching. As adults, the capons were injected with testosterone propionate daily for 2 weeks and then were tested for masculine sexual behavior in response to sexually receptive females. Males that had received as little as 2 μg of estradiol-17β in ovo failed to exhibit the head grabbing and mounting typical of the normal masculine sexual response to females. In a second experiment, this demasculinization was produced by prenatal treatment with 2 μg of estradiol-17α, estrone, estriol, or diethylstilbestrol, but not by this quantity of testosterone. These data suggest that an estrogen is the agent of behavioral demasculinization in the normal female, and that endogenous testosterone poses no difficulty for proper sexual development in the normal male.     

Precocious Mexican fruit fly methoprene‐fed males inhibit female receptivity and perform sexually as mature males

The sterile insect technique (SIT) has been used successfully for the control of fruit flies. The efficiency of this technique can be significantly reduced when sterile released insects are exposed to adverse conditions and predators, as a great number of sterile insects die before reaching sexual maturity and thus fail to mate with wild females. Treatments with juvenile hormone (JH) analogues such as methoprene (M) significantly reduce the time to reach sexual maturity by sterile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. In this study, we compared the sexual performance of non‐treated sexually mature males with young males that had been sexually accelerated with M. Furthermore, we compared the ability of M‐fed males in inhibiting female remating compared with sexually mature males. Results showed that at 5 days M‐fed males had lower mating success than mature males; however, 6‐day‐old (0.1%) M‐fed males had the same amount of matings as mature 13‐day‐old males. Young 5‐ to 10‐day‐old M‐fed males also had similar number of matings as mature non‐treated 12‐ to 17‐day‐old males. There were no differences in copula duration between treatments. Moreover, there were no differences between the fertility, fecundity or refractory period of females mated with either young male fed M or normal sexually mature males. These results indicated that young males that were sexually accelerated with M have the same sexual performance as non‐treated sexually mature males. Implications of using M as a pre‐release treatment for A. ludens controlled through SIT are discussed.     

Male Age Affects Female Mate Preference and Reproductive Performance in the Cabbage Beetle, <Emphasis Type="Italic">Colaphellus bowringi</Emphasis>

The influence of male age on female mate preference and reproductive performance in the cabbage beetle, Colaphellus bowringi was examined, using male and female adults of varying ages (young, middle-aged and old) after a single mating. In a simultaneous choice test, females of all age class preferentially mated with middle-aged males. Mating duration was positively related to male age. Longevity of females was not significantly affected by male age. Young females paired to middle-aged males had significantly higher egg production than those paired to old males, and the eggs of females paired to middle-aged males exhibited significantly higher hatching success than the eggs of females mated to young or old males. These results suggest that middle-aged males are more advantageous for female fitness than young and old males.     

Relation between circulating sex steroid concentrations and sexual behaviour during pregnancy and post partum in the domestic rabbit

Sexual behaviour of 16 female and 12 male rabbits was studied during pregnancy and early post partum. The main behavioural events of the male (nuzzling and mounting) did not differ in the presence of receptive or non-receptive females. When introduced into the cage of the male, receptive and non-receptive females flattened to the floor or circled around. Sexual receptivity to males decreased in early pregnancy and increased to a maximum a few days around parturition; on Days 1 and 6 post partum, all experimental rabbits submitted to mating. Two groups of females were distinguished: one group submitting to mating whatever the stage of pregnancy, the second being receptive only during the few days before parturition or post partum. During pregnancy and early post partum there was no relation between the colour of the vulva and the female sexual behaviour. Does remained sexually receptive even when progesterone concentrations were high. Nevertheless, the number of receptive females was higher when progesterone concentrations decreased around parturition and the mean daily progesterone values were consistently higher in non-receptive than in receptive females. Oestrogen concentrations during pregnancy were very low and were not related to receptive behaviour.     

Social preferences based on sexual attractiveness: a female strategy to reduce male sexual attention

Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female associates are more sexually attractive than themselves, thus influencing the decision-making of males to their advantage. We tested this hypothesis in the Trinidadian guppy (Poecilia reticulata), a species with high levels of male sexual harassment. First, we confirmed that non-receptive females were harassed less when they were paired with a more sexually attractive (receptive) female than with another non-receptive female. We then found that, indeed, females exploit this as a strategy to reduce sexual harassment; non-receptive females actively preferred to associate with receptive over non-receptive females. Importantly, when given access only to chemosensory cues, non-receptive females still showed this preference, suggesting that they use information from chemical cues to assess the sexual attractiveness of potential female partners. Receptive females in contrast showed no such preferences. Our results demonstrate that females can decrease male harassment by associating with females that are more sexually attractive than themselves and that they perform active partner choices based on this relative attractiveness. We propose that this strategy is likely to represent an important pathway by which females can construct social niches that influence the decision-making of others to their advantage; in this case, to reduce the sexual harassment they experience.     

Factors influencing aggression toward females by male rats exposed to anabolic androgenic steroids during puberty

Previous results showed that male rats pubertally exposed to anabolic androgenic steroids (AAS) displayed aggression towards females in response to physical provocation. This experiment examined two factors that may modulate AAS-induced behavior towards females: olfactory cues and frustration. Gonadally intact males began one of three AAS treatments at puberty (D40): testosterone propionate (T), stanozolol (S), T+S, or vehicle control. To test for the relevance of olfactory cues in the elicitation of behavior toward females, a hidden neighbor paradigm was used. The proximal stimulus was an ovariectomized (OVX) female, estrogen plus progesterone (E+P) female, or an E+P female with tape-obstructed vagina (OBS). Distal olfactory cues from a hidden neighbor were delivered from a separate cage connected to the testing arena. The vaginally obstructed, sexually receptive female (OBS) was used to determine the effects of frustration on behavior by AAS males. Both sexual and aggressive behaviors were measured. The presence of distal olfactory cues had no effect on either sexual or aggressive behavior. In the presence of E+P and OBS females, all males displayed sex behaviors, not aggression. However, AAS males displayed significantly more aggression towards proximal OVX females than controls. AAS males mounted OBS females significantly more than controls, indicating a persistence of once rewarded behavior. These results suggest (1) proximal cues of the conspecific female are more salient than distal olfactory cues in determining behavior and (2) AAS males display frustration-induced persistence in response to vaginally obstructed receptive females.     

Sex-specific effects of gonadal steroids on conspecific odor preference in the rat

Effects of gonadal steroids on conspecific odor preference for either (1) sexually active male or active female, (2) sexually active or gonadectomized (gdx) males, (3) sexually active or gdx females, and (4) gdx males or gdx females were determined in male and female rats in a three-chamber apparatus. For the first test, gdx females were made sexually active by treatments with estradiol benzoate (EB) and progesterone (P), and sexually active males were selected by prior screening. Sexually active males and females preferred opposite-sex odor over same-sex odor. Odor of sexually active opposite-sex conspecifics was preferred over that of inactive ones. Immediately after the completion of the first test, sexually active males were gdx and females were left without hormonal treatment. Second and third tests were carried out 2 and 5 weeks after the first test. In the second test, gdx males preferred odor of sexually active males rather than that of receptive females (male-directed preference); in the third test, both males and females showed no preference when tested with four stimulus pairs. The final tests were carried out in gdx males with EB and P, and gdx females with 2-week exposure to testosterone (T). Males with EB and P showed a male-directed preference again, whereas T-treated females kept their own female preference. Injection of EB alone to gdx males did not induce any preference. The present study clearly demonstrated sex difference in conspecific odor preference. Although both male and female preferences depend on their circulating sex steroids, the direction of male preference is more susceptible to their hormonal states, compared to that of females.     

Why some male Mongolian gerbils may help at the nest: testosterone, asexuality and alloparenting

In previous studies we have shown that those male Mongolian gerbils, Meriones unguiculatus, that as fetuses resided in intrauterine positions (IUPs) located between two female fetuses (2F males) have lower circulating levels of testosterone, less well-developed genital musculature, and lower reproductive success than males gestated in IUPs between two male fetuses (2M males). We have also found that such 2F males spend more time caring for conspecific young than do 2M males, and that presence of a 2F male, but not of a 2M male, with a lactating female and her litter decreases the cost to a dam of suckling one litter while gestating a second litter conceived in postpartum oestrus. Here we show that some 2F males, those with circulating levels of testosterone similar to those seen in females of their species, show no interest in females in oestrus and fail to impregnate females with which they are paired. Such 'asexual' 2F males spend 30-50% more time caring for nestlings than do sexually active 2F males. We suggest that such asexual, highly parental 2F males are incapable of direct reproduction and are obligate helpers at the nest that can contribute to their own fitness only by assisting to rear collateral kin. Copyright 2000 The Association for the Study of Animal Behaviour.     

Effects of Age and Experience on Male Mate Choosiness

Mate choosiness by males has been documented in many taxa but we still do not know how it varies with age even though such variation can be important for our understanding of sexual selection on females. Theory provides conflicting predictions: young males, who are less attractive to females than older males, may be less choosy, or older males, who face fewer expected future mating opportunities, may be less choosy. In our experiments with fruit flies (Drosophila melanogaster), young (1‐d‐old) males spent relatively less time courting recently mated females than did mature (4‐d‐old) males. Overall, there was a gradual decline in male mate choosiness from age 1–7 d. As male age was correlated with the duration of deprivation from females, we tested for the effect of deprivation and found that same‐age males previously exposed to females were choosier than female‐deprived males. We also assessed key male parameters that could affect choosiness and found that, compared to mature males, young males were less attractive to females, less competitive in intramale interactions and less fertile. Although the lesser attractiveness and competitiveness should select for lesser mate choosiness in young males, their limited fertility and more expected future mating opportunities seem to override the other factors and lead to high mate choosiness in young males. Overall, our data indicate that young males just after reaching sexual maturity are choosy and that subsequent exposure to females can maintain high levels of male mate choosiness with age. Hence, males can contribute much more to sexual selection than previously appreciated.     

Effects of male age on the mating behavior of both sexes in the sorghum plant bug, Stenotus rubrovittatus (Hemiptera: Miridae)

In the sorghum plant bug Stenotus rubrovittatus (Matsumura) (Hemiptera: Miridae), mating behavior consists of male courtship and female mating receptivity. Previous studies have found that female age is correlated with ovary development and that mature females with developed ovaries are more receptive to male courtship. Thus, we examined whether male age affects the mating behavior of both sexes and male accessory gland development. Unmated males 0–9 days after emergence and 3-day-old virgin females receptive to male courtship were studied. Immediately after emergence, only 20 % of the males courted females (n = 25). At 3 days old, 68 % of the males courted females (n = 25), the most active age. In contrast, more than 75 % of the courted females were receptive to the male courtship regardless of male age. These results indicate that only male courtship behavior is affected by male age, although it is not enhanced in proportion to male age. Male accessory glands developed with male age. However, no clear relationship was detected between male courtship behavior and accessory gland development. In S. rubrovittatus, it is difficult to explain male courtship behavior solely from male age and accessory gland development.     

The relationship of male-male mounting to the sexual preferences of young rams

The purpose of this study was to determine the relationship between the frequency of male-male mounting of young rams in all-male groups and their subsequent preferences for female vs. male sexual partners. Mount interactions were monitored in the home pen of 29 rams reared in 1984 and 25 rams reared in 1985. At ∼ 8–10 months of age, and prior to copulatory experience, individual rams were simultaneously exposed to two unfamiliar estrous ewes and two unfamiliar rams. The four stimulus animals were restrained and cloth covers were placed over their perinea to prevent copulations. The Binomial Test was used to verify sexual preferences.Of the 44 rams that were sexually active in the sexual performance tests, 30 (68.2%) met the criterion for female preference, 4 (9.1%) preferred males and 10 (22.7%) exhibited no preference (i.e., were bisexual in orientation). There was little relationship between the frequency of male-male mounting by rams in all-male rearing groups and their subsequent sexual preferences. The majority of young rams prefer to mount ewes, even prior to copulatory experience, but in the absence of females will often mount other males.     

The influence of female age on male mating preference and reproductive success in cabbage beetle,Colaphellus bowringi

The influence of female age on male mating preference and reproductive success has been studied using a promiscuous cabbage beetle, Colaphellus bowringi Baly （Coleoptera： Chrysomelidae）. In a simultaneous choice test, middle-aged females had significantly greater mating success than young and old females. In single pair trials, when paired with middle-aged virgin males, middle-aged females mated faster, copulated longer, and had greater fecundity and fertility than young or old females, while the longevity of males was not significantly affected by female age. This study on C. bowringi suggests that middle-aged females are more receptive to mating, which can result in the highest male reproductive success.     

Contextual determinants of female-female mounting in laboratory rats

Female-female mounting is widespread among mammalian species, but little is known about the proximal function of this behaviour. While such mounting is often regarded as a 'masculine' trait, its widespread occurrence may indicate that it serves specific functions within the context of female-female social behaviour. We valuated female mounting behaviour in Long-Evans rats in standard observation chambers and in a seminatural enclosure. Under these conditions, we examined a number of potential factors that might influence mounting, including the oestrous cycle, social hierarchy, familiarity and male presence. The female's mounting was not influenced by her own oestrous cycle, but did vary with the oestrous cycle of the stimulus female. Socially dominant females mounted significantly more than subordinate females, and mounting by the dominant female was most frequent when the subordinate female was sexually receptive. Females mounted (and fought with) unfamiliar females significantly more than they did with familiar cagemates. Female-female mounting was dramatically reduced when males were present. Further testing showed that female mounting did not affect the induction of the progestational state of pregnancy, suggesting that female mounting does not function as a pseudomale behaviour that can substitute for genital stimulation provided by the male. Based on these data, female mounting does not appear to function as a sexual behaviour per se, but may serve as a form of female social behaviour related to maintenance of the female's social status within female groups. In this regard, the results of this study suggest that female mounting is part of the normal female's complex behavioural repertoire and does not necessarily reflect masculinization of some underlying neural substrate. Copyright 1999 The Association for the Study of Animal Behaviour.