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

Chronic exposure to tebuconazole alters thyroid hormones and plumage quality in house sparrows (Passer domesticus)

Triazoles belong to a family of fungicides that are ubiquitous in agroecosystems due to their widespread use in crops. Despite their efficiency in controlling fungal diseases, triazoles are also suspected to affect non-target vertebrate species through the disruption of key physiological mechanisms. Most studies so far have focused on aquatic animal models, and the potential impact of triazoles on terrestrial vertebrates has been overlooked despite their relevance as sentinel species of contaminated agroecosystems. Here, we examined the impact of tebuconazole on the thyroid endocrine axis, associated phenotypic traits (plumage quality and body condition) and sperm quality in wild-caught house sparrows (Passer domesticus). We experimentally exposed house sparrows to realistic concentrations of tebuconazole under controlled conditions and tested the impact of this exposure on the levels of thyroid hormones (T3 and T4), feather quality (size and density), body condition and sperm morphology. We found that exposure to tebuconazole caused a significant decrease in T4 levels, suggesting that this azole affects the thyroid endocrine axis, although T3 levels did not differ between control and exposed sparrows. Importantly, we also found that exposed females had an altered plumage structure (larger but less dense feathers) relative to control females. The impact of tebuconazole on body condition was dependent on the duration of exposure and the sex of individuals. Finally, we did not show any effect of exposure to tebuconazole on sperm morphology. Our study demonstrates for the first time that exposure to tebuconazole can alter the thyroid axis of wild birds, impact their plumage quality and potentially affect their body condition. Further endocrine and transcriptomic studies are now needed not only to understand the underlying mechanistic effects of tebuconazole on these variables, but also to further investigate their ultimate consequences on performance (i.e. reproduction and survival).

FACTORS AFFECTING ABNORMAL MOLTING IN THE MANAGED AFRICAN PENGUIN (SPHENISCUS DEMERSUS) POPULATION IN NORTH AMERICA

Abnormal molting, including partial or incomplete molt, arrested molt cycle, or inappropriate frequency of molt, is a primary concern for the managed African penguin (Spheniscus demersus) population and is documented across institutions. To identify factors associated with increased odds of abnormal molts and characterize intervention opportunities, a comprehensive survey evaluating numerous husbandry and medical parameters was created. Survey results represent 45 North American African penguin holding facilities and 736 unique animals. Of these individuals, 135 (18.3%) demonstrated an abnormal molt over the 5-yr study period (2012-2017). Increased odds ratios for abnormal molt included biologic (age, sex, etc.), geographic (elevation, latitude), and husbandry (exhibit design, diet, etc.) variables. The mean age of affected animals was 15.2 yr (1-45 yr, n = 135) compared with 9.92 yr (4 mo-38 yr, n = 601) for unaffected animals. In addition, although statistically insignificant, males were overrepresented in the affected cohort compared with a near even distribution among unaffected animals. Identified factors with increased odds for abnormal molting included advanced age and facilities using freshwater pools. Normally molting penguins were more commonly found with saltwater pool access and natural lighting exposure. Anecdotal medical intervention attempts are discussed, although further research is needed to define their use. Of attempted interventions, subcutaneous 5.4-mg melatonin implants placed in anticipation of environmental molting cues showed the most promise at inducing catastrophic molt, with 14 of 17 (82.3%) of affected individuals molting normally following this treatment. Survey analysis indicated that abnormal molt is a complex, multifactorial process, and modifiable factors that may predispose animals to abnormally molt exist. Addressing these factors in future exhibit design may mitigate the prevalence of this condition. Despite these efforts, it is likely that medical interventions will be required to aid in the treatment of abnormal molting in this species.

Avaliação dos níveis séricos de hormônios tireoidianos em araras (Ara spp.) pelo método de quimioluminescência

RESUMO Este trabalho investigou a eficiência do método de quimioluminescência para obtenção das concentrações séricas de hormônios tireoidianos em 23 exemplares de araras [Ara ararauna (n=12) e Ara chloropterus (n=11)], de ambos os sexos [machos (n=11) e fêmeas (n=12)], mantidas em cativeiro. Os valores de T4 total, T4 livre, T3 livre e TSH variaram, respectivamente, de 0,3 a 2,5µg/dL (média=0,94µg/dL), 0,11 a 0,46ɳg/dL (média=0,28ɳg/dL), 1,46 a 3,59pg/mL (média= 2,42pg/mL) e 0,01 a 0,12µUI/mL (média=0,04µUI/mL). Houve interação entre espécie e sexo (P<0,05) sobre as concentrações de T4 total: os machos possuem maiores valores do que as fêmeas de Ara ararauna, enquanto as fêmeas de Ara chloropterus dispõem de níveis mais altos do que os machos desta espécie. Efeito de sexo não foi observado (P>0,05) para os valores de T4 livre, T3 livre e TSH, mas o efeito de espécie foi constatado (P<0,05) para as concentrações de T3 livre. Neste caso, as concentrações de T3 livre são menores em Ara ararauna do que em Ara chloropterus. Os intervalos de referência obtidos sugerem que é possível mensurar as concentrações séricas de hormônios tireoidianos em araras pelo método de quimioluminescência, devendo-se considerar variações relevantes entre diferentes espécies e sexos.

FORCED MOLT IN FOUR JUVENILE YELLOW-EYED PENGUINS (MEGADYPTES ANTIPODES)

Penguins are dependent on waterproof plumage for survival. The molt in sub-Antarctic penguin species is a seasonal and catastrophic process during which the animals go through periods of fasting and high levels of stress. Their entire plumage is usually replaced in 3 wk. Attempts at consistent hormonal induction of molt in penguins have been unsuccessful. Four Yellow-eyed Penguins ( Megadyptes antipodes ) were referred for treatment at Wildbase, Massey University, Palmerston North, New Zealand, in late April 2014, following loss of waterproofing, feather breakage, increased body weight, pododermatitis, and damage to caudal feathers from hock sitting. Feather plucking of damaged areas to stimulate feather regrowth was attempted with poor results. Waiting 10-12 mo for a natural molt was not tenable. Catastrophic molt was induced by treatment with 10 g/kg of fresh beef thyroid gland orally once a day. The molt was complete in 18-26 d during which the animals regained full plumage and waterproofing after feather regrowth. The forced molt feathers had abnormal pigmentation but were of sufficient quality to allow release of the birds back to the wild.

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.

The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction

This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds.

Is fledging in king penguin chicks related to changes in metabolic or endocrinal status?

This study examines the possibility that metabolic or endocrinal factors initiate fledging in the king penguin, a semi-altricial seabird species breeding a single chick on the ground. Chick fledging (departure to sea) occurred 5d after completion of the molt. It was preceded by a 16d fasting period and by a 7-fold increase in locomotor activity. From the measurement of the plasma concentration of metabolites and of glucagon and insulin, pre-fledging king penguin chicks were found to adapt to fasting in a classical way, i.e. by sparing body protein and mobilizing fat stores. At fledging, chicks were in phase II of fasting and their departure to sea was not stimulated by reaching critical energy depletion (phase III), in contrast to that which has been reported in breeding-fasting adults. The plasma level of corticosterone remained unchanged throughout the whole pre-fledging period, providing no support for a role of this stress-hormone in the facilitation of fledging. Thus, king penguin fledglings did not appear to be environmentally or nutritionally stressed. The plasma levels of thyroid hormones were elevated during the pre-fledging molt, in accordance with their key role in molt control in adult penguins. These levels declined by the time of the molt end, the plasma level of T4 thereafter being directly related to the time left before fledging. These results do not support the view that chronically elevated levels of thyroid hormones are required for the energy-demanding transition between being ashore and in cold water, but they suggest that the maintenance of high T4 levels may delay fledging.

Plasma thyroid hormone pattern in king penguin chicks: a semi-altricial bird with an extended posthatching developmental period

Plasma concentrations of thyroid hormones (TH) were investigated during the extended posthatching developmental period (approximately 11 months) of a semi-altricial bird species, the king penguin (Aptenodytes patagonicus). The first period of growth in summer was marked by a progressive rise in plasma T4 concentration that paralleled rapid increases in body mass and in structural and down growth. By contrast, plasma T3 concentration had already reached adult levels in newly hatched chicks and did not change thereafter. Circulating TH of king penguin chicks thus follow an original pattern when comparing to altricial and precocial species. During the austral winter, the long period of undernutrition of king penguin chicks was characterized by a decrease in circulating TH that can be related to a seasonal stop in growth and energy saving mechanisms. Plasma TH concentrations increased again during the second growth phase in spring, and they reached their highest levels at the end of the fledging period, slightly before juveniles initiated their first foraging trip at sea. As expected, plasma T4 levels were elevated when chicks moulted, developing a true-adult type waterproof plumage. The data also suggest that T4 plays a major role in skeletal development and pectoral muscle maturation in anticipation of marine life. Plasma T3 was at its highest during the period when juveniles improved resistance to cold waters by going back and forth to the sea, suggesting a role for circulating T3 in cold acclimatization occurring at that time.

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.

Do T3 levels in incubating eiders reflect the cost of incubation among clutch sizes?

Complete development of avian eggs requires external heat, inducing in most species an energetic cost of incubation for the parents. Triiodothyronine (T(3)) has been implicated in the control of the metabolic rate and is decreased during fasting in most bird species. This raises the question of the regulation of T(3) during reproduction when incubation (thus heat production) is associated with fasting (and energy sparing). In this study, plasma concentrations of T(3) were studied for different clutch sizes in incubating, as well as in nonincubating, fasting female eiders. Our results show that the T(3) levels decrease during fasting in nonincubating birds, whereas they were maintained during the incubation fast. T(3) levels increased in female eiders at hatching. The plasma T(3) level did not vary among natural clutch sizes in eiders but did so when manipulated. T(3) levels increased when eggs were added (to a maximum of six eggs, i.e., the biggest natural clutch size) or removed (to two eggs, i.e., the smallest natural clutch size). Our results suggest that (1) high T(3) levels during incubation may participate to a threshold of heat production and incubation metabolic rate in eiders despite the fact that they are fasting; (2) since T(3) is associated with the energy expenditure in birds, incubating an enlarged or reduced clutch size may lead to a higher energetic cost of incubation in eiders; and (3) the energy demand of the ducklings at hatching is probably important, as the female T(3) concentrations are then at their highest levels. Thus, any modification of the natural clutch size leads to a rise in the T(3) level of the incubating female, suggesting an additional cost of incubation. Knowing that there is no variation of T(3) levels among natural clutch sizes, this study suggests that a female eider produces a number of eggs corresponding to the energy she can invest in incubation.

Long-term fasting and re-feeding in penguins

Spontaneous fasting during reproduction (sometimes with a full stomach) and moult is a major characteristic of the annual cycle of penguins. Long-term fasting (up to four months in male emperor penguins) is anticipated by the accumulation of fat (incubation fast) and of fat and protein (moult fast). During most of the incubation fast, birds rely almost entirely on lipids as an energy source, body proteins being spared. However, below a critical (but non-total) fat store depletion, marked behavioural, metabolic, and endocrine changes occur. Spontaneous locomotor activity increases and the egg is transitorily left unincubated for increasingly long periods, until its definitive abandon and the bird departs to re-feed at sea. These changes are thought to be activated by an endogenous re-feeding signal triggered before lethal energy depletion. An increase in body protein catabolism in the face of a reduction in lipid availability and utilisation, and an increase in circulating corticosterone vs. a decrease in plasma prolactin, are likely to be major metabolic and hormonal components of this signal. The survival and rapid restoration of energy stores in birds having departed to re-feed at a stage of near total lipid depletion demonstrates the effectiveness of the re-feeding signal. Penguins, and possibly other seabirds, are therefore appropriate animal models for understanding the long-term interactions between body energy reserves and fasting, breeding and feeding physiology and behaviour.

Photoperiod regulation of neuron death in the adult canary

The avian brain undergoes naturally occurring cell death and neuronal replacement in adulthood. Little is known about how neuron survival in adult birds is regulated. However, previous work suggests that this process is open to environmental control. We now report that a reduction in day length from spring-like to fall-like conditions can dramatically increase cell death in adult male canaries. Many of the dying cells are projection neurons in the motor pathway controlling song learning and production. Circulating levels of gonadal steroids were not correlated with photoperiod-induced changes in the magnitude of cell death. Our results suggest that neuronal death in adult male canaries is regulated by seasonal changes in photoperiod, and that this occurs independent of chronic changes in gonadal steroid hormone levels. Day length may serve as a predictive environmental cue to time cell death in accordance with seasonal reproduction.

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.

The effect of severe starvation and captivity stress on plasma thyroxine and triiodothyronine concentrations in an antarctic bird (emperor penguin)

The effect of confinement and severe starvation on the plasma thyroxine (T4) and triiodothyronine (T3) concentrations was determined in emperor penguins (Aptenodytes forsteri). During their annual cycle, emperor penguins fast freely for periods of up to 4 months and may thus represent a unique subject to study endocrine adaptations to fasting. Plasma T4 concentrations progressively decreased following capture and confinement of naturally fasting penguins, and within 15-20 days stabilized at levels three times lower than in free-living penguins. A transient fourfold increase in plasma T3 concentration developed within the day following confinement in parallel with a rise in daily body mass loss. Both plasma T3 concentration and mass loss subsided to normal levels within 15 days. The decrease in plasma T4 concentration is in accordance with the well-known inhibitory effect of stress on thyroid function in birds and mammals, whereas the transient increase in plasma T3 concentration seems related to enhancement of energy expenditure as a consequence of restlessness. Starvation severe enough to exhaust fat stores and to activate protein catabolism induced a 6- and 5 to 10-fold fall in plasma T4 and T3, respectively. This is in marked contrast with maintenance of plasma thyroid levels during long-term natural fasting associated with protein sparing (R. Groscolas and J. Leloup (1986) Gen. Comp. Endocrinol. 63, 264-274). Surprisingly, there was a final reincrease in plasma T4 concentration in very lean penguins. These results suggest that the effect of starvation on plasma thyroid hormones seems to depend on how much protein catabolism is activated and demonstrate the acute sensitivity of thyroid hormone balance to stress in penguins.

Early changes in plasma hormones and metabolites during fasting in king penguin chicks

Chicks of the king penguin (Aptenodytes patagonica) can tolerate a fast of 4-6 months during the subantarctic winter. The aim of this work was to study their initial response to food deprivation. Nine chicks were starved for 18 days. Two phases of starvation were defined according to changes in the specific daily loss in body mass: it decreased by 92% in phase I (6.6 +/- 0.3 days) and remained steady and low in phase II. Phase I was marked by a large decline in protein utilization, indicated by decreases in plasma levels of alanine (58%), uric acid (89%) and urea (76%) together with a decrease in circulating corticosterone (60%) and thyroxine (75%). In phase I, plasma insulin concentration decreased (61%) in some birds, but did not change in others; plasma pancreatic glucagon was stable whereas gut-glucagon decreased by 75%. Free fatty acids and beta-hydroxybutyrate concentrations gradually rose during the fast to 5 to 6 times pre-fast levels. Glycemia remained unchanged. Phase II was characterized by no change in plasma concentrations of protein-derived metabolites and by no or little change in circulating hormone levels. From comparison with previous data, we conclude that there are similar early adjustments to food deprivation in king penguin chick, rat and man: (1) a decrease in resting metabolic rate, (2) a decrease in protein utilization, and (3) mobilization of fat stores. The key adaptations to long-term fasting in these species are therefore effectiveness in protein sparing and ability to prolong this situation.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma thyroid hormones, luteinizing hormone (LH), estradiol, progesterone and corticosterone of laying hens during a forced molt

1. Circulating concentrations of iodothyronines, luteinizing hormone(LH), estradiol(E2), progesterone and corticosterone were measured in hens before, during, and after a forced molt induced by fasting. 2. Corticosterone increased at the onset of molt, peaked at the maximal molt and returned to pre- and post-molt levels. LH, E2 and progesterone declined during the molt, and the decline was coincident with the cessation of egg production. 3. Thyroxine(T4), triiodothyronine (T3) and reverse triiodothyronine(rT3) increased during the molt. The increases of T4 and T3 were not abolished even if the forced molt was conducted in mild weather.