Effects of exogenous gonadotropic and steroid hormones on the social behaviour and gonadal maturation of male domestic ducklings Anas platyrhynchos L.

Male domestic ducklings were injected during their first month of life with mammalian gonadotrophins (ovine LH or FSH, HMG) or gonadal steroids (testosterone or oestradiol). LH and testosterone stimulated sexual behaviour while oestradiol inhibited the increase of aggression observed in control birds during the experiment. The mammalian gonadotrophins did not increase plasma testosterone but nevertheless they all stimulated the testis growth. Several hypotheses which could explain this finding (stimulation of spermatogenesis without any apparent effect on testosterone) are discussed and the possibility of a direct action of LH on the sexual behaviour is analysed. Social displays were only moderately stimulated by testosterone and not at all by gonadotrophins. The hormonal controls of these behaviour patterns remains thus largely unknown.     

Sexual and aggessive behaviour of castrated male sheep after injection of gonadal steroids and implantation of androgens in the hypothalamus: A preliminary study

The combined effects of hypothalamic steroid implants and subcutaneous hormone injections on the courtship, copulatory and aggressive behaviour of five castrated male sheep (wethers) were assessed in thrice weekly tests with sexually receptive ewes. The animals were prepared with bilateral guide tubes for the insertion of removable hormone-containing cannulae aimed at the preoptic/anterior hypothalamic region of the brain. The sheep were treated as follows: weeks 1-4, cholesterol implants + oestradiol dipropionate injections; weeks 5-7, dihydrotestosterone propionate implants + oestradiol dipropionate injections; weeks 10-12, testosterone terone propionate implants + oil injections; weeks 13-15, testosterone propionate implants + dihydrotestosterone propionate injections. During peripheral treatment with oestradiol dipropionate (weeks 1-4), two of five sheep displayed ejaculatory reflexes in the absence of erection and intromission. Moreover, no obvious behavioural effects could be attributed to the additional presence of central dihydrotestosterone propionate implants (weeks 5-7). By contrast, testosterone propionate implants at the same central sites (weeks 10-12) maintained sexual behaviour in four of five sheep, induced mounting in the remaining animal and stimulated aggressive behaviour in all five sheep. Subsequently, additional peripheral treatment with dihydrotestosterone propionate (weeks 13-15) also stimulated three of the animals to exhibit penile erections.     

Acute changes in plasma testosterone levels and their relation to measures of sexual behaviour in the male house mouse (Mus musculus)

There is an increasing amount of evidence, from several mammalian species, that plasma testosterone levels increase acutely when the male is exposed to sexual stimuli. Work reported here investigates whether such responses occur in male mice, and whether their incidence is related to measures of sexual behaviour. Close proximity of oestrous female mice was found to result in increased plasma testosterone levels in some strains within 15 min. Immediately after a sexual behaviour test, plasma testosterone levels were higher in males showing sexual responses. There were correlations between testosterone levels and mount latency, but none with ejaculation latency. Testosterone levels were greatest at the initiation of mounting responses, and declined during copulation, although not significantly.     

Effects of ovarian hormones on the behavior of captive Macaca fascicularis

To examine the effects of ovarian hormones on the behavior of female Macaca fascicularis and their male partners, daily 1-hr behavior tests were conducted while ovariectomized females were (1) untreated, (2) given estradiol benzoate (EB) (5 μg subcutaneously [s.c.]/day), (3) given estradiol benzoate together with increasing doses of progesterone (P) (5 mg, 10 mg, and 20 mg. s.c./day), and (4) given testosterone propionate (TP) (0.25 mg s.c./day) (six pairs, 540 tests). Weekly blood samples were analyzed by radioimmunoassay for plasma hormone levels (81 samples). Estrogen treatment produced plasma estradiol levels similar to those of intact females during the late follicular phase of the menstrual cycle. Additional progesterone at the lowest dose produced plasma progesterone levels similar to or somewhat higher than those during the midluteal phase, while higher doses produced supraphysiological levels. Androgen treatment resulted in plasma levels well above the physiological range. Hormone treatments produced highly significant effects on the sexual, social, and aggressive interactions of the pairs. As in rhesus monkeys, estrogen increased male and female sexual activity, and increasing doses of additional progesterone reversed these effects. Unlike in rhesus monkeys, testosterone propionate increased both female sexual motivation (invitations) and also male sexual activity and ejaculatory performance. The direction of the hormone-dependent changes in grooming and aggressive interactions confirmed earlier results with intact females and indicated that aggressive interactions and male grooming times were highest, and female grooming times were lowest, when copulatory activity was at its height.     

Timing of reproductive behaviour in male musk turtles,Sternotherus odoratus: effects of photoperiod,temperature and testosterone

Although male turtles are usually regarded as having a post-nuptial pattern of gonadogenesis (i.e. gonadal growth dissociated from time of mating), they do mate both in the spring (when testes are regressed, plasma testosterone levels are low, epididymides are enlarged, and temperature and daylength increasing) and in the autumn (testes and epididymides are enlarged, plasma testosterone levels are elevated, and temperature and daylength are decreasing). Therefore different proximate cues may operate in mediating male reproductive behaviour at different times of year. When temperature, photoperiod and testosterone levels were altered in male Sternotherus odoratus during the year in both laboratory and semifield conditions, reproductive behaviour occurred more readily in autumn than in spring (the supposed major breeding period). Short daylength was the key environmental condition stimulating male sexual activity, while temperature changes ‘fine-tuned’ this behaviour. Testosterone was effective in stimulating male behaviour only under certain environmental conditions and males could become refractory to artificially elevated plasma testosterone levels.     

Quantitative Untersuchungen zu Wechselbeziehungen zwischen Balzaktivität und Testosterontitern bei männlichen Zebrafinken

The determination of hormone titers in small plasma volumes by radioimmunoassay makes it possible to demonstrate the mutual relationship between testosterone titers and sexual behaviour. Testosterone titers were measured after courtship tests in male Zebra Finches to determine whether these levels are influenced by sexual behaviour. The results show that immediately after a courtship test there is a significant difference in hormone levels between sexually experienced and inexperienced birds. Sexual experience can also be shown to influence baseline testosterone titers in male Zebra Finches: experienced ♂♂ have a high baseline level while inexperienced ♂♂ have a low baseline level. In two other behaviour patterns, undirected song and courtship song, it could be demonstrated, that the amount of these behaviours shown is linearly correlated with the amount of testosterone in the blood plasma. Both song types have different hormonal threshold values. The comparison of testosterone titers between different treatment groups can only be made if the groups are maintained under identical conditions, since housing conditions appear to have a very marked influence on testosterone titers. The mechanism of action of testosterone in sexual behaviour is discussed.     

Diurnal variations in plasma testosterone concentrations in the male lesser mouse lemur (Microcebus murinus)

In 6 isolated adult male lesser mouse lemurs, concentrations of testosterone in plasma were determinated at 6-h intervals over a 24-h period. Blood samples were collected at monthly intervals and for a period of 12 months under natural photoperiod. In this nocturnal prosimian, there were no apparent diurnal changes in testosterone concentrations during the non-breeding season (autumn). During seasonal sexual activity (January-August), diurnal changes in testosterone concentrations were characterized by a significant rise during the light phase. The daily testosterone peak occurred about 8.5 h after sunrise from February to July, but at the beginning (January) or at the end (August) of the breeding season, the daily testosterone peak was displaced to the morning. A circannual testosterone rhythm occurred with the highest testosterone values in May/June and the lowest values 6 months later. The dramatic fall in testosterone concentrations after the summer solstice may be associated with a change in the peripheral metabolism of testosterone.     

Removing the confound of time in investigating the regulation of serial behaviours: testosterone, prolactin and the transition from sexual to parental activity in male American kestrels

Understanding the relationships among variables can be difficult if the variables covary with time. Using a simple, commonly used statistical procedure to control for the passage of time, we demonstrate that some hormonal changes traditionally assumed to be causally related to the transition from sexual to parental behaviour can be explained by seasonal changes in the hormones and the fact that parental behaviour follows sexual behaviour in the course of breeding. We quantified immunoreactive prolactin (ir-prolactin) and testosterone concentrations in laboratory-housed and free-living male American kestrels, Falco sparverius, over the course of the breeding season and during sexual and parental phases of reproduction. We found that ir-prolactin increased while testosterone decreased with the transition from sexual to parental behaviour. ir-Prolactin increased with date (i.e. seasonally), whereas testosterone peaked when the frequency of clutch initiation was greatest and then decreased with date thereafter. Controlling for the effects of date eliminated the change in ir-prolactin associated with the transition from sexual to parental behaviour, revealing that prolactin variation associated with this behavioural transition in male kestrels is due, in large part, to seasonal changes in hormone concentrations and the serial nature of these behavioural states. Controlling for the effects of date further revealed that the testosterone difference between sexual and parental males decreases seasonally. It is possible that other phenomena traditionally attributed to environmental, behavioural, social, or other variables also may be explained by the association between such variables and the passage of time.     

Influence of housing and season on pubertal development,boar taint compounds and skin lesions of male pigs

Rearing entire pigs may lead to meat quality and welfare problems in relation to pubertal development. A better knowledge of the sources of variation of pubertal development, behaviour and boar taint is needed before generalizing entire male pigs. From 84 days of age, entire male pigs were reared in groups of 10 either in a conventional (C, 1 m²/animal, slatted floor) or an enriched (E, 2.5 m²/animal, straw bedding, outdoor run) housing during spring or autumn and fed ad libitum (n=10/housing/season). Mounting behaviour was observed for 3 h during the third (M3), fourth (M4) and fifth (M5) months of age. The total number of skin lesions was counted on both sides of the pigs 1 day before the behavioural recordings. The time spent in the outdoor run was also recorded during 3 days per month. The animals were slaughtered at 161±1 days of age (122±9 kg live weight). Blood samples were collected at 89 (M3), 119 (M4) and 152 (M5) days of age and at slaughter for the testosterone and oestradiol measurements. The testes were collected at slaughter, freed from the surrounding tissues and weighed. The fat samples were collected for the androstenone and skatole concentration measurement. Plasma testosterone and oestradiol-17β (oestradiol), fat androstenone and skatole and weight of the testes did not differ between the housing systems. Plasma testosterone (8.3 v. 3.9 nmol/l, P<0.05) and oestradiol (12.0 v. 9.2 pmol/l, P<0.1) at M3, fat skatole (0.124 v. 0.043, P<0.03) and weight of the testes (587 v. 512 g, P<0.05) were higher in the autumn than in the spring trial, suggesting that the pubertal development was accelerated. The number of received mounting behaviours was slightly higher in the autumn (P=0.08) trial and was markedly higher in the E than in the C environment (P<0.003). Skin lesions were more numerous in the C than in the E housing at M4 and M5 and in the spring than in the autumn trial at M3 and M4 (P<0.05). Fat androstenone and the number of performed mounting behaviours were significantly correlated between each other and with numerous indicators of the pubertal development (P<0.05). The number of skin lesions was correlated with plasma testosterone and live weight (P<0.05). Overall, this study suggests the effect of season on sexual development, the effect of the housing system on behaviour, and demonstrates the links between sexual hormones, behaviour and boar taint.     

Exposure of embryos to an aromatization inhibitor increases copulatory behaviour of male quail

This experiment examined the possibility that endogenous embryonic androgen contributes to sexual differentiation of behaviour in male or female quail ($\text{Coturnix}$$\text{coturnix}$$\text{japonica}$), and that it does so via aromatization (conversion to oestrogen). Eggs were injected on day 9 of incubation with oil or ATD (an aromatization inhibitor). As adults, males and females were exposed to short days, injected with testosterone propionate, tested for male-typical behaviour, then injected with oestradiol benzoate and tested for female-typical receptivity. ATD increased the level of male-typical copulatory behaviour in males. Male-typical behaviour in females was not affected, nor was female-typical behaviour in either sex. Thus normal male quail are actually slightly demasculinized by their own androgen during embryonic development, and this process is mediated by aromatization.     

Sexual behaviour of female rats subjected to early protein energy malnutrition

Young rats (left with the mother until weaned) were exposed from birth to the age of 49 days to a low protein (malnutritional) diet. At 80 days the young females were ovariectomized and were subjected to standard long-term treatment with oestradiol and progesterone. The females' sexual behaviour was studied in interaction tests with an intact male. It was evaluated according to a scale of sexual responsiveness comprising copulatory (a lordosis posture) and precopulatory (a presenting posture, hopping, ritualized darting) patterns. All the experimental females displayed a high copulatory readiness and precopulatory behaviour; a tendency to lower sexual responsiveness, interpreted as diminished sensitivity to the given doses of the hormones, was manifested only after their repeated administration. Compared with the control females, the number of experimental animals in which the given doses of the hormones induced complete precopulatory behaviour--ritualized darting--was smaller. The results contrast with findings on the sexual behaviour of males subjected to malnutrition from an early age.     

Some contrasting effects of surgical and “chemical” castration on the behavior of male cynomolgus monkeys (Macaca fascicularis)

In nonhuman primates, surgical castration reduces plasma testosterone levels and male sexual behavior, and testosterone replacement restores them. Chemical castration with compounds that lower plasma testosterone levels is used clinically in the treatment of certain forms of cancer and to reduce aberrant sexual behavior in male sex offenders. In the United States, medroxyprogesterone acetate (MPA) is the drug most used to help reduce serious sexual behavioral problems in men. We were therefore interested in comparing the behavioral effects of MPA treatment (40 mg once a week) in 4 intact male cynomolgus monkeys (4 pairs, 120 tests) with data from an earlier study in our laboratory on 4 males observed before and after surgical castration (16 pairs, 192 tests). Both MPA treatment and surgical castration reduced plasma testosterone to very low levels and decreased ejaculatory activity, but MPA treatment additionally affected measures of male sexual motivation (decreased numbers of male mounting attempts and increased mounting attempt latencies) which were not primarily affected by surgical astration. However, surgical castration decreased intromission ability (percentage of intromitted thrusts per test) and male yawning behavior more rapidly than did MPA treatment. This suggested a hypothesis that different mechanisms could be involved in the behavioral effects—namely, that surgical castration may act primarily via testosterone-dependent peripheral mechanisms, while chemical castration with MPA does so primarily via central mechanisms regulating sexual motivation.     

Sex steroid correlates of female-specific colouration,behaviour and reproductive state in Lake Eyre dragon lizards, <Emphasis Type="Italic">Ctenophorus maculosus</Emphasis>

In some species, females develop bright colouration to signal reproductive status and exhibit behavioural repertoires to incite male courtship and/or reduce male harassment and forced copulation. Sex steroids, including progesterone and testosterone, potentially mediate female reproductive colouration and reproductive behaviour. We measured associations among plasma profiles of testosterone and progesterone with variation in colour expression and reproductive behaviour, including unique courtship rejection behaviours, in female Lake Eyre dragon lizards, (Ctenophorus maculosus). At onset of breeding, progesterone and testosterone increased with vitellogenesis, coincident with colour intensification and sexual receptivity, indicated by acceptance of copulations. As steroid levels peaked around the inferred ovulation time, maximal colour development occurred and sexual receptivity declined. When females were gravid and exhibited maximal mate rejection behaviours, progesterone levels remained consistently high, while testosterone exhibited a discrete second peak. At oviposition, significant declines in plasma steroid levels, fading of colouration and a dramatic decrease in male rejection behaviours co-occurred. Our results indicate a generally concordant association among steroid levels, colouration, behaviour and reproductive events. However, the prolonged elevation in progesterone and a second peak of testosterone was unrelated to reproductive state or further colour change, possibly suggesting selection on females to retain high steroid levels for inducing rejection behaviours.     

Seasonal changes in serum steroid hormones in a protandrous teleost, the sobaity (Sparidentex hasta Valenciennes)

Serum concentrations of 11-ketotestosterone, 11β-hydroxytestosterone, testosterone, testoster-one glucuronide, oestradiol and 17,20β -dihydroxy-4-pregnen-3-one (17,20β -P) were measured in the sobaity at monthly intervals through their second breeding season. Concentrations of the 11-oxygenated androgens in the males and of oestradiol in the females peaked during the spawning season in January-February, while maximum levels of testosterone were found in the summer when these steroids were low. Testosterone glucuronide showed two peaks, one in the post-spawning period as oestradiol and the 11-oxygenated androgens were falling and the other coincident with the summer peak of testosterone. 17,20β -P was detectable in only one male and one female fish in February. Serum concentrations of 11-oxygenated androgens are more reliable than those of oestradiol for determining the sex of sobaity, and may also be used as indicators of the occurrence of sex reversal. The seasonal pattern of serum steroids correlated well with the changes of sexual status of the gonads during regression and recrudescence observed histologically and suggests that oestradiol may be involved in the sex inversion of this species.     

Seasonal and social correlates of fecal testosterone and cortisol levels in wild male muriquis (Brachyteles arachnoides)

Fecal testosterone and cortisol levels were analyzed from six wild male muriquis (Brachyteles arachnoides) over a 19-month period at the Esta??o Biológica de Caratinga in Minas Gerais, Brazil, to investigate the hormonal correlates of seasonal sexual behavior and environmental conditions. Group mean testosterone levels based on weekly samples from the six males did not differ between copulatory and noncopulatory periods or between rainy and dry seasons. Cortisol levels did change with copulatory periods, and were significantly higher during the second dry season, when mating continued following an exceptionally heavy rainy season, than during the first dry season, when mating ceased. Males exhibited individual variation in the timing of their hormone shifts relative to their sexual activity, but neither hormone levels nor sexual activity were related to male age. Despite individual differences in the timing of testosterone fluctuations around the onset and offset of the copulatory season, all males exhibited elevated cortisol concentrations following a slight increase in testosterone at the beginning of the copulatory season. Both the lack of significant changes in testosterone levels with the onset of the rainy and copulatory season and the lack of prebreeding increases in cortisol may be related to the low levels of overt aggression displayed by male muriquis over access to mates.     

Effect of female sexual displays on the endocrine physiology and behaviour of male white-crowned sparrows, Zonotrichia leucophrys

In photoperiodic birds, endocrine responses to behavioural interactions between males and females may be involved in temporally "fine-tuning" the onset of reproduction to yearly variations in the environment. This study examined the endocrine and behavioural responses of male White-crowned sparrows ( Zonotrichia leucophrys ) to changes in the endocrine state of the female, as signalled by changes in her behaviour. Males on different photoperiodic regimes were paired with oestrogen-treated, sexually receptive females. Males exposed to gonadostimulatory long days mounted and copulated with oestrogen-treated females even before gonadal development was complete. These males had higher plasma levels of testosterone and luteinizing hormone and maintained enlarged testes longer than control males paired with untreated, nonreceptive females. Males maintained on nonstimulatory short days also mounted oestrogen-treated females; however, testes of these males remained nonfunctional and their plasma levels of testosterone and luteinizing hormone were basal. Thus, reproductive function of photostimulated males is profoundly affected by changes in the endocrine state and behaviour of the female. However, male sexual behaviours are expressed in response to visual and auditory stimuli from the female regardless of male hormonal condition or photoperiodic treatment.     

The regulation of the biologically available fractions of oestradiol and testosterone in plasma

The albumin bound fractions of oestradiol and testosterone have been measured in samples of plasma obtained over a 24 h period from women with breast cancer or polycystic ovarian disease and from pre- and postmenopausal control subjects and related to plasma levels of free fatty acids. For most subjects changes in the fraction of oestradiol bound to albumin were related to changes in plasma levels of free fatty acids. A significant decrease in the albumin bound testosterone fraction during the night was associated with increased plasma levels of cortisol.     

Placebo-controlled study of effects of epimestrol on the pituitary-testicular axis in normal men

Twenty healthy male volunteers were randomly allocated to the treatment with either 15 mg/day of epimestrol or placebo for 10 days. The plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), oestradiol (E2) and prolactin (PRL) were measured before, during and 4 days after the medication by radioimmunoassays. Data were statistically evaluated by means of an analysis of covariance. Circulating LH and FSH, and also T and E2 significantly increased in the epimestrol treated subjects. In the placebo treated subjects no significant changes in the plasma hormone levels were observed. There were no significant changes in the plasma levels of PRL in either group.     

Effects of testosterone implants on pair behaviour during incubation in the Yellow-legged Gull Larus cachinnans

The Yellow-legged Gull Larus cachinnans is monogamous with bi-parental incubation. In this study, the effects of high levels of plasma testosterone in male Yellow-legged Gulls during the incubation period were analysed. Free-living male gulls were implanted with testosterone (T-males), and their sexual behaviour within the pair was observed and compared with that of control pairs. Egg temperatures, length of incubation and hatching success were also analysed. T-males and their mates displayed more sexual behaviour than the controls. T-males engaged in mounting behaviour with their mates, whereas control males did not. Proportionally less time was spent incubating (in relation to time present in the colony) by T-males than control males. However, the mates of T-males did not spend more time incubating than control females to compensate for male neglect, although they did spend more time on the territory. Egg temperature in T-male nests was significantly lower than in control nests, but no significant difference in the length of incubation or hatching success between the two groups was found. In birds, the effects of high testosterone levels on male behaviour during incubation have only been analysed in a polyandrous species whose females usually do not contribute to incubation. The present results thus suggest that those males of a monogamous species with bi-parental incubation that sustain high testosterone levels after laying, thus reducing their contributions to incubation, will be confronted with a lack of compensation from their mates during incubation. Finally, this lack of female compensation seems to be mediated by behavioural interactions with the male rather than by her absence from the colony.     

Effects of testosterone on the behavior of male cynomolgus monkeys (Macaca fascicularis)

To determine the threshold doses of testosterone propionate (TP) that cause clear-cut behavioral changes in the sexual behavior of castrated male cynomolgus monkeys, observations were made on three males during successive 5-week treatment periods while they received daily subcutaneous doses of 100 μg TP increasing in octaves to 25.6 mg TP. Males were tested with each of the same two ovariectomized, estrogen-treated females (6 pairs, 330 1-hr behavior tests). To mimic the diurnal plasma testosterone rhythm, TP injections were given at 1600 hr and blood samples were obtained at 0800 hr (141 samples). Male ejaculatory activity increased at the threshold dose of 200 μg TP per day giving plasma testosterone levels of 830 ng/100 ml, which is in the physiological range of 600–1600 ng/100 ml for intact males. This threshold dose was eight times higher than in rhesus monkeys on a dose per kilogram body weight basis. There was a further marked increase in ejaculatory performance at higher doses (6.4 to 25.6 mg) giving supraphysiological plasma levels of 4000–9000 ng/100 ml. There were individual differences in the behavioral changes occurring with TP treatment, and the female partner modulated the effects. These findings were generally similar to those obtained with male rhesus monkeys, but certain species differences were noted.