Androgen and the elaborate courtship behavior of a tropical lekking bird

In most bird species, male courtship behavior is controlled by testosterone (T) and its metabolites. In species breeding in temperate and arctic regions T circulates at high levels during a relatively short courtship period because high levels of T can be costly in terms of immunocompetence and parental care. Few studies have investigated androgen modulation of courtship behavior in tropical birds. Male golden-collared manakins (Manacus vitellinus) aggregate in leks for several months and perform spectacular, acrobatic courtship displays. Here we examined whether T is elevated in golden-collared manakins during the displaying period and if courtship behavior is modulated by androgen action on androgen receptors. We measured T levels in displaying males at the beginning of the breeding season and again, one month later. In addition, both wild and captive males were treated with the anti-androgen, flutamide, and their courtship behavior was recorded for several weeks. T levels were relatively high shortly after leks were established but decreased substantially a month later, even though the amount of courtship did not change. Flutamide reduced male courtship activity for one week, but display behavior then increased after two weeks of flutamide treatment. Our studies show that androgens modulate male manakin courtship, but the amount of courtship is not directly correlated with the concentration of circulating T. These results suggest that the relationships between androgen and courtship might differ between tropical and temperate birds.     

Testosterone increases display behaviors but does not stimulate growth of adult plumage in male golden-collared manakins (Manacus vitellinus)

In order to attract females, male golden-collared manakins gather in leks and perform a complex display consisting of acrobatics accompanied by loud "wingsnapping". During this display, males show off their yellow beard and yellow, black, and green plumage that is striking in comparison to the dull green plumage of young males and females. We investigated the role of testosterone (T) in activating the display of manakins and in stimulating the growth of the adult male plumage. T regulates song, copulation, and territorial aggression in temperate species. In tropical species, however, T levels can be relatively low year round, which has raised questions about the involvement of T in courtship display and male aggression in these species. In neither temperate nor tropical species has the role of hormones in the shift from juvenile to adult plumage been well studied. Therefore, we implanted green-plumaged birds and adult males with either a T pellet or an inert pellet (controls) and observed the display behaviors of these birds in the field and in captivity. In captive birds, we also plucked feathers from sexually dimorphic regions and observed color and regeneration rate of new feathers. We found that birds implanted with T increased several display behaviors compared to controls. All plucked feathers grew back the same color as prior to treatment; however, we observed some differences in feather growth rate between T-treated birds and controls.     

Testosterone control of male courtship in birds

A sequence of behaviours which we call courtship initiates reproduction in a large number of species. In vertebrates, as a component of male sexual behaviour courtship is strongly influenced by testicular androgen. Here I will review some salient issues about the regulation of courtship by testosterone in birds. The first section will briefly summarize the first 100 years of research on this topic. The specific role of testosterone or its oestrogenic metabolites in the control of different components of courtship will be the subject of the second section. Then, I will discuss how behavioural patterns can be recruited into courtship and modified in their structure by testosterone action. In the following section, the role of sexual selection and female choice in shaping the link between testosterone and courtship will be addressed. The problematic nature of the quantitative relationships between testosterone and behaviour will be topic of the fifth section. Finally, I will discuss how courtship traits that are activated by testosterone can be apparently independent of hormone blood concentrations. These issues will be examined in an evolutionary perspective, in an attempt to understand how natural and sexual selection have shaped the links between the hormone and the behaviour.     

Testosterone response to courtship predicts future paternal behavior in the California mouse, Peromyscus californicus

In the monogamous and biparental California mouse (Peromyscus californicus), paternal care is critical for maximal offspring survival. Animals form pair bonds and do not engage in extrapair matings, and thus female evaluation of paternal quality during courtship is likely to be advantageous. We hypothesized that male endocrine or behavioral response to courtship interactions would be predictive of future paternal behavior. To test this hypothesis, we formed 20 pairs of California mice, and evaluated their behavior during the first hour of courtship interactions and again following the birth of young. We also collected blood from males at baseline, 1 hr after pairing, 3 weeks paired, and when young were 4 days old to measure testosterone (T). We found that male T-response to courtship interactions predicted future paternal behavior, specifically the amount of time he huddled over young when challenged by the temporary removal of his mate. Males that mounted T increases at courtship also approached pups more quickly during this challenge than males who had a significant decrease in T at courtship. Proximity of the male and female during courtship predicted paternal huddling during a 1-hr observation, and a multiple regression analysis revealed that courtship behavior was also predictive of birth latency. We speculate that male T-response to a female in P. californicus is an honest indicator of paternal quality, and if detectable by females could provide a basis for evaluation during mate choice.     

Hormonal correlates of dominance in meerkats (Suricata suricatta)

In cooperatively breeding meerkats (Suricata suricatta), individuals typically live in extended family groups in which the dominant male and female are the primary reproductives, while their offspring delay dispersal, seldom breed, and contribute to the care of subsequent litters. Here we investigate hormonal differences between dominants and subordinates by comparing plasma levels of luteinizing hormone (LH), estradiol and cortisol in females, and testosterone and cortisol in males, while controlling for potential confounding factors. In both sexes, hormone levels are correlated with age. In females, levels of sex hormone also vary with body weight and access to unrelated breeding partners in the same group: subordinates in groups containing unrelated males have higher levels of LH and estradiol than those in groups containing related males only. When these effects are controlled, there are no rank-related differences in circulating levels of LH among females or testosterone among males. However, dominant females show higher levels of circulating estradiol than subordinates. Dominant males and females also have significantly higher cortisol levels than subordinates. Hence, we found no evidence that the lower levels of plasma estradiol in subordinate females were associated with high levels of glucocorticoids. These results indicate that future studies need to control for the potentially confounding effects of age, body weight, and access to unrelated breeding partners before concluding that there are fundamental physiological differences between dominant and subordinate group members.     

Lateralization in response to social stimuli in a cooperatively breeding cichlid fish

Cerebral lateralization, an evolutionarily ancient and widespread phenomenon among vertebrates, is thought to bestow cognitive advantages. The advantages of lateralization at the individual-level do not necessarily require that the entire population share the same pattern of lateralization. In fact, directional bias in lateralization may lead to behavioural predictability and enhanced predator success or prey evasion. Recent theory has suggested that population-level lateralization may be favored if individuals are better able to perform coordinated behaviours, providing a distinct advantage in cooperative contexts. Here we test whether the highly social, cooperatively breeding cichlid fish Neolamprologus pulcher shows lateralized responses to a social stimulus. We found population-level biases in males; on average male N. pulcher use their right eye/left hemisphere to view their mirror image. Individual females had a preferred hemisphere, but these preferences appeared not to be directionally aligned among females. We discuss these results in the context of coordinated social behaviour and suggest future research directions.     

Flexibility in the multi-modal courtship of a wolf spider, Schizocosa ocreata

Male Schizocosa ocreata wolf spiders court females with synchronous visual and seismic displays. We tested whether male S. ocreata modify their courtship in relation to light environment, and associated utility of the visual components. Males were generally more active and more likely to perform the major courtship element (jerky tapping) when in the light. One courtship element (arching) was only observed in the light while another (vertical leg-extend) was only observed in the dark. Courtship in the dark retained visual components, suggesting spiders cannot disengage these components of multi-modal display even when superfluous. Once initiated, there was no evidence that performance rate or time spent in each courtship element differed in the light and in the dark.     

The methylation status of FBXW7 beta-form correlates with histological subtype in human thymoma

FBXW7 is reported to be a tumor suppressor gene, and the functional inactivation of FBXW7 has been reported in various human tumors. In this study, we investigated the FBXW7 gene in human thymoma; although no mutations were evident, a significantly high frequency of methylation in the FBXW7 β-form promoter was observed in types B1 or higher (P = 0.014). We propose a novel mechanism for the pathogenesis of thymoma by FBXW7 β-form and hypothesize that expressional suppression plays an important role in the malignant potential of thymoma.     

Effects of testosterone on the development of neuromuscular systems and their target tissues involved in courtship and copulation in green anoles (Anolis carolinensis)

Male green anole lizards court females using a red throat fan (dewlap) and copulate by intromitting one of two penises (hemipenes). These structures begin sexually monomorphic, but by adulthood males have larger dewlaps, only males have hemipenes, and many of the neuromuscular components of both systems show male-biased dimorphisms. We hypothesized that testosterone (T), which increases in juvenile males but not females about a month after hatching, facilitates masculinization. To test this idea, on post-hatching day 30, gonadally intact females received either a blank or T implant, and males were either castrated or sham-castrated. At day 90, juveniles were euthanized and the length of the cartilage and cross-sectional areas of the muscle fibers and motoneurons required for dewlap extension were examined. We also measured the cross-sectional areas of the hemipenes and associated muscle fibers and motoneurons, and counted the motoneurons. T-treated females had longer cartilages and larger dewlap muscle fibers compared to those with blank implants. No effects on motoneurons were detected, and no females possessed hemipenes or associated musculature. In males, castration produced shorter dewlap cartilages and smaller hemipenes; other measures were not affected by treatment. These data indicate that components of the dewlap system differentiate relatively late in development, that T likely mediates the process, and that although components of the copulatory system are plastic in juvenile males, sexual differentiation of peripheral features is complete before day 30. The data also suggest that target structures (dewlap cartilage and hemipenes), compared to their neuromuscular effectors, are particularly sensitive to developmental T exposure.     

Simultaneous treatment with an aromatase inhibitor and an anti-androgen decreases the likelihood of dawn song in free-living male great tits, Parus major

Gonadal steroids, most importantly testosterone (T), are considered to be a major factor in the expression of adult song behavior in temperate-zone songbirds. The action of T within specific brain regions involved in the regulation of song may occur either directly, or through its androgenic or estrogenic metabolites. In the present study, we tested steroid-dependence of great tit dawn song by blocking both known pathways of T action by simultaneous implantation of flutamide, an anti-androgen, and ATD, an aromatase inhibitor. By our knowledge, this is the first study investigating the effects of androgen inhibitors on dawn song in free-living birds. Male great tits were implanted during their mate's egg laying stage, being the time of maximal male song activity at dawn. Treatment with ATD and flutamide significantly increased plasma T levels, probably because feedback mechanisms on T secretion were inhibited. The treatment decreased the likelihood of showing dawn song, which is in line with the hypothesis that sex steroids are involved in the endocrine control of song behavior. In males that did show dawn song, we found no evidence for a treatment effect on song quality. Although the implants were present for the larger part of the breeding season, males were able to maintain control of a territory and mate and to complete their brood cycle as successful as control males.     

The EGFR ligands Spitz and Keren act cooperatively in the Drosophila eye

The EGFR signalling cascade is responsible for coordinating a wide variety of events during Drosophila eye development. It remains something of a mystery how it is that cells are able to interpret the signal so as to choose the appropriate response from the battery of possibilities: division, differentiation, cell shape change and so on. Since the cascade is essentially linear below the receptor, different cellular responses cannot be regulated by alternative signal transduction pathways. The main diversity lies upstream, in the multiple activating ligands. Spitz, Gurken and Vein have been long studied, but little is known about the physiological functions of the fourth ligand, Keren, although various roles have been predicted based on the differences between mutants in the known ligands and those of the receptor. Here, we have isolated a mutant in the keren gene, and demonstrate that Keren does indeed participate in EGFR signalling in the eye, where it acts redundantly with Spitz to control R8 spacing, cell clustering and survival. Thus, specificity cannot be determined by ligand choice, and must instead be a consequence of cell-intrinsic factors, although we speculate that there may be some quantitative differences in signalling elicited by the two ligands.     

Hormonal correlates of siblicide in Nazca boobies: support for the Challenge Hypothesis

The androgen hormone testosterone (T) mediates vertebrate aggression in many contexts and according to the Challenge Hypothesis is up-regulated during social challenges. While originally applied to challenges experienced by breeding adults, we show for the first time that T is similarly up-regulated during deadly sibling aggression in young birds. When two nestling Nazca boobies hatch, one--usually the older chick--virtually always kills the other chick by pushing it from the nest. We compared concentrations of T, dehydroepiandrosterone (DHEA; a precursor of T), and corticosterone (Cort; a stress hormone) of chicks at various stages. T was elevated during fights in both chicks in two-chick broods, but not before and after fights, and not in chicks lacking a nest mate. DHEA was elevated 1 day after hatching and declined with age but appeared not to vary in concert with aggression. Cort did not vary across fighting and nonfighting periods. In conjunction with an earlier study [Tarlow, E.M., Wikelski, M., Anderson, D.J., 2001. Hormonal correlates of siblicide in Galapagos Nazca boobies. Horm. Behav. 40:14-20], these results indicate that T is temporarily up-regulated around the time of fights, as predicted by the Challenge Hypothesis. Our data suggest a general role for T during challenges at any time in life, not just during breeding.     

The effects of social isolation on steroid hormone levels are modulated by previous social status and context in a cichlid fish

Social isolation is a major stressor which impacts the physiology, behaviour and health of individuals in gregarious species. However, depending on conditional and contextual factors, such as social status and group composition, social isolation may be perceived differently by different individuals or even by the same individuals at different times. Here we tested the effects of social status (territorial vs. non-territorial) and previous group composition (i.e. type of social group: mixed sex group with two territorial males, TT vs. mixed sex group with one territorial and one non-territorial male, TnT) on the hormonal response (androgens and cortisol) to social isolation in a cichlid fish (Oreochromis mossambicus). The different steroid hormones measured responded differentially to social isolation, and their response was modulated by social factors. Social isolation elicited a decrease of 11-keto formation only in territorial males, whereas non-territorial males present a non-significant trend for increasing KT levels. Testosterone did not respond to social isolation. Cortisol only increased in isolated individuals from TnT groups irrespective of social status (i.e. both in territorials and non-territorials). These results suggest that it is the perception of social isolation and not the objective structure of the situation that triggers the hormonal response to isolation.     

Transformations of testosterone and related steroids by Botrytis cinerea

Botrytis cinerea (strain AM235) was used to investigate the transformations of testosterone and related steroids. It was found that the position and stereochemistry of the introduced hydroxyl group, as well as the yield of products, depended on the structure of the substrate. Botrytis cinerea converts the examined substrates mainly to 7 alpha-hydroxy derivatives. 1-Dehydrotestosterone was also significantly hydroxylated at a 14 alpha-position.