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.     

Testosterone and year‐round territoriality in tropical and non‐tropical songbirds

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life‐history characteristic typical of the tropics, i.e. year‐round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year‐round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non‐tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life‐history traits may play a more important role in determining testosterone profiles of tropical and non‐tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons.     

Sex and testosterone effects on growth, immunity and melanin coloration of nestling Eurasian kestrels

1. Sex differences in testosterone levels and sex-biased sensitivity to testosterone are the basis of some ideas postulated to account for sex-linked environmental vulnerability during early life. However, sex variation in circulating testosterone levels has been scarcely explored and never manipulated at post-natal stages of birds in the wild. 2. We measured and experimentally increased circulating testosterone levels in nestling Eurasian kestrels Falco tinnunculus. We investigated, possible sexual differences in testosterone levels and the effect of this hormone on growth (body mass and tarsus length) and cell-mediated immunity in males and females. We also explored testosterone effects on rump coloration, a highly variable melanin-based trait in male nestlings. We analysed data on circulating testosterone levels of nestlings in 15 additional bird species. 3. Increased levels of testosterone tended to negatively affect body condition, reduced cell-mediated immune responses in male and female nestlings and also diminished the expression of grey rump coloration in male nestlings. No sex differences were observed in testosterone levels in either control or increased testosterone group nestlings, and no interactions were found between sex and treatment. However, male nestlings showed a lower cell-mediated immune response than females in both groups. 4. Our results indicate first, that a high level of testosterone in all nestlings in a brood entails costs, at least in terms of immunity, coloration and probably growth. Secondly, sex differences in post-natal cell-mediated immunity, and consequently in the capacity to prevent diseases, cannot be explained by sex differences in circulating testosterone levels. Finally, by comparing published data at an interspecific level, contradictory sex patterns in circulating testosterone levels have been found, supporting the idea that circulating testosterone might not be a proximate factor causing sex-dependent vulnerability in bird species.     

Ultrastructural changes in the uropygial gland of the male Japanese quail,Coturnix coturnix,after testosterone treatment

Summary The ultrastructure of the uropygial gland of the male quail was compared to that of the sebaceous gland of the male rat after castration and testosterone treatment of both species. In intact animals, the differentiating cells of these glands displayed almost the same pattern as regards their smooth endoplasmic reticulum, an organelle involved in lipogenesis in both cases. Castration reduced the volume of this organelle, while testosterone administration restored cell morphology to a normal or supranormal level. Finally, this study showed that at ultrastructural level, there is a close functional analogy between the uropygial gland of quail and the sebaceous glands of rats as regards their androgen dependency. Consequently, the uropygial gland might be an attractive model for study of action of androgens on sebaceous-like glands.     

Effects of season and social interaction on fecal testosterone metabolites in wild male giant pandas: implications for energetics and mating strategies

In the first-ever study of reproductive endocrinology in wild male giant pandas (Ailuropoda melanoleuca), we provide new insights into the reproductive ecology of the species. We tracked and observed pandas in Foping Nature Reserve of the Qinling Mountains for 3 years, collecting fecal samples for testosterone metabolite analysis and data on reproductive activity. Males encountered multiple potential mates and competed for reproductive access to females. Male testosterone metabolites increased in February, peaked in March and April, and fell back to baseline after the mating season. However, males did not maintain a high testosterone level throughout the mating season. Male testosterone instead peaked during encounters with potential mates and declined between encounters. These results indicate that testicular activity is typically dormant until mobilized by interactions with females and potentially by interactions with male competitors. This suggests that male pandas may be energetically constrained, elevating testosterone levels only when necessary to meet the demands of intrasexual competition and courtship and fertilization of females. Maintaining a high testosterone level is metabolically expensive and male pandas enter the mating season during a period of low food availability. If this hypothesis is correct, male panda body condition may be an important determinant of reproductive outcome, and anthropogenic activities that diminish foraging resources may have significant impacts on the mating ecology of the species, affecting its conservation.     

Boom and bust: a review of the physiology of the marsupial genus <Emphasis Type="Italic">Antechinus</Emphasis>

The marsupial genus Antechinus is a group of small carnivorous marsupials from the order Dasyuromorphia (Family Dasyuridae) and is found in eastern Australia. The life history of all species in the genus is characterized by a complex, but highly synchronized life cycle in both sexes, culminating in a short mating period followed by total male mortality (semelparity). The breeding season is defined by a specific rate of increase in photoperiod, which is different for each species. In Antechinus spp., male mortality is due to the effects of high free testosterone and cortisol levels on many organ systems. Unusually, spermatogenesis is complete before testosterone levels begin to rise at the winter solstice. In males, low sperm counts have been compensated for by high proportions of sperm reaching the isthmus of the female reproductive tract and long-term storage in the crypts. The females survive to rear their young and may mate again in their second year. Gestation lasts from 26 to 34 days, depending on the species. However, developmental arrest can occur at several stages during embryogenesis, elongating the apparent gestation duration by several days. Several species have strong female sex biases in their litters. The high degree of life history synchrony and the cascade of endocrine-driven physiological events that result in male death are unusual physiological characteristics for mammals. Suggestions why semelparity may have evolved in Antechinus are discussed.     

Examining the Role of Testosterone in Mediating Short-Term Aggressive Responses to Social Stimuli in a Lizard

Hormones have been suggested as a key proximate mechanism that organize and maintain consistent individual differences in behavioural traits such as aggression. The steroid hormone testosterone in particular has an important activational role in mediating short-term aggressive responses to social and environmental stimuli within many vertebrate systems. We conducted two complementary experiments designed to investigate the activational relationship between testosterone and aggression in male Egernia whitii, a social lizard species. First, we investigated whether a conspecific aggressive challenge induced a testosterone response and second, we artificially manipulated testosterone concentrations to examine whether this changed aggression levels. We found that at the mean level, plasma T concentration did not appear to be influenced by an aggression challenge. However, there was a slight indication that receiving a challenge may influence intra-individual consistency of plasma T concentrations, with individuals not receiving an aggression challenge maintaining consistency in their circulating testosterone concentrations, while those individuals that received a challenge did not. Manipulating circulating testosterone concentrations had no influence on either mean-level or individual-level aggression. Combined with our previous work, our study adds increasing evidence that the relationship between testosterone and aggression is not straightforward, and promotes the investigation of alternative hormonal pathways and differences in neuro-synthesis and neuroendocrine pathways to account for species variable testosterone - aggression links.     

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 variation in male testosterone levels in a tropical bird with year‐round territoriality

Testosterone is important in mediating investment in competing activities such as territoriality, parental care, and maintenance behavior. Most studies of testosterone function have focused on temperate species and less is known about the role of testosterone in territoriality or variation in mating systems of tropical species. Results of studies of tropical species with year‐round territoriality indicate that territorial aggression during the non‐breeding season is maintained with low levels of testosterone, and increased levels of testosterone in males during the breeding season may increase mating opportunities or aid in competition for mates. We studied seasonal variation in testosterone levels of male Red‐throated Ant‐tanagers (Habia fuscicauda), a socially monogamous species with year‐round territoriality and with high levels of extra‐pair matings (41% of young), to determine if testosterone levels increased during the breeding season. We captured males during the non‐breeding and breeding seasons and collected blood samples for hormone analysis. We found that mean testosterone concentrations were low during the non‐breeding season (0.18 ± 0.05 [SD] ng/ml, range = 0.11–0.31 ng/ml), and significantly higher during the breeding season (2.37 ± 2.47 ng/ml, range = 0.14–6.28 ng/ml). Testosterone levels of breeding males were not related to aggression levels as measured by attack rates toward a stuffed decoy or singing rates during simulated territorial intrusions. These results suggest that the higher testosterone levels of breeding male Red‐throated Ant‐tanagers may be important in an extra‐pair mating context, possibly in display behavior or mate attraction, but additional study is needed to clarify the role of testosterone during the breeding season.     

Exogenous testosterone inhibits several forms of male parental behavior and stimulates song in a monogamous songbird: the blue-headed vireo (Vireo solitarius)

Natural variation in circulating testosterone is thought to play a role in creating inter- and intraspecific variation in paternal care in birds. Experimental elevation of plasma testosterone in males has reduced rates of male care in many species. However, a small number of studies suggest that male care is not inhibited by testosterone when there appears to be strong selection for male care. Both genetic monogamy and male incubation are thought to be the result of selection for biparental care, yet the sensitivity of male care to inhibition by T had not been examined in a species with both characteristics. Male blue-headed vireos have been shown to be strictly monogamous and provide extensive parental care, including incubation. Males received subcutaneous implants of testosterone, flutamide (an anti-androgen), or empty controls. Consistent with previous studies, testosterone treatment decreased the relative contribution to incubation by males and increased the average duration that the nest was left unattended during incubation, relative to control and flutamide treatments. The relative and absolute rates of feeding offspring and nest sanitation by T-treated males also decreased relative to controls. Flutamide-treated males incubated eggs and brooded young more than testosterone-treated males, with control males performing at intermediate values. Testosterone-treated males sang more often and at higher rates, and flutamide-treated males sang less often, than controls. These results demonstrate that even in a strictly monogamous songbird with biparental incubation, all forms of paternal care remain sensitive to elevated plasma testosterone, suggesting a shift from parental effort to mating effort.     

Female choice and the benefits of mate guarding by male mallards

Pair formation and breeding in many species of waterfowl are separated both temporally and spatially. Most studies of female choice in this group have focused on male characteristics at the time of pairing, with less attention given to how mate choice affects breeding season outcomes. In this study I compared pairing success, male plasma testosterone level and mate-guarding ability of male mallards, Anas platyrhynchos, in two experiments. In the first experiment females and males were group housed with equal sex ratios, thus allowing all of these males to pair. At the same time, an equal number of males was housed in groups without access to females and remained unpaired. In this experiment testosterone levels of paired and unpaired males during autumn (baseline) and spring (breeding) did not differ, indicating that the process of pair formation and breeding does not cause elevated spring testosterone levels in males. However, testosterone did temporarily decrease in paired males during the winter (pair formation) season. In the second experiment groups were male biased, allowing only half of the males to pair. Here paired males had significantly higher testosterone levels than unpaired males during the breeding season, but not during the preceding autumn. Together the results of these experiments indicate that successful pair formation predicts but does not alter male testosterone level during the breeding season. I also found that females paired to males with high levels of testosterone were missing fewer feathers due to forced copulation attempts by nonmates, suggesting that females may choose males based on their mate-guarding abilities. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Plasma Testosterone in Cows Related to Day of Gestation and Sex of the Foetus,and Plasma Testosterone Levels Around Parturition

No significant differences in plasma testosterone level were observed between cows carrying a male foetus and cows carrying a female foetus at any ten-day interval from day 35 of gestation until parturition. Reported higher abortion rates for male than for female foetuses would thus appear not to be due to effects of foetal testosterone on the maternal endocrine balance. In spite of a great individual variation in plasma testosterone values at similar stages of gestation, certain trends are evident. From the 35th to the 80th day of gestation the average concentration was 90–100 pg/ml. Later it rose and reached 200 pg/ml on the 180th day, remaining at this level until after partus. During the first day after parturition plasma testosterone fell significantly and stabilized around 120 pg/ml.     

Testosterone, testes size, and mating success in birds: a comparative study

Reproductive behaviors of vertebrates are often underpinned by temporal patterns of hormone secretion. We investigated interspecific patterns of circulating testosterone in male birds to test the hypothesis that testosterone plays a crucial role in sexual selection as determined by degree of polygyny and extra-pair paternity. We predicted that the evolution of increased levels of polygyny and extra-pair paternity would have resulted in the evolution of increased levels of testosterone to allow males more efficiently to compete for mates. This hypothesis was tested in comparative analyses of 116 species of birds using Generalized Least Squares Models. We assessed the importance of latitudinal distribution, because this can confound the relationship between testosterone and mating success. There were weak positive phylogenetic correlations between measures of testosterone and estimates of mating success at the social level, but this association appeared to be confounded by latitudinal distribution, a significant correlate of testosterone titers. However, we found a significantly positive relationship between peak and residual peak testosterone (which is the peak testosterone level that is controlled for the baseline level) and extra-pair paternity independent of latitude. These results suggest that selection pressures arising from social and sexual mating differently affected testosterone levels with the former being mediated by factors associated with latitudinal distribution. An analysis of residual testes size revealed a positive association between peak and residual testosterone and testes size relative to body size. In a path analysis, we show that relative testis size primarily evolved in association with intense sperm competition and thus high sperm production, and these mechanisms had a secondary impact on blood testosterone levels at a phylogenetic scale. Our results suggest that sperm competition has played an important role in the evolution of reproductive mechanisms in birds.     

Dynamic changes in plasma luteinizing hormone and testosterone after stress in the male rat. Influence of adrenalectomy

In 60-day old intact male rats, stress imposed by a strange environment increased the levels of plasma LH and testosterone. Adrenalectomy, performed at 50 days of age, decreased plasma level of testosterone in basal conditions. However, without affecting the plasma level of LH significantly, stress increased plasma testosterone, albeit to a lesser extent, in the adrenalectomized rats. Stimulation of the testicular secretion by the high level of ACTH seems to be the most likely explanation for the observed testosterone peak in the adrenalectomized rat.     

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.     

The role of thyroid and adrenal cortical hormones in the modulation of the gonadal function in birds

The role of the thyroid gland in modulating the gonad function depends on the functional state of the gonads. In sexually inactive (short-day's) male Japanese quails, thyroidectomy and thyroxine treatment prove ineffective. Thyroxine administered simultaneously with photo-gonadostimulation inhibits the maturation of the gonads: the testes decrease in weight, the metabolic clearance rate of testosterone accelerates, resulting in a decrease in the plasma level, and androsterone production increases. Photo-gonadostimulation of thyroidectomized quails shows down the growth of the testicles and decreases the plasma testosterone level. The latter change can be related to the inhibition of the secretion rate. Both thyroidectomy and thyroxine administration performed in mature male quail, cock, pigeon or Peking duck lower the testosterone plasma level. The loss of the testicular weight is more expressed in hyperthyroid than in normal quails, referring to the role of the increased thyroxine level in the seasonal (summer) gonadal involution. Thyroidectomy performed on sexually inactive (short-day's) female Japanese quails does not affect the ovarian structure, but 17 beta-oestradiol and testosterone plasma levels show a slight increase. Thyroxine administration is followed by a moderate increase in the size of the white follicles, and an increase of both the progesterone and the oestrogen concentrations. Photo-gonadostimulation of thyroidectomized quails causes an inhibition of the mechanism of ovulation without inhibiting the development of the yellow follicles. A similar phenomenon has been observed in mature quails and domestic fowls after thyroidectomy. In both cases, an unbalanced secretion of the sexual steroids occurs: the 17 beta-oestradiol plasma level declines, while the progesterone level increases. Simultaneous application of thyroxine and photo-gonadostimulation on female quails inhibits gonadal maturation: the growing of the yellow follicles slows down. In thyroxine-treated birds, the plasma level of all of the sexual steroids shows a considerable decrease, which can be attributed to a reduced secretion rate and increased metabolic clearance. In hatching turkeys, we failed to observe the increase of the T3 level described for other species, however, the T4 plasma concentration was increasing at the early period of hatching. The role of the thyroid hormones in the development of hatching has not been cleared up so far. Corticosterone administration shows a slight stimulating effect on the gonadal function of sexually inactive male and female Japanese quails.(ABSTRACT TRUNCATED AT 400 WORDS)     

Spermatogenesis parameters and testosterone production at puberty as predictors of testicular functional activity in mice (<Emphasis Type="Italic">Mus musculus</Emphasis>)

The aim of this study was to investigate fertility-associated parameters of spermatogenesis and androgenic status in male laboratory mice at puberty and to assess their prognostic significance in the realization of the definitive testicular function. In three inbred murine strains, BALB/cLac, CBA/Lac and PT, the serum testosterone level, its testicular concentration, epididymal sperm count (sperm reserve) and portion of sperm with abnormal head morphology were evaluated on days 45 (puberty) and 90 (adulthood) of postnatal development. CBA/Lac males were characterized by a lower epididymal sperm count vs. other strains at both ages indicative of poorer spermatogenesis. At the same time, CBA/Lac males had a lower portion of sperm with abnormal head morphology, and this could be considered as a compensatory reaction aimed at improving sperm fertility. Distinct inter-strain differences in the portion of sperm with morphologically abnormal heads were established at both ages, while the inter-strain ratio remained invariable (BALB/cLac > PT > CBA/Lac). Thus, the level of abnormal spermatogenesis in the pubertal period may have a predictive significance for the definitive testicular activity in adult mice. No inter-strain and age-dependent changes were found in serum and testicular testosterone levels except for the PT strain, in which both testosterone levels rose from puberty to adulthood, suggesting a shift of the pubertal testosterone peak towards later times. Our data show that in male laboratory mice the genetic peculiarities of the testicular function manifest themselves during puberty and persist until adulthood.     

Hormonal Correlates of Social Rank in an Asocial Species, the Common Brushtail Possum (Trichosurus vulpecula)

Dominance hierarchies play an important role in access to mates or resources in many species. Rank is sometimes correlated with circulating testosterone levels or morphological traits such as body weight. The relationship of glucocorticoid secretion and rank, however, is less clear. In this study, we investigated the relationship of male rank to body weight, circulating testosterone and cortisol concentrations in captive possum triads (Trichosurus vulpecula). We carried out two experiments to examine hierarchy formation and the effects of castration of the dominant male during the non‐breeding season. A third experiment measured the effects of removal of the dominant male from a stable hierarchy during the breeding season. We found that dominant male rank was significantly correlated with higher circulating testosterone levels during periods of hierarchy formation and during the breeding season but not during periods of hierarchy stability in the non‐breeding season. Lack of correlation between plasma testosterone concentration and rank after male castration suggests that stable social rank is not dependent on hormone level and may be more dependent on behavioural traits. Any biocontrol measures that rely on manipulation of hormone levels may be unreliable when applied to unstable hierarchical situations, including the establishment of territories by subadult males, and the pre‐breeding season when circulating testosterone concentrations peak in males and a period of hierarchy establishment may occur.     

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.     

Lack of trade-offs between the male and female sexual functions in the gynodioecious herb <Emphasis Type="Italic">Geranium sylvaticum</Emphasis>

Resource allocation trade-offs between sexual functions are predicted, but these are usually measured only at the whole plant level. In some gynodioecious species, individuals with partially restored male fertility exist providing an opportunity to investigate whether the costs associated with male fertility restoration are linked to seed production. In this study, we examined whether there is a relationship between the numbers of stamens and seeds produced both at the flower level and at the plant level in the gynodioecious herb Geranium sylvaticum. We individually marked flowers in plants varying in the degree of male sterility in the field and counted the number of seeds produced. There was no significant correlation between the numbers of stamens and seeds produced at the flower level suggesting an absence of resource trade-off between female and male functions. Furthermore, the numbers of stamens and seeds were positively correlated at the plant level. The lack of trade-offs between the two sexual functions in this species indicates that relative sex allocation was not affected by resources within a single season and/or that the male costs were relatively small.