Gonadal hormones masculinize and defeminize reproductive behaviors during puberty in the male Syrian hamster

Three experiments were conducted to test whether testicular hormones secreted during puberty masculinize and defeminize the expression of adult reproductive behavior. Experiment 1 tested the hypothesis that gonadal hormones during puberty masculinize behavioral responses to testosterone (T) in adulthood. Male hamsters were castrated either before puberty (noTduringP) or after puberty (TduringP). All males were implanted with a 2.5-mg T pellet 6 weeks following castration and tested once for masculine reproductive behavior 7 days after the onset of T replacement. TduringP males displayed significantly more mounts, intromissions, and ejaculations than noTduringP males. Experiment 2 tested the hypothesis that gonadal hormones during puberty defeminize behavioral responses to estrogen (EB) and progesterone (P). Eight weeks following castration, noTduringP and TduringP males were primed with EB and P and tested for lordosis behavior with a stud male. Behavioral responses of males were compared to that of ovariectomized (OVX) and hormone primed females. NoTduringP males and OVX females displayed significantly shorter lordosis latencies than TduringP males. Experiment 3 investigated whether prolonged T treatment or sexual experience could reverse the deficits in masculine behavior caused by the absence of T during puberty. Extending the T treatment from 7 to 17 days did not ameliorate the deficits in masculine behavior caused by absence of T during puberty. Similarly, when the level of sexual experience was increased from one to three tests, the deficits in masculine behavior persisted. These studies demonstrate that gonadal hormones during puberty further masculinize and defeminize neural circuits and behavioral responsiveness to steroid hormones in adulthood.     

Effects of neonatal septal lesions on reproductive behavior of male and female rats

The purpose of this study was to examine the effects of neonatally placed septal lesions (SL) in male, female, and androgenized female rats on reproductive behavior. Animals were castrated as adults and tested for both feminine and masculine sexual behavior. After treatment with estradiol benzoate (EB) alone (2 μg daily for 3 days), only the females with SL which had not been given testosterone propionate (TP) neonatally showed a facilitation of lordosis behavior. Following EB (2 μg for 3 days) plus 0.5 mg progesterone (P), both the lesioned and the sham-operated female groups showed an increase in the display of lordosis in either hormonal condition. All animals were given a pretest for masculine sexual behavior and tested on Days 4, 7, 11, and 15 of daily TP treatment (150 μg/day). There was no effect of the neonatally placed SL on masculine sexual behavior in female rats or in female rats androgenized with 30 μg TP. However, lesioned females treated neonatally with 1 mg TP showed a marginal enhancement of masculine sexual behavior. Male rats given SL neonatally showed a marked enhancement of masculine sexual behavior compared to that of controls. These results suggest that, depending on the neonatal hormone environment, SL selectively increase behavioral sensitivity to hormones. Although neonatally lesioned females show behavioral responses similar to females given SL as adults, male rats given SL neonatally are unique in that they show enhanced masculine sexual behavior whereas males lesioned as adults do not.     

Role of septum and preoptic area in regulating masculine and feminine sexual behavior in male rats

The effects of septal or preoptic lesions on both masculine and feminine sexual behaviors were examined in castrated adult male rats. Three weeks after brain surgery, animals were implanted with Silastic tubes containing testosterone (T) and observations of masculine sexual behavior were carried out four times every 5 days. T tubes were removed immediately after the end of the masculine behavioral tests. Two weeks later, animals implanted with Silastic tubes containing estradiol-17 beta(E2) were subjected to three feminine sexual behavioral tests at 5-day intervals. The bilateral lateral septal lesion (LSL) and the medial preoptic lesion (MPOL) effectively suppressed the performance of mounts, intromissions, and ejaculations, whereas the medial septal lesion (MSL), the dorsolateral preoptic lesion (DPOL), and the sham operation did not show any significant suppression of these behaviors. In the feminine sexual behavioral tests, intact and sham-operated control males showed only a low lordotic activity. However, the performance of the lordosis reflex was markedly facilitated by LSL or DPOL, while the lordotic activity of MSL and MPOL males was not significantly different from that of control males. These results suggest that the lateral septum exerts not only a facilitatory influence on masculine sexual behavior but also an inhibitory influence on feminine sexual behavior in male rats. On the other hand, the medial preoptic area may play a critical role in regulating masculine sexual behavior in male rats.     

Copulatory behavior of adult tamarins (Saguinus fuscicollis) castrated as neonates or juveniles: Effect of testosterone treatment

The sexual interactions of Saguinus fuscicollis males castrated as neonates, at 37 days of age, or prepubertally with adult intact females were studied. Prepubertally castrated males were observed while receiving testosterone, and while being treated with saline. Males castrated neonatally or at 37 days of age were observed while receiving testosterone. Neonatal castrates had previously been studied without hormone treatment and therefore no control condition was included for these animals. Prepubertally castrated males showed Mounts, Mounts with Thrusts, and Sexual Tongue Flicking when treated with saline only. In three of the four males, all measures of sexual behavior increased with testosterone treatment. Neonatally castrated males had failed to display any mounting or thrusting without testosterone treatment during a previous study. During the present study, three of the four males did not respond to testosterone treatment with sexual behavior. The fourth male and one male castrated at 37 days of age displayed some sexual behavior. These results suggest that most neonatally castrated males are not able to respond to testosterone with the activation of copulatory behavior. The findings are consistent with the hypothesis that in callitrichids the sensitive period for behavioral differentiation is shifted into neonatal life. However, some neonatally castrated males show a weak response to testosterone. This may reflect an extended and perhaps partially prenatal period of sensitivity.     

Changes in masculine sexual behavior, corticosterone and testosterone in response to acute and chronic stress in male rats

Chronic exposure to stressors increases HPA axis activity and concomitantly reduces HPG axis activity. This antagonistic relationship between both these axes has been proposed to underlie the inhibition of reproductive function due to stress. Sexual behavior in males may be the most vulnerable aspect of male reproduction to acute and chronic stress and it has been suggested that alterations in sexual behavior during stress are due to the antagonistic relationship between testosterone and corticosteroids. However, only in a few studies has a correlation between the levels of testosterone and corticosterone, and sexual behavior been made. In this study, we evaluated the effects of different stressors, applied both acute and chronically, on masculine sexual behavior and whether or not these effects on sexual behavior are accompanied by changes in plasma levels of corticosterone and testosterone. Additionally, we evaluated the effect of testosterone treatment on the effects of stress on sexual behavior. Sexually experienced male rats were exposed to one of the following stressors: immobilization (IMB), electric foot shocks (EFS) or immersion in cold water (ICW). Sexual behavior and plasma levels of testosterone and corticosterone were assessed on days 1, 5, 10, 15, and 20 of stress. In a second experiment, males were castrated, treated with 3 different doses of testosterone propionate (TP) and exposed to ICW for 20 consecutive days. Sexual behavior was assessed on days 1, 5, 10, 15, and 20 and steroids were evaluated on day 20. Parameters of masculine sexual behavior were modified depending on the characteristics of each stressor. Mount, intromission and ejaculation latencies increased significantly, the number of mounts increased, and ejaculations decreased significantly in males exposed to EFS and to ICW but not in males exposed to IMB. Associated with these effects, testosterone decreased in the EFS and ICW groups on days 1, 15, and 20. However, corticosterone increased only in males exposed to ICW. In castrated males, TP treatment failed to block the effects of stress by ICW on sexual behavior and corticosterone. These results indicate that the effects of stress on sexual behavior depend on the characteristics of each stressor, and these effects, as well as the decrease in testosterone are not necessarily associated with the increase in corticosterone. The fact that testosterone treatment did not prevent the effects of stress on sexual behavior suggests that other mediators could be involved in the alterations of sexual behavior caused by stress.     

Sex differences and effects of neonatal aromatase inhibition on masculine and feminine copulatory potentials in prairie voles

Copulatory behaviors in most rodents are highly sexually dimorphic, even when circulating hormones are equated between the sexes. Prairie voles (Microtus ochrogaster) are monomorphic in their display of some social behaviors, including partner preferences and parenting, but differences between the sexes in their masculine and feminine copulatory behavior potentials have not been studied in detail. Furthermore, the role of neonatal aromatization of testosterone to estradiol on the development of prairie vole sexual behavior potentials or their brain is unknown. To address these issues, prairie vole pups were injected daily for the first week after birth with 0.5 mg of the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) or oil. Masculine and feminine copulatory behaviors in response to testosterone or estradiol were later examined in both sexes. Males and females showed high mounting and thrusting in response to testosterone, but only males reliably showed ejaculatory behavior. Conversely, males never showed feminine copulatory behaviors in response to estradiol. Sex differences in these behaviors were not affected by neonatal ATD, but ATD-treated females received fewer mounts and thrusts than controls, possibly indicating reduced attractiveness to males. In other groups of subjects, neonatal ATD demasculinized males' tyrosine hydroxylase expression in the anteroventral periventricular preoptic area, and estrogen receptor alpha expression in the medial preoptic area. Thus, although sexual behavior in both sexes of prairie voles is highly masculinized, aromatase during neonatal life is necessary only for females' femininity. Furthermore, copulatory behavior potentials and at least some aspects of brain development in male prairie voles are dissociable by their requirement for neonatal aromatase.     

Behavioral action of estrogen in male hamsters: effect of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD)

This study examines three independent behavioral variables known to be activated by testosterone in the male hamster; namely, the tendency to approach the female, the tendency to leave the female, and the amount of sniffing directed to her. Both intact and testosterone-maintained castrated male hamsters were given the aromatase inhibitor 1,4,6-androstatriene-3,17-dione (ATD) in subcutaneous, Silastic capsules. In intact males, there was an ATD dose-dependent increase in the tendency to leave the female and a decrease in the amount of olfactory investigation. The tendency of the male to approach the female was unaffected. The higher doses of ATD also abolished the ability of males to discriminate between females using vaginal odor cues. These results were confirmed in castrated males whose behavior was maintained at the intact level by testosterone implants. In addition, in both intact and castrated males, estradiol or diethylstilbestrol was able to reverse the behavioral changes induced by ATD. Our results indicate that estrogen produced by aromatization of testosterone activates behavior. We conclude that estrogen, by influencing some, but not all, components of masculine behavior, has a specific role in modulating male-female interactions.     

Differential effects of the anti-estrogen MER-25 and of three 5alpha-reduced androgens on mounting and lordosis behavior in the rat.

Four experiments were performed in order to evaluate further the hypothesis that androgen must be aromatized to estrogen for the activation of masculine sexual behavior in the male rat. In Experiment 1 it was found that the anti-estrogen MER-25 failed to disrupt mounting behavior in castrated males which simultaneously received testosterone propionate (TP). However, in Experiment 2 it was found that MER-25 as weil as 3β-androstanediol effectively activated masculine behavior in castrated males treated simultaneously with dihydrotestosterone propionate. Both MER-25 and 3β-androstanediol had previously been shown to display an affinity for cytoplasmic estradiol-17β receptors present in male rat anterior hypothalamus. In Experiments 3 and 4, performed with ovariectomized females, it was found that whereas MER-25 antagonized the stimulatory effect of estradiol benzoate (EB) on lordosis behavior, 3β-androstanediol did not. In addition, 5α-dihydrotestosterone and 3α-androstanediol, two compounds which had previously been shown to have almost no affinity for estradiol-17β receptors in the hypothalamus, both inhibited the stimulatory effect of EB on lordosis. It is concluded that the fact that anti-estrogens suppress lordosis induced in females with either EB or TP, but fail to disrupt TP-induced mounting behavior in male rats does not argue against the aromatization hypothesis for masculine sexual behavior.     

A single injection of 17 beta-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Expression of male-typical behavior in adult female pseudohermaphroditic rhesus: Comparisons with normal males and neonatally gonadectomized males and females

Two types of pseudohermaphroditic female rhesus produced by exposure to either testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) prior to birth were ovariectomized postpuberally and evaluated for the display of male-typical sexual behavior in response to exogenous TP in adulthood (2 mg/kg/day for 12 weeks). Their performance in standardized tests with estrogenized female partners was compared to that of neonatally gonadectomized males and females identically tested and treated with exogenous TP as adults. In addition intact adult males not given exogenous TP were tested with the same estrogenized female partners. There were no reliable differences between the two types of pseudohermaphrodites on any measure of behavior shown during the tests. Accordingly results were combined. Reliable behavioral changes induced by the TP given in adulthood were limited to increases in purse-lip responses, the induced increases were similar in pseudohermaphrodites and castrated males, and increases were reliably greater in these two groups of subjects than in females. Pseudohermaphrodites and castrated males did not differ reliably from intact males in performance of purse-lip gestures during TP treatment. In the performance of mounting, however, pseudohermaphrodites and castrated males remained consistently below the standard of the intact males. The estrogenized female partners displayed proceptive responses most frequently to the intact males and least frequently to the females. Their proceptive responses with castrated males resembled their performance with intact males, but with pseudohermaphrodites their proceptive responses more closely resembled their performance with females. Receptive behavior of the female partners was displayed most frequently to intact males, at intermediate levels to castrated males, and least often to pseudohermaphrodites. Results are completely consistent with the notion that androgens in high concentrations before birth alter mechanisms related to the later display of masculine behavior. These alterations in behavioral mechanisms are of such a nature that the display of male-typical behavior induced by androgens in adulthood is more pronounced and more frequent than it would have been otherwise. The alterations in masculine behavior observed in pseudohermaphroditic rhesus are not different in kind or scope than those reported extensively for lower mammals.(ABSTRACT TRUNCATED AT 400 WORDS)     

The influence of androgenic and estrogenic hormones on sexual behavior in castrated adult male pigs

The objectives of these studies were to evaluate the influence of testosterone propionate (TP), estradiol cypionate (EC), dihydrotestosterone propionate (DHTP), EC + TP, EC + DHTP, and TP + DHTP on traits of masculine sexual behavior in castrated adult male pigs of different breeds. Masculine sexual behavior was restored and maintained by TP, whereas EC initially activated sexual behavior, including copulation and ejaculation, but was unable to sustain copulatory behavior for the 8- to 18-week periods that were evaluated. Treatment with DHTP was ineffective for stimulation of sexual behavior; thus, it is suggested that testosterone promotes some aspects of masculine sexual behavior in male pigs via aromatization to estrogen, but both androgen and estrogen are required for maintenance of the full complement of masculine sexual behavior traits.     

Period of maximal susceptibility to behavioral modification by testosterone in the golden hamster

Male hamsters castrated on the day of birth (Day 1) and female hamsters were treated with the free form of testosterone (100 μg/day) on Days 1 and 2, 3 and 4, 5 and 6, 7 and 8, or 9 and 10 postnatally. Following androgen treatment in adulthood, animals treated on Days 1 and 2 or 3 and 4 showed significantly higher mounting and intromission frequencies than animals treated later in life. Sexual receptivity measures following ovarian hormone treatment showed no differences among the male groups, whereas females treated on Days 1 and 2 or 3 and 4 were significantly lower in sexual receptivity measures than females in other treatment groups. Histology of the adult ovaries indicated no modification of normal function in any treatment group. In a subsequent experiment, Day 1 castrated male and intact female hamsters were treated with the free form of testosterone on Days 1–5 (40 or 100 μg/day), 6–10 (40 or 100 μg/day), or Days 1–10 (50 μg/day). Masculine behavior measures were significantly higher in males treated Days 1–10 than in other groups. Among the females, masculine behavior was highest in those treated Days 1–5 postnatally. Sexual receptivity in both males and females was significantly depressed by testosterone treatment Days 1–10 postnatally. Ovarian histology also revealed alterations in gonadal function in females treated Days 1–5 and 1–10 postnatally. Compared with previously published findings, these data suggest that testosterone can be as effective in inducing behavioral masculinization and defeminization as testosterone propionate, provided that treatment extends over a prolonged period during early postnatal development.     

A single injection of 17β-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Castration, sex steroids, and heterosexual behavior in adult male laboratory-housed stumptailed macaques (Macaca arctoides)

The sociosexual behaviors of six stable male-female pairs of stumptailed monkeys were studied in half-hour pair tests. Their performance before and after castration of the males was compared. The effects of replacement therapy with sex steroids on male-female interaction were studied. Also the effects of new females as sexual partners were investigated. Castration caused a significant decrease in sexual behavior. Individual males could display ejaculatory behavior up to about 1 year postcastration. Dihydrotestosterone propionate (75 mg/week/male) alone or in combination with estradiol benzoate (0.9 or 3 mg/week/male) was not effective in restoring sexual behavior to precastration levels in the three castrated males tested. Replacement therapy with testosterone propionate (75 or 10 mg/week/male) was effective in restoring copulatory behavior in half of the castrated males. In some males the introduction of a new female caused an increase in sexual activity, usually when sexual activity with their familiar partner was low. This occurred both in the castration condition and in the steroid treatment period, suggesting, that low activity was caused by low "motivation" and not by the inability to perform.     

Photoperiodic influences on sexual behavior in male Syrian hamsters

The effect of photoperiodic conditions on sexual behavior was investigated in male Syrian hamsters that were either gonadally intact, or castrated and treated with low doses of testosterone throughout the experiment. Hamsters were exposed to long (LD 16:8) or short (LD 8:16) days for 7 weeks; for the next 8 weeks, either they were exposed to an intermediate daylength (LD 12:12), or daylength conditions remained unchanged. Sexual behavior was affected by photoperiod conditions in both gonadally intact animals and testosterone-treated castrates, but to different degrees. Intact males exposed to short days for 15 weeks exhibited gonadal regression, and their copulatory performance was impaired. The percentage of animals that intromitted or ejaculated was significantly reduced. Additional measures of sexual performance among the copulating males were also affected. In contrast, among the castrates with testosterone clamped at low but stable levels, the proportion of males that mounted, intromitted, or ejaculated was not affected by photoperiod. However, among the males that continued to copulate, sexual performance changes were present in the short-day castrates that resembled those displayed by the intact males. We infer that these behavioral effects in both hormonal conditions reflect primarily a difficulty in the attainment of intromission. Gonadal regression alone cannot easily account for the behavioral deficits of the intact males, because circulating testosterone levels at the end of the experiment were not significantly different between the gonadally intact hamsters and the castrated, testosterone-treated hamsters exposed continuously to short days. Males transferred from either long or short days to the intermediate-daylength condition responded behaviorally to this photoperiod as if it were a short day, that is, their ejaculatory frequency declined. We conclude that male hamsters exposed to photoinhibitory daylengths exhibit deficits in their sexual behavior, not only because endogenous levels of testosterone decrease, but also because the substrates on which this hormone acts become less responsive. We hypothesize that under physiological conditions, the episodic secretion of testosterone imposes constraints on the maintenance or restoration of copulation, and that the potent behavioral effects achieved by constant-release implants of testosterone may mask the presence of photoperiodically induced alterations in the hamster's sensitivity to this gonadal hormone.     

Changes in androgen receptor, estrogen receptor alpha, and sexual behavior with aging and testosterone in male rats

Reproductive aging in males is characterized by a diminution in sexual behavior beginning in middle age. We investigated the relationships among testosterone, androgen receptor (AR) and estrogen receptor alpha (ERα) cell numbers in the hypothalamus, and their relationship to sexual performance in male rats. Young (3 months) and middle-aged (12 months) rats were given sexual behavior tests, then castrated and implanted with vehicle or testosterone capsules. Rats were tested again for sexual behavior. Numbers of AR and ERα immunoreactive cells were counted in the anteroventral periventricular nucleus and the medial preoptic nucleus, and serum hormones were measured. Middle-aged intact rats had significant impairments of all sexual behavior measures compared to young males. After castration and testosterone implantation, sexual behaviors in middle-aged males were largely comparable to those in the young males. In the hypothalamus, AR cell density was significantly (5-fold) higher, and ERα cell density significantly (6-fold) lower, in testosterone- than vehicle-treated males, with no age differences. Thus, restoration of serum testosterone to comparable levels in young and middle-aged rats resulted in similar preoptic AR and ERα cell density concomitant with a reinstatement of most behaviors. These data suggest that age-related differences in sexual behavior cannot be due to absolute levels of testosterone, and further, the middle-aged brain retains the capacity to respond to exogenous testosterone with changes in hypothalamic AR and ERα expression. Our finding that testosterone replacement in aging males has profound effects on hypothalamic receptors and behavior has potential medical implications for the treatment of age-related hypogonadism in men.     

Testosterone Control of Male-Type Sexual Behavior in the Tammar Wallaby (Macropus eugenii)

In the tammar wallaby,Macropus eugenii,the expression of male-type sexual behavior is apparently determined by the activating effects of testicular hormones in adulthood. The incidence of male-type copulatory behavior and sexual checking behavior was compared in intact (control) males, control females, testosterone-treated females, and three groups of males castrated either postnatally (24–26 days of age), prepubertally (14.5 months of age), or in adulthood. All three groups of castrated male wallabies showed a very low incidence of male sexual behavior in adult life, comparable to that shown by the untreated females. Adult female wallabies with 100-mg testosterone implants showed a high incidence of male sexual behavior which was indistinguishable from that shown by intact males. The results suggest that sex differences in male-type behavior in the tammar wallaby are due to short-term inductive effects of testosterone acting on a sexually indifferent brain. There is no evidence of any long-term organizational effects of testosterone acting in fetal or neonatal life on the neural pathways controlling male-type sex behavior in this marsupial mammal.     

Androgenic control of male-typical behavior,morphology and sex recognition is independent of the mode of sex determination: A case study on Lichtenfelder's gecko (Eublepharidae: Goniurosaurus lichtenfelderi)

Previous work on lizards has shown that many sexually dimorphic traits depend on testosterone (T), but the details of this control can vary among species. Here, we tested the role of T on the expression of morphological, physiological, and behavioral traits in Lichtenfelder's gecko (Goniurosaurus lichtenfelderi), from the lizard family Eublepharidae notable for interspecific variation in sexually dimorphic traits and the mode of sex determination. Experiments included three groups of males (intact control, surgically castrated, castrated with T replacement) and two groups of females (intact control, T supplemented). In males, castration caused reductions in 1) the size of hemipenes, 2) offensive aggression, 3) male sexual behavior in a neutral arena, 4) activity of precloacal glands, and 5) loss of male chemical cues for sex recognition. These reductions were not observed in castrated males with T replacement. Interestingly, castrated males performed sexual behavior in their home cages, which shows that the effect of T depends on the environmental context. Notably, tail vibration, previously reported as a courtship behavior in other eublepharids, is displayed by males of G. lichtenfelderi during interactions with conspecifics of both sexes, suggesting an evolutionary shift in the meaning of this signal. In females, T induced growth of hemipenes and male-typical courtship but did not induce precloacal pore activity, aggression, or mounting. In comparison to previous reports on Eublepharis macularius, our results indicate that effects of T do not depend on the mode of sex determination. Further, our results extend our understanding of the complexity of control of male traits and illustrate how lability in the effects of T can be a general mechanism causing evolutionary changes in the components of suites of functionally correlated traits.     

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).