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Masculinization and feminization of rat sexual behavior has been supposed to occur during a short postnatal period. However, much data have made it evident that these processes may continue until adolescence. In the present study, we evaluated whether androgen treatment of females from postnatal day 20 and onwards could alter sexual motivation and behavior in a male direction. Juveniles were ovariectomized on day 20 and concurrently implanted with Silastic capsules containing either testosterone or dihydrotestosterone. Controls were implanted with an empty capsule. Tests for sexual incentive motivation and male sexual behavior were performed every fifth day when the females were between 50 and 75 days of age. At day 80, a test for female sexual behavior was performed. Females treated with testosterone approached a female sexual incentive far more than a male incentive, showing that sexual motivation had been changed in a male-like direction. Dihydrotestosterone had a similar, albeit smaller, effect. Females implanted with an empty capsule approached both incentives equally. Testosterone produced a high level of mounting behavior, whereas intromission-like behavioral patterns were rare and ejaculation-like behavior was absent. In the test for female sexual behavior, the testosterone-treated animals displayed a relatively high lordosis quotient, far above that displayed in females implanted with dihydrotestosterone or an empty capsule. It is concluded that treatment with an aromatizable androgen during the peripubertal-adolescent period masculinizes sexual motivation and partly sexual behavior. A non-aromatizable androgen weakly masculinize sexual motivation without enhancing male sexual behavior. It appears that simultaneous actions on androgen and estrogen receptors are needed for significant masculinization during the period studied here. Since the testosterone-treated females displayed lordosis, sexual behavior was not defeminized. In sum, these results suggest that sexual differentiation continues well into the peripubertal and adolescent periods., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Females of some species are considered sex-role reversed, meaning that they face stronger competition for mates compared to males. While much attention has been paid to behavioral and morphological patterns associated with sex-role reversal, less is known about its physiological regulation. Here, we evaluate hypotheses relating to the neuroendocrine basis of sex-role reversal. We refute the most widely tested activational hypothesis for sex differences in androgen secretion; sex-role reversed females do not have higher levels of androgens in circulation than males. However, we find some evidence that the effects of androgens may be sex-specific; circulating androgen levels correlate with some competitive phenotypes in sex-role reversed females. We also review evidence that sex-role reversed females have higher tissue-specific sensitivity to androgens than males, at least in some species and tissues. Organizational effects may explain these relationships, considering that early exposure to sex steroids can shape later sensitivity to hormones, often in sex-specific ways. Moving forward, experimental and correlative studies on the ontogeny and expression of sex-role reversal will further clarify the mechanisms that generate sex-specific behaviors and sex roles., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.)

Performance trade-offs can dramatically alter an organism's evolutionary trajectory by making certain phenotypic outcomes unattainable. Understanding how these trade-offs arise from an animal's design is therefore an important goal of biology. To explore this topic, we studied how androgenic hormones, which regulate skeletal muscle function, influence performance trade-offs relevant to different components of complex reproductive behaviour. We conducted this work in golden-collared manakins ( Manacus vitellinus ), a neotropical bird in which males court females by rapidly snapping their wings together above their back. Androgens help mediate this behavior by radically increasing the twitch speed of a dorsal wing muscle (scapulohumeralis caudalis, SH), which actuates the bird's wing-snap. Through hormone manipulations and in situ muscle recordings, we tested how these positive effects on SH speed influence trade-offs with endurance. Indeed, this latter trait impacts the display by shaping signal length. We found that androgen-dependent increases in SH speed incur a cost to endurance, particularly when this muscle performs at its functional limits. Moreover, when behavioural data were overlaid on our muscle recordings, displaying animals appeared to balance display speed with fatigue-induced muscle fusion (physiological tetanus) to generate the fastest possible signal while maintaining an appropriate signal duration. Our results point to androgen action as a functional trigger of trade-offs in sexual performance - these hormones enhance one element of a courtship display, but in doing so, impede another., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Investigating causes and consequences of variation in hormonal expression is a key focus in behavioral ecology. Many studies have explored patterns of secretion of the androgen testosterone in male vertebrates, using the challenge hypothesis (Wingfield, Hegner, Dufty, & Ball, 1990; The American Naturalist, 136(6), 829-846) as a theoretical framework. Rather than the classic association of testosterone with male sexual behavior, this hypothesis predicts that high levels of testosterone are associated with male-male reproductive competition but also inhibit paternal care. The hypothesis was originally developed for birds, and subsequently tested in other vertebrate taxa, including primates. Such studies have explored the link between testosterone and reproductive aggression as well as other measures of mating competition, or between testosterone and aspects of male behavior related to the presence of infants. Very few studies have simultaneously investigated the links between testosterone and male aggression, other aspects of mating competition and infant-related behavior. We tested predictions derived from the challenge hypothesis in wild male Barbary macaques (Macaca sylvanus), a species with marked breeding seasonality and high levels of male-infant affiliation, providing a powerful test of this theoretical framework. Over 11 months, 251 hr of behavioral observations and 296 fecal samples were collected from seven adult males in the Middle Atlas Mountains, Morocco. Fecal androgen levels rose before the onset of the mating season, during a period of rank instability, and were positively related to group mating activity across the mating season. Androgen levels were unrelated to rates of male-male aggression in any period, but higher ranked males had higher levels in both the mating season and in the period of rank instability. Lower androgen levels were associated with increased rates of male-infant grooming during the mating and unstable periods. Our results generally support the challenge hypothesis and highlight the importance of considering individual species' behavioral ecology when testing this framework., (© 2017 Wiley Periodicals, Inc.)

Male-typical reproductive behaviors vary greatly between different species of fishes with androgens playing a variety of roles that appear especially important in the gonochorist cypriniform fishes. The goldfish is an important model for the cypriniformes and while it is clear that male goldfish are fully feminized by prostaglandin F2α(PGF2α), it is not clear whether females will exhibit normal levels of male-typical reproductive behaviors as well as olfactory function when treated with androgens. To answer this question, we exposed sexually-regressed adult female goldfish to several types of androgen and monitored their tendencies to court (inspect females) and mate (spawn, or attempt to release gametes) while monitoring their olfactory sensitivity until changes in these attributes were maximized. Untreated adult males (intact) were included to determine the extent of masculinization. Treatments included the natural androgens, 11-ketotestosterone and testosterone (KT and T), administered via capsules (KT+T-implanted fish); the artificial androgen, methyltestosterone (MT), administered via capsules (MT-C); and MT administered in the fishes' water (MT-B). Male-typical olfactory sensitivity to a pheromone (15keto-PGF2α) increased in all androgen-treated groups and by week 6 was fully equivalent to that of males. Male-typical courtship behavior increased in all androgen-treated groups although slowly, and only MT-B females came to exhibit levels equivalent to those of males after 18weeks. In contrast, male-typical mating activity increased only slightly, with MT-B females reaching levels one-third that of males after 30weeks. We conclude that while androgens fully masculinize olfactory sensitivity and courtship behavior in goldfish, mating behavior is controlled by a different neuroendocrine mechanism(s) that has yet to be fully elucidated., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Testosterone, acting via estrogenic and androgenic pathways, is the major endocrine mechanism promoting sexual differentiation of the mammalian nervous system and behavior, but we have an incomplete knowledge of which cells and tissues mediate these effects. To distinguish between neural and nonneural actions of androgens in sexual differentiation of brain and behavior, we generated a loxP-based transgenic mouse, which overexpresses androgen receptors (ARs) when activated by Cre. We used this transgene to overexpress AR globally in all tissues using a cytomegalovirus (CMV)-Cre driver (CMV-AR), and we used a Nestin-Cre driver to overexpress AR only in neural tissue (Nes-AR). We then examined whether neural or global AR overexpression can affect socio-sexual behaviors using a resident-intruder paradigm. We found that both neural and global AR overexpression resulted in decreased aggressive behaviors and increased thrusting during mounting of intruders, consistent with a neural site of action. Global, but not neural, AR overexpression in males led to an increase in same-sex anogenital investigation. Together, these results suggest novel roles for nonneural AR in sexual differentiation of mice, and indicate that excess AR can lead to a paradoxical reduction of male-typical behavior.

Anabolic-androgenic steroids (AAS) increase libido and sexual behavior, but the underlying behavioral mechanisms are unclear. One way AAS may enhance expression of sexual behavior is by increasing the willingness to work for sex. In the present study, sexually-experienced male rats received daily injections of testosterone at supraphysiologic doses (7.5 mg/kg in water with 13% cyclodextrin) or vehicle and were tested for appetitive sexual behavior measured by operant responding for access to an estrous female. Initially, rats were trained in their home cage to respond on a nose-poke under a 10-min fixed-interval schedule for food reward. Once rats achieved stable response rates, the food was replaced by a female, followed by mating for 10 min. There was no effect of testosterone on operant responding for food (28.1 ± 4.4 responses/10 min for testosterone, 30.6 ± 4.3 for vehicle) or sex (35.0 ± 4.0 responses/10 min for testosterone, 37.3 ± 5.2 for vehicle). However, rats made significantly more responses for sex than for food (p < 0.05), and responses for food and sex were positively correlated among individuals (R(2) = 0.6). Additional groups of rats were trained to respond on a lever for the female under a 2nd-order schedule of reinforcement, where 5 responses opened a door to show the female for 5s. After 15 door openings, the male gained access to the female. There was no effect of testosterone on time to complete 75 responses: 38.4 ± 7.8 min for vehicle controls vs 43.3 ± 6.6 min for testosterone-treated rats (p > 0.05). These findings suggest that chronic high-dose testosterone does not enhance appetitive drive for sexual behavior., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The social organization of giraffes (Giraffa camelopardalis) imposes a high-cost reproductive strategy on bulls, which adopt a 'roving male' tactic. Our observations on wild giraffes confirm that bulls indeed have unsynchronized rut-like periods, not unlike another tropical megaherbivore, the elephant, but on a much shorter timescale. We found profound changes in male sexual and social activities at the scale of about two weeks. This so far undescribed rutting behaviour is closely correlated with changes in androgen concentrations and appears to be driven by them. The short time scale of the changes in sexual and social activity may explain why dominance and reproductive status in male giraffe in the field seem to be unstable.

Many of the brilliant plumage coloration displays of birds function as signals to conspecifics. One species in which the function of plumage ornaments has been assessed is the Eastern bluebird (Sialia sialis). Studies of a population breeding in Alabama (USA) have established that plumage ornaments signal quality, parental investment, and competitive ability in both sexes. Here we tested the additional hypotheses that (1) Eastern bluebird plumage ornamentation signals nest defense behavior in heterospecific competitive interactions and (2) individual variation in plumage ornamentation reflects underlying differences in circulating hormone levels. We also tested the potential for plumage ornaments to signal individual quality and parental investment in a population breeding in Oklahoma (USA). We found that Eastern bluebirds with more ornamented plumage are in better condition, initiate breeding earlier in the season, produce larger clutches, have higher circulating levels of the stress hormone corticosterone, and more ornamented males have lower circulating androgen levels. Plumage coloration was not related to nest defense behavior. Thus, plumage ornamentation may be used by both sexes to assess the physiological condition and parental investment of prospective mates. Experimental manipulations of circulating hormone levels during molt are needed to define the role of hormones in plumage ornamentation.

The female giant panda (Ailuropoda melanoleuca) experiences a brief (24-72 h) seasonal estrus, occurring once annually in spring (February-May). Our aim was to determine the existence and temporal profile of reproductive seasonality in the male of this species. The study was facilitated by 3 yr of access to eight giant panda males living in a large breeding center in China. Seasonal periods for the male were defined on the basis of female reproductive activity as prebreeding, breeding (early, peak, late), and nonbreeding seasons. Testes size, fecal androgen excretion, ejaculated sperm density, and frequency of reproductive behaviors (i.e., locomotion, scent marking, vocalizations) increased (P < 0.05) from the prebreeding period (October 1-January 31) to the early breeding season (February 1-March 21). Testes volume and sperm concentration were maximal from March 22 through April 15, a period coinciding with maximal female breeding activity. The occurrence of male reproductive behaviors and fecal androgen concentrations began declining during peak breeding and continued from April 16 through May 31 (late breeding period), returning to nadir throughout the nonbreeding interval (June 1-September 30). Reproductive quiescence throughout the latter period was associated with basal testes size/volume and aspermic ejaculates. Our results reveal that testes morphometry, fecal androgen excretion, seminal quality, and certain behaviors integrated together clearly demonstrate reproductive seasonality in the male giant panda. The coordinated increases in testes size, androgen production, sperm density, and sexual behaviors occur over a protracted interval, likely to prepare for and then accommodate a brief, unpredictable female estrus.

Callitrichine primates (marmosets and tamarins) often remain in their natal groups beyond the time of sexual maturity. Although studies have characterized the development of female reproductive function in callitrichine offspring, less is known about the male reproductive development. To document reproductive development in male marmosets, we monitored urinary androgen (uA) excretion in males housed in a captive colony of white-faced marmosets (Callithrix geoffroyi). Young male marmosets showed relatively low and stable rates of uA excretion early in life, with elevated production at the end of the juvenile period (9-10 months) and again at the onset of adulthood (16 months). uA levels of adult breeding males were also measured to compare to adult-aged sons. Although breeding males did have higher uA levels than their adult-aged sons, these differences did not reach conventional levels of significance. Evidence from some other reports has suggested that androgen levels of males in other species are influenced by social factors, such as the presence of a sexually receptive female or of dependent offspring. In this study, however, uA levels did not vary, based on their mothers' pregnancy status or the presence of younger siblings in the natal group. Patterns of androgen excretion in the white-faced marmoset roughly reflect those of other callitrichine species. Furthermore, unlike callitrichine daughters, gonadal activity in sons does not seem to be sensitive to within-group social cues., (© 2010 Wiley-Liss, Inc.)

Background: Testosterone (T) controls male Syrian hamster sexual behavior, however, neither of T's primary metabolites, dihydrotestosterone (DHT) and estradiol (E(2)), even in highly supraphysiological doses, fully restores sexual behavior in castrated hamsters. DHT and T apparently interact with androgen receptors differentially to control male sexual behavior (MSB), but whether these two hormones act synergistically or antagonistically to control MSB has received scant experimental attention and is addressed in the present study., Methodology/principal Findings: Sexually experienced male Syrian hamsters were gonadectomized and monitored 5 weeks later to confirm elimination of the ejaculatory reflex (week 0), at which time they received subcutaneous DHT-filled or empty capsules that remained in situ for the duration of the experiment. Daily injections of a physiological dose of 25 µg T or vehicle commenced two weeks after capsule implantation. MSB was tested 2, 4 and 5 weeks after T treatment began. DHT capsules were no more effective than control treatment for long-term restoration of ejaculation. Combined DHT + T treatment, however, restored the ejaculatory reflex more effectively than T alone, as evidenced by more rapid recovery of ejaculatory behavior, shorter ejaculation latencies, and a greater number of ejaculations in 30 minute tests., Conclusions/significance: DHT and T administered together restored sexual behavior to pre-castration levels more rapidly than did T alone, whereas DHT and vehicle were largely ineffective. The additive actions of DHT and T on MSB are discussed in relation to different effects of these androgens on androgen receptors in the male hamster brain mating circuit.

Background: The prostate is a sexual gland that produces important substances for the potency of sperm to fertilize eggs within the female reproductive tract, and is under complex endocrine control. Taking advantage of the peculiar behavioral pattern of copulating male rats, we developed experimental paradigms to determine the influence of sexual behavior on the level of serum testosterone, prostate androgen receptors, and mRNA for androgen receptors in male rats displaying up to four consecutive ejaculations., Methods: The effect of four consecutive ejaculations was investigated by determining levels of (i) testosterone in serum by solid phase RIA, (ii) androgen receptors at the ventral prostate with Western Blots, and (iii) androgen receptors-mRNA with RT-PCR. Data were analyzed with a one-way ANOVA followed by a post hoc application of Dunnett's test if required., Results: The constant execution of sexual behavior did not produce any change in the weight of the ventral prostate. Serum testosterone increased after the second ejaculation, and remained elevated even after four ejaculations. The androgen receptor at the ventral prostate was higher after the first to third ejaculations, but returned suddenly to baseline levels after the fourth ejaculation. The level of mRNA increased after the first ejaculation, continued to increase after the second, and reached the highest peak after the third ejaculation; however, it returned suddenly to baseline levels after the fourth ejaculation., Conclusion: Four consecutive ejaculations by sexually experienced male rats had important effects on the physiological responses of the ventral prostate. Fast responses were induced as a result of sexual behavior that involved an increase and decrease in androgen receptors after one and four ejaculations, respectively. However, a progressive response was observed in the elevation of mRNA for androgen receptors, which also showed a fast decrease after four ejaculations. All of these changes with the prostate gland occurred in the presence of a sustained elevation of testosterone in the serum that started after two ejaculations. A consideration of these fast-induced changes suggests that the nerve supply plays a key role in prostate physiology during the sexual behavior of male rats.

Nitric oxide-containing neurons are widely distributed within the CNS, including regions involved in the control of reproduction and sexual behavior. The expression of neuronal nitric oxide synthase is influenced by testosterone in male rat, and by estrogens in female. Moreover, nitric oxide synthase may co-localize with gonadal hormones' receptors. Gonadal hormones may influence nitric oxide synthase expression in adulthood as well as during the development. In fact, in mice knockout for estrogen receptor alpha, the nitric oxide synthase-expressing population is deeply reduced in specific regions. In physiological conditions, the female in mammalian species is exposed to short-term changes of gonadal hormones levels (estrous cycle). Our recent studies, performed in the rat vomeronasal system and in mouse hypothalamic and limbic systems reveal that, in rodents, the expression of nitric oxide synthase-producing elements within regions relevant for the control of sexual behavior is under the control of gonadal hormones. The expression of nitric oxide synthase may vary according to the rapid variations of hormonal levels that take place during the estrous cycle. This seems in accordance with the hypothesis that gonadal hormone activation of nitric oxide-cyclic guanosine-monophosphate pathway is important for lordosis behavior, as well as that this system is activated during mating behavior. Finally, comparative data available for other vertebrates suggest that class-specific and species-specific differences occur in the nitric oxide synthase system of hypothalamus and limbic structures. Therefore, particular caution is needed to generalize data obtained from studies in rodents.

Behavioral sex differences have traditionally been thought to arise from gonadal steroids during a neonatal sensitive period. However, it is possible to sex-reverse certain behaviors by reversing the levels of circulating androgen in adult males and females. These results suggest that the sexually dimorphic substrates of sex behavior are subject to a high degree of plasticity, even in adulthood. I have found that circulating androgen exerts a trophic effect on the Nissl-stained morphology of an important nucleus in the control of sex behavior, namely, the posterodorsal subnucleus of the medial amygdala. First, sex-reversing the level of circulating androgen reversed the sex difference in soma size and regional volume of the posterodorsal subnucleus of the medial amygdala in adult rats. Interestingly, activation of both androgen and estrogen receptors was necessary for the post-castration maintenance of a masculine phenotype in terms of posterodorsal subnucleus of the medial amygdala cell size, whereas only estrogen receptor activity was necessary to maintain a masculine posterodorsal subnucleus of the medial amygdala volume. Then, we showed that seasonal variation in androgen was correlated with morphologic plasticity in the posterodorsal subnucleus of the medial amygdala of the Siberian hamster. However, if the experimental males were housed with females, their posterodorsal subnucleus of the medial amygdalas failed to regress in response to winter-like short daylengths. Furthermore, when male hamsters were castrated and treated with testosterone, the posterodorsal subnucleus of the medial amygdala responded to the hormone only if the animals were in summer-like photoperiods. Overall, these findings indicate that circulating androgens are critical for the maintenance of greater posterodorsal subnucleus of the medial amygdala regional volumes and soma sizes, and that environmental variables can regulate testosterone secretion and responsiveness.

Background: Testicular development is arrested in the hypogonadal (hpg) mouse due to a congenital deficiency in hypothalamic gonadotropin-releasing hormone (GnRH) synthesis. Chronic treatment of male hpg mice with estradiol induces FSH synthesis and secretion, and causes testicular maturation and qualitatively normal spermatogenesis. As estradiol negative feedback normally inhibits FSH production in the male, this study tested whether this paradoxical response to estradiol in the male hpg mouse might be due to inadequate masculinisation or incomplete defeminization in the neonatal period. Previous studies have demonstrated that treatment of hpg mice with testosterone propionate in the immediate neonatal period is necessary to allow full reproductive behaviors to be expressed following suitable endocrine stimulation at adult ages., Methods: Hpg mice were treated with 100 mug testosterone propionate or vehicle on postnatal day 2. At 35 days of age, subgroups of these mice were treated with silastic implants containing estradiol or cholesterol. Reproductive behavior was scored in tests with steroid-primed female mice, then testicular development was assessed histologically, and measures of pituitary FSH content made at 85 days of age., Results: The neonatal testosterone propionate treatment successfully defeminized female litter mates, as revealed by impaired vaginal opening and deficiencies in lordosis behavior, and it allowed appropriate male reproductive behavior to be expressed in a proportion of the hpg males when tested at an adult age. However, neonatal androgen supplementation did not block or even reduce the subsequent actions of estradiol in increasing pituitary FSH content, nor did it affect the ability of estradiol to induce qualitatively normal spermatogenesis., Conclusion: The ability of the hpg male to show a "female" neuroendocrine response to estradiol is not a result of inadequate androgenization during neonatal development, and thus the actions of estradiol revealed in this rodent model are not an artefact of incomplete sexual differentiation, but reflect a physiological role of estradiol occurring during a specific early temporal window of male reproductive development.

In guinea pigs the behaviour of male offspring is infantilized in adulthood, when their mothers had lived in an unstable social environment during pregnancy and lactation (Kaiser and Sachser, Psychoneuroendocrinology, 26 (2001) 503). The present study was conducted to elucidate the mechanisms bringing about this phenomenon. Therefore, the spontaneous behaviour and endocrine parameters of females were compared that either lived in a stable social environment (SSE) during pregnancy (SE-females) or in an unstable social environment (USE) during this period of life (UE-females). The SSE was made by keeping the group composition (one male, five females) constant; in the USE situation (one male, five females) every third day two females from different groups were exchanged. The spontaneous behaviour of the UE-females was recorded on three successive days: the day before, the day of and the day after the transfer from one group to another. The behaviour of the SE-females was recorded at corresponding times. In addition, serum concentrations of cortisol, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) concentrations were determined. After transfer to another group UE-females showed distinctly more orientation behaviour and they received significantly higher amounts of courtship and sexual behaviour from the males than SE-females which remained in their familiar groups. In turn, UE-females displayed significantly higher amounts of urine spray towards the male, a defensive aggressive behavioural pattern. No differences were found in offensive aggressive and socio-positive behaviours between UE- and SE-females. With respect to endocrine parameters the transfer to an unfamiliar group did not cause an increase of cortisol, that is UE- and SE-females did not differ significantly. DHEAS and in part DHEA concentrations, however, were significantly lower in UE- than SE-females. Thus, for the first time it is shown that the social environment during pregnancy has significant effects on the androgen concentrations in female guinea pigs. Moreover, a decrease of androgens in pregnant females may be related to the infantilization of their male offspring.

Androgens are classically thought of as the sex steroids controlling male reproduction. However, in recent years evidence has accumulated showing that androgens can also be affected by the interactions between conspecifics, suggesting reciprocal interactions between androgens and behaviour. These results have been interpreted as an adaptation for individuals to adjust their agonistic motivation and to cope with changes in their social environment. Thus, male-male interactions would stimulate the production of androgens, and the levels of androgens would be a function of the stability of its social environment ['challenge hypothesis', Gen. Comp. Endocrinol. 56 (1984) 417]. Here the available data on social modulation of androgen levels in male teleosts are reviewed and some predictions of the challenge hypothesis are addressed using teleosts as a study model. We investigate the causal link between social status, territoriality and elevated androgen levels and the available evidence suggests that the social environment indeed modulates the endocrine axis of teleosts. The association between higher androgen levels and social rank emerges mainly in periods of social instability. As reported in the avian literature, in teleosts the trade-off between androgens and parental care is indicated by the fact that during the parental phase breeding males decreased their androgen levels. A comparison of androgen responsiveness between teleost species with different mating and parenting systems also reveals that parenting explains the variation observed in androgen responsiveness to a higher degree than the mating strategy. Finally, the adaptive value of social modulation of androgens and some of its evolutionary consequences are discussed.

Courtship behaviors are androgen-dependent in many vertebrates and castration often decreases courtship. We examined the effectiveness of castration in reducing courtship behaviors and 11-ketotestosterone (KT) and testosterone (T) in restoring them in male white perch. Castrates were given implants containing KT, T or no hormone. Sham-operated males received implants without hormone. Three weeks later, males were exposed to an ovulated female for 1 h and two courtship behaviors were quantified. Attending behavior involves close and continuous following of a female with occasional contact. Circling involves rapid transits around the female in a circular pattern or back and forth in front of her. In plasma samples taken immediately after observations, KT and T were below detectable levels in castrated males but at high physiological levels in males implanted with KT or T. Castrated males given KT attended females more than castrated males given T implants or implants containing no hormone, but not more than sham-operated males. Circling was eliminated by castration but restored by implantation with T or 11-KT to values exhibited by sham-operated males. This is one of the few demonstrations that KT can regulate courtship behavior in a non-territorial and economically important fish species.

Steroid hormones play major roles in the organization of the phenotype and in the activation of behavior. From hatching to fledging, they are involved in growth, development, and learning. We investigated the relationship between the ontogenetic patterns of steroid hormones and the sexual and social development of greylag goslings (Anser anser). Two groups of individually marked goslings (n = 10/5) were hand-raised under near-field conditions. 17beta-OH-androgen (AM), estrogen (EM), and corticosterone (BM) immunoreactive metabolites were measured noninvasively by enzyme immunoassay of individual fecal samples. Feces were regularly sampled from hatching to fledging. All excreted steroids were found to peak at hatching and to decrease thereafter. Gonadal steroids fluctuated more than BM, which remained at low levels throughout ontogeny after a slow decrease during the first 20 days. The pattern of BM is discussed in relation to learning processes (i.e., filial imprinting) and social stress. It is suggested that high initial BM may constrain energy allocation to growth. AM increased around the age of 20 days, when the feathers start growing, and later, together with EM, at the age of 40 days. These elevated values of gonadal steroids are discussed in relation to the sensitive phase of sexual imprinting. Females show higher EM levels than males throughout ontogeny. Furthermore, the ratio of excreted estrogen to androgen (EM/AM) of females before fledging correlates with the number of hatched and fledged goslings in their first years of reproduction. In conclusion, our data suggest a role for steroid hormones in the modulation of behavioral and morphological development in the precocial greylag geese, in agreement with the organizational-activational hypothesis., (Copyright 2001 Academic Press.)

Anogenital distance was used as a biomarker for natural variation in prenatal androgenization of female rats and was associated with individual differences in a suite of reproductive characteristics. Females with short anogenital distances were likely to have first vaginal estrus earlier than females with longer anogenital distances and to have first vaginal estrus on the same day as vaginal opening. In young adulthood, females with short anogenital distances had shorter ovarian cycles and less intense lordosis reflexes in response to manual palpation than those with longer anogenital distances, but only when living individually, not in groups. Taken together, these findings indicate that prenatal androgenization affects reproductive traits throughout the life span., (Copyright 2001 John Wiley & Sons, Inc.)

In the Azorean rock-pool blenny male sexual polymorphism occurs. Larger and older males (M+ males) fully express male secondary sex characters (SSC), particularly an anal gland that produces a sex pheromone, whereas smaller and younger sexually active males do not express SSC (M- males). Two mating tactic types can be identified among M+ males: nest-holders that establish nests and court females and floaters that move around in the breeding area and try to achieve parasitic fertilizations and/or to take over nests. Two behavioral tactic types can also be identified within M- males: satellites that are associated with particular nests and actively participate in territorial defense (when females go inside the nest to spawn they try to enter to fertilize some of the eggs) and sneakers that do not help nest holders (when spawning occurs they also try to enter the nest to fertilize eggs). It was found that M+ males have significantly higher levels of 11-ketotestosterone (KT), but not testosterone (T), than M- males [M+ male androgen levels (mean +/- SE): total T = 11.6 +/- 3.0 ng ml(-1), total KT = 4.5 +/- 1.1 ng ml(-1); M- male androgen levels (mean +/- SE): total T = 9.6 +/- 1.0 ng ml(-1), total KT = 2.5 +/- 1.1 ng ml(-1)]. There were no differences in plasma T or KT among individuals using different mating tactics within the same male morph; that is, among M+ males, nest-holders did not differ in androgen levels from floaters [nest-holder androgen levels (mean +/- SE): total T = 12.3 +/- 4.4 ng ml(-1), total KT = 4.3 +/- 1.4 ng ml(-1); floater androgen levels (mean +/- SE): total T = 5.9 +/- 0.8 ng ml(-1), total KT = 3.4 +/- 0.3 ng ml(-1)], and among M- males, satellites did not differ in androgen levels from sneakers [satellite androgen levels (mean +/- SE): total T = 7.7 +/- 1.5 ng ml(-1), total KT = 1.3 +/- 0.3 ng ml(-1); sneaker androgen levels (mean +/- SE): total T = 8.3 +/- 1.6 ng ml(-1), total KT = 1.4 +/- 0.3 ng ml(-1)]. Thus, the observed differences appear to be correlated with the expression of different male morphotypes and not with the expression of different behavioral tactics within the morphotype. Androgen levels were not correlated with the behavior activity of nest-holders, except for a negative correlation between KT levels and parental behavior. Furthermore, nest-holder males that succeeded in having females spawn in their nests during the observation period had significantly lower KT levels than unsuccessful males. Since behavioral observations preceded blood sampling in time, it is suggested that these results indicate a negative relationship between KT and parental care, since successful males were parenting when blood samples were collected. Male SSC were better correlated with KT than with T and the use of total blood levels (i.e., free + conjugates) yielded higher correlation coefficients than when only the free fraction of each steroid was considered. Since conjugates are nonactive metabolites of the free androgen they should reflect active free steroids in a previous time. Thus, their incorporation into the hormonal measurements increases the time frame captured, and because steroids are released in a pulsatile way, this time-integrated measure can be more meaningful than the free steroids, which represent a snapshot of the hormone levels at a given point in time., (Copyright 2001 Academic Press.)

Morphological and behavioural traits which improve agonistic power are subject to intrasexual selection and, at the proximate level, are influenced by circulating androgens. Because intrasexual selection in mammals is more intense among males, they typically dominate females. Female social dominance is therefore unexpected and, indeed, rare. Ring-tailed lemurs (Lemur catta) are sexually monomorphic primates in which all adult females dominate all males. The goal of our study was to test the prediction that female dominance in this species is associated with high androgen levels. Using two captive groups, we collected data on agonistic behaviour and non-invasively assessed their androgen concentrations in faeces and saliva by enzyme immunoassay. We found that adult female L. catta do not have higher androgen levels than males. However, during the mating season there was a twofold increase in both the androgen levels and conflict rates among females. This seasonal increase in their androgen levels was probably not due to a general increase in ovarian hormone production because those females showing the strongest signs of follicular development tended to have low androgen concentrations. At the individual level neither the individual aggression rates nor the proportion of same-sexed individuals dominated were correlated with their androgen levels. We conclude that female dominance in ring-tailed lemurs is neither based on physical superiority nor on high androgen levels and that it is equally important to study male subordination and prenatal brain priming effects for a complete understanding of this phenomenon.

The larynx of Xenopus laevis is a sexually differentiated vocal organ in which male muscle is entirely fast twitch and expresses high levels of a fast twitch myosin heavy chain gene, LM. Female muscle, however, is mostly slow twitch and expresses little LM. Androgen is unable to induce expression of LM until after metamorphosis is complete. The expression of LM during metamorphic and early postmetamorphic development parallels secretion and expression of the pituitary hormone prolactin. Here, we show that exposure to prolactin is necessary to allow androgen-induced LM expression in postmetamorphic froglets. In prolactin-deprived animals, androgen-induced changes in the contractile properties of laryngeal muscle are blocked, which prevents the rapid rates of muscle contraction required for males to produce courtship songs. Thus, prolactin opens the sensitive period for androgen-induced LM expression in the larynx and controls the ability of male sex hormones to masculinize the vocal system both at the level of gene expression and vocal organ physiology., (Copyright 1999 John Wiley & Sons, Inc.)

The neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 micrograms testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 micrograms estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 micrograms EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I-sCCK-8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK-8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.

Plasma levels of androstenedione (AE), testosterone (T), and dihydrotestosterone (DHT) were measured at 1, 56, 112, and 168 days of age by radioimmunoassay in lines of cockerels divergently selected for male mating frequency. Values for total androgen (total A = AE + DHT + T) were also computed. No significant differences in mean hormone values were found between lines at any age. Hormone patterns throughout development were also similar for both lines. Plasma AE and T increased between Days 1 and 56, stabilized through Day 112, and rose again prior to 168 days of age. In contrast, DHT levels were low throughout Day 112 and rose significantly by Day 168. Total A in the high mating line was low throughout Day 112 with significant increases occurring by Day 168. In the low mating line, total A was low on Day 1, increased significantly by Day 56, and it remained unchanged through Day 112. Peak values occurred by Day 168. Within line correlation analyses between AE, T, DHT, and total A revealed a more uniform hormonal state throughout development in the high mating line than in the low mating line. Because no differences were found between the mating lines in baseline levels of individual androgens or in concentration patterns of androgens up through the attainment of sexual maturity, it appears that neither posthatch baseline levels nor posthatch temporal androgen concentrations control male sexual behavior in the mating lines of birds.

Though unnecessary for life itself, androgens are essential for the propagation of the species and for establishment and maintenance of the quality of life of males through their support of sexual behavior and function, muscle strength, and sense of well-being. In carrying out its many functions, T acts both as hormone and prohormone. It is an outstanding example of the diverse evolutionary utilization of a primitive informational molecule both among and within species. Not only does T act through the androgen receptor both unchanged and via 5 alpha-reduction, but it acts in tissues with a high aromatase level as an estrogen via the estrogen receptor. Furthermore, DHT, binding to the estrogen receptor, can act as an inhibitor of estrogen action. The products of androgen metabolism may also play active regulatory roles in hematopoiesis and in the regulation of certain hepatic enzymes. Table 3 summarizes the actions of secreted T in males indicating the probable effector hormone. While gross hypogonadism is uncommon, mild androgen insufficiency may be much more frequent, especially in older men, and in those receiving treatment for chronic medical conditions. It is quite possible that such individuals would benefit from appropriate androgen therapy were it available, but the current forms of replacement therapy are not very satisfactory. Better approaches are required. With the exception of a small number of secreted proteins, the products of transcription induced by androgens are not, as yet, known. When the androgen receptor gene is cloned it will be possible to identify androgen-regulated genes and their products. It will then be possible to design agents selectively producing specific desired androgenic effects.

Seasonal variations in levels of serum testosterone, dihydrotestosterone (DHT), reproductive behavior, and social behavior were investigated in 12 adult males (5 to 20+ years of age) of the Oregon troop of Japanese macaques (Macaca fuscata). Blood samples were collected at 2- to 4-month intervals, and behaviors were monitored twice weekly over a 15-month period. Significant seasonal variations in levels of testosterone and DHT, and in frequencies of mount series, ejaculations, number of female partners, displays, courtship, and aggression were observed. Seasonal variations in reproductive and social behaviors did not correlate with seasonal variations in androgen levels because seasonal increases in these behaviors followed seasonal increases in the androgens with a 1- to 2-month delay. However, significant correlations between increased androgen levels and the onset of mating activity occur when mean monthly frequencies of mount series are shifted 1 to 2 months earlier to coincide with the rise in serum androgen levels. The frequency of adult male play and male-male mounting increased significantly when androgen levels were low. We suggest that photoperiod changes may function as a proximate cue in male Japanese macaques which induces a state of biological readiness for mating, and the behavioral consequences (i.e., mating) are then dependent upon the presence of receptive females.

Female rats were exposed to immobilization and illumination stress from day 15-22 of pregnancy. Their male offspring showed demasculinization, i.e. significantly decreased male sexual behaviour, and feminization, i.e. significantly increased female sexual behaviour, in adulthood. This permanent demasculinization and feminization of the brain, induced by prenatal stress, could be prevented by perinatal androgen treatment.

1. In male voles developed under three different photoperiods (L:D = 24:0, L:D = 18:6, L:D = 6:18) the following results were obtained. 2. Higher variability of most of the parameters (except testes weight and protein fraction levels) was observed in young males. Hormonal synchronization of parameters studied in adult voles was discussed. 3. Sexual activity measured by morphological symptoms was related to increase of body and testes weights, RBC count, alpha 2- and gamma-globulin levels. There was no parallelism between testes weight and androgen concentration. 4. The increasing photoperiod synchronized groups as far as testes weight, WBC count and androgen concentration was concerned. Constant illumination inhibited sexual maturity and probably haemopoesis and androgen secretion. 5. A long "summer" photoperiod was optimal for male vole reproductive form which was related to high body and testes weight as well as value of red blood cell indices. 6. In the shortest "winter" photoperiod puberty was attained more slowly and blood cell counts showed high values. The high level of androgens might play a role in winter reproduction and aggressive behaviour observed in natural vole population. 7. The lowest values of total protein, albumin and alpha 2-globulin levels were observed in the "summer" photoperiod. Constant light and a long photoperiod did not suppress alpha 1- and beta-globulin fractions which showed the lowest level in short photoperiod ("winter"). It was suggested that light was not the most important factor acting on gamma-globulin (immunoglobulin) level in animals developed in laboratory conditions but can act on their heterogeneity in occurrence of the fraction.

Urinary excretion of oestrogens and androgens by a pair of giant pandas was monitored by radioimmunoassay during behavioural oestrus through two successive breeding seasons. The excretion of oestrogens by the female was at a maximum during the proceptive period and lower during the period of receptivity. In the first breeding season studied, elevated androgen excretion in the male coincided with peak receptivity in the female. The study indicates that accurate timing of natural mating or artificial insemination could be achieved by monitoring oestrogen excretion in the female.

Several experimental and clinical findings suggest that different sex hormones (oestrogens and/or androgens) are responsible for sex-specific brain differentiation of gonadotrophin secretion, sexual orientation and gender role behaviour.