Hormones and Behavior 54 (2008) 227–233

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Hormones and Behavior

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Review Testosterone control of male in

Leonida Fusani ⁎

Department of Biology and Evolution, University of Ferrara Via Luigi Borsari 46, 44100 Ferrara, Italy

ARTICLE INFO ABSTRACT

Article history: A sequence of behaviours which we call courtship initiates reproduction in a large number of species. In Received 19 February 2008 vertebrates, as a component of male sexual behaviour courtship is strongly influenced by testicular androgen. Revised 8 April 2008 Here I will review some salient issues about the regulation of courtship by testosterone in birds. The first Accepted 10 April 2008 section will briefly summarize the first 100 years of research on this topic. The specific role of testosterone or Available online 23 April 2008 its oestrogenic metabolites in the control of different components of courtship will be the subject of the fi Keywords: second section. Then, I will discuss how behavioural patterns can be recruited into courtship and modi ed in Courtship their structure by testosterone action. In the following section, the role of and female choice in shaping the link between testosterone and courtship will be addressed. The problematic nature of the Sexual behavior quantitative relationships between testosterone and behaviour will be topic of the fifth section. Finally, I will Androgen discuss how courtship traits that are activated by testosterone can be apparently independent of hormone Testosterone blood concentrations. These issues will be examined in an evolutionary perspective, in an attempt to Sexual selection understand how natural and sexual selection have shaped the links between the hormone and the behaviour. © 2008 Elsevier Inc. All rights reserved. Avian

Contents

A brief history of the behavioural endocrinology of avian courtship ...... 227 Hormonal specificity in the activation of courtship displays ...... 228 Changes in display structure related to courtship context ...... 229 Theroleofsexualselectioninshapingthelinkbetweentestosteroneandcourtship...... 229 The puzzling relationship between plasma T concentrations and courtship behaviour ...... 230 Can courtship be androgen-dependent and -independent at the same time? ...... 230 Conclusions ...... 231 Acknowledgments ...... 231 References ...... 231

Courtship is a fundamental component of reproduction in animals. primarily via visual and acoustic signals in a frequency range similar to Courtship may have several non exclusive functions: species recogni- that used by humans, making them a good model system for studying tion, pair bond formation, synchronization of reproductive physiology, the evolution, endocrinology and neurobiology of sexual signals. In and advertisement of mate quality. In many species reproduction this paper I will discuss a few salient issues concerning the control of involves behavioural coordination between males and females, courtship by testosterone and its metabolites in male birds. Readers particularly when successful fertilization requires physical contact interested in the hormonal control of courtship in female birds and in between the sexes. Given its importance in reproduction, it is not other taxa can find many excellent, recent books and reviews on these surprising that courtship behaviour in males and females is topics (Adkins-Regan, 2005; Miles et al., 2007; Moore et al., 2005; Neal modulated by gonadal hormones. Birds have proven to be valuable and Wade, 2007; Oliveira et al., 2005; Woolley et al., 2004). subjects for studies on the behavioural endocrinology of courtship for many years. Species with elaborate courtship are found in many other A brief history of the behavioural endocrinology of avian courtship taxa, from insects to fish to , however birds communicate The study of the hormonal control of avian courtship dates back to the work of Colonel George Montagu (1802), who observed that in ⁎ Fax: +39 0532 207143. male songbirds the singing activity was higher in the periods in which E-mail address: [email protected]. birds had enlarged testes. Almost 50 years later, Berthold (1849)

0018-506X/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2008.04.004 228 L. Fusani / Hormones and Behavior 54 (2008) 227–233 performed the first experiment in behavioural endocrinology. It was 2004; Gahr, 2007). For example, genetically male quails chimera that well known by breeders and farmers that castration of young had received a female forebrain primordium during development cockerels prevents the development of male sexual traits including before sexual differentiation had started showed only rudimentary crowing and sexual behaviour. Berthold showed that these traits could male sexual behavior (Gahr, 2003). be restored in the castrated male by implanting the testes of the same The activation of courtship in adults results from the action of bird or of other males intraperitoneally, and noted that the grafted steroid hormones in the preoptic areas and the anterior hypothalamus testes did not build any tissue connection with the body of the host (HPOA). In the 1970s it was shown in several bird species including (Berthold, 1849). Thus, almost a century before gonadal hormones ring doves, domestic fowls, and quails, that implantation of testoster- were isolated, it was shown that substances secreted by the testes – one T crystals directly in the HPOA of castrated males elicits courtship ‘androgens’–are responsible for the activation of male sexual behaviour (Adkins-Regan, 1981; Barfield, 1971; Hutchison, 1970b; behaviour, including courtship. Hutchison, 1971). In all species studied so far, the activation of At the end of the 1940s', there was convincing evidence that in courtship by steroid action in the HPOA seems to be the rule (reviewed birds male sexual behaviour is facilitated by androgens secreted by the by Balthazart and Ball, 2007). Even in songbirds, that have a testes (reviewed by Beach, 1948; Collias, 1950). By this time, a number specialized neural network for the control of song, the activation of of observations had suggested a correlation between testicular cycles singing (as opposed to the quality of song produced) might depend and seasonal variations in courtship behaviour, and androgen- mainly on hormonal action within the HPOA (Riters and Ball, 1999; dependence of distinctive male behaviour had been demonstrated reviewed by Ball et al., 2004). experimentally in Galliformes, Columbiformes, Charadriiformes, Courtship, however, is not a unitary behaviour but rather the Ciconiformes, Anseriformes and Passeriformes (Beach, 1948; Collias, coordination or assemblage of several distinct behavioural patterns 1950). The establishment of a relationship between androgens and that might have separate hormonal control. The ring dove remains one male courtship represented an important advance in the under- of the best-studied species in this respect. The courtship of the male standing of the behavioural differences between the sexes. However, ring dove includes three principal patterns: the bowing display, the several observations suggested that the differences in the circulating chasing display, and the nest-soliciting display. The first two displays, levels of gonadal hormones were not the sole determinant of sexual chasing and bowing, have been called ‘aggressive’ displays because dimorphic behaviour. Already in 1918, Goodale had observed that it they are also used in male-male aggressive interactions, whereas nest- was not possible to elicit female sexual behaviour in capons by soliciting is exclusively a courtship display (Davies, 1970; Lovari and implants of ovarian tissue (cited by Young et al., 1964). Attempts to Hutchison, 1975; Martinez-Vargas and Erickson, 1973; Miller and induce male behaviour in females by androgen treatment provided Miller, 1958). A series of classical studies demonstrated that the conflicting results. For example, Hamilton (1938) could induce aggressive displays (chasing and bowing) are androgen treatment, crowing in young male domestic fowls by injecting testosterone (T) whereas the nest-soliciting is oestrogen-dependent (Adkins-Regan, propionate from the second day after hatching. Crowing could not be 1981; Cheng and Lehrman, 1975; Hutchison, 1970a; Hutchison, 1971). induced in female chicks, despite “no apparent reason why the female For example, intra-hypothalamic implantation of T induces the full fowl should not crow provided it had the instinct to do so properly courtship that includes both aggressive and nest-orientated displays, developed” (Myers, 1917 and Appel, 1929; cited in Hamilton, 1938,pg whereas implantation of 17β-oestradiol (E2) crystals elicits nest- 56). In the following 2 years three researchers were able to bring adult soliciting specifically (Barfield, 1971; Hutchison, 1970b; Hutchison, female canaries into song by treating them with T (Baldwin et al., 1971). Courting male doves have elevated levels of T but very low 1940; Leonard, 1939; Shoemaker, 1939). T-treated female canaries not levels of E2 (Korenbrot et al., 1974), and it was therefore suggested that only developed a song similar to that of males, but also other male nest-soliciting is elicited by oestrogen formed within the brain by courtship behaviours never observed among untreated females aromatization of circulating androgen (Hutchison, 1976). Later work (Shoemaker, 1939). In general, induction of male-specific behaviour provided further support to this hypothesis (Hutchison and Steimer, and vocalisations in females at this time was either unsuccessful or 1984; Steimer and Hutchison, 1980, 1981). But why are different required administration of androgen for a longer time or in larger courtship displays controlled by different hormones? One explanation doses (Collias, 1950). Similar observations in mammals led to the could lie in the separate contextual origins of the displays. It is not formulation of the ‘Organisation-vs.-Activation’ hypothesis for the unusual that courtship sequences are composed of behavioural sexual differentiation of behaviour (Phoenix et al., 1959): during patterns that also occur in other contexts, and aggressive displays in development, gonadal hormones organise in an enduring way the particular are typical components of courtship (Berglund et al., 1996; sexual differentiation of neural tissues; in adulthood, gonadal Tinbergen, 1965). For example, in several species of bowerbirds hormones act on sexually dimorphic neural centres to activate sex- courtship includes displays that have been co-opted from aggressive specific behaviour. contexts (Borgia and Coleman, 2000). In the ring dove, chasing is a typical aggressive display shown by both sexes during aggressive Hormonal specificity in the activation of courtship displays interactions (Lovari and Hutchison, 1975; Miller and Miller, 1958), and bowing is a male-specific display performed by males during Work with domesticated species such as the ring dove (Streptopelia territorial interactions (Davies, 1970). Nest-soliciting, on the contrary, risoria), the Japanese quail (Coturnix coturnix japonica), and the is performed by both males and females during nest-building and domestic fowl (Gallus gallus), elucidated the mechanisms responsible incubation (Miller and Miller, 1958). Most likely, the three displays for the development and adult activation of sexual dimorphic have been assembled to form the courtship but each has maintained behaviour. Similar to mammals, the sexual differentiation of sexual its own hormonal control mechanisms. This separation could have behaviour in birds is organized by hormones secreted by the been maintained because of developmental constraints related to the embryonic gonads. However, while in mammals it is T secreted by sexual differentiation of the courtship behaviour. For example, bowing the testes which masculinises the brain and behaviour, in birds the is a male-specific behaviour, whereas nest-soliciting is common to situation is reversed: a bird would develop into a male phenotype males and females. Thus, it appears that androgen-dependent bowing unless oestrogen secreted by the embryonic gonads de-masculinises undergoes developmental sexual differentiation whereas oestrogen- brain and behaviour (reviewed by Adkins-Regan, 1987; Balthazart and dependent nest-soliciting does not. Ball, 1995). Although gonadal hormones play a primary role in the The hypothesis of a combination of behavioural patterns with sexual differentiation of brain and behavior, there is increasing different origins, in fact, may apply also to the coordination of the evidence that non hormonal factors contribute to this process (Arnold, vocal and postural components of the display (Fusani et al., 1997b). L. Fusani / Hormones and Behavior 54 (2008) 227–233 229

The vocalizations of the bowing display and of the nest-soliciting are gate when opened (McCabe and Hawkins, 1946). The rusty-gate call very similar and the small structural differences between bow-calls functions as a gathering call during the winter but becomes a and nest-calls are probably due to the different postures in which they territorial, courtship and mate contact call in the breeding season are emitted (Fusani et al., 1997b). The best evidence for the fact that (McCabe and Hawkins, 1946). The call, however, changes seasonally in postural movements and vocal patterns assembled in a display can its structure, becoming longer in duration in winter as compared to have separate origins comes from studies on crowing of quail-chicken spring (Fusani et al., 1993; Rotella and Ratti, 1988). Because this midbrain chimeras, which crows like roosters but with the typical transition parallels the vernal rise in circulating androgen (Lupo et al., head-shaking of quails (Balaban, 1997). 1990), we hypothesized that the lengthening of the call was driven by An alternative (but not exclusive) hypothesis is that the separate the seasonal increase in circulating T. Indeed, when male partridges hormonal control might function to regulate the behavioural transi- are given T implants in the early winter, their calls become longer in tions that occur during the progression of courtship. Initially males duration and resemble spring calls (Fusani et al., 1994). Interestingly, T perform all three displays, but the performance of nest-soliciting has another effect on the behaviour of the male: it increases the increases progressively to peak 2–3 days after the first courtship amount of time the animal spends in vigilance behaviour, i.e. interactions, and the aggressive displays become infrequent (Lovari screening the surrounding to detect the presence of predators (Fusani and Hutchison, 1975). The increase in nest-soliciting follows the sharp et al., 1997a). This effect might appear, at a first glance, unrelated to rise in the rate of aromatization within the brain, which starts the effect on call duration. However, there is a link between the increasing as soon as 4 h after the beginning of the courtship (Dudley two traits, the call and the vigilance, and this link relates to criteria et al., 1984). We tested if aromatization of circulating androgen could used by females to choose males. In fact, females prefer to mate with be responsible of the changes in the composition of courtship by males who spend more time in vigilance, probably because this treating intact males that were already courting with an aromatase indicates that they will effectively protect them and their offspring inhibitor, Fadrozole (Fusani et al., 2001a). In males treated with a (Dahlgren, 1990). This brings us to an important point: to under- relatively low dose of Fadrozole, targeted to reduce significantly stand more clearly the proximate mechanisms of hormonal control of aromatase activity without blocking it completely, nest-soliciting courtship, we need to examine them in an evolutionary framework, decreased during the 6 days of treatment (Fusani et al., 2001a). Thus, it that is, in light of the interplay between male courtship traits and is likely that the regulation of brain aromatization of gonadal T is the female choice. mechanism that allows rapid changes in courtship behaviour in male doves. Importantly, these behavioural changes directly influence The role of sexual selection in shaping the link between testosterone female reproductive development: High rates of aggressive displays and courtship results in a longer interval between pairing and egg laying (Hutchison and Lovari, 1976). It was Daniel Lehrman, a founder of behavioural endocrinology, who first studied how males and females influence the endocrine Changes in display structure related to courtship context state of each other through the behavioural interactions of courtship (Cheng and Lehrman, 1975; Erickson and Lehrman, 1964; Silver et al., In the large majority of seasonally breeding birds of temperate 1973). Lehrman and his collaborators illustrated how the courtship European and North American regions, the testes are regressed in behaviour of the male affects the development of the female autumn and start growing in size in winter, with the lengthening of , in a perspective of behavioural and physiological the photoperiod after the winter solstice (Dawson et al., 2001). coordination between the sexes. In fact, at that time courtship was Gonadal recrudescence and the consequent rise in circulating T levels mainly seen as a behavioural tool to recognize a conspecific mate and activate the full set of reproductive behaviours including territorial synchronize breeding. Later progress in evolutionary theories (e.g. see aggression and courtship (Wingfield and Farner, 1993). Thus, the Andersson, 1994; Trivers, 1985) highlighted the existence of a conflict appearance of courtship is one indicator that the birds have gone between the sexes because of differences in the extent of parental from a non-breeding to a breeding condition, and this transition is investment: For males, reproductive success depends mainly on the marked by the increase in circulating T. Courtship, as a component of number of females, thus males will try to mate with as many females sexual behaviour, follows an on-off mechanism: it appears at the as possible. Females, on the contrary, will try to select the best males beginning of the breeding season and disappears at its end. Thus, to make a good investment for their energetically expensive eggs. there is a qualitative difference between sexual behaviours including Females may choose their mates on the basis of many different factors, courtship and other behaviours associated with reproduction and which range from territory size, to morphological traits, to behaviour. increased plasma T levels: Whilst the former are not shown in other Female choice is one of the processes of sexual selection, that periods of the year or life history stages, the latter might be present particular type of selection described by Darwin as the force behind all the time but are enhanced by T during the breeding season. the evolution of ‘odd’ seemingly maladaptive morphological and For example, in most species in which males defend a territory behavioural traits — i.e. elaborate ornaments and courtship (Darwin, during the breeding season territorial aggression is regulated by T 1871). Such traits may reduce the survival of the bearer and thus they (Wingfield and Farner, 1993; Wingfield et al., 1990). However, some seem to have evolved ‘against’ natural selection. However, the survival species defend a territory also outside the breeding season, and in costs of ornaments and courtship are balanced by the increased these cases territorial aggression can be independent of T (Canoine reproductive success of males that are preferred by females. Current and Gwinner, 2002; Schwabl et al., 2005; Schwabl and Kriner, 1991; theories on the evolution of elaborate courtship traits have addressed Soma et al., 1999). the link between testosterone and sexually selected male traits. To be In the previous section, we pointed out that courtship displays a reliable indicator of the quality of the male, the trait needs to be an often include behaviour common to other social contexts, and we honest signal: only males of good quality can afford the costs of made the example with aggressive displays. In some cases, hormones elaborate courtship. It has been hypothesized that sexual selection is not only recruit behavioural patterns into courtship, they also modify based on traits which are testosterone-dependent, because high the structure of these behaviours. In the grey partridge (Perdix perdix) testosterone levels are ‘costly’ in term of energy, metabolism, males and females spend the winter in groups and monogamous pairs immunocompetence, and more (Folstad and Karter, 1992; Wingfield form in the late winter. A key factor in pair formation is the long- et al., 2001; Zuk et al., 1995). However, calculating the actual costs of T distance call of the male (Beani and Dessì-Fulgheri, 1995), which has is not an easy task and it is still unclear if and how costly high plasma been called ‘rusty-gate’ call for it resembles the noise made by a rusty T levels are (Adkins-Regan, 2005). 230 L. Fusani / Hormones and Behavior 54 (2008) 227–233

Birdsong is a classical example of a behavioural ornament. It would be hard to explain the evolution of this behaviour without putting sexual selection in play. It has been shown in many species that singing activity is closely related to gonadal androgen (reviewed by Ball,1999). It is more difficult, however, to link a specific aspect of the song structure – i.e. extension of the syllable repertoire, spectral features, complexity — with hormonal action (Gil and Gahr, 2002). The literature on the influence of hormones on song development and expression is vast and reviewing it is beyond the scope of this paper. I focus here on one specific aspect: the action of oestrogenic metabolites of T. In the 1970s', Naftolin and collaborators showed that the action of T within the brain can be mediated by its aromatization into E2 (Naftolin et al., 1975). Songbirds have very high concentrations of aromatase in the forebrain (Schlinger and Arnold, 1991, 1992)(Metzdorf et al., 1999; Saldanha et al., 1998). The ‘master’ nucleus of the neural song system, Fig. 1. Hypothetical model of a physiological trade-off for hormone-controlled traits. Androgen such as testosterone can be converted into oestrogen within the brain. If a the HVC, contains oestrogen receptors (Gahr et al.,1987,1993; Nordeen sexually attractive trait is enhanced by oestrogen whereas an agonistic trait involved in et al., 1987)(Bernard et al., 1999) and is surrounded by the forebrain male-male interaction is enhanced by androgen, the investment into each trait will limit region with the highest density of aromatase, the caudo-medial the investment into the other one when the amount of androgen substrate is limited nidopallium (NCM) (Metzdorf et al., 1999; Saldanha et al., 1998; Shen and the concentrations of androgen and oestrogen are thus inversely proportional. et al., 1995; Vockel et al., 1990). The expression of aromatase in NCM changes between seasons in parallel with T levels (Fusani et al., 2000; been shown for some morphological traits (Briganti et al., 1999; Peters Soma et al., 1999; but see Silverin et al., 2000) and is increased after et al., 2000), there is little support for the view that courtship displays T treatment (Fusani et al., 2001b). Several authors had described effects are correlated with testosterone in a proportional fashion (Adkins- of oestrogen on the structure of the song (DeVoogd,1986; Marler et al., Regan, 2005; Hews and Moore, 1997). Several studies that reported a 1988; Marler et al., 1987; Weichel et al., 1989; Weichel et al., 1986) and dose-dependent relationship between courtship behaviour and in two species oestrogen are specifically involved in the regulation of testosterone examined courtship in males who had been castrated courtship song, i.e. song clearly directed at females (Harding et al., and then treated with exogenous hormone. For example, in castrated 1988; Walters et al., 1991). We studied the specific role of oestrogen in Japanese quails the frequency of behaviour shown by males given defining the structure of song using a peculiar model: the induction of testosterone implants of variable lengths is proportional to the size of song development in female canaries by T treatment. the implant (and thus probably to the amount of circulating Female canaries usually produce little or no song, but when they are testosterone) but the maximum frequencies does not differ from treated with T they develop a robust, male-like song within 3–4 weeks those recorded in intact males (Balthazart et al.,1990). These effects do (Leonard, 1939). This behavioural development is accompanied by the not require a proportional correlation between the hormone and the masculinisation of the song system (DeVoogd et al., 1985; Heid et al., behaviour. The activation of courtship could require a threshold 1985; Nottebohm, 1980). We compared the songs of females that were concentration of androgen to be reached, and the apparent dose- implanted with Talone or with Tand the aromatase inhibitor Fadrozole dependent response would result from the existence of individual to reduce the formation of oestrogen. Females canaries implanted with thresholds: a larger dose would activate courtship in a larger T and Fadrozole developed male-like songs that did not differ from proportion of birds (“Multiple Threshold Hypothesis”, Hews and those of T implanted females in their overall structure (Fusani et al., Moore, 1997). Female choice for T-dependent behavioural traits, 2003). However, songs of females treated with T and Fadrozole had a however, implies that among males in reproductive conditions – i.e. lower proportion of tours – i.e. repetition of the same syllable – with above the activation threshold – there are individual differences in the high syllable repetition rates (Fusani et al., 2003). The interesting plasma concentration of T that are proportionally related to the aspect of these results is that sexually receptive female canaries show expression of the traits under selection. So far, there is little evidence higher sexual responses to songs with high syllable repetition rates, no that behavioural traits follow this type of relationship when courtship matter if the songs are recorded from males (Vallet and Kreutzer,1995) is fully expressed (this issue is reviewed in detail by Adkins-Regan, or T-treated females (Vallet et al., 1996). Thus, one of the sexually 2005; Ball and Balthazart, 2007). In part, this is due to the fact that few attractive parameters of canary song, the syllable repetition rate, studies have specifically tested this hypothesis (Hews and Moore, seems to depend on oestrogenic metabolites of T. Similar effects of 1997). In ring doves, T treatment of intact males already in full Fadrozole on the syllable repetition rate were described recently for reproductive condition and actively courting produces no change male canaries (Rybak and Gahr, 2004), suggesting that our results in either in the amount of courtship or in the relative proportion of females (Fusani et al., 2003) represents a more general phenomenon. courtship displays (Fusani and Hutchison, 2003). In some cases the These studies points to a trade-off between androgen- and lack of a proportional correlation between behavioural traits and oestrogen-controlled traits: androgen is responsible for the develop- circulating T could result from the choice of the behavioural variables ment and stabilization of the sexually dimorphic song structure, or the level of analysis. Studies on the behavioural aspects of the whereas oestrogen favours the organization of sexually selected courtship have focused on the intensity of courtship (frequency and aspects of the song (Fusani et al., 2003). In such a scenario, enhancing duration of display) and less on its structure. However, in male ring the sexual attractiveness of the trait would be at the cost of androgen- doves a detailed behavioural analysis of both vocal and postural dependent components that may be important for male–male components of the bowing display found no effect of increased interactions (Adkins-Regan, 2005; Fusani et al., 2003)(Fig. 1). circulating T (Fusani and Hutchison, 2003), suggesting that courtship traits in this species do not reflect T concentrations. The puzzling relationship between plasma T concentrations and courtship behaviour Can courtship be androgen-dependent and -independent at the same time? Modern theories on the evolution of sexually selected traits assume that the selective value of the trait is related proportionally Whatever the relationships between T and courtship, we usually to circulating T levels (Folstad and Karter, 1992). Although this has say that a behaviour is hormone dependent if its expression is robustly L. Fusani / Hormones and Behavior 54 (2008) 227–233 231

androgen levels are low (Canoine et al., 2007). Alternatively, androgen and/or oestrogen might be synthesized within the manakin brain de novo or from circulating precursors (e.g. see London et al., 2006). Social stimuli can maintain hormone-activated behaviour, like in the case of maternal behaviour that is maintained by the presence of pups after the initial hormonal stimulation (Rosenblatt et al., 1979). Social stimulation could play an important role in maintaining courtship in male manakins, which have a lek system in which several males display simultaneously in individual courts placed few meters from each other. Finally, we need to study in more details the courtship behaviour to see whether androgen and oestrogen can modulate specific aspects of the displays. Recently, we have shown that there are individual differences in the structure of the jump-snap Fig. 2. In male golden-collared manakins, courtship is activated by T at the beginning of display, the main component of the courtship (Fusani et al., 2007b). the breeding season. Plasma levels of T decline then substantially but courtship activity For example, the speed and the duration of the jumps and the time does not. Thus, other factors such as increased brain androgen sensitivity, brain required by males to restore posture after each jump differ androgen formation, or social cues may contribute to maintain intense courtship activity after the decrease in plasma T levels. consistently between individuals, and these features could be those under sexual selection and more directly influenced by T. associated with the presence of a substantial amount of the hormone. Conclusions In the first section of this article, I reviewed the experimental work which showed how in birds the sexual differentiation of male sexual The hormonal regulation of male courtship is one component of a behaviour including courtship is regulated by testicular T, and the complex set of mechanisms that requires a multi-level approach to be same hormone is responsible for the appearance of the behaviour in better understood. It will be particularly important in the future to adult males. However, there are a few examples of species in which examine in the same species both the proximate and ultimate causes castration does not abolish courtship, at least not immediately of courtship. Our knowledge of the action of hormones in the brain (Hutchison et al., 1996; Moore and Kranz, 1983). This does not prove areas controlling courtship has greatly increased in the last decade, that the behaviour is androgen-independent, because steroidogenesis and we have discovered the importance of steroid receptors and can occur at many extragonadal sites including the brain (London steroid metabolic enzymes in regulating local hormone action. et al., 2006; Simpson, 2003). Additional molecules such as steroid-binding proteins and steroid Some cases, however, are puzzling and illustrate the complexity of receptor co-regulators may influence hormone action and modulate hormonal regulation of behaviour. The golden-collared manakin courtship (reviewed by Ball and Balthazart, 2007). Furthermore, an (Manacus vitellinus) is a Neotropical sub-oscine passerine. The males evolutionary perspective will help to identify the aspects of courtship of this species – and of manakins in general – have some of the most that are more relevant for female choice and eventually for the elaborate courtship behaviour in the animal world, including reproductive success of the male and to reveal links between the acrobatic displays, mechanical sound production —‘wingsnaps’, and behavioural effects of hormones and other physiological parameters. group displays (Chapman, 1935; Fusani et al., 2007b; Lill, 1974; Prum, Bridging neuroendocrinology and behavioural ecology is a challenging 1990). We have investigated if and how androgen influences the but very promising approach. courtship behaviour of male manakins. A number of observations and experiments indicate that manakin courtship is in fact activated by Acknowledgments androgen. Treatment of males with the antiandrogen Flutamide dur- ing the displaying season reduces courtship activity (Fusani et al., I am very grateful to the colleagues who nominated me for the 2007a). Females and juvenile males, which usually do not produce Franck A. Beach Award and to all those who supported my wingsnaps, can be induced to perform them by T treatment (Day et al., nomination. Many people helped me in the field and in the lab and 2006). Similarly, treatment of adult males with T outside the breeding my work would have not been possible without their precious help. I season, when displaying activity and plasma T levels are low, induces also want to thank my former advisors for their support: Francesco an increase in wingsnapping (Day et al., 2006). Other experiments Dessì-Fulgheri, Laura Beani, John and Rose Hutchison, Manfred Gahr, have provided contrasting results. The courtship season of manakins is Eberhard Gwinner, and Barney Schlinger. Finally, I thank Greg Ball, long lasting up to 7 months. However, plasma T levels are relatively Manfred Gahr, Barney Schlinger, and two anonymous referees for their high only at the beginning of the displaying season and decrease helpful comments on a previous version of the manuscript. significantly afterwards although courtship activity is unchanged (Fusani et al., 2007a). Moreover, treatment with T of adult males who are actively courting cause no change in courtship activity (Day et al., References 2007). Altogether these data suggest that T activates courtship in male – manakins, but courtship is then maintained by basal levels of Adkins-Regan, E., 1987. Sexual differentiation in birds. Trends Neurosci. 10, 517 522. Adkins-Regan, E., 2005. Hormones and animal social behavior. Princeton University circulating T and is unaffected by manipulation of plasma T levels. Press, Princeton. Nevertheless, courtship remains still sensitive to androgen as Adkins-Regan, E.K., 1981. Effect of sex steroids on the reproductive behavior of castrated – illustrated by treatments with Flutamide (Fusani et al., 2007a). male ring doves (Streptopelia risoria). Physiol. Behav. 26, 561 565. Andersson, M., 1994. Sexual Selection. Princeton University Press, Princeton, NJ. Clearly, other factors are involved in the control of courtship in Appel, F.W., 1929. Sex dimorphism in the syrinx of the fowl. J. Morphol. 47, 497–517. manakins (Fig. 2). Perhaps after its activation at the beginning of the Arnold, A.P., 2004. Sex chromosomes and brain gender. Nat. Rev. Neurosci. 5, 701–708. displaying season the expression of courtship requires only small Balaban, E., 1997. Changes in multiple brain regions underlie species differences in a complex, congenital behavior. Proc. Natl. Acad. Sci. U. S. A. 94, 2001–2006. concentrations of T, because the androgen sensitivity is increased in Baldwin, F.M., Goldin, H.S., Metfessel, M., 1940. 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