Seasonal relationships between plasma and fecal testosterone in response to GnRH in domestic ganders

Validation of enzyme immunoassays for quantifying sex steroid hormones in tropical screech owls (Megascops choliba)

Androgens and estrogens are steroid hormones that regulate reproductive processes in both males and females. Monitoring plasma levels of these steroids or their metabolites present in feces, offers diagnostic support for assessing the reproductive status of animals. Immunoassays are commonly used methods for quantifying these hormones, but their protocols require species-specific validation to ensure reliability. The objective of this study was to perform analytically and biologically validation of enzyme immunoassay (EIA) kits for measuring testosterone (T), estradiol (E2), faecal androgen metabolites (fAM), and faecal estrogenic metabolites (fEM) in the tropical screech owl (Megascops choliba). Serum and fecal samples were collected from six adult females and six males both before and during breeding season, with males' gonadal activity assessed using electroejaculation (EE). The parallelism test confirmed the immunogenic similarity of the antigens in the estradiol and testosterone standards and the antigens in the serum samples and fecal extracts of M. choliba. Additionally, the EIA kits displayed nearly 100% recovery rates, and showed coefficients of variation ranging from 8% to 14% at the intra-assay level and from 10% to 16% at the inter-assay level, underscoring result reliability and consistency. In males, the highest serum T and fAM levels were recorded concurrently with the presence of spermatozoa in samples collected via EE. Although females did not exhibit oviposition events, significantly higher E2 and fEM levels were observed in August compared to May, suggesting potential seasonal variations in estrogenic hormone production. Fecal androgen and estrogen levels were significantly different between sexes in August, with males having higher fAM and females having higher fEM levels. Overall, the immunoassays validated in this study were found to be efficient in diagnosing reproductive activity in owls.

Sperm mobility is predictive of the relative genetic contribution among competing mating geese, as determined by microsatellite genotype identification of potential sires

The low reproductive efficiency (RE) of geese limits their production in the poultry industry. To select ganders with high breeding potential, the effect of 3 sperm mobility ranks (SMRs; high-, medium-, and low-SMR) on the RE of naturally mating geese was determined. To exclude the confounding effect of social rank (SR) on RE in naturally mating flocks, a 2-factor nested experimental design was used to differentiate the effects of SMR and SR on RE. Twenty-seven ganders and 135 geese (Zi geese, Anser cygnoides L.) at approximately 1 yr of age were divided into 3 flocks, each of which included the 3 SMR groups. Each SMR group included 3 ganders and 15 female geese. Relative genetic contribution (RGC) is defined as the number of offspring sired by 1 male as a percentage of the entire goslings in each flock, and it was used to compare the differences in RE among ganders. The frequency of agonistic behavioral interactions (ABIs) among the ganders was video recorded in each SMR group, and the SR of each gander was determined. In total, 1,026 eggs were incubated, and 609 goslings hatched. Parent-offspring relationships among 771 individuals from the 2 generations were identified using 20 microsatellite markers, and the RGC was calculated. Results showed that the SMR and SR had significant effects on RGC in naturally mating geese (P = 0.001 and P = 0.000, respectively). Significant differences in RGC were observed among the high- and medium- and low-SMR groups, with average RGCs of 14.3, 10.6, and 8.4%, respectively. The high-SMR group had the highest RGCs in each flock, and the ganders with high SR had the highest RGCs among the 3 SMRs. The study showed that in a naturally mating geese population, selecting for the sperm mobility traits of a gander can effectively improve the RE.

Using an on-site laboratory for fecal steroid analysis in wild white-faced capuchins

Hormone laboratories located "on-site" where field studies are being conducted have a number of advantages. On-site laboratories allow hormone analyses to proceed in near-real-time, minimize logistics of sample permits/shipping, contribute to in-country capacity-building, and (our focus here) facilitate cross-site collaboration through shared methods and a shared laboratory. Here we provide proof-of-concept that an on-site hormone laboratory (the Taboga Field Laboratory, located in the Taboga Forest Reserve, Costa Rica) can successfully run endocrine analyses in a remote location. Using fecal samples from wild white-faced capuchins (Cebus imitator) from three Costa Rican forests, we validate the extraction and analysis of four steroid hormones (glucocorticoids, testosterone, estradiol, progesterone) across six assays (DetectX® and ISWE, all from Arbor Assays). Additionally, as the first collaboration across three long-term, wild capuchin field sites (Lomas Barbudal, Santa Rosa, Taboga) involving local Costa Rican collaborators, this laboratory can serve as a future hub for collaborative exchange.

Development of an in vitro tissue culture system for hammer coral (Fimbriaphyllia ancora) ovaries

In vitro gonad culture systems have proven useful to investigate intrinsic mechanisms of sexual reproduction in animals. Here we describe development of an in vitro culture method for coral ovaries. Mesenterial tissues containing both ovaries and mesenterial filaments were microscopically isolated from the scleractinian coral, Fimbriaphyllia ancora, and culture conditions were optimized. M199 diluted 10× (10% M199, pH 8.1) and supplemented with 25 mM HEPES and the antibiotics, ampicillin, penicillin and streptomycin, supported oocyte survival and maintained the structural integrity of ovaries during short-term culture (~ 6 days). Addition of a commercial antibiotic-antimycotic solution (Anti-Anti) and fetal bovine serum adversely affected ovary maintenance and caused tissue disintegration. Characterization of cultured ovaries showed that there is no difference in cell proliferation of ovarian somatic cells between culture Days 1 and 6. Moreover, the presence of oogonia and expression of a major yolk protein, vitellogenin, were confirmed in ovaries cultured for 6 days. This system will be useful for studying effects of a wide range of substances on coral oogenesis.

Determination of Annual Plasma Hormone Levels Associated with Reproduction in Long-Day Breeding Domestic Geese

Simple Summary

In domestic birds, breeding practices and optimisation of the microenviroment and nutrition ensure egg production throughout the entire year. However, domestic geese experience an annual cycle of reproductive quiescence and recrudescence. Thus, patterns of reproductive hormones related to the initiation and termination of the breeding–laying period between the sexes seems to be especially important. This paper presents annual patterns of prolactin (PRL), triiodothyronine (T3), thyroxine (T4), testosterone (T), progesterone (P4), and estradiol (E2) in ganders and female geese. Long-day breeding Zatorska geese kept in controlled commercial conditions experienced periods with elevated plasma PRL levels in both sexes post-breeding and during the second half of the breeding–laying period. Increased plasma PRL levels by the end of the breeding–laying period were detected earlier in ganders than in female geese. Annual patterns of thyroid hormones (THs) were partially in agreement with existing theories on the specific role of THs in termination of breeding, which is permissive rather than causal. It may be suggested that ganders terminate their breeding–laying period one month earlier than female geese. These results may be useful in the manipulation of the endocrine axis to extend the duration of seasonal hatching egg production.

Abstract

This paper examines the dynamics of circulating hormone changes connected with reproduction in geese during the annual period related to gonad morphometry. One hundred geese were examined. The levels of prolactin (PRL), triiodothyronine (T3), thyroxine (T4), testosterone (T), progesterone (P4) and estradiol (E2) were estimated. In both sexes, PRL level patterns fit a quadratic trend with elevations in the post-breeding and the second half of the breeding–laying periods. During these periods, differences in the PRL level between sexes were noted. In ganders, increased PRL levels during the laying period occurred earlier compared to in female geese. Cubic trends for T and E2 in ganders and quadratic for T, P4, and E2 in female geese were observed. PRL was negatively correlated with T in both sexes and with P4 and E2 in female geese. A higher level of T3 and variation in T4 in ganders with a quartic trend in ganders vs. a quadratic in female geese were noted. Patterns of PRL, T, and E2 suggested that the breeding–laying period in ganders may be shorter than in female geese. These findings will be used to explore experimental manipulations of the endocrine axis to increase synchronisation of both sexes.

Endocrine correlates of gender and throat coloration in the southern ground-hornbill (Bucorvus leadbeateri)

The southern ground-hornbill (SGH) is a cooperatively breeding bird endemic to eastern and southern Africa, but is endangered in its southern distributional range. The national conservation restoration program harvests redundant chicks for captive breeding and reintroduction; with sexing and social grouping of the species evaluated by throat-skin coloration, with adult males displaying a completely red color compared to dark blue within the red observed in adult females. However, recent findings indicate that dominant and subordinate adult males exhibit patches of blue throat-skin. To optimize SGH management practices, it is vital to determine the role of red and blue coloration, as well as the possible drivers thereof. As a prerequisite, an enzyme immunoassay for monitoring fecal androgen metabolite (fAM) concentrations in SGH was established. Following this, fresh fecal samples were collected from 78 SGH, of various demographics and origin, across 12 captive institutions, to determine whether fAM concentrations differ between blue (B), partially blue (sB), and fully red (R) throat-skin colored SGH. Furthermore, fAM concentrations were compared between males housed in different social groups of different age and sex classes. Individual median fAM concentrations of B, sB, and R adult males did not differ significantly but were considerably higher in B and sB males compared to R males. Social dynamics within captivity, for example, dominance, played no role as a driver of male gonadal activity or throat skin coloration. The results of the study indicate that androgens and apparent social dynamics are not primary determinants of throat coloration in male SGH.

ACTH Stimulation Induced Self-Mutilation Behavior in the Golden Conure (Guaruba guarouba)

Simple Summary

Psittacidae are very susceptible to chronic stress and behavioral disorders. We report a successful physiological validation of an enzyme immunoassay for the non-invasive monitoring of adrenocortical activity and, thus, stress in the golden conure. In addition, as an incidental finding, we demonstrate a link between increased glucocorticoid levels and behavioral disorders. Our results are of great relevance for conservation projects and endocrine-behavioral studies of captive golden conures, where the stress evaluation is a fundamental part of animal welfare programs.

Abstract

Psittacidae are very susceptible to chronic stress and behavioral disorders. Information regarding the endocrinology of the golden conure is scarce, especially about adrenocortical activity. Endocrine studies using non-invasive methods are useful, because they allow longitudinal analysis with high numbers of samples without causing additional stress and are viable in the psittacidae management. The objective was to physiologically validate an enzyme immunoassay for measuring glucocorticoid metabolites (GCMs) in this species. Serial droppings were collected from 16 animals. First, one subgroup received adrenocorticotropic hormone (ACTH; Synacthen Depót^®) and the other group served as controls. This procedure was reversed afterwards. All birds presented self-mutilation approximately 6 h after the ACTH injection. This behavior disappeared after two days. Peak concentrations (on average nine times higher than baseline values) of GCMs were found 6 (4–8) h after ACTH administration; in all (but one) animals also a second peak was found 14 (10–20) h post injection. GCM levels returned to the baseline after 24 h. We physiologically validated a cortisone enzyme immunoassays to measure adrenocortical activity in the golden conure. Such non-invasive methods are important for studies, which are related to welfare, reproductive, and conservation programs. In addition, we could demonstrate a link between increased glucocorticoid levels and behavioral disorders.

Meta-analysis: Supplementary artificial light and goose reproduction

Photoperiod affects poultry reproduction, and in birds, photoperiod regulation is a complex physiological process. In modern poultry production, lighting management has become an important and effective management approach for increasing egg production. Geese are domesticated fowl and in many goose production enterprises animals are allowed to roam in outside pens during the day and are housed indoors at night, so the animals can be exposed to artificial lighting during the night periods. Supplementary artificial lighting resulted in improved reproduction in some studies, but reports have been inconsistent. To evaluate the results from previous studies of supplementary lighting on goose egg production, a meta-analysis was conducted to determine optimal supplementary artificial lighting regimens for geese egg production. Results indicated supplementary artificial light increases mean egg production, the length of the period of egg production before there is cessation of egg production capacity, and fertility. In summary, there were evaluations of data from five studies focused on White Roman geese in the meta-analysis conducted in the present study, however, examination of more breeds is necessary to make more definitive assessments of the findings from this meta-analysis.

Response to gonadotropin-releasing hormone challenge: Seasonal variation in steroid production in a viviparous lizard, Tiliqua nigrolutea

The hypothalamic-pituitary-gonadal axis plays a central role in the regulation of gamete maturation, sex steroid production and the stimulation of reproductive behaviours in vertebrates. In seasonal breeders, the timely activation and deactivation of this control system is important to ensure successful reproduction: this process is not well understood in species which breed irregularly. Males of the viviparous blotched blue-tongued lizard, Tiliqua nigrolutea, breed annually, while females display a multiennial cycle. We investigated seasonal variation in hypothalamic-pituitary-gonadal axis responsiveness in both sexes of T. nigrolutea. We measured changes in plasma concentrations of testosterone and estrogen in response to a single intraperitoneal injection of a GnRH agonist, chicken-II LH-RH, at three reproductively distinct times of year. Plasma testosterone concentrations in males were significantly increased during gonadal quiescence, but not initial or final spermatogenesis. There was no estrogen response in males at any time of year. Conversely, in females, there was an increase in plasma testosterone, but not estrogen, concentration, in reproductively quiescent females several months in advance of a successful pregnancy. These results indicate clear variation in HPG axis activity with sex, season and reproductive condition in this seasonally breeding viviparous lizard. This study opens the way for further investigation into the mechanisms by which internal (body condition) and external seasonal cues (temperature and photoperiod) are coordinated to regulate reproduction in irregularly-breeding reptiles.

First attempt to monitor luteinizing hormone and reproductive steroids in urine samples of the Amazonian manatee (Trichechus inunguis)

The aims of this study were to validate an enzyme immunoassay (EIA) for the measurement of luteinizing hormone (LH) in urine samples of Amazonian manatees (Trichechus inunguis; Mammalia: Sirenia) and to monitor urinary LH and reproductive steroids during the ovarian cycle in this species. Urine samples were collected from two captive males following a hormonal challenge with a gonadotropin-releasing hormone (GnRH) analogue. The urinary LH results from hormonal challenge were compared with urinary androgens for the purpose of EIA validation. Furthermore, urine samples were collected daily, over a 12-wk period, from two captive adult females, for 2 consecutive yr. The urinary LH pattern from females was compared with the patterns of urinary progestagens and estrogen conjugates throughout the ovarian cycle. An LH peak was observed in both male Amazonian manatees after the hormonal challenge, occurring prior to or together with peak androgen levels. In the females, the ovarian cycle ranged from 40 to 48 days (mean of 43.7 days). Two distinct peaks of estrogen conjugates were observed across all cycles analyzed, and the urinary LH peaks observed were accompanied by peaks of urinary estrogen conjugates. The EIA was validated as a method for the quantification of urinary LH from Amazonian manatees, as it was able to detect variations in the levels of LH in urine samples. These results suggest that T. inunguis exhibits a peculiar hormonal pattern during the ovarian cycle. Therefore, further studies are desirable and necessary to clarify the relationship between this hormonal pattern and morphological changes, as well as mating behavior, in Amazonian manatee.

Food restriction negatively affects multiple levels of the reproductive axis in male house finches, Haemorhous mexicanus

Nutrition influences reproductive functions across vertebrates, but the effects of food availability on the functioning of the hypothalamic-pituitary-gonadal (HPG) axis in wild birds and the mechanisms mediating these effects remain unclear. We investigated the influence of chronic food restriction on the HPG axis of photostimulated House Finches, Haemorhous mexicanus. Food-restricted birds had underdeveloped testes with smaller seminiferous tubules than ad libitum-fed birds. Baseline plasma testosterone (T) increased in response to photostimulation in ad libitum-fed but not in food-restricted birds. Food availability did not, however, affect the plasma T increase resulting from a gonadotropin-releasing hormone (GnRH) or a luteinizing hormone (LH) challenge. The number of hypothalamic GnRH-I immunoreactive (ir) but not proGnRH-ir perikarya was higher in food-restricted than ad libitum-fed finches, suggesting inhibited secretion of GnRH. Hypothalamic gonadotropin-inhibitory hormone (GnIH)-ir and neuropeptide Y (NPY)-ir were not affected by food availability. Plasma corticosterone (CORT) was also not affected by food availability, indicating that the observed HPG axis inhibition did not result from increased activity of the hypothalamic-pituitary-adrenal (HPA) axis. This study is among the first to examine multilevel functional changes in the HPG axis in response to food restriction in a wild bird. The results indicate that food availability affects both hypothalamic and gonadal function, but further investigations are needed to clarify the mechanisms by which nutritional signals mediate these effects.

Ambient temperature and air pressure modulate hormones and behaviour in Greylag geese (Anser anser) and Northern bald ibis (Geronticus eremita)

Ambient temperature and air pressure are relevant stimuli that can elicit hormonal responses in alignment with adjusting individuals' physiology and behaviour. This study investigated possible changes in corticosterone (C) and testosterone (T) and contingencies with behaviour in response to ambient temperature and air pressure, and it evaluated the temporal response dynamics of these hormones in 12 individual Greylag geese (Anser anser) over 26 and 12 individual Northern bald ibis (Geronticus eremita) over 27 days, during late winter. Immunoreactive metabolites of C and T were analysed non-invasively from 626 fecal samples by means of group-specific antibodies and correlated to behaviour and weather factors. In both species, high C levels correlated with low temperatures 24h before sampling, but low C levels correlated with high air pressure 6-12h before sampling. In both species, C levels and behavioural activity were negatively correlated. In addition, temperature had a positive influence on T levels in both species 12-24h before sampling. The fact that weather conditions influenced changes in levels of C, while social interactions did not, is indicative of a general mechanism of graduated physiological adjustment to environmental variations affecting metabolism, stress responses and behaviour.

Regulation of plasma testosterone, corticosterone, and metabolites in response to stress, reproductive stage, and social challenges in a desert male songbird

In many male vertebrates, the secretion of reproductive (gonadal androgens) and adrenocortical (glucocorticoids) hormones varies seasonally and in response to environmental stimuli, and these hormones exert numerous behavioral and metabolic effects. We performed two field studies on adult male Rufous-winged Sparrows, Peucaea carpalis, a Sonoran Desert rain-dependent sedentary species, to (a) determine seasonal changes in initial (baseline) and acute stress-induced plasma testosterone (T), corticosterone (CORT), and two metabolites (uric acid and glucose) and (b) compare the effects of two types of social challenge (song playback or simulated territorial intrusion consisting of song playback plus exposure to a live decoy bird) on plasma T, CORT, these metabolites, and territorial behavior. Initial plasma T was higher during the summer breeding period than during post-breeding molt. Acute stress resulting from capture and restraint for 30 min decreased plasma T in breeding condition birds but not in the fall, revealing that this decrease is seasonally regulated. Initial plasma CORT did not change seasonally, but plasma CORT increased in response to acute stress. This increase was likewise seasonally regulated, being relatively smaller during autumnal molt than in the summer. We found no evidence that acute stress levels of CORT are functionally related to stress-depressed plasma T and, therefore, that plasma T decreases during stress as a result of elevated plasma CORT. Thirty minutes of exposure to simulated territorial intrusion resulted in different behavior than 30 min of exposure to song playback, with increased time spent near the decoy and decreased number of overhead flights. Neither type of social challenge influenced plasma T, thus offering no support for the hypothesis that plasma T either responds to or mediates the behavioral effects of social challenge. Exposure to both social challenges elevated plasma CORT, but simulated territorial intrusion was more effective in this respect than song playback. Plasma uric acid and glucose decreased during acute stress, but only plasma uric acid decreased during social challenge. Thus, an elevation in plasma CORT was consistently associated with a decrease in plasma uric acid, but not with a change in glycemia. These results enhance our understanding of the short-term relationships between T, CORT, and avian territorial behavior. They provide novel information on the endocrine effects of acute stress, in particular on plasma T, in free-ranging birds, and are among the first in these birds to link these effects to metabolic changes.

Longitudinal monitoring of sex steroid hormones in excrement of spectacled eiders (Somateria fischeri)

From the 1970s to the 1990s, the breeding population of spectacled eiders (Somateria fischeri) in western Alaska declined by 96%, which led to the listing of this species as threatened under the Endangered Species Act in 1993. Since then, the population has stabilized, but has not recovered to pre-decline numbers. While little is known about reproductive endocrinology in spectacled eiders, in other avian species, estrogen and testosterone are known to initiate and modulate various reproductive processes including yolk protein synthesis, reproductive behaviors and secondary sex characteristics. Measurement of the metabolites of estrogen and testosterone (EM and TM, respectively) in excrement reflect circulating hormone concentrations and provide a non-invasive method to monitor reproductive physiology. We measured concentrations of excreted EM in captive females and TM in males to (1) determine the efficacy of commercially available radioimmunoassay kits to detect EM and TM, (2) describe annual profiles of EM and TM concentrations, and (3) define the reproductive season of captive spectacled eiders using endocrine status. Excrement samples were collected from captive female and male spectacled eiders three times per week throughout 1 year. Female EM and male TM levels were quantified using radioimmunoassay. Mean female EM profile exhibited values exceeding the threshold for "peak" values (EM>193.3 ng/g) from mid-February to early July, and again in September. Additionally, the highest average concentrations of EM were seen in March, May and September. Elevated TM concentrations occurred in mid March, mid May and late June. These data suggest that levels of excreted sex steroids reflect patterns predicted by breeding landmarks in the annual cycle and will assist in field monitoring and captive breeding programs for spectacled eiders.

Seasonal changes in the expression of the androgen receptor in the testes of the domestic goose (Anser anser f. domestica)

It is generally acknowledged that seasonal fluctuations in the morphology and function of bird testes are primarily regulated by seasonal changes in circulating concentrations of testosterone (T) which mediates its action via the androgen receptor (AR). However, it has not yet been elucidated whether gonadal sensitivity to androgens also varies across the bird reproductive cycle. In order to answer the above question, this study makes the first ever attempt to account for the gonadal expression of the AR gene and protein in relation to circulating and testicular T concentrations in the gonads of male birds during the reproductive cycle. The experimental model used in this study was the domestic goose, Anser anser f. domestica, a species with three distinct phases of the annual reproductive cycle: the breeding season in March, the non-breeding season in July and the sexual reactivation phase in November. The plasma and testicular T concentrations were highest in the breeding season, followed by a dramatic decline in the non-breeding season with a successive rise in the sexual reactivation phase. Interestingly, we observed the divergent effect of season on AR mRNA and protein expression. Whereas the AR gene expression showed a nearly inverse relationship with T levels, the seasonal variations in AR protein levels primarily reflected the differences in T concentrations. The results of our study also indicated that regardless of the examined phase of the season, an abundance of AR protein was found only in the nuclei of Leydig and Sertoli cells and myoid cells. The above supports the observation that somatic cells are the targets for androgen action in bird testes. Summarizing, this study revealed that seasonal variations in sensitivity to androgens in the gonads of male birds are reflected in variations in the availability of their cognate receptors. Furthermore, a different pattern of seasonal expression of the AR gene and protein suggests that the AR system is subject to complex regulation that includes both steroid-dependent and steroid-independent factors.

Non-breeding gonadal testosterone production of male and female northern cardinals (Cardinalis cardinalis) following GnRH challenge

Yearly, testosterone (T) levels fluctuate as many vertebrates cycle through reproductive and non-reproductive periods. Among many temperate birds, it is well established that levels of T peak as gonads recrudesce for breeding and then fall as gonads regress prior to the non-breeding season. While the tissues producing breeding season T are well studied, the tissues responsible for non-breeding T have received less investigative attention. We examined the ability of male and female Northern Cardinals (Cardinalis cardinalis) to elevate gonadal T following standardized injections of gonadotropin-releasing hormone (GnRH) across three non-breeding seasons. Males and females were capable of significantly elevating gonadal T production following GnRH injections during periods of reproductive quiescence. The magnitude of T elevation varied across the non-breeding season, but not between sexes. To our knowledge, this is the first report of a significant increase in gonadal T production following GnRH injections administered in the non-breeding season.

Individual variation in plasma testosterone levels and its relation to badge size in House Sparrows Passer domesticus: it's a night-and-day difference

The steroid hormone testosterone (T) plays a central role in the regulation of reproduction in animals. Although seasonal variation in T levels is well-studied, differences between day and night have only been described in relatively few species, and daily within-individual variation has been largely neglected when evaluating the relationship between T and the expression of sexual ornaments or behavior. We measured plasma T levels during day and night in a captive population of House Sparrows, and analyzed their relationship with an important male ornament--badge size. T levels were on average twice as high at night than during daytime. This was true in all seasons, and in both males and females. Disturbance of the birds at night, but not during the day, led to significantly lower T levels, suggesting a rapid drop after an individual wakes up. The relationship between T levels and badge size depended on the time when T was measured. During the breeding season, badge size was strongly positively correlated with night-time, but not with daytime T levels. This suggests that badge size signals information related to an individual's maximum potential T level such as social dominance. Our study highlights that integrative research on the endocrine control of ornament expression needs to take diel variation in hormone levels into account.

Using a GnRH agonist to obtain an index of testosterone secretory capacity in the cockatiel (Nymphicus hollandicus) and sulphur-crested cockatoo (Cacatua galerita)

OBJECTIVE

Validation of a stimulation test for determining the steroidogenic capacity of the parrot testis. The major aim was to characterise testosterone secretion after injection of a gonadotropin-releasing hormone agonist (GnRHa), then use the test to investigate seasonal reproduction in the male cockatiel.

PROCEDURE

A synthetic GnRHa (buserelin; 8.0 microg of peptide/kg bodyweight) was injected IM into male cockatiels (n = 7) and sulphur-crested cockatoos (n = 3) and serial blood samples collected at 0, 30, 60, 90 and 120 min after administration. Once validated, the technique was subsequently used to examine seasonal changes (23 months) in the testosterone profile of a captive cockatiel population.

RESULTS

Injection of buserelin resulted in a significant increase in the testosterone concentration of cockatiel plasma, with maximal concentrations occurring at approximately 60 (1.33 +/- 0.08 ng/mL) to 90 min (1.22 +/- 0.08 ng/mL) after injection. Although no clear pattern of seasonal variation in testosterone secretion was detected in cockatiel plasma, samples taken 60 and 90 min after administration showed a significant increase in all seasons. Injection of buserelin in the sulphur-crested cockatoo also resulted in increased testosterone secretion, with maximal concentrations obtained after 90 min.

CONCLUSION

Buserelin can be used to obtain a reliable index of the prevailing testosterone capacity of the cockatiel and cockatoo testis. With further studies, this test may be incorporated into clinical assessment of reproductive status.

Female androgen patterns and within-pair testosterone compatibility in domestic geese (Anser domesticus)

For successfully raising offspring, long-term monogamous pair partners need to be behaviorally and hormonally coordinated. In the monogamous, biparental greylag geese (Anser anser) a dyadic pairbond-specific measure, 'within-pair testosterone compatibility' (TC) indicated how closely synchronized are seasonal androgen levels, which co-varied with reproductive output. Males, in particular, were assumed to respond to their females' hormonal and fecundity phases. We now present experiments with biparental domestic geese (Anser domesticus) kept as pairs to ask whether TC occurs also in these generally polygynous animals. We further ask how different conditions of mate choice affect TC and whether established TC is maintained during a polygynous flock situation. We measured androgen metabolites (AM) non-invasively from individual droppings. In females, AM was related with gonadal activity as it increased after GnRH but not ACTH challenge. Females with preferred partners had higher maximum AM during egg laying and higher rates of initiating incubation than randomly paired females. Domestic ganders had seasonal AM patterns typical for polygynous males. Within-pair TC ranged from almost perfectly positive to non-correlated in domestic geese but mate choice did not explain TC variation. TC of previous pairs was generally reduced in the flock situation, probably confounded by factors of the social environment, i.e. mating opportunity and availability of multiple partners. On top of the underlying reproductive physiology our results suggest two episodic components of TC: a female androgen responsiveness to the preferred partner at least during egg formation, and the male's facultative potential to respond to her readiness to breed.

Benefits of family reunions: social support in secondary greylag goose families

Social interactions are among the most potent stressors. However, social allies may diminish stress, increase success in agonistic encounters and ease access to resources. We studied the role of social support as a major mechanism for individual stress management in families of free-ranging greylag geese (Anser anser). Greylag geese are long-term monogamous, live in a female-bonded social system, and fledged offspring stay with their parents until the next breeding season ('primary families'). Should parents then fail to fledge young, subadults might rejoin them in summer after molt is completed ('secondary families'). We have previously shown that primary greylag goose families reap benefits from active social support in agonistic encounters, and also excrete lower levels of immuno-reactive corticosterone metabolites (CORT, 'passive social support'). Here we investigated how far active and passive social support continues in secondary goose families. Although we found that active support in agonistic encounters was almost absent in secondary families, subadult male geese won an increased number of agonistic encounters due to the mere presence of their secondary family. Particularly adult and subadult females benefited from passive social support through decreased CORT, whereas males did not. Decrease in the hormonal stress response during challenging situations, induced by social allies, may help the females' long-term energy management, thereby improving the odds for successful future reproduction. We discuss whether joining a secondary family may be an alternative tactic for young geese towards optimizing their start into a complex social life.

Display activity and seasonality of faecal sexual steroids in male great bustard (Otis tarda L.)

The non-invasive faecal sampling and RIA was used to measure faecal equivalents of testosterone (T), dehydroepiandrosterone (DHEA), oestradiol-17beta (E2) and progesterone (P4) in juvenile and adult great bustard males. Possible connections of diurnal and seasonal changes of sexual steroid levels and display activity were studied. Correlations were found between sexual steroid equivalent levels of faeces and display activity and agonistic behaviour in the different phases of annual cycle of adult males. In early display period increasing levels of androgens were measured, during main display period very high androgen dominance was observable against E2 and P4. During postnuptial moult strong T decrease and DHEA and P4 increase were detected. Elevation of E2 was measured during wintering. In juveniles level of DHEA was higher than level of T suggesting its importance in immature males. Decrease of T was detected between reproductive period and postnuptial moult and DHEA between reproduction and wintering, accompanying with E2 elevation. The inhibiting effect of inclement weather on gonad functions also was detected in our study. We suppose that the unexpected cold weather with strong wind depressed the levels of androgens both in juveniles and adults and the increase of faecal E2 was also detected.

Seasonal and individual variation in response to GnRH challenge in male dark-eyed juncos (Junco hyemalis)

Concentrations of gonadal steroids such as testosterone (T) often vary widely in natural populations, but the causes and particularly the consistency of this variation is relatively unexplored. In breeding males of a wild population of the dark-eyed junco (Junco hyemalis), we investigated seasonal and individual variation in circulating T during two breeding seasons by measuring the responsiveness of the HPG axis to a standardized injection of gonadotropin-releasing hormone (GnRH). Individuals were bled prior to and 30min after injection. Pre- and post-challenge levels of T were measured using EIA. Many subjects were sampled repeatedly across multiple breeding stages. Plasma T concentrations nearly doubled in response to GnRH during early spring, but showed significantly smaller increases in later breeding stages. When controlling for seasonal variation in response to challenge, we also found repeatable differences among individuals, indicating individual consistency in the release of T in response to a standardized stimulus. These seasonal and individual differences may arise from comparable variation in responsiveness of the pituitary or a decline in gonadal sensitivity to downstream gonadotropins. In contrast, pre-challenge T showed almost no seasonal changes and did not differ consistently among individuals. To our knowledge, this is the first demonstration of individual repeatability of short-term hormonal changes in a wild population. Such repeatability suggests that hormonal plasticity might evolve in response to changing selection pressures.

Hormonal and behavioural symmetries between the sexes in the Northern bald ibis

Seasonal patterns of fecal androgen and corticosteroid levels were measured in a semi-tame colony of Northern bald ibis (Geronticus eremita) and put in perspective with socio-sexual patterns. Northern bald ibis are monomorphic, monogamous, year-round social colonial breeders. Steroids levels were assessed from the pre-mating until the end of the mating season in the sexes, age groups, and social categories. Male immunoreactive androgen concentrations, determined by enzyme immuno-assay from feces, were relatively low, even during the mating phase, and were close to the female levels. Sexual monomorphy and symmetries in socio-sexual and parental roles may account for this similarity. Males and females responded in a similar way to social challenges from conspecifics, particularly during pair-formation. Singletons showed higher androgen metabolites levels than paired individuals. Corticosterone metabolites were relatively high during periods of social instability in the mating phase and were highest in low-ranking, young individuals. We suggest that the challenge hypothesis may even apply to females in this non-passerine bird.

Effect of testosterone loading on the kinetic of faecal testosterone excretion in mallards

Intestinal passage time of coloured fodder and testosterone turnover were examined by faecal steroid analysis in mallards in the reproductive and postrefractory period. In the latter, the discharge of coloured fodder began 36 minutes after ingestion in males, and 56 minutes in females. During reproduction the discharge began 93 minutes and 112 minutes after ingestion in males and females, respectively. Total passage time was similar in the reproductive and postrefractory period in both sexes. After intraperitoneal testosterone injection, faecal samples were collected for 8 hours and testosterone levels were measured using RIA. In the postrefractory period, 1-2 hours after testosterone loading a strong increase of faecal testosterone content developed in males, meanwhile a slighter testosterone peak appeared in females. During reproduction testosterone excretion began 1.5-2 hours after injection in both sexes but in females its increase was smaller. The duration of response to testosterone loading was 5 hours in both periods and both sexes. Intensive excretion after T loading appeared earlier in males than in females, but total passage time finished at the same time: 5 hours after loading. The character of testosterone excretion was corresponding to the passage of fodder-chimus-faeces in the reproductive and postrefractory period in both sexes.

Synthesis of Measuring Steroid Metabolites in Goose Feces

The reliability of noninvasively measuring steroid hormones from feces in greylag geese (Anser anser) and domestic geese (A. domesticus), both qualitatively and quantitatively, was tested experimentally. Geese are mainly herbivorous birds with a short gut-passage time (2-3 h). Groups of eight outdoor-housed male domestic geese were subjected to two different experiments, injection of either GnRH or ACTH, which were replicated in three different seasons (spring, summer, and fall). GnRH stimulation resulted in significant increases of response fecal testosterone metabolites (TM; 17beta-OH-androgens) in spring and fall, but not during the summer photorefractoriness. Testosterone response patterns obtained from plasma samples paralleled those from feces; however, no direct correlation between individual immunoreactive plasma and feces contents was observed. To improve the sample handling during extraction and the assay sensitivity, we promote the use of a group-specific antibody against 17-oxoandrogens that does not require deconjugation prior to the analysis. ACTH robustly increased fecal corticosterone in all seasons. The polar nature of glucocorticoids, however, seems to make a distinction between conjugated and nonconjugated types difficult, and the available avian literature on this topic is discussed.

Active and passive social support in families of greylag geese (Anser anser)

In general, support by social allies may reduce stress, increase success in agonistic encounters and ease access to resources. Social support was mainly known from mammals, particularly primates, and has been studied in birds only recently. Basically two types are known: (i) 'active social support', which describes the participation of a social ally in agonistic encounters, and (ii) 'passive social support' in which the mere presence of a social ally reduces behavioural and physiological stress responses. In greylag geese (Anser anser) offspring stay with their parents for an entire year or even longer and therefore are a candidate avian model to study support by social allies. We investigated the effects of active and passive social support in ten families (ten males, ten females, 33 juveniles) in a free-roaming, semi-tame flock of greylag geese. Focal individuals were observed during three time periods: (i) re-establishment of the flock in the fall, (ii) stable winter flock, and (iii) disintegration of the flock and break-up of family bonds. We recorded all agonistic interactions of the members of one focal family during morning feedings for two consecutive days: a control day, in which food was distributed widely, and a social density stress situation, in which the same amount of food was spread over a much smaller area. In addition, we collected faeces of all individuals within this family for three hours from the beginning of the feeding situation for determining excreted corticosterone immuno-reactive metabolites by enzyme immuno assay. We found that the small families, i.e. pairs with one or two accompanying young, were involved in more agonistic interactions, mainly through the lack of active social support, as compared to large families in the same situation. Members of greylag goose families lost agonistic encounters significantly less often when actively supported. In addition, the excretion of corticosterone metabolites was significantly decreased in large families during a social density stress situation, probably as an effect of passive social support. Via such a socially induced decrease in hormonal stress response during challenging situations, an individual's long term energy management may benefit.

Sampling effort/frequency necessary to infer individual acute stress responses from fecal analysis in Greylag geese (Anser anser)

Measuring hormone metabolites from excreta is a powerful method to study hormone-behavior relationships. Currently, fecal corticosterone metabolite concentrations are used to estimate individual short-term stress responses. From the free-roaming, semitame flock of greylag geese (Anser anser), as many fecal samples as possible were collected over 3 h following a challenge (social density stress) or in a control situation. This time span corresponds to the gut passage time of geese. It was asked how many samples were necessary to determine differences in excreted corticosterone immunoreactive metabolites (CORTs) between control and social density stress and which parameters (means, maxima, range) reliably showed this difference. A large variation of CORT was found between consecutive samples. Still, means, maxima, and ranges of the samples in a fecal series consistently showed the response to a stressor both within and between individuals. Three samples sufficed if the maximum value of CORT was used, whereas four or more samples were necessary to work with the mean. It was concluded that by increasing the number of fecal samples collected, the course of CORT could be measured more precisely and an individual's acute stress response inferred more reliably.

Enhanced yolk testosterone influences behavioral phenotype independent of sex in Japanese quail chicks Coturnix japonica

Studies have demonstrated an effect of yolk testosterone levels on the physiology and behavior of nestling birds. In order to investigate this phenomenon experimentally in a precocial bird, we enhanced yolk testosterone, but within the physiological range, by injecting 50 ng testosterone in ethanol into Japanese quail Coturnix japonica eggs prior to incubation. The chicks hatching from these as well as from control eggs that had received the carrier-only or were left unmanipulated were subject to a number of behavioral tests from hatching to the age of 3 weeks. In addition, fecal samples were taken during a 90-min isolation period to determine a physiological response to a stressor. Experimental chicks performed a detour task faster and approached novel objects sooner than did the controls. Chicks from treated eggs took a longer time to start distress vocalizing and also produced less distress calls during open-field trials, took on average a larger number of trials for them to show tonic immobility and also excreted lower levels of corticosterone metabolites (BM) than did the controls. In response to a stressor, excreted BM was initially higher in the control chicks, as compared to the experimental birds. Induced behavioral effects were independent of sex with no sex treatment interactions found. In sum, experimentally enhanced testosterone levels in the eggs shifted individual behavioral phenotype towards "bold" or "proactive", irrespective of sex. We conclude that testosterone in the yolk influences the coping style of hatchlings and may be a potential means of maternal influence on offspring phenotype.

Excreted corticosterone metabolites co-vary with ambient temperature and air pressure in male Greylag geese (Anser anser)

In many species, seasonal activities such as reproduction or migration need to be fine-tuned with weather conditions. Air pressure and temperature changes are the best parameters for such conditions. Adapting to climatic changes invariably involves physiological and behavioral reactions associated with the adrenals. In the present study, we investigated the effects of ambient temperature and air pressure on excreted immuno-reactive metabolites of corticosterone (BM) and androgens (AM). Focal individuals were 14 paired male greylag geese (Anser anser) from a semi-tame, unrestrained flock. BM and AM were measured in individual fecal samples over 25 days in November and December. Two different ACTH-validated assays were used for the assessment of BM: the first one cross-reacting with 11beta,21-diol-20-one structures ("old assay") and the second one with 5beta,3alpha,11beta-diol structures ("new assay"). With the "new assay," BM correlated negatively with the minimum ambient temperature of the night before, which may reflect corticosterone involvement in thermoregulation. BM also correlated positively with the minimum air pressure of the previous afternoon, which supports the value of air pressure for predicting weather conditions. Together, these reactions suggest a role of the adrenals in responding behaviorally and physiologically to changes in weather. Preliminary analysis indicated a higher sensitivity to the excreted glucocorticosteroid metabolites in the "new assay." As expected for outside the mating season, no relationships were found between excreted AM and the weather parameters considered. The gradual changes in BM excretion in parallel with weather conditions may be part of the fine-tuning of physiology and behavior by environmental clues.

Social allies modulate corticosterone excretion and increase success in agonistic interactions in juvenile hand-raised graylag geese (Anser anser)

In mammals, support by a social partner may reduce stress levels and ease access to resources. We investigated the effects of the passive presence of a nearby social ally on excreted corticosterone immunoreactive metabolites and behaviour in juvenile graylag geese (Anser anser). Two groups of hand-raised juveniles (N1 = 9, N2 = 3) were tested over 1 year by positioning humans of different familiarity (i.e., the human foster parent, a familiar human, a nonfamiliar human, no human) at a standard distance to the focal geese. Their success in agonistic interactions significantly decreased with age and with decreasing familiarity of the accompanying human. The humans present modulated the excretion of corticosterone immunoreactive metabolites, with the strongest effects recorded after fledging when corticosterone metabolites were also positively correlated with agonistic behaviour. This suggests that a human foster parent may provide similar supportive benefits as goose parents do in natural families. We discuss the benefits of social alliances with regard to the integration into the flock, access to resources, and life history.

Non-invasive methods to measure androgen metabolites in excrements of European stonechats, Saxicola torquata rubicola

Traditionally androgen concentrations are measured invasively in blood plasma. However, non-invasive methods to detect androgens are desirable, as this reduces interference with the natural behavior of the study species and multiple samples can be obtained relatively easy. The aim of this study was to validate a method to measure androgens non-invasively in excrements of male European stonechats (Saxicola torquata rubicola). Extracts of excrements of a male stonechat injected with [3H]testosterone ([3H]T) were chromatographically separated using high performance liquid chromatography (HPLC). The resulting HPLC fractions were then analyzed with a radioimmunoassay against testosterone (T-RIA). The results showed that the assay picked up major metabolites of [3H]T. The physiological relevance of excreted androgen metabolites was further validated by showing that injection of exogenous GnRH to seven males led to a significant increase in excreted androgen metabolites. In contrast, androgen metabolite levels of six saline-injected control males did not increase. Furthermore, excrements from nine males were collected from January until April to see whether the typical seasonal increase in testosterone levels can also be traced when measuring excreted androgen metabolites. As expected, there was a significant seasonal increase in androgen metabolite concentrations. Thus, the T-RIA measures androgen metabolites in droppings of male European stonechats and to our knowledge this study represents the first validation of a non-invasive androgen assay in a passerine bird.

Excreted metabolites of gonadal steroid hormones and corticosterone in greylag geese (Anser anser) from hatching to fledging

Steroid hormones play major roles in the organization of the phenotype and in the activation of behavior. From hatching to fledging, they are involved in growth, development, and learning. We investigated the relationship between the ontogenetic patterns of steroid hormones and the sexual and social development of greylag goslings (Anser anser). Two groups of individually marked goslings (n = 10/5) were hand-raised under near-field conditions. 17beta-OH-androgen (AM), estrogen (EM), and corticosterone (BM) immunoreactive metabolites were measured noninvasively by enzyme immunoassay of individual fecal samples. Feces were regularly sampled from hatching to fledging. All excreted steroids were found to peak at hatching and to decrease thereafter. Gonadal steroids fluctuated more than BM, which remained at low levels throughout ontogeny after a slow decrease during the first 20 days. The pattern of BM is discussed in relation to learning processes (i.e., filial imprinting) and social stress. It is suggested that high initial BM may constrain energy allocation to growth. AM increased around the age of 20 days, when the feathers start growing, and later, together with EM, at the age of 40 days. These elevated values of gonadal steroids are discussed in relation to the sensitive phase of sexual imprinting. Females show higher EM levels than males throughout ontogeny. Furthermore, the ratio of excreted estrogen to androgen (EM/AM) of females before fledging correlates with the number of hatched and fledged goslings in their first years of reproduction. In conclusion, our data suggest a role for steroid hormones in the modulation of behavioral and morphological development in the precocial greylag geese, in agreement with the organizational-activational hypothesis.