Behavioural and Physiological Effects of Testosterone Propionate and Cyproterone Acetate in Immature Male Domestic Ducks,Anas platyrhynchos

The behavioural and morphological effects of testosterone propionate and of the anti-androgen cyproterone acetate were studied in male domestic ducks. Testosterone was also measured by radioimmunoassay in the plasma of these birds to relate the behaviour to the actual circulating levels of hormone. Testosterone stimulates sexual behaviour but has few effects on social displays. There is no correlation between the individual variations of plasma testoterone and sexual behaviour.     

Inhibition of adult social behaviour in ducks induced by juvenile administration of gonadal hormones

This experiment was designed to study the long-term behavioural effects of gonadal hormone injections into domestic ducklings. Ten male and four female ducklings were injected daily from their 4th day onwards: the males with testosterone propionate and the females with oestradiol benzoate. Five males were injected for 40 days, the other ducklings (5♀ + 4♂) for 80 days. Behavioural effects of these treatments were assessed when the birds were six months old. Social displays were strongly inhibited in the injected males as compared with control birds but no general significant effect was observed for the aggressive and sexual behaviour. The inhibition of social displays is consistent with the view that these behaviour patterns are regulated by the pituitary-gonadal axis and the different levels at which the functional inhibition could have occured are discussed. Far fewer social displays were performed by the males presented with injected females which, on the other hand, showed less sexual behaviour than the control females. This supports the idea that the female plays an important part in the social display of ducks.     

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.     

Behavioural and morphological effects of testosterone and gonadotropins in the young male domestic duck (Anas platyrhynchos L.)

Young male domestic ducks 20–72 days old were successively injected with two hormonal preparations. The first hormone treatment included males injected with testosterone propionate (TP), human chorionic gonadotropin (HCG), pregnant mare serum (PMS), control oil injected males (C) and males injected with TP and submitted at the same time to a permanent intense light. During the second hormonal treatment all males except controls were injected with TP.Almost no behavioural effects were observed in any group of males following the first treatment. The second one, however, induced intense social display and sexual behaviour in the four TP-injected groups. Some qualitative and quantitative differences were found between groups according to the first hormone treatment to which they had been submitted. This suggests a possible role of gonadotropic hormones in the control of social behaviour in ducks. Experimental data supporting this hypothesis are briefly reviewed and discussed.     

Behavioural comparison of aylesbury and mallard ducks: Sexual behaviour

The sexual behaviour of the aylesbury duck is compared with that of its progenitor, the Mallard duck. There have been changes in intensity of the social displays of the Aylesbury duck which tend to reduce the attention-catching features of these displays, and the down-up display is performed less frequently than in the Mallard duck. Aylesbury ducks incite several drakes, Mallard ducks incite only one drake. Similar differences between the two varieties were seen in pre-copulatory pumping. Using several other criteria, as well as inciting and pre-pumping, it was found that Aylesbury ducks do not form pairs whereas Mallard ducks will. The significance of these changes for domestication is discussed.     

Sexual behavior and plasma androgen concentrations in the male eider duck (Somateria mollissima)

Eider ducks showed clear tidal and seasonal cycles of display when involved in pair-formation behaviour. Plasma androgen (testosterone and dihydrotestosterone) concentrations did not follow similar tidal cycles but there was a 4-fold increase of androgen in spring when rates of display increased 2-fold. There was no difference in androgen levels in blood samples taken from paired birds before and after coitus. Androgens therefore appear to be essential for the expression of sexual behaviour, but there is no apparent quantitative correlation between overt sexual activity and androgen concentrations.     

The evolution of courtship display repertoire size in the dabbling ducks (Anatini)

Many animals possess multiple ornaments or behaviours that seem to have evolved via sexual selection. A complete understanding of sexual selection requires an explanation for such multiple traits. The dabbling ducks (Tribe: Anatini) exhibit considerable variation among species in the number of displays in the male courtship repertoire. I tested five hypotheses concerning the evolution of the variation in display repertoire size of dabbling ducks: (1) species recognition, (2) courtship habitat, (3) sexual selection intensity, (4) display media tradeoff and (5) time constraints on pair formation. I tested these hypotheses, using an explicit phylogenetic hypothesis developed from DNA sequences for the dabbling ducks, with two types of statistical comparative methods (discrete and continuous character). The variation observed in male courtship display repertoire size in dabbling ducks was consistent with the courtship habitat and sexual selection intensity hypotheses. Specifically, the size of the display repertoire was larger in species that exhibit courtship exclusively on water and larger in species with dimorphic plumage. These results suggest that ecological (habitat) as well as social (sexual selection) factors may be important in driving the evolution of displays in the dabbling ducks.     

Testosterone and the trade-off between mating and paternal effort in extrapair-mating superb fairy-wrens

High investment in mating and parental effort in male birds are considered mutually exclusive, as testosterone suppresses paternal care and stimulates sexual and aggressive behaviours. Superb fairy-wrens, Malurus cyaneus, are unusual in that males concurrently engage in courtship and paternal care. Fairy-wrens live as stable socially monogamous pairs with up to four subordinate male helpers. The majority of offspring are not sired by any of the males in the group but all group males provide parental care. Throughout the period of care males visit and court neighbouring females. To examine the role of testosterone in this trade-off, I determined the effect of testosterone treatment on the males' time budget, in particular their investment in within- and extrapair sexual behaviours and paternal care. Testosterone did not affect time spent foraging and resting or the number of songs produced. However, the relative investment in sexual and parental behaviours changed, confirming proximate control of this trade-off by testosterone. While there was a large increase in within-pair courtship, which is always rare during the nestling period, testosterone had only a small effect on the most frequent sexual behaviour, extragroup courtship displays. Testosterone failed to induce the maximum frequency of courtship flights of which male fairy-wrens are capable, and I argue that this is because, at prevailing testosterone levels, males are always motivated to leave their territory and social circumstances largely dictate the actual departure rate. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Androgen control of transcortin binding capacity in adult male ducks

In adult male ducks submitted to marked variations in plasma testosterone concentration, plasma transcortin (CBG) levels were shown to be closely related to the level of plasma testosterone. In connection with previous data on female ducks, the results strongly support the evidence that at least in this species, CBG is under a stimulatory control by testosterone.     

Immune activation suppresses plasma testosterone level: a meta-analysis

Females often select mates on the basis of sexual signals, which can be reliable indicators of male quality when the costliness of these signals prevents cheating. The immunocompetence handicap hypothesis (ICHH) provides a mechanistic explanation of these costs, by proposing a trade-off between immune function and sexual displays. This trade-off arises because testosterone enhances sexual signals, but suppresses immune function. Many studies have investigated the ICHH by administrating testosterone, and a recent meta-analysis found little evidence that testosterone suppressed immune function. However, another component of the ICHH, which has received less empirical interest, suggests that there may also be an interaction in the other direction, with immune activation suppressing testosterone levels. We present a meta-analysis to test for this effect. Overall, there was a strong suppressive effect of experimental immune activation on testosterone levels (r=-0.52), regardless of whether live pathogens or non-pathogenic antigens were used to challenge the immune system. The latter is important because it shows that immune activation per se suppresses testosterone levels. Thus, a trade-off between immunocompetence and sexual displays may primarily be generated by the effect of immune activation on testosterone, rather than the opposite effect that has received most attention.     

Oestradiol and prostaglandin F2α regulate sexual displays in females of a sex-role reversed fish

The mechanisms regulating sexual behaviours in female vertebrates are still poorly understood, mainly because in most species sexual displays in females are more subtle and less frequent than displays in males. In a sex-role reversed population of a teleost fish, the peacock blenny Salaria pavo, an external fertilizer, females are the courting sex and their sexual displays are conspicuous and unambiguous. We took advantage of this to investigate the role of ovarian-synthesized hormones in the induction of sexual displays in females. In particular, the effects of the sex steroids oestradiol (E2) and testosterone (T) and of the prostaglandin F2α (PGF2α) were tested. Females were ovariectomized and their sexual behaviour tested 7 days (sex steroids and PGF2α) and 14 days (sex steroids) after ovariectomy by presenting females to an established nesting male. Ovariectomy reduced the expression of sexual behaviours, although a significant proportion of females still courted the male 14 days after the ovary removal. Administration of PGF2α to ovariectomized females recovered the frequency of approaches to the male''s nest and of courtship displays towards the nesting male. However, E2 also had a positive effect on sexual behaviour, particularly on the frequency of approaches to the male''s nest. T administration failed to recover sexual behaviours in ovariectomized females. These results suggest that the increase in E2 levels postulated to occur during the breeding season facilitates female mate-searching and assessment behaviours, whereas PGF2α acts as a short-latency endogenous signal informing the brain that oocytes are mature and ready to be spawned. In the light of these results, the classical view for female fishes, that sex steroids maintain sexual behaviour in internal fertilizers and that prostaglandins activate spawning behaviours in external fertilizers, needs to be reviewed.     

Monthly patterns of testosterone and behavior in prospective fathers

The individual time patterns of salivary testosterone of adult healthy men, self-reported sexual behavior and their co-occurrence with regular weekly or monthly intervals were studied. Twenty-seven volunteer males (mean age 33 +/- 1 years) collected daily morning saliva over a period of 90 days. Evening questionnaires provided daily information on sexual activity. From the saliva, testosterone immunoreactive substances were determined using enzyme immunoassay. To detect events in which increases of testosterone were associated with sexual activity and at the same time controlling for regular internal patterns in men, data were analyzed using Theme software. First results indicated a varying number of complex nonrandom interaction patterns of testosterone with sexual activity, but also with weekly (i.e., Saturdays) and monthly intervals (i.e., 28-day full-moon intervals). The social context of the occurrence of specific pattern combinations was elaborated using parameters from the men's self-reported general life history profiles. Peak hormone levels occurred around weekends in the majority of the males. The 28-day monthly interval coincided with testosterone peaks only in those of the paired men who reported a current wish for children ("prospective fathers"), but not in unpaired men or in those who did not wish to have children with their current partner. Rather than representing a direct regular pattern of the male testosterone per se, the observed patterns suggest that men have the facultative potential to adjust their testosterone responses to their female partner's cycle. In line with the interactions between behavior and androgens observed in vertebrates in general, this study adds an example of the mutual character of hormone-behavior interactions and, thus, for the social context of testosterone patterns in human males.     

Experimental Addition of Green Plants to the Nest Increases Testosterone Levels in Female Spotless Starlings

Multiple male traits and displays may act in signalling sexually selected processes during courtship. Spotless starling males (Sturnus unicolor) carry green plants into their nests before egg laying, and recent studies have shown that this behaviour is related to female breeding decisions and the production of male‐biased broods. Although the functional implications of this effect on females are not yet clear, data suggest that it could be mediated by female circulating hormones. Additionally, females may show higher androgen levels as a consequence of the increased female–female competition generated by the increase in male attractiveness. We tested this hypothesis using the same manipulation of green nesting material that has been previously shown to result in an increase of male attractiveness in male spotless starlings. We found that females in experimental nests increased their circulating testosterone levels during the laying period. In addition, there was an increase of social interferences in the experimental nests because of the addition of green plants. We hypothesise that testosterone may allow females to maintain their mating status when competing with other females for the preferred males. Addition of green plants also increased the variance in the levels of circulating testosterone, suggesting plasticity between females in their response to the manipulation. We propose that there is a functional link between high testosterone levels, male‐biased sex ratios and female resource‐holding potential in intra‐sexual competition in this species.     

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.     

Social mediation of sexually selected ornamentation and steroid hormone levels in male junglefowl

Honest signals in sexual selection may be maintained by a variety of mechanisms. Comb size in male red junglefowl, Gallus gallus, a well-known predictor of female mate choice, is mediated by health and condition. Social status has also been shown to mediate comb size. To determine whether hormones related to male dominance behaviour might be related to social status and comb size, we monitored changes in plasma levels of testosterone and corticosterone following manipulation of social status. We removed young adult male junglefowl from their all-male flocks and placed them either in individual cages or in smaller flocks. We measured comb size and other morphological variables, as well as testosterone and corticosterone levels, before and after the manipulation of social status. Males in small flocks showed reduced comb growth, increased corticosterone and decreased testosterone levels compared with individually housed males. Within flocks, comb size was positively related to dominance rank and to testosterone level, although not always significantly. However, dominance rank was unrelated to either corticosterone or testosterone levels. In isolated birds, testosterone level was not related to comb size. Corticosterone level was not related to comb size in either treatment group. Our results are consistent with social mediation of comb size and testosterone and corticosterone levels, but it is unclear whether these hormones contribute to the observed social limitation of comb length.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

The lower salivary testosterone levels among unmarried and married sexually active men

We examined the influences of regular sexual activity and marital status on salivary testosterone levels in healthy adult Japanese men. Forty-four men (20–66 years) collected their saliva thrice a day (0900–1000, 1300–1400, and 1700–1800). The testosterone levels at each collection time negatively correlated with the ages of the participants; therefore, residual testosterone levels were used for analyses after correcting for age by linear regression. The testosterone-lowering effect of marriage was marginal and the regular sexual activity more strongly associated with lower testosterone levels in morning saliva. The possible neurofeedback systems underlying the phenomenon are discussed.     

Testosterone and Linear Social Dominance Status in Captive Male Dabbling Ducks in Winter

Dominance hierarchies play an important role in avoidance and/or solving conflicts in gregarious species. In dabbling ducks (Anas species), dominance allows for feeding‐site monopolization in winter quarters where resources are generally limited. In addition, male social rank should theoretically favour access to mates. Dominance rank can be associated with morphological traits, and is often correlated with aggressiveness, a behavioural trait generally related to high testosterone levels. In this study, we investigated the existence of a winter group structure based on dominance relationships and tested for a linear hierarchy, in three species of captive male dabbling ducks (mallard Anas platyrhynchos, pintail A. acuta and wigeon A. penelope). We then analysed the relationship between dominance ranks, morphological parameters and testosterone levels measured in early (Oct.) and mid‐winter (Dec./Jan.). We found that the three male groups of the three species exhibited a linear hierarchy. Testosterone levels differed during winter and between species. Morphologic measurements, body mass and body condition were not correlated with individual dominance ranks, whereas dominant males had higher testosterone levels than subordinates. The slopes of the relationships were similar between species and winter period, but the y‐intercepts differed between species and between early and mid‐winter phases. The linear hierarchy found in the three species indicates that dominance relationships strongly structure dabbling duck groups in winter. Lack of correlation between rank and morphological characters, but correlation of rank with testosterone levels suggests that social rank is more dependent on behavioural traits such as aggressive behaviour. The differences between species and winter periods are discussed in relation to migration and wintering phenology.     

Behavioural and hormonal responses of male rhesus monkeys introduced to females in the breeding and non-breeding seasons.

Six adult male rhesus monkeys were introduced individually to an all-female group for 10 days during the mating season. The initial aggressive responses of the females were rapidly replaced by positive social behaviour, and each male achieved alpha status and had access to social and sexual partners. A repetition of this paradigm in the non-breeding season produced significantly more female aggression, and no male attained high rank or engaged in sexual or other social behaviour. Male testosterone levels rose following introduction to the females in both seasons, but were significantly higher during the breeding season. Hormonal levels following removal from the females suggest a complex interplay between social, sexual and seasonal variables and recent social experiences. The differences in female social behaviour with newly introduced males, as a function of season, suggest an explanation for the seasonal limitation of male troop transfers.     

Seasonally of adult male japanese macaques (Macaca fuscata): Androgens and behavior in a confined troop

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.     

Agonistic behaviour and endogenous plasma hormones in male Japanese quail

Agonistic relationships established among male Japanese quail (Coturnix coturnix) in shortterm dyadic encounters of a round-robin tournament were stable and appeared to be maintained by a form of recognition. The aggressive or submissive behaviour displayed by competitors throughout the tournament did not relate to their circulating levels of luteinizing hormone, androstenedione, 5 α-dihydrotestosterone or corticosterone. However, plasma levels of testosterone were correlated with fighting success in the early phases of the tournament, before agonistic associations were defined. Once relationships stabilized, levels of plasma testosterone in winners declined to values comparable with those of the losers and the qualitatively distinct displays observed in winners or losers were no longer correlated with plasma levels of testosterone. In light of other work, these data suggest that androgens, primarily testosterone, influence the aggressiveness of an individual in initial encounters, helping in turn to determine dominance relationships between opponents. Thereafter, other factors such as learned response biases take precedence. The maintenance of stable social relationships appears to be independent of circulating levels of testosterone in adult male Japanese quail.