Yolk Testosterone Research Articles

Dynamics of maternal androgens and its metabolites during early embryonic development: embryonic modification of a maternal effect.

In birds, exposure to maternal (yolk) testosterone affects a diversity of offspring post-hatching traits, that eventually affect offspring competitiveness. However, maternal testosterone is heavily metabolized at very early embryonic developmental stages to hydrophilic metabolites that are often assumed to be much less biologically potent. The rapid metabolism could either keep the maternal testosterone from reaching the embryos, opening the possibility for a mother-offspring conflict, or the metabolites may facilitate the uptake of the lipophilic testosterone from the yolk into the embryonic circulation after which they are either converted back to the testosterone or functioning directly as metabolites. To test these possibilities, we injected isotope-labeled testosterone (T-[D5]) into the yolk of freshly laid Rock pigeon (Columba livia) eggs and determined the concentration and distribution of T-[D5] and its labelled metabolites within different egg fractions by LC-MS/MS at day 2, 5 and 10 of incubation. Although under a supraphysiological dosage injection, yolk testosterone decreased within 2 days and was metabolized into androstenedione, conjugated testosterone, etiocholanolone and other components that unidentifiable due to methodological limitation. We show for the first time that testosterone, androstenedione and conjugated testosterone, but not etiocholanolone, reached the embryo including its brain. Their high concentrations in the yolk and extraembryonic membranes suggest that conversion takes place here. We also found no sex-specific metabolism, explaining why maternal testosterone does not affect sexual differentiation. Our findings showed that maternal testosterone is quickly converted by the embryo, with several but not all metabolites reaching the embryo providing evidence for both hypotheses.

Does contaminant exposure disrupt maternal hormones deposition? A study on per- and polyfluoroalkyl substances in an Arctic seabird

Maternal effects are thought to be essential tools for females to modulate offspring development. The selective deposition of avian maternal hormones could therefore allow females to strategically adjust the phenotype of their offspring to the environmental situation encountered. However, at the time of egg formation, several contaminants are also transferred to the egg, including per- and polyfluoroalkyl substances (PFAS) which are ubiquitous organic contaminants with endocrine disrupting properties. It is, however, unknown if they can disrupt maternal hormone deposition. In this study we explored relationships between female PFAS burden and maternal deposition in the eggs of steroids (dihydrotestosterone, androstenedione and testosterone), glucocorticoids (corticosterone) and thyroid hormones (triiodothyronine and thyroxine) in a population of the Arctic-breeding black-legged kittiwake (Rissa tridactyla). Egg yolk hormone levels were unrelated to female hormone plasma levels. Second-laid eggs had significantly lower concentrations of androstenedione than first-laid eggs. Triiodothyronine yolk levels were decreasing with increasing egg mass but increasing with increasing females' body condition. Testosterone was the only transferred yolk hormone correlated to maternal PFAS burden: specifically, we found a positive correlation between testosterone in yolks and circulating maternal perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDcA) and perfluoroundecanoic acid (PFUnA) in first-laid eggs. This correlative study provides a first insight into the potential of some long-chain perfluoroalkyl acids to disrupt maternal hormones deposition in eggs and raises the question about the consequences of increased testosterone deposition on the developing embryo.

The presence of a mother counteracts prenatal stress in a precocial bird

In many species, prenatal maternal stress leads to long-lasting changes in physiological and behavioural individual characteristics. However, these prenatal effects can be modulated by the postnatal environment and especially by maternal care. The impact of maternal care on the modulation of prenatal maternal stress effects has been investigated mainly in mammalian models but, surprisingly, remains little explored in avian species. In this study, we determined the extent to which the subsequent effects of prenatal maternal stress on offspring growth and emotional responses are modulated by the presence of an adoptive mother during postnatal development using a precocial bird, the Japanese quail, Coturnix coturnix japonica , as our study species. All experimental quail chicks were the offspring of females that experienced an environmental stressor induced by a socially unstable environment during laying and egg production. Previous reports showed that social instability of laying quail increased their offspring's emotional reactivity and that this was related to an increase in yolk testosterone levels in their eggs. In this study, offspring hatched from socially unstable females were raised either with or without adoptive mothers. We found that mothered chicks were lighter during their first 3 weeks of age and that their emotional reactivity was lower (i.e. as shown by increased exploratory behaviours in a novel environment, decreased neophobic responses in the home cage and decreased responses to social separation) relative to nonmothered chicks. Thus, our results highlight that maternal care could counteract the phenotypic consequences of prenatally stress-exposed birds. Our results clearly highlight that even in precocial species the presence of the mother has a fundamental importance in modulating the effects of prenatal conditions on the ontogeny of offspring behaviour and that this might be a key mechanism driving phenotypic plasticity in wild populations. • Maternal care in Japanese quail counteracts prenatal stress effects. • Mothered chicks have a lower level of emotional reactivity than nonmothered ones. • Maternal care's influences are similar in mammals and birds.

Maternal age and maternal environment affect egg composition, yolk testosterone, offspring growth and behaviour in laying hens

Maternal effects have been reported to alter offspring phenotype in laying hens. In this study, we investigated the effects of maternal environment and maternal age on egg traits and offspring development and behaviour. For this, we ran two experiments. First (E1), commercial hybrid hens were reared either in aviary or barren brooding cages, then housed in aviary, conventional cages or furnished (enriched) cages, thus forming different maternal housing treatments. Hens from each treatment were inseminated at three ages, and measures of egg composition, yolk testosterone concentration and offspring’s development, anxiety and fearfulness were assessed. In experiment 2 (E2), maternal age effects on offspring's growth and behaviour were further investigated using fertile eggs from commercial breeder flocks at three different ages. Results from E1 showed that Old hens laid heavier eggs with less yolk testosterone and produced offspring with fewer indicators of anxiety and fearfulness. Maternal rearing and housing affected egg traits, offspring weight and behaviour, but not in a consistent way. Effects of maternal age were not replicated in E2, possibly due to differences in management or higher tolerance to maternal effects in commercial breeders. Overall, our research confirms that maternal age and maternal environment affects egg composition, with maternal age specifically affecting yolk testosterone concentration, which may mediate physical and behavioural effects in offspring.

Characterizing the timing of yolk testosterone metabolism and the effects of etiocholanolone on development in avian eggs.

Maternal transfer of steroids to eggs can elicit permanent effects on offspring phenotype. Although testosterone was thought to be a key mediator of maternal effects in birds, we now know that vertebrate embryos actively regulate their exposure to maternal testosterone through steroid metabolism, suggesting testosterone metabolites, not testosterone, may elicit the observed phenotypic effects. To address the role steroid metabolism plays in mediating yolk testosterone effects, we used European starling (Sturnus vulgaris) eggs to characterize the timing of testosterone metabolism and determine whether etiocholanolone, a prominent metabolite of testosterone in avian embryos, is capable of affecting early embryonic development. Tritiated testosterone was injected into freshly laid eggs to characterize steroid movement and metabolism during early development. Varying levels of etiocholanolone were also injected into eggs, with incubation for either 3 or 5days, to test whether etiocholanolone influences the early growth of embryonic tissues. The conversion of testosterone to etiocholanolone was initiated within 12 h of injection, but the increase in etiocholanolone was transient, indicating that etiocholanolone is also subject to metabolism, and that exposure to maternal etiocholanolone is limited to a short period during early development. Exogenous etiocholanolone manipulation had no significant effect on the growth rate of the embryos or extra-embryonic membranes early in development. Thus, the conversion of testosterone to etiocholanolone may be an inactivation pathway that buffers the embryo from maternal steroids, with any effects of yolk testosterone resulting from testosterone that escapes metabolism; alternatively, etiocholanolone may influence processes other than growth or take additional time to manifest.

Telomere dynamics from hatching to sexual maturity and maternal effects in the 'multivariate egg'.

Avian eggs contain a large number of molecules deposited by the mother that provide the embryo with energy but also potentially influence its development via the effects of maternally derived hormones and antibodies: the avian egg is thus 'multivariate'. Multivariate effects on offspring phenotype were evaluated in a study on captive zebra finches, by simultaneously manipulating maternally derived antibodies (MAb) by lipopolysaccharide (LPS) treatment of mothers and injection of testosterone into the egg yolk. LPS treatment had a positive effect on body mass growth at 30 days after hatching and immune response at sexual maturity, while egg testosterone treatment positively influenced immune response at fledging and courtship behaviour in sexually mature male offspring. Maternal effects are known to modulate offspring telomere length (TL). However, the multivariate effects of egg-derived maternal components on offspring telomere dynamics from hatching to sexual maturity are undefined. Here, we tested: (1) the effects of LPS and testosterone treatments on TL from hatching to sexual maturity (day 82); (2) how LPS treatment modulated TL over reproduction in adult females; and (3) the relationship between maternal and offspring TL. We predicted that TL would be shorter in LPS fledglings (as a cost of faster growth) and that TL would be longer in sexually mature adults after yolk testosterone treatment (as a proxy of individual quality). In adult females, there was an overall negative relationship between laying and rearing investments and TL, this relationship was weaker in LPS-treated females. In chicks, there was an overall negative effect of LPS treatment on TL measured at fledging and sexual maturity (day 25-82). In addition, at fledging, there was a Sex×LPS×Testosterone interaction, suggesting the existence of antagonistic effects of our treatments. Our data partially support the hypothesis that telomeres are proxies of individual quality and that individual differences in TL are established very early in life.

Developmental programming of the adrenocortical stress response by yolk testosterone depends on sex and life history stage.

Developmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus-pituitary-adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific and life history stage-dependent manner. Compared with controls, males from testosterone-treated eggs had higher baseline corticosterone levels, whereas females from testosterone-treated eggs showed prolonged stress-induced corticosterone secretion during the reproductive but not the non-reproductive phase. Adult RMR was unaffected by in ovo testosterone treatment but correlated with integrated corticosterone stress secretion levels. We conclude that exposure of the embryo to testosterone programs the hypothalamus-pituitary-adrenal axis in a sex-specific manner that in females depends, in expression, on reproductive state. The modified baseline corticosterone levels in males and stress-induced corticosterone levels in females may explain some of the long-lasting effects of maternal testosterone in the egg on behavior and could be linked to previously observed reduced mortality of testosterone-treated females.

Does paternal immunocompetence affect offspring vulnerability to maternal androgens? A study in domestic chickens.

ABSTRACTExposure of yolk androgens can positively stimulate chick growth and competitive ability, but may negatively affect immunity. It has been hypothesized that only chicks from immunologically superior fathers can bear the cost of prenatal exposure to high androgen levels. To test this hypothesis, we paired roosters from two selection lines, one up- and one down-selected for natural antibodies (NAbs), with hens from a control line. We measured yolk testosterone and androstenedione levels, and we injected the treatment group of eggs of each female with testosterone suspended in sesame oil and the control group with sesame oil only. We then measured hatching success and growth, and characterized the humoral and cellular immune responses using three different challenges: a phyto-hemagglutinin, a lipopolysaccharide and a sheep red blood cell challenge. We found that the hatching success, body mass, initial levels of natural antibodies and the chicks’ immunological responses to the three different challenges and development were affected neither by paternal immunocompetence nor by treatment. These results do not support the hypothesis that chicks from low-NAb line fathers are more sensitive to testosterone exposure during embryonic development than chicks from high-NAb line fathers.

Testosterone and Triiodothyronine in Franklin's Gull (Leucophaeus pipixcan) Eggs

maternally derived hormones are known to influence the growth and development of offspring. the differential deposition of these maternally derived hormones into egg yolk is one way by which females can alter their chicks' growth or survival. yolk constituents, especially testosterone, have been described for a wide variety of species. however, few studies have focused on multiple maternally derived hormones regulated by independent axes in the endocrine system, and those studies that have, mainly focus on corticosterone and testosterone. in this study, within and among female variation in testosterone and triiodothyronine concentrations in egg yolks were measured in three free-living franklin's gull (leucophaeus pipixcan) populations. testosterone (t), but not triiodothyronine (t3), concentrations increase within a female's clutch such that eggs laid later in the clutch have increasingly higher concentrations (from a mean of 1.97 log pg t/mg yolk for the first egg to 2.98 log pg t/mg yolk for the third egg compared to a mean of 0.14 log pg t3/mg yolk for the first egg to 0.31 log pg t3/mg yolk for the third egg). both testosterone and triiodothyronine concentrations increase among females across the breeding season such that eggs laid later in the season have significantly higher hormone concentrations (mean of 2.37 log pg t/mg yolk and mean of -0.03 log pg t3/mg yolk) than eggs laid early in the season (mean of 1.95 log pg t/mg yolk and mean of -0.17 log pg t3/mg yolk).

Genetic variation in maternal yolk testosterone allocation predicts female mating decisions in Japanese quail

Maternal reproductive effort can be adjusted through the transfer of hormones into the eggs, where they influence embryo development, mediating short- and long-term maternal effects on offspring phenotype. While studies usually explore how females can increase their reproductive success through an allocation of yolk testosterone (T) under external environmental variability, it is less clear whether intrinsically driven interfemale differences in yolk T deposition may themselves predict female reproductive decisions. In our study, we used Japanese quail, Coturnix japonica, lines divergently selected for high (HET) and low (LET) egg T concentrations to examine whether this genetic variation in yolk T levels is linked to female mating decisions. First, we analysed line differences in male-typical reproductive behaviour and how this behavioural response is affected by female line identity. Males were tested with females from the same (match pairs) and opposite (cross pairs) lines. Next, female mate preferences were evaluated in a two-choice test in which females were allowed to choose between males from the same and opposite lines. We found no line differences in male copulatory behaviour. Interestingly, a shorter latency to copulate and a higher number of copulations were recorded in LET males when they were mated with HET than LET females. No differences between match and cross pairs were found in HET males. In the two-choice test, LET females displayed a preference for males from the same over the opposite line, but HET females did not discriminate between LET and HET males. Collectively, these results demonstrate that genetically high yolk T deposition is related to higher receptivity and reduced choosiness in female mate preferences in Japanese quail. Moreover, our results indicate an important link between maternal investment, reproductive physiology and female mating decisions, pointing out evolutionary implications and a role of variation in female mate choice in sexual selection.

Covariation between eggshell colouration and eggshell bacteria abundance and egg characteristics in blackbirds

Several functions have been proposed to explain eggshell colouration in birds. Eggshell colour may, for instance, signal female egg investment and hence the quality of the female and/or the egg. Such a covariation between eggshell colour and egg quality is supported by several studies, but what is related to eggshell colour is not necessarily consistent between populations, species or egg compounds.In this study, we examined several maternally derived egg compounds; namely yolk mass, egg white lysozyme and pH, yolk testosterone, oestrogens and eggshell colour and we determined the abundance of cultivable bacteria on the eggshell surface of blackbirds’ eggs Turdus merula. Based on that, we examined whether there is an association between eggshell colour parameters derived via spectrophotometric analyses and eggshell spot size and any of the investigated egg parameters.Our results suggest that two eggshell colour components derived by a principle component analyses and eggshell spot size covary with different egg parameters. We found that eggs containing more UV, yellow and red chroma in their eggshells contain heavier yolks. In contrast more bluish, greener and brighter eggs have to face higher loads of bacteria i.p. haemolytic bacteria and bacteria originating from the urogenital tract of the female. No other egg compound investigated seemed to be reflected in any eggshell colour parameter. Our data do not support an antibacterial function of eggshell colour as the abundance of bacteria originating from the female urogenital tract is negatively related to eggshell colouration. Furthermore, we found a positive but weak association between egg spot size and egg white lysozyme levels. Possible functional implications of our results are discussed.

Are there synergistic or antagonistic effects of multiple maternally derived egg components on offspring phenotype?

Eggs are 'multivariate' in that they contain multiple maternally derived egg components (e.g. hormones, antibodies, mRNA, antioxidants) which are thought to influence offspring phenotype. However, most studies have focused on single egg components and on short-term effects. Here, we simultaneously manipulated two egg components, maternally derived antibodies (MAb) and yolk testosterone, to assess potential synergistic or antagonistic effects on zebra finch offspring phenotype from hatching to sexual maturity. We found no evidence for short- or long-term effects of either MAb or yolk testosterone alone, or their interaction, on hatching mass, size at fledging (tarsus length), body mass at sexual maturity (day 82), chick survival, humoral immune function or any measured female reproductive trait at sexual maturity. There was a positive effect of yolk testosterone, but not MAb, on offspring phytohaemagglutinin (PHA) response at 26 days of age but at 82 days of age, MAb, but not yolk testosterone, had a positive effect on PHA response. There was also a MAb×sex interaction on 30 day chick mass, and a positive effect of yolk testosterone on male courtship behaviour at sexual maturity. However, we found no evidence for synergy, i.e. where offspring treated with both MAb and yolk testosterone had higher trait values than offspring treated with either MAb or yolk testosterone alone for any measured trait. Similarly, evidence for antagonistic (compensatory) effects, where offspring treated with both MAb and yolk testosterone had intermediate trait values compared with offspring treated with either MAb or yolk testosterone alone, was equivocal.

Physiological increase of yolk testosterone level does not affect oxidative status and telomere length in gull hatchlings.

Conditions experienced during early-life can cause the onset of oxidative stress, resulting in pervasive effects on diverse life-history traits, including lifespan. In birds, maternally-transferred egg substances may exert positive or negative influence over the offspring phenotype. Among these, testosterone can upregulate the bioavailability of certain antioxidants but simultaneously promotes the production of pro-oxidants, leading to an oxidative stress situation, which is one of the main forces causing telomere attrition However, no study has investigated the role of this androgen on telomere dynamics in birds and little is known about the effects of yolk testosterone on oxidative status in early-life of these species. We physiologically increased the levels of yolk testosterone by in ovo injections in yellow-legged gull (Larus michahellis) to evaluate the effects induced by this androgen on hatchlings plasma total antioxidant capacity, amount of pro-oxidant molecules and telomere length at hatching. Testosterone supplementation did not increase hatchling body growth, did not result in the overproduction of pro-oxidant molecules nor a reduction of antioxidant capacity. Accordingly, telomere length at hatching was not affected by testosterone treatment, although hatchlings from the third-laid eggs showed shorter telomeres than their siblings from first- and second-laid eggs, independently of testosterone treatment. Our results suggest that injection of physiological levels of testosterone does not induce oxidative stress to hatchlings and, consequently do not affect telomere dynamics during early post-natal periods.

Age-specific patterns of maternal investment in common gull egg yolk.

While the general patterns of age-specific changes in reproductive success are quite well established in long-lived animals, we still do not know if allocation patterns of maternally transmitted compounds are related to maternal age. We measured the levels of yolk testosterone, carotenoids and vitamins A and E in a population of known-aged common gulls (Larus canus) and found an age-specific pattern in yolk lutein and vitamin A concentrations. Middle-aged mothers allocated more of these substances to yolk compared to young and old mothers. These results can be explained through differences in age-specific foraging, absorption or deposition patterns of carotenoids and vitamins into yolk. If these molecules play a role in antioxidant defence and immune modulation, our results suggest a possible physiological pathway underlying the age-specific changes in reproductive success of long-lived birds in the wild.

Correction: Social environment during egg laying: Changes in plasma hormones with no consequences for yolk hormones or fecundity in female Japanese quail, Coturnix japonica.

[This corrects the article DOI: 10.1371/journal.pone.0176146.].

In ovo yolk carotenoid and testosterone levels interactively influence female transfer of yolk antioxidants to her eggs.

Mothers can influence prenatal conditions by varying the amount of nutrients, hormones or antioxidants they provide to their developing young. Some of these substances even affect the transfer of these compounds in the next generation, but it is less clear how different maternally transmitted compounds interact with each other to shape reproductive resource allocation in their offspring. Here, we found that female Japanese quails (Coturnix japonica) that were exposed to high carotenoid levels during embryonic development transferred lower concentrations of yolk antioxidants to their own eggs later in life. This effect disappeared when both testosterone and carotenoid concentrations were manipulated simultaneously, showing long-term and interactive effects of these maternally derived egg components on a female's own egg composition. Given that exposure to high levels of testosterone during embryo development stimulates the production of reactive oxygen species (ROS) and impairs antioxidant defenses, we propose that carotenoids act as in ovo antioxidants in an oxidatively stressful environment (i.e. when levels of testosterone are high) but might have prooxidant properties in an environment where they are not used to counteract an increased production of ROS. In line with this hypothesis, we previously showed that prenatal exposure to increased concentrations of yolk carotenoids leads to a rise of oxidative damage at adulthood, but only when yolk testosterone concentrations were not experimentally increased as well. As a consequence, antioxidants in the body may be used to limit oxidative damage in females exposed to high levels of carotenoids during development (but not in females exposed to increased levels of both carotenoids and testosterone), resulting in lower amounts of antioxidants being available for deposition into eggs. Since prenatal antioxidant exposure is known to influence fitness-related traits, the effect detected in this study might have transgenerational consequences.

Protoporphyrin‐based eggshell pigmentation predicts hatching success and offspring sex ratio in the barn swallow

Inter‐ and intraspecific variation in eggshell colouration has long fascinated evolutionary biologists. Among species, such variation may accomplish different functions, the most obvious of which is camouflage and background matching. Within species, it has been proposed that inter‐female variation in eggshell pigmentation patterns can reflect egg, maternal or paternal traits and hence may provide cues to conspecifics about egg, maternal or paternal phenotypic quality. However, the relationship between protoporphyrin‐based eggshell pigmentation and egg or maternal/paternal traits appears to be highly variable among species. We investigated patterns of intraspecific variation in Eurasian barn swallowHirundo r. rusticaprotoporphyrin‐based eggshell pigmentation, and analysed its association with egg and clutch characteristics, maternal/paternal phenotypic traits and parental feeding effort. Eggshell pigmentation pattern significantly varied between breeding colonies, was significantly repeatable in first clutches laid by the same females in different years (intraclass correlation coefficient ranging between 0.56 and 0.63), but it was not significantly associated with egg traits, such as position in the laying sequence, egg mass, yolk testosterone concentration and antioxidant capacity. It was weakly or non‐significantly associated with female and male traits (sexual ornaments), but females laying darker (higher pigment intensity) first clutches had higher hatching success, suggesting that eggshell pigment intensity may predict fitness. Male nestling feeding effort was not predicted by eggshell pigmentation. In addition, females with darker breast plumage colouration (a melanin‐based trait related to fitness) laid highly protoporphyrin‐covered eggs, suggesting the presence of a previously unappreciated link between protoporphyrin biosynthesis and plumage melanisation. Moreover, the proportion of male offspring increased in clutches originating from highly protoporphyrin‐covered eggs, suggesting that parents could acquire visual cues about their future brood sex composition before egg hatching. Our results support the idea that intraspecific signalling via eggshell pigmentation is a species‐specific rather than a general feature of avian taxa.

An experimental test of the relationship between yolk testosterone and the social environment in a colonial passerine

Maternal hormones can be transferred to offspring during prenatal development in response to the maternal social environment, and may adaptively alter offspring phenotype. For example, numerous avian studies show that aggressive competition with conspecifics tends to result in females allocating more testosterone to their egg yolks, and this may cause offspring to have more competitive phenotypes. However, deviations from this pattern of maternal testosterone allocation are found, largely in studies of colonial species, and have yet to be explained. Colonial species may have different life‐history constraints causing different yolk testosterone allocation strategies in response to conspecific competition, but few studies have experimentally tested whether colonial species do indeed differ from that of solitary species. To test this, we collected eggs from zebra finchesTaeniopygia guttata, a colonial species, in the presence and absence of conspecific intrusions. Females did not alter the concentration of testosterone deposited in eggs laid during intrusions despite becoming more aggressive. These results suggest that maternal effects are not characterized by a uniform response to the social environment, but rather need to be contextualized with life‐history traits.

Variable effects of elevated egg yolk testosterone on different arms of the immune system in young quail

Variable effects of elevated egg yolk testosterone on different arms of the immune system in young quail

Social environment during egg laying: Changes in plasma hormones with no consequences for yolk hormones or fecundity in female Japanese quail, Coturnix japonica.

The social environment can have profound effects on an individual’s physiology and behaviour and on the transfer of resources to the next generation, with potential consequences for fecundity and reproduction. However, few studies investigate all of these aspects at once. The present study housed female Japanese quail (Coturnix japonica) in pairs or groups to examine the effects on hormone concentrations in plasma and yolk and on reproductive performance. Circulating levels of androgens (testosterone and 5-α-dihydrotestosterone) and corticosterone were measured in baseline samples and after standardised challenges to assess the responsiveness of the females’ endocrine axes. Effects of the social environment on female fecundity were analysed by measuring egg production, egg mass, fertilization rates, and number of hatched offspring. Counter to expectation, females housed in pairs had higher plasma androgen concentrations and slightly higher corticosterone concentrations than females housed in groups, although the latter was not statistically significant. Pair vs. group housing did not affect the females’ hormonal response to standardised challenges or yolk testosterone levels. In contrast to previous studies, the females’ androgen response to a gonadotropin-releasing hormone challenge was not related to yolk testosterone levels. Non-significant trends emerged for pair-housed females to have higher egg-laying rates and higher fertility, but no differences arose in egg weight or in the number, weight or size of hatchlings. We propose that our unexpected findings are due to differences in the adult sex ratio in our social treatments. In pairs, the male may stimulate female circulating hormone levels more strongly than in groups where effects are diluted due to the presence of several females. Future studies should vary both group size and sex composition to disentangle the significance of sexual, competitive and affiliative social interactions for circulating and yolk hormone levels, and their consequences for subsequent generations.