Effects of androgen (testosterone, 5 alpha-dihydrotestosterone, 19-nortestosterone) administration on growth in turkeys

Chronic exposure to tebuconazole impairs offspring growth and survival in farmland birds: An experiment in captive house sparrows

European farmland bird populations have declined by over 60% in 40 years, with the use of pesticides suspected to be one of the main causes of this decline. However, it remains difficult to test the impact of these pesticides in field studies due to confounding environmental variables that can also affect avian wildlife (e.g., food resources, habitat fragmentation and alteration). Triazoles are a family of fungicides that are ubiquitous in agro-ecosystems due to their use on a wide range of crops. Triazoles are suspected to affect non-target avian species by disrupting key physiological mechanisms and by detrimentally affecting their reproduction. In this captive study, we experimentally investigated the effect of the most commonly used triazole fungicides (i.e., tebuconazole) on the reproduction of an avian species representative of farmlands, the house sparrow (Passer domesticus). We examined the impacts of tebuconazole at realistic concentrations (550 μg.L-1 in drinking water to achieve ∼ 60 pg g-1 in plasma of sparrows) under controlled conditions on multiple indicators of breeding performance (clutch size, hatching success, chick growth and survival). We found that chronic exposure to tebuconazole (9 months, including the breeding period) significantly altered the reproduction of sparrows. Although clutch size and hatching success were not affected by tebuconazole, chicks from the exposed group showed reduced growth and a higher mortality rate. Interestingly, these effects were exacerbated in female chicks, highlighting a sex-dependent effect of tebuconazole on sparrow offspring. This study demonstrates that tebuconazole can be detrimental to the reproduction of farmland birds. Further studies are now required to distinguish the direct effects of tebuconazole (toxic and sublethal effects on the developing chick/embryo) from the indirect ones (alteration of egg quality and parental care).

Sex steroids as mediators of phenotypic integration, genetic correlations, and evolutionary transitions

In recent decades, endocrinologists have increasingly adopted evolutionary methods and perspectives to characterize the evolution of the vertebrate endocrine system and leverage it as a model for developing and testing evolutionary theories. This review summarizes recent research on sex steroids (androgens and estrogens) to illustrate three ways in which a detailed understanding of the molecular and cellular architecture of hormonally mediated gene expression can enhance our understanding of general evolutionary principles. By virtue of their massively pleiotropic effects on the expression of genes and phenotypes, sex steroids and their receptors can (1) structure the patterns of phenotypic variance and covariance that are available to natural selection, (2) alter the underlying genetic correlations that determine a population's evolutionary response to selection, and (3) facilitate evolutionary transitions in fitness-related phenotypes via subtle regulatory shifts in underlying tissues and genes. These principles are illustrated by the author's research on testosterone and sexual dimorphism in lizards, and by recent examples drawn from other vertebrate systems. Mechanistically, these examples call attention to the importance of evolutionary changes in (1) androgen- and estrogen-mediated gene expression, (2) androgen and estrogen receptor expression, and (3) the distribution of androgen and estrogen response elements in target genes throughout the genome. A central theme to emerge from this review is that the rapidly increasing availability of genomic and transcriptomic data from non-model organisms places evolutionary endocrinologist in an excellent position to address the hormonal regulation of the key evolutionary interface between genes and phenotypes.

Biological origins of sexual orientation and gender identity: Impact on health

Gynecologic Oncologists are sometimes consulted to care for patients who present with diverse gender identities or sexual orientations. Clinicians can create more helpful relationships with their patients if they understand the etiologies of these diverse expressions of sexual humanity. Multidisciplinary evidence reveals that a sexually dimorphic spectrum of somatic and neurologic anatomy, traits and abilities, including sexual orientation and gender identity, are conferred together during the first half of pregnancy due to genetics, epigenetics and the diversity of timing and function of sex chromosomes, sex-determining protein secretion, gonadal hormone secretion, receptor levels, adrenal function, maternally ingested dietary hormones, fetal health, and many other factors. Multiple layers of evidence confirm that sexual orientation and gender identity are as biological, innate and immutable as the other traits conferred during that critical time in gestation. Negative social responses to diverse orientations or gender identities have caused marginalization of these individuals with resultant alienation from medical care, reduced self-care and reduced access to medical care. The increased risks for many diseases, including gynecologic cancers are reviewed. Gynecologic Oncologists can potentially create more effective healthcare relationships with their patients if they have this information.

Effect of age and caponization on blood parameters and bone development of male native chickens in taiwan

An experiment was carried out to determine the effect of age and caponization on the development blood and bone characteristics development in male country chickens in Taiwan. A total of two hundred 8-wk-old LRI native chicken cockerels, Taishi meat No.13 from LRI-COA, were used as experimental animals. Cockerels were surgically caponized at 8 wks of age. Twelve birds in each group were bled and dressed from 8 wks to 35 wks of age at 1 to 5 wk intervals. The results indicated that the plasma testosterone concentration was significantly (p<0.05) lower in capons after 12 wks of age (caponized treatment after 4 wks) than that of the intact males. The relative tibia weight, bone breaking strength, cortical thickness, bone ash, bone calcium, bone phosphorus and bone magnesium contents were significantly (p<0.05) higher in intact males, while capons had higher (p<0.05) plasma ionized calcium, inorganic phosphorus and alkaline phosphatase concentration. The plasma testosterone concentration, relative tibia weight, tibia length, breaking strength, cortical thickness, bone ash, calcium, and phosphorus contents of intact males chickens increased significantly (p<0.05) with the advance of age. In addition, the relative tibia weight of capons peaked at 18 wks of age, and declined at 35 wks of age. The bone ash, calcium and phosphorus content increased most after 14 wks of age in male native chickens in Taiwan. Also, tibia length and cortical thickness peaked at 22 wks of age. However, the peak of bone strength was found at 26 wks of age. These findings support the assertion that androgens can directly influence bone composition fluxes in male chickens. Caponization caused a significant increase in bone loss at 4 wks post treatment, which reflected bone cell damage, and demonstrated reductions in the relative tibia weight, breaking strength, cortical thickness, bone ash, calcium, phosphorus and magnesium contents, and increases in plasma ionized calcium, inorganic phosphorus and alkaline phosphatase concentration.

Experimental and observational studies of seasonal interactions between overlapping life history stages in a migratory bird

Prior to reproduction, migratory animals are at the juxtaposition of three life history stages in which they must finish the non-breeding stage, initiate and complete migration, and prepare for the onset of breeding. However, how these stages interact with one another is not fully understood. We provide evidence that, for migratory birds that begin breeding development prior to departure from non-breeding sites, the level of breeding preparation can drive migration phenology, a critical behavioral determinant of reproductive success. Specifically, male American redstart (Setophaga ruticilla) plasma androgen levels, which increase in males during the period leading into migration, were positively correlated with energetic condition. We empirically tested the hypothesis that elevated androgen simultaneously supports migratory and breeding preparation in a hormone manipulation field experiment. Males with testosterone implants showed advanced preparation for migration and breeding, and ultimately departed on migration earlier than controls. It is assumed that early departure leads to early arrival at breeding areas, which increases breeding success. Collectively, our observational and experimental results demonstrate how overlapping life history stages can interact to influence important components of an individual's fitness. This highlights the critical need for understanding population processes across the full life cycle of an organism to better understand the ecological and evolutionary origins of complex life history events.

Steroid use and human performance: Lessons for integrative biologists

While recent studies have begun to address how hormones mediate whole-animal performance traits, the field conspicuously lags behind research conducted on humans. Recent studies of human steroid use have revealed that steroid use increases muscle cross-sectional area and mass, largely due to increases in protein synthesis, and muscle fiber hypertrophy attributable to an increased number of satellite cells and myonuclei per unit area. These biochemical and cellular effects on skeletal muscle morphology translate into increased power and work during weight-lifting and enhanced performance in burst, sprinting activities. However, there are no unequivocal data that human steroid use enhances endurance performance or muscle fatigability or recovery. The effects of steroids on human morphology and performance are in general consistent with results found for nonhuman animals, though there are notable discrepancies. However, some of the discrepancies may be due to a paucity of comparative data on how testosterone affects muscle physiology and subsequent performance across different regions of the body and across vertebrate taxa. Therefore, we advocate more research on the basic relationships among hormones, morphology, and performance. Based on results from human studies, we recommend that integrative biologists interested in studying hormone regulation of performance should take into account training, timing of administration, and dosage administered when designing experiments or field studies. We also argue that more information is needed on the long-term effects of hormone manipulation on performance and fitness.

Hormones, sexual signals, and performance of green anole lizards (Anolis carolinensis)

The evolutionary processes that result in reliable links between male signals and fighting capacity have received a great deal of attention, but the proximate mechanisms underlying such connections remain understudied. We studied a large sample of male green anole lizards (Anolis carolinensis) to determine whether testosterone or corticosterone predicted dewlap size and/or bite-force capacity, as dewlap size is known to be a reliable predictor of bite-force capacity in territorial males. We also examined whether these relationships were consistent between previously described body size classes ("lightweights" and "heavyweights"). Heavyweights had 50% higher testosterone concentrations than lightweights during the breeding season, suggesting a mechanism for the disproportionately larger heads and dewlaps and higher bite-forces of heavyweights. Plasma testosterone concentrations were positively correlated with dewlap size and bite-force performance in lightweights (but not heavyweights) but only because of mutual intercorrelation of all three variables with body size. We suggest two possibilities for the relationship between testosterone levels and body size: (1) testosterone promotes growth in this species or (2) smaller sexually mature males are unable to compete with larger males such that the benefits of elevated testosterone do not outweigh the costs. Corticosterone levels did not differ between the male morphs, and lightweights, but not heavyweights, showed an inverse relationship between testosterone levels and corticosterone levels. Our results suggest that testosterone is important for traits related to dominance in adult male green anoles and may influence the ability to compete with rivals via fighting ability or through the use of signals.

Testosterone has opposite effects on male growth in lizards(Sceloporus spp.) with opposite patterns of sexual size dimorphism

Sexual size dimorphism (SSD) has received considerable attention from evolutionary biologists, but relatively little is known about the physiological mechanisms underlying sex differences in growth that lead to SSD. Testosterone (T) stimulates growth in many male-larger vertebrates, but inhibits growth in the female-larger lizard Sceloporus undulatus. Thus, opposite patterns of SSD may develop in part because of underlying differences in the hormonal regulation of male growth. In the present study,we examined the effects of T on male growth in two sympatric congeners with opposite patterns of SSD (S. virgatus: female-larger; S. jarrovii: male-larger). During the mating season, yearling males of both species have higher plasma T levels than females, but whereas yearling males of S. virgatus grow only half as fast as females, yearling males of S. jarrovii grow more quickly than females. Thus, we hypothesized that T inhibits growth in yearling S. virgatus males, but promotes growth in yearling S. jarrovii males. In support of this hypothesis,we found that castrated (CAST) males of S. virgatus grew faster than castrated males given T implants (TEST). In contrast, TEST males of S. jarrovii grew faster than CAST males. Our results provide the first direct evidence for opposite effects of T on male growth in closely related species with opposite patterns of SSD. We speculate that growth inhibition by T reflects an energetic trade-off between growth and reproductive investment,and propose that such `costs' of male reproduction may help explain the evolution of female-larger SSD in Sceloporus.

Testosterone Inhibits Growth in Juvenile Male Eastern Fence Lizards (Sceloporus undulatus): Implications for Energy Allocation and Sexual Size Dimorphism

In the eastern fence lizard, Sceloporus undulatus, female-larger sexual size dimorphism develops because yearling females grow faster than males before first reproduction. This sexual growth divergence coincides with maturational increases in male aggression, movement, and ventral coloration, all of which are influenced by the sex steroid testosterone (T). These observations suggest that male growth may be constrained by energetic costs of activity and implicate T as a physiological regulator of this potential trade-off. To test this hypothesis, we used surgical castration and subsequent administration of exogenous T to alter the physiological and behavioral phenotypes of field-active males during the period of sexual growth divergence. As predicted, T inhibited male growth, while castration promoted long-term growth. Males treated with T also exhibited increased daily activity period, movement, and home range area. Food consumption did not differ among male treatments or sexes, suggesting that the inhibitory effects of T on growth are mediated by patterns of energy allocation rather than acquisition. On the basis of estimates derived from published data, we conclude that the energetic cost of increased daily activity period following T manipulation is sufficient to explain most (79%) of the associated reduction in growth. Further, growth may have been constrained by additional energetic costs of increased ectoparasite load following T manipulation. Similar studies of the proximate behavioral, ecological, and physiological mechanisms involved in growth regulation should greatly improve our understanding of sexual size dimorphism.

Patterns of peripheral steroid metabolism vary with sex, season, and tissue type in blotched blue-tongued lizards (Tiliqua nigrolutea)

We examined sexual and seasonal variation in the ability of reproductively relevant tissues (liver, skin, adrenal gland, cloaca, kidney, renal sexual segment, epididymis, oviduct, muscle, testis, and ovary) to metabolise a primary steroid [testosterone (T) or estradiol (E2)] in the scincid lizard, Tiliqua nigrolutea. We observed considerable variation between sexes and across seasons in the patterns of conjugation and derivatisation of the primary steroids by these tissues. All tissues demonstrated the ability to conjugate the relevant primary steroid. Other general trends included increased conjugation by all tissues of gestating females, reduced metabolism of E2 by female tissues during late vitellogenesis, and reduced metabolism of T by males during early spermatogenesis. 5alpha-Dihydrotestosterone was the most commonly detected derivative in males, and production varied with season and tissue type. We suggest that seasonal variation in the ability of reproductively relevant tissues may be important in the physiological regulation of reproduction in this species.

European starling chicks benefit from high yolk testosterone levels during a drought year

Avian egg yolk contains androgenic hormones, such as testosterone, of maternal origin. Experimental elevation of yolk testosterone levels enhances growth of canary chicks. Success in sibling competition, due to increased begging, is presumed to underlie this growth enhancement, because canary hatchlings from testosterone-treated eggs beg longer in response to vibrational stimuli than controls. Furthermore, experimental elevation of both yolk androstenedione and testosterone increased chick growth and begging in black-headed gulls. We measured daily growth of European starling (Sturnus vulgaris) chicks hatching from testosterone-treated or vehicle-treated (control) eggs until 14 days of age, and measured begging behavior at hatching and at 5 days of age. A temporary drought caused relatively high levels of early brood reduction for this population; 2- and 3-day-old chicks were most likely to starve. We found that chicks from testosterone-treated eggs were less likely to starve than control chicks, and were heavier on the days when most brood reduction occurred. However, chicks from testosterone-treated eggs begged less than control chicks on the day of hatching, and begged similarly at 5 days of age. Thus, while yolk testosterone did increase growth during periods of (presumably) high competition, increased begging does not appear to mediate this effect. Instead, testosterone may induce more efficient energy use, for example, by decreasing ineffective begging. While our results indicate that elevated yolk testosterone enhances survival, and thus offspring and parental fitness, further evidence regarding the fitness consequences of yolk androgens are vital to understanding their role in avian life history.

The effects of testosterone manipulation on the body condition of captive male yellow-legged gulls

Persistently high testosterone levels are believed to be costly to males due to their negative effect on body condition. However, this assumption could not be validated when we analysed birds isolated from all social interactions. The hypothesis was tested on birds kept in isolation in order to analyse the effects of testosterone per se, and thereby exclude the influence of social interactions. Adult male yellow-legged gulls (Larus cachinnans) were captured, and after a period of adjustment, some individuals were subcutaneously implanted with testosterone, while the rest were used as controls. The gulls received ad libitum food for 10 days and were then fasted for 4 days. Thyroid hormones, body-mass change, daily food intake, hematocrit and several plasma biochemical parameters were analysed. Treated (T)-males maintained constant levels of plasma total protein throughout the experiment, whilst control (C)-males showed a decrease. We did not find any other differences between groups for the other variables analysed. Since the implanted birds sustained high testosterone levels for a number of days, any cost to body condition would have been revealed if these costs levels were actually important. Our results do not support the hypothesis that a reduction in body condition can be directly produced by plasma testosterone, although total protein changes do suggest different anabolic patterns in testosterone-treated gulls.

Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated males assiduously mate guard females on their territory. Yellow-throated males do not defend a territory, but patrol a large home range. They obtain secretive copulations from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, activity, and home range size and concomitantly gained greater control over female home ranges than blue- or yellow-throated males. Experimentally elevating plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels that were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is not without costs. Orange-throated males had low survival compared to the other morphs. Finally, some yellow-throated males transformed to a partial blue morphology late in the season and the endurance of these transforming yellow-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly higher plasma T late in the season compared to the plasma T earlier in the season. T appears to play an important role in the physiological changes that all three color morphs undergo during the process of maturation. In some yellow males, T plays an additional role in plastic changes in behavior and physiology late in the reproductive season. We discuss natural and sexual selection on physiological and behavioral traits that leads to the evolution of steroid regulation in the context of alternative male strategies.

A tradeoff between immunocompetence and sexual ornamentation in domestic fowl

Females often select their mates on the basis of the size or intensity of sexual ornaments, and it is thought that such traits are reliable indicators of male quality because the costliness of these traits prevents cheating. The immunocompetence handicap hypothesis is a recently proposed mechanistic explanation of these costs and states that males carry ornaments at the expense of their resistance to disease and parasites. The tradeoff between immunocompetence and sexual ornamentation was hypothesized to arise as a consequence of the dual effect of androgens on ornamentation (+) and immune function (-). To test this hypothesis, we compared comb size between male domestic chickens Gallus domesticus of lines divergently selected for antibody responses to sheep erythrocytes (three lines: selected for low response or high response and a control line). The importance of comb size in inter- and intrasexual selection is well established, and comb size is strongly dependent on testosterone level. Comb size was larger in the males of the low line than in the high line, and comb size of control males was intermediate, indicating a tradeoff between ornamentation and immunocompetence. Testosterone (T) levels varied in a similar fashion (TLow > TControl > THigh), suggesting that this hormone could mediate the tradeoff between ornamentation and immunocompetence. These results support the idea that a tradeoff with immune function may constrain the expression of secondary sexual ornaments.

In ovo treatment with an aromatase inhibitor masculinizes postnatal hormone levels, abdominal fat pad content, and GH pulsatility in broiler chickens

Vorozole, a selective aromatase inhibitor, was administered in ovo to test the specific embryonic role of estrogen in conferring the sex distinction in GH release and body phenotype in broilers. On Day 6 of incubation, eggs were injected with saline or with different concentrations of vorozole. Postnatal blood samples were analyzed for T3, T4, GH, estradiol (E2), and testosterone (T). At the age of 4 wk, control and vorozole-treated birds were cannulated, and serial blood samples were withdrawn every 10 min for 5 hr, wherein GH pulsatility characteristics were determined using deconvolution analysis. The proportional abdominal fat pad weight was reduced significantly in the treated groups, especially in female birds. The vorozole treatment increased plasma T3, E2, T, and GH concentrations, and decreased T4. The frequency of the GH pulses was lower and the interval between the bursts (min) was higher in the vorozole-treated group, as were the mass secreted per burst (ng/ml), the amplitude (ng/ml/min) and the production rate (ng/ml/5 hr). In conclusion, early in ovo treatment with a potent aromatase inhibitor is able to increase the mean serum T3 and GH concentration and masculinize the GH pulse pattern, resulting in an economically favorable decrease in abdominal fat pad content in male and female broilers at slaughter age.

The suppressive effects of testosterone on growth in young chickens appears to be mediated via a peripheral androgen receptor; studies of the anti-androgen ICI 176,334

ICI 176,334 is a nonsteroidal anti-androgen that has been shown to selectively block peripheral androgen receptors in rats and is presumed to do so in chickens. In chickens, androgens stimulate secondary sexual characteristics (e.g., comb), but inhibit growth and the immune tissues. The present study examined the effect of dietary ICI 176,334 (5 or 25 mg/kg body weight) on growth in chickens in the presence or absence of testosterone treatment (as 1-cm long silastic implants). Treatments began at 2 wk of age and continued through 6 wk of age. Testosterone alone reduced body growth (average daily gain and shank-toe length, together with weights of the body, skeletal muscle, and the bursa of Fabricius, an immune tissue), and stimulated comb development. At the low dose (5 mg/kg), ICI 176,334 alone had no effect on body growth or organ weight with the exception that comb weight was reduced. At the high dose (25 mg/kg), ICI 176,334 decreased growth (body weight, average daily gain, and shank-toe length) and organ weights (breast muscle, bursa of Fabricius, testis, and comb weights). This effect may represent a toxicity. As might be expected with an anti-androgen, ICI 176,334 (at either 5 or 25 mg/kg) completely suppressed the stimulation of comb growth evoked by testosterone. Similarly, ICI 176,334 (5 mg/kg) overcame, albeit partially, the growth-suppressive effects of testosterone (on body weight, average daily gain, shank-toe length, and breast muscle weight) and also had inhibitory effects on the weights of the testis and bursa of Fabricius. The anti-androgen, ICI 176,334, did not influence the reduction in circulating concentrations of luteinizing hormone occurring after testosterone treatment. The present data are consistent with the growth-suppressive effects of testosterone in chickens being mediated via a peripheral androgen receptor. No effects of either testosterone or ICI 176,334 were observed on circulating concentrations of insulin-like growth factor-I despite the marked changes in growth rate.

Effect of lighting treatment on the productivity, health, behavior and sexual maturity of heavy male turkeys

1. Turkey poults (1620) were used to compare the effects of three lighting programmes on heavy strain males reared to 188 d: constant light (24L:0D, CON); increasing light (6L:18D at 7 d gradually increasing to 20L:4D by 63 d, INC); a pattern identical to INC followed by a decrease in daylength from 84 d to 10L:14D at 112 d (DID). 2. Lighting affected growth pattern but had no effect on body weight at 118 d or overall food to gain ratio. 3. Both INC and DID lighting reduced overall mortality in comparison to CON light primarily because of a reduction in the incidence of skeletal disease and spontaneous cardiomyopathy. INC and DID lighting increased the incidence of cannibalism. 4. Turkeys given INC or DID lighting had a superior ability to walk in comparison to those birds given CON light. 5. INC and DID males stood, ate and drank more frequently, and sat less often than CON turkeys during behavioural observation. 6. There were no lighting effects on carcase composition except that INC and DID birds had heavier keel bones. The ultimate force per cm2 (stress) required to break femora was greater for turkeys given INC and DID lighting (P = 0.065). 7. Plasma testosterone concentrations at 117 d were 272.5, 115.2 and 29.5 pg/ml for turkeys given CON, INC and DID lighting, respectively (P = 0.072). Testosterone concentration was not related to growth rate.

Effect of early castration on body weight, muscle growth, and bone characteristics of male Nicholas strain turkeys

Body weight of male Nicholas strain turkeys, castrated at 8 to 10 d of age, averaged .60, 2.20, 5.26, 8.26, and 10.83 kg at 3, 6, 9, 12, and 15 wk of age, respectively. These weights did not differ significantly from those of sham-operated control birds, but were significantly less than those of unoperated controls at 12 and 15 wk of age. Pectoralis major weights of 15-wk-old castrated turkeys were not significantly different than the sham-operated controls, but were less than those of intact controls. Pectoralis weights, expressed as a percentage of BW, did not differ among these groups. There were no differences in tarsometatarsal lengths, weight, or percentage ash among the groups. The incidence of tibial dyschondroplasia ranged from 66.7 to 80.0%, with average scores ranging from 1.00 to 1.42, with no differences among groups. Plasma testosterone concentrations of unoperated and sham-operated controls averaged .16 and .26 ng/mL at 15 wk, whereas concentrations in 7 of 12 castrates were undetectable and amounts in the other 5 castrates averaged .03 ng/mL.