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Avian egg yolks provide critical nutrients and energy reserves for a growing embryo. Once a follicle is selected into the ovulatory hierarchy, rings of yolk precursors are deposited daily until the yolk is large enough to ovulate. The composition of hen egg yolk and the mechanisms responsible for deposition in the ovarian follicle are well-studied. However, the factors that affect the rate of yolk deposition, and the number of days it takes for follicles to grow to the optimal size for ovulation, are less well-known. Social interactions appear to impact the rate of yolk deposition in many avian species and testosterone is a key hormone involved in regulating those interactions. Therefore, we hypothesized that testosterone would influence the rate of follicle growth. We tested the influences of exogenous testosterone treatment by rubbing either testosterone propionate cream (1.25 %) or a control cream to hen combs daily for 7 days to increase plasma testosterone concentrations. We then collected eggs and measured egg and yolk weight, yolk diameters, and stained and counted the number of concentric rings in each yolk. Testosterone-treated hens laid fewer eggs and grew their yolks more slowly than control hens. Testosterone also caused an increase in yolk weight but not yolk diameter. These results indicate that testosterone may play a role in the rate of yolk deposition in birds., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Inc.)

Chronic exposure to low doses of anthropogenic chemicals in the environment continues to be a major health issue. Due to concerns about the effects in humans and wildlife, use of persistent organic pollutants, such as dichlorodiphenyltrichloroethane (DDT), is prohibited. However, their ubiquitous nature and persistence allows them to remain in the environment at low levels for decades. Dichlorodiphenyldichloroethylene (DDE) is the most persistent metabolite of DDT and has been shown to cause hepatotoxicity, nephrotoxicity, hormonal disorders, and induce oxidative stress in many organisms. Although the effects of acute exposure to DDT and its metabolite DDE have been extensively studied, the chronic effects of sub-lethal DDE exposure at levels comparable to those found in the environment have not been well documented. Long-Evans male rats were used to determine the effect of relatively chronic and short term DDE (doses ranged from 0.001 to 100 μg/L) exposure on endocrine function and oxidative stress at different developmental time points. We found that circulating serum testosterone (T) levels were significantly decreased and T secretion in testicular explants were significantly influenced in a dose dependent manner in both pre-pubertal and pubertal male rats after DDE exposure, with pubertal rats being the most affected contrary to our original prediction. Additionally, exposure to DDE increased expression of protein oxidation indicating a possible increase in cellular damage caused by oxidative stress. This study suggests that chronic exposures to environmentally relevant levels of DDE affected testicular function and decreased T secretion with implications for reproductive capacity., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Squamates (lizards and snakes) have independently evolved viviparity over 100 times, and exhibit a wide range of maternal investment in developing embryos from the extremes of lecithotrophic oviparity to matrotrophic viviparity. This group therefore provides excellent comparative opportunities for studying endocrine and immune involvement during pregnancy, and their possible interactions. We studied the cottonmouth (Agkistrodon piscivorus), since they exhibit limited placentation (e.g., ovoviviparity), allowing comparison with squamate species hypothesized to require considerable maternal immune modulation due to the presence of a more extensive placental connection. Furthermore, the cottonmouth's biennial reproductive cycle provides an opportunity for simultaneously comparing pregnant and non-pregnant females in the wild. We document significantly elevated concentrations of progesterone (P4) and significantly lower concentrations of estradiol (E2) in pregnant females relative to non-pregnant females. Pregnant females had lower plasma bacteria lysis capacity relative to non-pregnant females. This functional measure of innate immunity is a proxy for complement performance, and we also determined significant correlations between P4 and decreased complement performance in pregnant females. These findings are consistent with studies that have determined P4's role in complement modulation during pregnancy in mammals, and thus this study joins a growing number of studies that have demonstrated convergent and/or conserved physiological mechanisms regulating viviparous reproduction in vertebrates., (Copyright © 2011. Published by Elsevier Inc.)

Corticosteroid-binding globulin (CBG) is a plasma protein that binds corticosterone and may regulate access of hormone to tissues. The role of CBG during a stress response is not clear. At least two hypotheses have been proposed: 1) CBG levels may increase in response to a stressor, thereby decreasing the amount of circulating free corticosterone, or 2) CBG levels may decline, making corticosterone available for its role in increased metabolic needs during stress. In this study, southern toads, Bufo terrestris, were exposed to a chronic pollutant (coal-combustion-waste), to determine changes in CBG and free corticosterone levels. Since toads exposed to chronic pollutants in previous studies did not exhibit the predicted changes in metabolic rate and mass, but did experience a significant elevation in total corticosterone, we hypothesized that CBG would likewise increase and thus, mitigate the effects of a chronic (i.e. 2 months) pollutant stressor. To conduct this study, we first characterized the properties of CBG in southern toads. Toad CBG has a K(d)=20.6+/-1.0 nM and a B(max)=332.2+/-5.1 nmol/L plasma. The rank order potencies for steroid inhibition of tritiated corticosterone are: dihydrotestosterone > corticosterone >> progesterone=testosterone >>> estrogen=dexamethasone. After characterization, we monitored the changes in CBG, total corticosterone, and free corticosterone in male toads that were exposed to either coal-combustion-waste or control conditions. CBG increased in all groups throughout the experiment. Total corticosterone, on the other hand, was only significantly elevated at four weeks of exposure to coal-combustion-waste. The increase in CBG did not parallel the increase in total corticosterone; as a result, free corticosterone levels were not buffered by CBG, but showed a peak at four weeks similar to total corticosterone. This finding indicates that, in this species, CBG may not provide a protective mechanism during long-term pollution exposure.

From April to October of 1996 and 1997, we measured seasonal changes in plasma testosterone (T) in male and plasma T and estradiol-17beta (E(2)) in female yellow-blotched map turtles, Graptemys flavimaculata, from the Pascagoula River, Mississippi. In 1996, plasma from females was analyzed for progesterone. In 1997, ovaries of adult females were ultrasound imaged to determine stages of follicular development. Males exhibited peak T levels in September and October of both years, indicating fall gonadal activity. Males also exhibited a low level spring peak in T during April. Female E(2) levels increased significantly in May and June, the primary period of ovarian development. Females with preovulatory follicles did not have significantly higher E(2) levels than females with medium- or small-sized follicles. When compared to other freshwater turtle species, peak levels of E(2) were low. Testosterone levels did not follow a distinct yearly pattern in females. Progesterone levels were elevated in June when peak nesting was observed. Ultrasound and hormone data indicate that females lack ovarian development in the fall and produce on average only one clutch per year., (Copyright 2000 Academic Press.)

We sampled a population of gopher tortoises (Gopherus polyphemus) from May to October 1997 to determine seasonal cycles of steroid hormones (testosterone, T; 17beta-estradiol, E; and progesterone, P) and related them to observations of mating behavior. In males, plasma T levels peaked in July and August and remained elevated through October. This coincides with the reported time of peak mating and spermatogenesis, indicating that males display an associated pattern of reproduction. In females, E levels were high in September and October. Plasma T levels in females were elevated in May, decreased to basal levels in June and July, and rose again in August and September. Elevated E and T levels correspond to the reported time of peak vitellogenic activity, indicating that females also display an associated cycle. Plasma P in females remained basal throughout the active season, suggesting that ovulation occurs in late winter. We also determined levels of corticosterone (B) to assess the influence of capture stress on tortoises and correlated B levels with tortoise activity patterns and sex steroid levels. We found no seasonal variation in levels of B in males or females. Plasma B levels were not correlated with levels of T or E, but were positively correlated with female P levels. Further, we found no relationship between plasma B levels in males and mean distance moved, mean number of burrows used, or mean home range size. However, there was a significant negative correlation between plasma B levels and male body size. In females, there was no relationship between B levels and mean distance moved, but B levels were significantly negatively correlated with the number of burrows females occupied. Lastly, there was no relationship between levels of B and the number of minutes required to obtain blood from an animal. However, B levels increased with the length of time that a tortoise spent in a trap, suggesting that trapped tortoises do exhibit capture stress., (Copyright 2000 Academic Press.)

This study describes an interrenal stress response in adult toads, Bufo terrestris, after exposure to coal combustion waste (characterized by a variety of trace elements). In the first portion of this study, free-ranging male toads captured at the coal ash polluted site exhibited significantly higher circulating levels of corticosterone (B) in both June/July and August than conspecifics captured at uncontaminated sites. In addition, both calling and noncalling males from the polluted site had higher B levels than conspecifics engaged in the same behaviors at reference sites. Testosterone levels were elevated in toads from the polluted site, regardless of capture month or behavioral state, suggesting altered androgen production, utilization, and/or clearance. In the second portion of this study, male toads from reference sites were transplanted to enclosures at the polluted site or an uncontaminated site. Toads held at the polluted site exhibited significant increases in B after 10 days of exposure compared to toads held at the reference site. B levels remained significantly elevated in toads transplanted to the polluted site after 12 weeks. We hypothesize that high concentrations of various trace elements in the polluted site are responsible for these hormonal responses., (Copyright 1997 Academic Press. Copyright 1997 Academic Press)

We measured plasma levels of testosterone, dihydrotestosterone (DHT), and corticosterone for male marbled salamanders (Ambystoma opacum) collected during the breeding season. Our goal was to ascertain whether steroid levels changed in response to particular reproductive behaviors or laboratory confinement. Six groups of salamanders were examined: (a) MIGRATING, males migrating toward the pond basin during the breeding season; (b) LABORATORY, males kept under confined conditions in the laboratory for 10 days; (c) LAB-FIELD, laboratory males that were later released into seminatural enclosures in the field; (d) COURTING, males from male-female pairs in which the male actively courted the female (and deposited at least one spermatophore); (e) SOLO, males that were individually isolated from conspecifics; and (f) MALE-MALE, males that were placed together in pairs, and in which one male actively courted the other male. In three groups (COURTING, SOLO, and MALE-MALE), salamanders were placed in containers for observation and each male was observed for at least 2 hr prior to a plasma sample being taken. Circulating levels of testosterone, DHT, and corticosterone did not differ significantly for males in these groups. The similarity of androgen levels among the three groups indicated a lack of behaviorally evoked change under experimental conditions designed to reveal a behavior-androgen response. Male A. opacum differ taxonomically from other amphibians showing a behavior-androgen response (three species of toads in the genus Bufo) and also lack amplexus and male-male combat during competition for mates. The effects of confinement were indicated by levels of testosterone and DHT in LABORATORY males that were significantly lower than average levels of males in the following groups: MIGRATING, LAB-FIELD, and MALE-MALE. We inferred that LAB-FIELD males, following their release to seminatural enclosures, were able to regain plasma androgen levels typical of migrating males. This increase is one of very few demonstrations for amphibians of an increase in androgen levels upon release from laboratory confinement. Levels of corticosterone did not differ significantly between males that were active in the field and males that were kept in the laboratory. The similarity of corticosterone levels among these groups differs from the typical pattern of elevated corticosterone and depressed androgen levels in captive amphibians. Maximal corticosterone levels in breeding male A. opacum may act differently than in other species in which chronic elevations inhibit the pituitary-gonadal axis.

We report seasonal and annual variation in the daily cycle of plasma melatonin levels in male red-sided garter snakes, Thamnophis sirtalis parietalis. In autumn of 1989 and 1990, levels averaged a maximum of 210 pg/ml during scotophase and a minimum of 45 pg/ml during photophase and had a similar diel pattern. Under hibernation conditions (4 degrees, 0:24 L:D), melatonin was undetectable and a diel cycle could not be determined. In Spring 1990, melatonin levels rose rapidly and precipitously within an hour of emergence (while in photophase), peaked at levels significantly higher than those seen in the autumn (approximately 900 pg/ml) and remained significantly high for 24 hr after emergence (though the majority of animals did have decreased levels at the 0400 sample). By the 10th day after emergence, a diel cycle was reestablished and absolute melatonin levels had decreased. The next spring (1991), melatonin again rose within an hour after emergence, while in photophase, but not as high as the previous year. Also unlike the previous year, a diel cycle was observed within 24 hr of emergence. Melatonin levels at emergence were significantly higher than those observed 10 days later. Disruption of a diel rhythm of plasma melatonin (by pinealectomy the previous autumn) inhibits courtship behavior by males the next spring, implying a role for melatonin in the stimulation of sexual behavior. Males in 1991 (with quickly established melatonin cycles) courted much sooner after emergence than did males in 1990. Therefore, the initial day/night difference in melatonin levels at emergence (i.e., establishment of a normal diel cycle) may function in synchronizing and modulating reproductive behavior in male red-sided garter snakes.

Fluctuations in plasma androgen (testosterone and 5 alpha-dihydrotestosterone), corticosterone (B), and luteinizing hormone (LH) of male bullfrogs in central California were measured during the spring mating season. Androgen and LH levels generally increased in the population prior to the initiation of chorusing and establishment of territories, whereas plasma B peaked in a 2-week period at the start of heavy chorusing; this coincided with a transitory, 1 week decline in androgen. Individual males showed fluctuations in plasma androgen and LH levels throughout the breeding season, often within 1 day, but there was no clear correlation between changes in the two hormones. No time of day effect was apparent on any of the hormones. B and androgen levels were significantly but weakly correlated, (r = 0.35) but LH and androgen were not. Although the seasonal trend of increasing androgen corresponded with the start of intense chorusing (and presumably sexual activity) by the population, behavior of individuals and their circulating androgen levels did not correlate. After acquiring territories, males showed no overall trend of increased plasma androgen. Moreover, males that showed no vocal or territorial behavior had significantly higher androgen and lower B levels than calling males. Increased B levels suggest that territorial behavior and especially direct agonistic encounters represent stresses that could have an inhibitory effect on androgen secretion.