The endocrine control of reproduction and molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. I. Annual changes in plasma levels of gonadal steroids and LH

Quantifying capital versus income breeding: New promise with stable isotope measurements of individual amino acids

Capital breeders accumulate nutrients prior to egg development, then use these stores to support offspring development. In contrast, income breeders rely on local nutrients consumed contemporaneously with offspring development. Understanding such nutrient allocations is critical to assessing life-history strategies and habitat use. Despite the contrast between these strategies, it remains challenging to trace nutrients from endogenous stores or exogenous food intake into offspring. Here, we tested a new solution to this problem. Using tissue samples collected opportunistically from wild emperor penguins Aptenodytes forsteri, which exemplify capital breeding, we hypothesized that the stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope values of individual amino acids (AAs) in endogenous stores (e.g. muscle) and in egg yolk and albumen reflect the nutrient sourcing that distinguishes capital versus income breeding. Unlike other methods, this approach does not require untested assumptions or diet sampling. We found that over half of essential AAs had δ¹³ C values that did not differ between muscle and yolk or albumen, suggesting that most of these AAs were directly routed from muscle into eggs. In contrast, almost all non-essential AAs differed in δ¹³ C values between muscle and yolk or between muscle and albumen, suggesting de novo synthesis. Over half of AAs that have labile nitrogen atoms (i.e. 'trophic' AA) had higher δ¹⁵ N values in yolk and albumen than in muscle, suggesting that they were transaminated during their routing into egg tissue. This effect was smaller for AAs with less labile nitrogen atoms (i.e. 'source' AA). Our results indicate that the δ¹⁵ N offset between trophic-source AAs (Δ¹⁵ N_{trophic-source} ) may provide an index of the extent of capital breeding. The value of emperor penguin Δ¹⁵ N_Pro-Phe was higher in yolk and albumen than in muscle, reflecting the mobilization of endogenous stores; in comparison, the value of Δ¹⁵ N_Pro-Phe was similar across muscle and egg tissue in previously published data for income-breeding herring gulls Larus argentatus smithsonianus. Our results provide a quantitative basis for using AA δ¹³ C and δ¹⁵ N, and isotopic offsets among AAs (e.g. Δ¹⁵ N_Pro-Phe ), to explore the allocation of endogenous versus exogenous nutrients across the capital versus income spectrum of avian reproduction.

Semen cryopreservation in black-footed (Spheniscus demersus) and gentoo (Pygoscelis papua) penguins: Effects of thawing temperature on semen characteristics

In this study, there was an examination of the effect on the characteristics of cryopreserved black-footed (Spheniscus demersus) and gentoo (Pygoscelis papua) penguin semen, of thawing at 37 and 5 °C. For two consecutive years, semen was collected and frozen during the April-June period from six gentoo penguins, and during the October-November period from 13 black-footed penguins. After thawing, sperm motility variables were examined by computer-assisted sperm analysis. Propidium iodide and SYBR-14 were used as fluorochromes for the examination of membrane integrity. For the gentoo penguins, no differences were detected in the values of frozen-thawed semen characteristics after thawing at 37 or 5 °C. For the black-footed penguins, however, thawing at 5 °C resulted in greater values (P < 0.05) for straight-line velocity (VSL), average path velocity (VAP), linearity (LIN), straightness (STR), and wobble (WOB) as compared with thawing at 37 °C. After thawing at 37 ºC, there were greater values with gentoo penguin sperm for percentage motile sperm, progressive motility, curvilinear velocity (VCL), VSL VAP, LIN, STR, WOB and beat-cross frequency (BCF; P < 0.05) than that for black-footed penguin sperm. After thawing at 5 ºC, there were no differences in values for any variables between the two species. In conclusion, thawing temperature affects semen characteristics in a species-specific manner. The present data strongly suggest that cryopreservation procedures should be adapted for use with each penguin species. Cryopreserved black-footed penguin semen should be thawed after cryopreservation at 5 ºC, while that of gentoo penguins can be thawed at either 5 or 37 ºC.

Time-lapse cameras reveal latitude and season influence breeding phenology durations in penguins

Variation in the phenology of avian taxa has long been studied to understand how a species reacts to environmental changes over both space and time. Penguins (Sphenicidae) serve as an important example of how biotic and abiotic factors influence certain stages of seabird phenology because of their large ranges and the extreme, dynamic conditions present in their Southern Ocean habitats. Here, we examined the phenology of gentoo (Pygoscelis papua) and chinstrap penguins (Pygoscelis antarctica) at 17 sites across the Scotia arc, including the first documented monitoring of phenology on the South Sandwich Islands, to determine which breeding phases are intrinsic, or rather vary across a species range and between years. We used a novel method to measure seabird breeding phenology and egg and chick survival: time-lapse cameras. Contrary to the long-standing theory that these phases are consistent between colonies, we found that latitude and season had a predominant influence on the length of the nest establishment, incubation, and guard durations. We observe a trend toward longer incubation times occurring farther south, where ambient temperatures are colder, which may indicate that exposure to cold slows embryo growth. Across species, in colonies located farther south, parents abandoned nests later when eggs were lost or chicks died and the latest record of eggs or chicks in the nest occurred earlier during the breeding period. The variation in both space and time observed in penguin phenology provides evidence that the duration of phases within the annual cycle of birds is not fundamental, or genetic, as previously understood. Additionally, the recorded phenology dates should inform field researchers on the best timing to count colonies at the peak of breeding, which is poorly understood.

Paternity testing using microsatellite DNA markers in captive Adélie penguins (Pygoscelis adeliae)

We investigated the paternity of 39 Adélie penguins (Pygoscelis adeliae) hatched at the Port of Nagoya Public Aquarium between 1995 and 2005 breeding seasons using microsatellite DNA markers. Among the 13 microsatellite marker loci tested in this study, eight markers amplified and were found to be polymorphic in the colony's founders of the captive population (n = 26). Multiple marker analysis confirmed that all the hatchlings shared alleles with their social fathers and that none of them were sired by any male (all males ≥4 years old in the exhibit tank during each reproductive season; n = 9-15) other than the one carrying out parental duties, except in the case of two inbred hatchlings whose half-sibling parents shared the same father. These results demonstrated that extra-pair paternity (EPP) did not occur in this captive population and that even if EPP has been detected among them, the probability of excluding all other possible fathers in the exhibit tank is extremely high based on paternity exclusion probabilities across the investigated loci. The paternity exclusion probabilities were almost the same between 1994 and 2005. The probability of identity across the investigated loci declined between the two time points, but was still high. These results are reflected in a very short history of breeding in this captive population. In other words, the parentage analyses using a suite of microsatellite markers will be less effective as generations change in small closed populations, such as zoo and aquarium populations.

Linking physiological approaches to marine vertebrate conservation: using sex steroid hormone determinations in demographic assessments

Sex, age and sexual maturation are key biological parameters for aspects of life history and are fundamental information for assessing demographic changes and the reproductive viability and performance of natural populations under exploitation pressures or in response to environmental influences. Much of the information available on the reproductive condition, length at sexual maturity and sex determinations of endangered species has been derived from direct examination of the gonads in dead animals, either intentionally or incidentally caught, or from stranded individuals. However, morphological data, when used alone, do not provide accurate demographic information in sexually monomorphic marine vertebrate species (e.g. sharks, sea turtles, seabirds and cetaceans). Hormone determination is an accurate and non-destructive method that provides indirect information about sex, reproductive condition and sexual maturity of free-ranging individuals. Correlations between sex steroid concentrations and biochemical parameters, gonadal development and state, reproductive behaviour and secondary external features have been already demonstrated in many species. Different non-lethal approaches (e.g. surgical and mark-recapture procedures), with intrinsic advantages and disadvantages when applied on free-ranging organisms, have been proposed to asses sex, growth and reproductive condition. Hormone determination from blood samples will generate valuable additional demographic information needed for stock assessment and biological conservation.

Environmental influences on Adelie penguin breeding schedules, endocrinology, and chick survival

To understand how the social and physical environment influences behaviour, reproduction and survival, studies of underlying hormonal processes are crucial; in particular, interactions between stress and reproductive responses may have critical influences on breeding schedules. Several authors have examined the timing of breeding in relation to environmental stimuli, while others have independently described endocrine profiles. However, few studies have simultaneously measured endocrine profiles, breeding behaviour, and offspring survival across seasons. We measured sex and stress hormone concentrations (oestrogens, testosterone, and corticosterone), timing of breeding, and chick survival, in Adelie penguins (Pygoscelis adeliae) at two colonies in two different years. Clutch initiation at Cape Bird South (CBS; year 1, ~14,000 pairs) occurred later than at Cape Crozier East (CCE; year 2, ~ 25,000 pairs); however, breeding was more synchronous at CBS. This pattern was probably generated by the persistence of extensive sea ice at CBS (year 1). Higher corticosterone metabolite and lower sex hormone concentrations at CBS correlated with later breeding and lower chick survival compared to at CCE - again, a likely consequence of sea ice conditions. Within colonies, sub-colony size (S, 50-100; M, 200-300; L, 500-600; XL, >1000 pairs) did not influence the onset or synchrony of breeding, chick survival, or hormone concentrations. We showed that the endocrine profiles of breeding Adelie penguins can differ markedly between years and/or colonies, and that combining measures of endocrinology, behaviour, and offspring survival can reveal the mechanisms and consequences that different environmental conditions can have on breeding ecology.

Role of gonadal and adrenal steroids and thyroid hormones in the regulation of molting in domestic goose

Plasma levels of testosterone (T), 17-β-estradiol (E2), progesterone (P4), dehydroepiandrosterone (DHEA), corticosterone (B), thyroxine (T4) and triiodothyronine (T3) were monitored during postnuptial and the prenuptial molt in domestic goose (Anser anser domesticus) in both sexes. 1. At the beginning of postnuptial molt (when the old, worn dawny-, and cover feathers' loss starts) in ganders, the levels of T, E2, P4 decrease while DHEA and B significantly increase. The elevated levels of T4 and low T3 concentrations characteristic of the last phase of the reproduction, remain unchanged. In layers, similar changes were observed, however, B decreases. 2. In the early phase of outgrowth of wing and cover feathers, plasma levels of T, E2 and P4 are low. Elevated B, DHEA and T4 concentrations decrease in ganders, while in layers DHEA increases and B and T4 levels remain unchanged. T3 increases in both sexes. 3. The subsequent intensive outgrowth period of wing- and cover feathers both in ganders and in layers is characterized by very low levels of T, E2, DHEA and T4, but P4 increased, and T3 concentration remain high. 4. At the end of postnuptial molt - when the outgrowth of dawny, cover-, and wing feathers stops - very low T, E2, P4, DHEA and T4 levels and and high T3 plasma levels were found in both sexes. Fast increase of plasma B was detected in ganders, while in geese, B concentration remain high. 5. During prenuptial molting (outgrowth of contour and tail feathers) low E2, P4 and T4, increasing T and DHEA, but very high T3 and B plasma concentration were measured in ganders. In layers, very low T, E2, P4, DHEA and T4 levels, and very high B and T3 levels were found. 6. At the beginning of the fall-winter sexual repose (postmolting stage) T, E2, P4, DHEA and T4 levels increase, T3 and B declines in both sexes. 7. In the subsequent phase of fall-winter period (preparatory stage) there is a further increase in T, P4 and T4, a fast increase of B and a decrease of E2, DHEA and T3 in ganders. In layers, T, P4 and DHEA decrease, B increases and the T4 and T3 do not change. 8. At the beginning of reproduction high T level, unchanged DHEA, slightly declined P4, and decreased E2, T4, T3 and a strong decline of B concentrations occur in ganders. In layers, T is further increased, E2 and P4 shows high levels, and, at the same time DHEA and T3 remain unchanged, while B and T4 decrease.

Reproductive endocrinology of wild, long-lived raptors

The last decades have witnessed a surge of studies analyzing the role of sex hormones on the behavior and ecology of wild bird populations, allowing a more integrated view of the evolution of avian physiology and life histories. Despite a marked progress, field studies show a considerable bias towards research on specific phylogenetic groups, neglecting a significant fraction of the class Aves. Here we analysed changes in the circulating levels of sex steroids in relation to reproductive behaviour in wild black kites (Milvus migrans), a long-lived and socially monogamous Accipitridae raptor. Males and females displayed a single seasonal peak of circulating testosterone (males) and estradiol (females) during pre-laying and laying. Absolute male testosterone levels were low even at the seasonal maximum and remained below detection limits in females. The latter results supports the idea that avian species establishing long-term pair bonds require lower amounts of circulating androgens for reproduction. Circulating progesterone showed a single seasonal peak in females and males, but their timing (during Incubation and Post-brooding respectively) did not overlap. The fact that females black kites perform the majority of incubation and males provide the majority of care to fledglings suggests that progesterone is involved in the expression of parental behaviors.

Spontaneous egg or chick abandonment in energy-depleted king penguins: a role for corticosterone and prolactin?

Various exogenous or endogenous factors may induce an emergency response in birds, redirecting current activity towards survival. In fasting, breeding penguins, the achievement of a critical energy depletion was suggested to induce egg abandonment and departure to sea for re-feeding. How such a behavioral shift is hormonally controlled remains unknown. The possible involvement of corticosterone and prolactin was examined by characterizing the nutritional and hormonal states of king penguins at egg abandonment. Further, we tested if these states differ according to whether an egg or a chick is abandoned, and according to the timing of breeding. In every case of abandonment, birds were in phase III fasting characterized by accelerated protein catabolism. However, body condition at egg abandonment was lower in early than in late breeders, suggesting that king penguins are willing to tolerate a larger energy depletion when their potential breeding success is high. At egg and chick abandonment, plasma corticosterone levels were, respectively, increased by 2- and 4-fold, whereas plasma prolactin levels were, respectively, depressed by 3- and 1.4-fold. The increase in plasma corticosterone and the decrease in plasma prolactin could be involved in the control of abandonment by, respectively, stimulating the drive to re-feed and diminishing the drive to incubate or brood. The smaller decrease in prolactin levels and the greater increase in corticosterone levels observed at chick vs egg abandonment suggest that, in addition to nutritionally-related stimuli, tactile or audible stimuli from the egg or chick could intervene in the endocrine control of abandonment.

Effects of artificial eggs on prolactin secretion, steroid levels, brood patch development, incubation onset and clutch size in the yellow-eyed penguin (Megadyptes antipodes)

Several studies have shown that the transition from egg laying to incubation behavior in birds is associated with changes in plasma levels of prolactin and steroid hormones. However, any effect of the tactile and visual input provided by eggs at initiating these hormonal changes has not been fully investigated in wild birds. A few days before yellow-eyed penguins, Megadyptes antipodes, started egg laying, we placed an artificial egg into their nests or under cages next to their nest. We then investigated the effect of the tactile and/or visual stimulus of such an artificial egg on prolactin secretion, steroid hormone levels (total androgen, estradiol and progesterone), brood patch development, incubation onset and clutch size in these penguins. Prolactin levels rose in females in response to having an artificial egg in the nest, while they declined considerably in males. Total androgen concentrations in males were less than 7% of those of control males and the levels prior to egg placement. Brood patch width increased in both males and females. Additionally, an egg in the nest caused yellow-eyed penguin pairs to attend and sit prone on their nest more frequently. Females that initiated egg laying 1 or 2 days after placement of the artificial egg in the nest, laid a full clutch of two eggs, while most other females that were exposed to an artificial egg in their nest, laid only a single egg. In contrast, the visual stimulus of an artificial egg alone (that was placed under a cage) did not influence hormone levels, brood patch development, incubation behavior or clutch size. The stimulation of an egg in the nest influences prolactin and total androgen levels in yellow-eyed penguins, particularly in males. While brood patch development and incubation behavior were initiated and egg laying was terminated in response to an artificial egg in the nest, the exact endocrine mechanisms underlying these physiological and behavioral changes remain poorly understood. We encourage further studies on other bird species taking an experimental approach to investigate the direct influence of hormones in initiating brood patch development and incubation behavior. Moreover, such experimental studies will widen our understanding of the endocrine mechanisms that regulate clutch size.

High levels of LH and testosterone in a tropical seabird with an elaborate courtship display

For birds breeding in temperate areas, territoriality and courtship co-occur during spring and are mirrored by elevated plasma levels of luteinizing hormone (LH) and testosterone. By contrast, several tropical species show no major changes in LH and testosterone throughout the year and plasma levels are often low. This study describes changes in body condition, LH and testosterone levels throughout breeding in a tropical seabird, the magnificent frigatebird (Fregata magnificens). Although bi-parental care is the rule in frigatebirds, these seabirds are unique among seabirds in having a lek-like mating system where males perform an elaborate courtship display during which an extravagant sexual ornament (gular pouch) is inflated. Body condition peaked during the displaying stage in males and declined gradually in both sexes, being the lowest during chick-rearing. LH and testosterone titers were the highest in displaying males with a fully inflated gular pouch (means: 23.6 ng/ml for LH and 6.2 ng/ml for testosterone) and remained low (means: 3.8 ng/ml for LH and 0.3 ng/ml for testosterone) during incubation and chick-rearing in both sexes. Body condition was positively related to testosterone levels in displaying males. In male frigatebirds, high levels of testosterone are not associated with aggression but are probably required to display the inflated gular pouch and to perform an elaborate courtship display. Because males invest in incubation and chick-rearing, testosterone has to return to low levels, to permit parental care. This hormonal pattern differs greatly with that of the few tropical seabirds studied so far and is probably related to the unique reproductive strategy of frigatebirds.

Nonbreeding season pairing behavior and the annual cycle of testosterone in male and female downy woodpeckers, Picoides pubescens

Studies in birds show that testosterone (T) concentrations vary over the annual cycle depending on mating system and life history traits. Socially monogamous species show pairing behavior throughout the year and low levels of male-male aggression and are underrepresented in these studies, yet the function of testosterone could be particularly important for sexual and social interactions occurring outside the breeding season. We measured fecal T concentrations over the annual cycle and the frequency of interactions between male and female downy woodpeckers (Picoides pubescens) from late fall through early spring. We validated the fecal assay by collecting blood in conjunction with a subsample of our fecal samples: fecal T correlated with circulating levels in the blood. The annual peak level of T in males was relatively low and short-lived, similar to that of other bird species with low levels of male-male aggression and high paternal care. The annual cycle of female T resembled the male pattern, and the ratio of male T to female T was close to 1.0. Likewise, the frequency of aggression among females was similar to the frequency among males. Overall, testosterone levels in both sexes were variable, even in winter. In other bird species, sexual behavior during nonbreeding periods correlates with circulating levels of T in males. Based on this observation, we tested the hypothesis that T in winter was positively related to the frequency of interaction between mated downy woodpeckers. The results showed no such relationship. We discuss this finding and further relate the annual cycle of T in both males and females to behaviors that appear to facilitate mate choice and retention of the pair bond during conspecific challenge.

Blood profile of pigeons (Columba livia) during growth and breeding

Changes in the blood profile of domestic pigeons (Columba livia) were studied during growth and breeding cycle. Counts of erythrocytes and leucocytes, and values of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), blood volume, plasma volume (BV), width of erythrocytes, and length, width and volume of erythrocyte nuclei of squabs almost reached adult values by the 4th week of age. During courtship and mating, while the level of plasma glucose increased, those of albumin, potassium, cholesterol, calcium and uric acid decreased. At nest-building, plasma albumin and plasma calcium increased significantly. The initial phase of incubation showed an elevation in plasma calcium and a decline in cholesterol and sodium, whereas mid-phase of incubation indicated a marked rise in cholesterol and uric acid. Terminal phase of incubation had significantly low plasma protein level. During feeding and brooding period, a significant rise in sodium, protein and glucose levels and a fall in calcium were observed. Following egg-laying, there was a significant rise in calcium and a drop in protein, haemoglobin, cholesterol, sodium and MCH values. Concomitant with the phenomenal rate of growth of squabs, their haematological indices neared adult values by the 4th week of age and during breeding activity significant changes in blood values occurred.

Hormonal correlations at transition from reproduction to molting in an annual life cycle of Humboldt penguins (Spheniscus humboldti)

To understand the hormonal mechanism behind a unique strategy of breeding and molting in Humboldt penguins, six pairs of captive Humboldt penguins kept in an outdoor open display pen were observed and blood collected weekly for a year. They all molted between the middle of June and the middle of August within 10 days except one pair that molted about a month later. The late pair had been rearing a hatchling until July due to the successful second clutch after the first clutch failed. A peak of plasma levels of thyroxine and triiodothyronine, respectively, overlapped a period of molting in both sexes. Plasma testosterone concentrations in the males and females were lowest for two month during a period of pre-molt and molting. Plasma concentrations of estradiol were also lowest during the molt in both sexes. Except for the period of molting, sex steroid hormone concentrations were high although there was great individual variation. During the molt, the birds were forced to fast since they did not enter the pool in the display pen where they usually forage live fish. To compensate this forced fasting, they took more food than usual during pre-molting period and gained body mass to about 20% more than the baseline value. Increased flipper thickness was parallel to increased body mass indicating that the gained body mass attributed to fat reservoir. These data indicate that rapid molting in Humboldt penguins is correlated with a drastic increase and decrease of thyroid hormones during the period of lowest concentrations in sex steroid hormones.

Comparative analysis of male androgen responsiveness to social environment in birds: the effects of mating system and paternal incubation

Male androgen responses to social challenges have been predicted to vary with mating system, male-male aggressiveness, and the degree of paternal investment in birds ("challenge hypothesis," Am. Nat. 136 (1990), 829). This study focused on the interspecific predictions of the challenge hypothesis. Comparative methods were used to control for effects of the phylogenetic relatedness among the sampled species. Male androgen data of 84 bird species were collected from literature records on seasonal androgen patterns. From these, the androgen responsiveness (AR) was calculated as described in the original challenge hypothesis (i.e., maximum physiological level/breeding baseline). Scatterplots of AR versus mating strategy, male-male aggressiveness, and the degree of paternal care confirmed the expected interspecific patterns. When phylogenetic analyses were performed among all of the sampled species, the effects of paternal investment disappeared while the AR remained covarying to a high degree with mating system and male-male aggressiveness. Although these mechanisms may be different at the intraspecific level, this suggests that interspecific differences of AR in male birds may have evolved in response to changes of mating strategies, rather than in response to altered paternal duties. However, control for phylogeny among the subsample of 32 passerine species revealed that if any paternal investment contributed to the observed variance in AR, then the change from "no male incubation" to "male shares incubation duties" represented the most effective, whereas the male's contribution to feeding offspring did not explain the observed variation of AR.

Strategic allocation of ejaculates by male Adélie penguins

Sperm competition theory suggests that males should strategically allocate sperm to those females that will bring them the best possible genetic returns. Although males of a number of species of insects and fishes have been shown to allocate sperm strategically, we provide, to our knowledge, the first evidence that an avian species is also capable of allocating ejaculates. Male Adélie penguins (Pygoscelis adeliae) are more likely to transfer sperm during extra-pair copulations (EPCs) than during pair copulations. We investigated the question of how males allocate ejaculates within the constraints of limited sperm availability and found (i) that males that engaged in EPC attempts ejaculated less often when copulating with their social partner than males that made no EPC attempts, and (ii) that there was no difference between males that were involved in failed EPC attempts and those that were involved in successful EPCs in the proportion of copulations that resulted in sperm transfer. These results indicate that males achieve strategic allocation of sperm within the constraints of limited sperm availability by withholding ejaculates from their social partners.

Reproductive endocrinology of tropical seabirds: sex-specific patterns in LH, steroids, and prolactin secretion in relation to parental care

Plasma levels of luteinizing hormone, prolactin, testosterone, and progesterone were measured throughout breeding in masked boobies, red-footed boobies, and red-tailed tropicbirds at Europa and Tromelin Islands (Indian Ocean). LH secretion showed a dampened pattern in the three species, particularly in tropicbirds. Such specific differences may be related to the less elaborate courtship displays in tropicbirds. Testosterone levels were very low throughout breeding in all three species, particularly in boobies. Low testosterone values in boobies may be related to their year-round attendance at the colony. Prolactin secretion increased from the prelaying period until the incubation and brooding periods and declined thereafter in boobies but stayed relatively unchanged throughout the breeding cycle in tropicbirds. The relatively constant prolactin secretion in the more pelagic tropicbirds might allow them to undertake parental care despite long absences at sea. Boobies perform postfledging care with basal prolactin levels. For all species, females always have higher prolactin levels than males. This hormonal dimorphism, being more pronounced in boobies, may be associated with differences in parental care between mates.

Interactions between behavior and plasma steroids within the scramble mating system of the promiscuous green turtle, Chelonia mydas

We measured plasma androgen (combined testosterone and 5alpha-dihydrotestosterone) (A) and corticosterone (B) in the promiscuous green turtle (Chelonia mydas) during courtship in the southern Great Barrier Reef. This study examined if reproductive behaviors and intermale aggression induced behavioral androgen and adrenocortical responses in reproductively active male and female green turtles. Associations between reproductive behavior and plasma steroids were investigated in green turtles across the population and within individuals. Levels across a range of both asocial and social behaviors were compared including (a) free swimming behavior; (b) initial courtship interactions; (c) mounted behavior (male and female turtles involved in copulatory activities); (d) intermale aggression (rival males that physically competed with another male turtle or mounted males recipient to these aggressive interactions); and (e) extensive courtship damage (male turtles that had accumulated excessive courtship damage from rival males). Behavioral androgen responses were detected in male turtles, in that plasma A was observed to increase with both attendant and mounted behavior. Male turtles who had been subjected to intermale aggression or who had accumulated severe courtship damage exhibited significantly lower plasma A than their respective controls. No pronounced adrenocortical response was observed after either intermale aggression or accumulation of extensive courtship damage. Female turtles exhibited a significant increase in plasma B during swimming versus mounted behavior, but no change in plasma A. We discuss our results in terms of how scramble polygamy might influence behavioral androgen interactions differently from more typical combative and territorial forms of male polygamy.

Sex steroid and corticosterone levels of Adélie penguins (Pygoscelis adeliae) during courtship and incubation

Plasma levels of sex steroids (progesterone, 17alpha-hydroxyprogesterone, total androgens, and estradiol) were measured at six stages from courtship to late incubation in Adélie penguins. The pattern of change detected in the levels of plasma total androgens (males) and estradiol (females) was consistent with that found in many birds, with elevated levels during courtship (total androgens, 4 ng/ml; estradiol, 0.5 ng/ml) declining to low, stable levels during incubation. Progesterone levels declined moderately from 1.3 to 0.75-1.0 ng/ml in females following egg laying, but levels of 0.8-1.2 ng/ml persisted in males throughout the study period. 17alpha-Hydroxyprogesterone levels were consistently low (approximately 0.2 ng/ml) in females but progressively declined in males from 0.75 during courtship to <0.3 ng/ml at egg laying and during foraging. Plasma corticosterone levels were measured over the same period and were elevated in both males and females at courtship (16-18 ng/ml) and while fasting on the nest (11-15 ng/ml), but had declined in birds returning from foraging at sea, suggesting that elevated levels are related to the metabolic demands of fasting.

Fatty acid composition of the adipose tissue and yolk lipids of a bird with a marine-based diet, the emperor penguin (Aptenodytes forsteri)

The emperor penguin (Aptenodytes forsteri) is an Antarctic seabird feeding mainly on fish and therefore has a high dietary intake of n-3 polyunsaturated fatty acids. The yolk is accumulated in the developing oocyte while the females are fasting, and a large proportion of the fatty acid components of the yolk lipids are derived by mobilization from the female's adipose tissue. The fatty acid composition of the total lipid of the yolk was characterized by high levels of n-3 polyunsaturated fatty acids. However, it differed in several respects from that of the maternal adipose tissue. For example, the proportions of 14:0, 16:1n-7, 20:1n-9, 22:1n-9, 20:5n-3, and 22:6n-3 were significantly greater in adipose tissue than in yolk. Thus adipose tissue lipids contained 7.6+/-0.3% and 8.0+/-0.3% (wt% of total fatty acids; mean +/- SE; n = 5) of 20:5n-3 and 22:6n-3, respectively, whereas the yolk total lipid contained 1.6+/-0.1 and 5.5+/-0.3% of these respective fatty acids. The proportions of 16:0, 18:0, 18:1n-9, 18:2n-6, and 20:4n-6 were significantly lower in the adipose tissue than in the yolk lipids. The proportions of triacylglycerol, phospholipid, free cholesterol, and cholesteryl ester in the yolk lipid were, respectively, 67.0+/-0.2, 25.4+/-0.3, 5.3+/-0.2, and 1.8+/-0.2% (wt% of total yolk lipid). The proportions of 20:4n-6, 20:5n-3, 22:5n-3, and 22:6n-3 were, respectively, 5.7+/-0.3, 2.8+/-0.2, 1.4+/-0.1, and 11.7+/-0.5% in phospholipid and 0.4+/-0.0, 1.2+/-0.1, 0.8+/-0.1 and 3.6+/-0.3% in triacylglycerol. About 95% of the total vitamin E in the yolks was in the form of alpha-tocopherol with gamma-tocopherol forming the remainder. Two species of carotenoids, one identified as lutein, were present.

Endocrine correlates of parental care in an Antarctic winter breeding seabird, the emperor penguin, Aptenodytes forsteri

Plasma levels of luteinizing hormone (LH) and prolactin associated with parental behavior were measured in the Antarctic winter breeding emperor penguin, Aptenodytes forsteri. Males exclusively incubate the egg while females exclusively brood the nonhomeothermic young; both sexes alternate in rearing the homeothermic young. Birds were sampled on arrival from the sea through egg laying, incubation, and brooding. All parent birds lost their chicks at the end of the brooding period due to harsh weather but sampling continued. In females, LH titers dropped after egg laying but levels were restored when the birds returned from the sea to brood the chicks and were not depressed by high prolactin levels. Plasma prolactin remained low in males captured on arrival and kept until the free-living males finished incubation. In breeders, prolactin secretion increased during the prelaying period when day length decreased. Prolactin levels stayed elevated in males during incubation and in brooding females returning after a 2-month absence at sea. Prolactin values were higher in brooding females than in males ending incubation or returning in late brooding. These levels did not drop after chick loss, and the sexual difference in prolactin values was maintained after breeding failure. In emperor penguins, increased prolactin secretion appears to be triggered around the time of egg laying and continues, driven by an endogenous mechanism, through incubation and brooding until rearing is completed. Prolactin secretion independent of external stimuli may have evolved in pelagic seabirds to maintain parental care despite long absences at sea from the breeding colony.

Reproductive endocrinology of macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins. I. Seasonal changes in plasma levels of gonadal steroids and LH in breeding adults

Changes in plasma luteinizing hormone (LH), testosterone, oestradiol, and progesterone were measured throughout the breeding and molt cycle in free-living male and female macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins, at Bird Island, South Georgia (54 degrees S, 38 degrees W). These two species are sympatric but have a markedly different breeding cycle. In macaroni penguins plasma levels of all hormones, except LH in males, were significantly elevated at the time of arrival at the breeding colony. In both species and sexes plasma LH, testosterone (males), and estradiol (females) levels were highest during nest-building and postcopulation, coincident with the period of frequent agonistic interactions in males and egg-formation in females. Elevated testosterone levels occurred in females of both species during the postcopulation period and may be associated behaviourally with both sexes being involved in nest defence. Male birds also had elevated estradiol levels. Following copulation, plasma levels of LH, testosterone, and estradiol decreased to basal levels in both sexes and species and, except for a transient increase in testosterone in male macaroni penguins, remained low through to the end of molt. There was no associated rise in LH or testosterone during premolt and early molt despite a further period of agonistic and social interaction, suggesting that birds were in a photorefractory state at this time. Plasma progesterone showed a pattern of variation different from that of the other hormones. In both species and sexes, plasma levels were elevated between arrival and early chick-rearing and then decreased slowly to low levels during molt.

Reproductive endocrinology of macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins. II. Plasma levels of gonadal steroids and LH in immature birds in relation to deferred sexual maturity

Plasma levels of LH, testosterone, estradiol, and progesterone were measured, during the breeding season, in adult and immature macaroni (Eudyptes chrysolophus) and gentoo (Pygoscelis papua) penguins, at Bird Island, South Georgia (54 degrees S, 38 degrees W), in relation to deferred sexual maturity. Macaroni penguins do not breed until 6-8 years of age whereas gentoo penguins first breed at 2 years of age. Plasma LH was elevated in 3- to 5-year-old macaroni penguins, but not in 1- to 2-year-old birds nor 1-year-old gentoos. However, 1 year olds of both species responded to an injection of exogenous LH-RH by increasing LH secretion. Some individual 3-, 4-, and 5-year-old macaroni penguins had circulating testosterone levels within the range of peak values in adults, suggesting that in males, gonads were physiologically mature several years in advance of the age of first breeding. One year old macaroni penguins had elevated progesterone levels and basal estradiol levels, but in 2-4 year olds plasma levels of both progesterone and estradiol were low. This does not support the hypothesis that high progesterone levels "block" ovarian maturation in immature penguins. Immature gentoo penguins showed a different pattern of hormone secretion. Plasma testosterone was low in all breeding periods, but estradiol levels increased to a peak during the incubation period, 4 weeks later than peak values occurred in adults. In both species, therefore, deferred sexual maturity was associated with delayed and/or reduced secretion of LH and gonadal steroids.

Avian reproductive endocrinology

Hypothalamic-releasing factors regulate the secretion of anterior pituitary hormones. The anterior pituitary gland secretes the same six hormones as found in mammals: FSH, LH, prolactin, GH (somatotropic hormone), ACTH, and TSH, plus the melanotropic hormone. The endocrine hormones of the avian posterior pituitary gland concerned with reproduction are mesotocin and AVT. The pineal gland, through the secretion of the hormone melatonin, modulates the periodic autonomic functions of the central nervous system. The ovary produces estrogens, progestogens, and androgenic compounds. The testes produce testosterones and progesterone. The thyroid glands produce two hormones, T4 and T3. The avian adrenal glands produce corticosterone and aldosterone. The bursa of Fabricius is considered an endocrine organ since it is involved in the production of humoral factors. The male reproductive system undergoes hormonal changes associated with puberty, the breeding season, and molt. Some avian species undergo a type of disintegration and seasonal reconstruction of the testis and epididymis. The relationship of the ovarian follicular hormones and the plasma hormones varies depending on the stage of the reproductive cycle and the seasonal photostimulation. Female birds may conceive in the absence of a mate as a result of the fertile period phenomena. The blood chemistry of laying birds is different from that seen in nonlaying hens. Domestication has had a definite influence on the hormone cycles of some avian species. This may lead to certain reproductive problems.

Annual changes in plasma levels of LH, and prolactin in free-living female great tits (Parus major)

Plasma levels of LH and prolactin were measured in free-living female great tits throughout the year. Plasma concentrations of LH increased at the onset of winter (January), onset of spring (March), nest-building period, (for both the first and the second clutch), last part of the incubation period, (for both the first and the second clutch), and early autumn (August). Plasma prolactin increased between March and April. A further increase occurred during the nest-building period, which continued during the early part of the egg-laying period. Prolactin levels increased further once incubation had started. During nest-building and egg-laying of the second clutch, prolactin levels were low, but not basal. Prolactin levels increased again during incubation of the second clutch. Between July and March prolactin levels usually were below the limit of detection of the assay.

Photoperiodic control of reproduction and molt in the kestrel, Falco tinnunculus

An adaptive decline in average clutch size with progressive date of laying is characteristic of most bird species with a single clutch of variable size per year. The effect of photoperiod on timing of laying, clutch size, and subsequent molt was investigated in kestrel pairs breeding and raising their young in captivity. In natural daylight (nLD), clutch size, under ad libitum feeding, showed the same decline with date as in nature. Birds breeding later also started molt later and molted faster (more feathers simultaneously), so that all birds completed molt more or less at the same time. Constant long days (LD 17.5:6.5 and LD 13:11) from December 1 onward advanced both reproduction and molt. The LD 17.5:6.5 group developed the reproductive system faster, had a shorter courtship period, and laid eggs earlier than the LD 13:11 group. In both photoperiods there was a decrease in clutch size with progressive laying date, similar to that in nLD. Molt started in both groups at about the end of the laying period and slowed down in the longer photoperiod, especially in males. Plasma luteinizing hormone (LH) changes in the two photoperiods were different for males and females. Males showed the expected slower LH response in the shorter photoperiod, but the initial LH response by females was the same in both photoperiods. Data on LH, reproductive behavior, and body mass suggest that females have a wider annual reproductive window than males. Data on time of laying and number of eggs suggest that clutch size in the kestrel is determined by laying date itself, following an endogenous rhythm that is phase-locked to the reproductive cycle.

Identity of gonadotropin-releasing hormone in passerine birds: comparison of GnRH in song sparrow (Melospiza melodia) and starling (Sturnus vulgaris) with five vertebrate GnRHs

Gonadotropin-releasing hormone (GnRH) was detected in the brains of passerine birds, a recently evolved and diverse avian group. The molecular forms of GnRH in two species of birds under breeding conditions were deduced using methods of HPLC and immunology. The brain extracts of song sparrows (Melospiza melodia) contained a form of GnRH identified as chicken I GnRH-like peptide by its HPLC elution pattern and cross-reactivity with four antisera. In contrast, starling (Sturnus vulgaris) brain extracts showed molecular heterogeneity of GnRH forms; equal amounts of chicken I and chicken II GnRH-like peptides were present. Neither bird contained GnRH that could be identified as mammalian, salmon, or lamprey GnRH. Chicken II GnRH-like peptide may not have evolved after the separation of the song sparrow and starling as both peptides are found in chicken, a more primitive bird. The possibility remains that different stages of the life cycle are associated with the expression of these GnRH-like peptides or their ratio. Only determination of the primary structure will establish whether our chromatographic and immunological evidence is correct that chicken I and II GnRH are present in passerine birds and have been conserved in representatives throughout the reptiles and birds. Starlings can be added now to the growing list of submammalian species that express multiple forms of GnRH in their brains.

The endocrine control of reproduction and molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. II. Annual changes in plasma levels of thyroxine and triiodothyronine

Changes in plasma thyroxine (T4) and triiodothyronine (T3) levels were studied during a breeding season and in more detail during the postbreeding molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins under natural conditions in the Antarctic. During the 4-month natural fast that accompanies courtship and incubation in male emperors, plasma T4 and T3 levels were maintained around 11 and 0.6 ng/ml, respectively. In courting, fasting female emperors plasma T4 levels were maintained around 10 ng/ml for more than 1 month; plasma T3 levels were around 0.8 ng/ml but were markedly depressed (0.1 ng/ml) at the time of copulation although they increased again (2.2 ng/ml) at oviposition. During the 5-month period of chick rearing, plasma T3 (males and females) and T4 (females) were maintained at the same levels as during courtship and incubation, but plasma T4 levels in male emperors were slightly lower (7 ng/ml). Similar plasma T4 and T3 levels were observed in breeding adelie penguins. These results do not provide any convincing evidence for thyroid-gonadal interrelations in breeding penguins, but demonstrate their capacity to maintain plasma thyroid hormone levels during very prolonged natural fasts. During the heavy postnuptial molt when the birds were fasting, in both species and sexes, marked but separate peaks in plasma T4 and T3 levels occurred concurrently with the initial growth of the new feathers, and with the subsequent shedding of the old plumage, respectively. Peak plasma T4 levels were observed at the time of the emergence of the new feathers out of the skin, and peak plasma T3 levels were roughly concurrent with the maximum daily body weight loss. This is the first strong evidence that increases in plasma T4 and T3 levels are correlated with different stages of molt in a wild seabird. Increased plasma T4 but not T3 levels at the time of feather papilla eruption suggest that T4 is concerned with feather growth, but is not exclusive of a role of T3. Increased plasma T3 but not T4 levels during the reduction in thermal insulation in molting penguins suggest that this hormone rather than T4 might be active in energy metabolism in penguins.