Albert J. Fivizzani

Effects of the herbicide atrazine on Ambystoma tigrinum metamorphosis: duration, larval growth, and hormonal response

We exposed larval tiger salamanders (Ambystoma tigrinum) reared in the laboratory from eggs collected from a prairie wetland in North Dakota to three concentrations of atrazine (0, 75, and 250 mg/L) in a static renewal test to determine the pesticides effect on (1) plasma corticosterone and thyroxine concentrations, (2) larval size, and (3) days‐to‐stage at stages 2 and 4 of metamorphic climax. We found significant effects of atrazine on each of these response variables. Plasma thyrox‐ine was elevated in both atrazine‐exposed groups compared with the control group; plasma corticosterone was depressed in the 75 mg/L treatment compared with both the control and 250 mg/L treatment. Larvae exposed to 75 mg/L atrazine reached stage 4 later but at a size and weight comparable to the control group. By contrast, larvae in the 250 mg/L treatment progressed to stage 4 at the same time but at a smaller size and lower weight than larvae in the control group. These results indicate that the herbicide has the potential to influence tiger salamander life history. We present a model consistent with our results, whereby corticosterone and thyroxine interact to regulate metamorphosis of tiger salamanders based on nutrient assimilation and adult fitness.

Testosterone-induced inhibition of incubation in the spotted sandpiper (Actitis mecularia)

The spotted sandpiper (Actitis macularia) is characterized by intense female intrasexual competition and predominantly male parental care. Females often are polyandrous. Incubating males were implanted with testosterone (T)-filled Silastic tubes. Plasma T levels were significantly elevated by T implants while prolactin (Prl) remained unchanged. Birds implanted with T deserted clutches (30%) or exhibited reduced incubation constancy (50%) while controls incubated normally. The T implants appeared to heighten sexual receptivity and hence reduce incubation constancy. Variation in male incubation behavior may have been further influenced by the degree to which males were exposed to courting females.

Plasma steroid hormone levels in free-living Wilson's phalaropes, Phalaropus tricolor

Blood samples collected from free-living Wilsons phalaropes during the reproductive season were analyzed for testosterone, dihydrotestosterone, estradiol-17 beta, and progesterone. Levels of testosterone were seven times greater in nonincubating males than in females. During incubation males underwent a reduction in testosterone and dihydrotestosterone to levels similar to those of females. Estradiol-17 beta values were higher in females than in incubating males and comparable to values reported for other avian species. Progesterone was significantly greater in females than in incubating or nonincubating males. Maximum levels of progesterone were detected in laying females. Progesterone levels increased in males during incubation while testosterone and dihydrotestosterone levels decreased. These results indicate that the greater intensity of competition for mates among females and exclusive male parental care characteristic of this species is not based upon a reversal of the typical avian levels of androgens and estrogens in males and females.

Yolk hormone levels in the eggs of snapping turtles and painted turtles.

Although yolk steroids appear to play important roles in the development, growth, and behavior of some birds, their effects in oviparous reptiles are largely unknown. These investigations were initiated to determine initial levels of steroid hormones in the yolks of eggs from two turtle species. Clutches of snapping turtle (Chelydra serpentina) and of painted turtle (Chrysemys picta) eggs were collected and individual egg yolks were analyzed for estradiol-17beta (E(2)) and testosterone (T) using specific RIAs. E(2) and T levels differed significantly between species, the mean E(2) value in snapping turtles was 2.78+/-0.095 (ng/g) compared to 0.89+/-0.064 (ng/g) for painted turtles, and the mean value for T in snapping turtle yolks was 2.56+/-0.098 (ng/g) compared to 0.68+/-0.045 (ng/g) for painted turtles. In addition, E(2) levels were greater than T levels in both species. Within each species, there were significant differences among clutches from different females. E(2) levels in the snapping turtle yolks varied from a clutch mean of 1.38 to 4.55 ng/g and in painted turtles, the clutch means for E(2) varied from 0.34 to 1.34 ng/g. T levels demonstrated similar phenomena within species, with levels in snapping turtles varying from a clutch mean of 0.68 to 4.71 ng/g. Painted turtle levels of T varied from a clutch mean of 0.22 to 0.72 ng/g. There were also significant differences in the E(2)/T ratio, however, E(2)/T ratios did not differ between species. Painted turtle follicles of different sizes showed significant differences in levels of both E(2) and T, and these differences may reflect differing deposition patterns of these steroids in the egg yolk of this turtle during vitellogenesis. The differences in E(2) and T concentration reported here could have important implications for development, growth, and behavior in oviparous reptilian species.

Dynamics of yolk steroid hormones during development in a reptile with temperature-dependent sex determination

Many oviparous reptiles exhibit temperature-dependent sex determination (TSD); i.e., the temperature at which the egg is incubated determines the sex of the offspring. In TSD reptiles, yolk steroids not only may influence sex determination, but also may mediate hormonal effects on subsequent growth and behavior, as in some avian species. We investigated changes in the levels of estradiol (E(2)) and testosterone (T) during development in yolks of snapping turtle eggs, examined how incubation temperature affects hormone levels, and determined how hormones in turtle eggs are influenced by individual females (=clutch effects). Results indicate significant decreases in both hormones (>50% decline) by the end of the sex-determining period, when two-thirds of the development is complete. The declines in both E(2) and T were significantly affected by incubation temperature, but in different ways. Eggs incubated at female-producing temperatures maintained high levels, those incubated at male-producing temperatures had low E(2) values, and eggs incubated at pivotal temperatures had intermediate levels of E(2). At all three temperatures, T values underwent significant but approximately equal declines, except during the developmental stages just after the sex-determining period, when T levels decreased more at the male-producing temperature than at either of the other two temperatures. Initially, there were significant clutch effects in both hormones, but such differences, attributable to individual females, were maintained only for E(2) later in development. Here we report for the first time that incubation temperature significantly affects the hormonal environment of the developing embryo of a turtle with temperature-dependent sex determination. Based on this and related findings, we propose that yolk sex steroids influence sexual differentiation in these TSD species and play a role in sex determination at pivotal temperatures.

Circulating prolactin of incubating male Wilson's Phalaropes corresponds to clutch size and environmental stress

We measured the effect of clutch-size changes on levels of circulating prolactin (prl) among incubating male Wilsons Phalaropes in order to identify the influence of clutch-size as an exogenous determinant of circulating prl, and to better understand the endocrinology of clutch abandonment. One year of the study was characterized by unusually high temperatures and drought, and incubating males appeared to be heavily stressed based on ambient temperatures and rates of weight loss. We used the contrasting environmental conditions between years to compare levels of circulating prl among males experiencing different levels of environmental stress. We found a strong inter-year effect, with significantly lower prl during the high stress year. We also found a clear effect of clutch-size on level of circulating prl during the low stress year of the study. Males with increased or decreased clutch-size had lower levels of circulating prl than did control males. Because prl levels were so variable, we sought alternative explanations to year and clutch-size effects. We examined nine environmental and physiological factors a posteriori for a relationship with circulating prl. Although we identified weak correlates, none of the additional factors could account for the variation in prl explained by year and clutch-size. Incubating male Wilsons Phalaropes appear to experience an adaptive endocrine change when the potential fitness of their clutch is compromised.

Reproductive tradeoffs and yolk steroids in female leopard geckos, Eublepharis macularius

Life history theory predicts tradeoffs among reproductive traits, but the physiological mechanisms underlying such tradeoffs remain unclear. Here we examine reproductive tradeoffs and their association with yolk steroids in an oviparous lizard. Female leopard geckos lay two eggs in a clutch, produce multiple clutches in a breeding season, and reproduce for several years. We detected a significant tradeoff between egg size and the number of clutches laid by females during their first two breeding seasons. Total reproductive effort was strongly condition‐dependent in the first season, but much less so in the second season. Although these and other tradeoffs were unmistakable, they were not associated with levels of androstenedione, oestradiol, or testosterone in egg yolk. Female condition and egg size, however, were inversely related to dihydrotestosterone (DHT) levels in egg yolk. Finally, steroid levels in egg yolk were not directly related to steroid levels in the maternal circulation when follicles were developing, indicating that steroid transfer to eggs is regulated. These findings suggest that maternal allocation of DHT could mitigate tradeoffs that lead to poor offspring quality (i.e. poor female condition) and small offspring size (i.e. small egg size).

Sex‐reversed and normal turtles display similar sex steroid profiles

In many oviparous reptiles, incubation temperature determines hatchling sex. Manipulation of the embryonic hormonal environment can result in sex reversal. We measured circulating estradiol 17-β (E2) and testosterone (T) levels in temperature-determined and sex-reversed snapping turtles (Chelydra serpentina). Eight-month-old turtles have sex steroid profiles that are sex specific and are consistent with gonadal sex. Males had higher levels of T than females, both before and after treatment with follicle stimulating hormone (FSH). In males, T levels increased approximately 11-fold after FSH challenge, whereas in females, T levels remained low. In contrast, levels of E2 after FSH challenge were higher in females than in males, but showed no difference before treatment. Sex-reversed individuals appear to have normal sex steroid profiles of T and E2, both at basal levels and in response to gonadotropin challenge. Our study indicates that the steroidogenic capability of these juvenile turtles was consistent with gonadal morphology and suggests that these sex-reversed individuals have normal gonadal function.

Changes in lipid metabolism and plasma concentrations of thyroxine, cortisol, and somatostatin in land-locked chinook salmon, Oncorhynchus tshawytscha, during smoltification

Abstract A land-locked strain of chinook salmon was used to discriminate seawater preadaptive aspects of smoltification from development-associated aspects of smoltification. Liver total lipid and lipid class composition, as well as plasma concentrations of thyroxine (T 4 ), cortisol, and somatostatin-25 (sSS-25), the predominant form of somatostatin in the pancreas and plasma of salmonids, were measured in age 0 + and 1 + freshwater land-locked fall chinook salmon between March and May 1990. Liver total lipids in age 0 + fish displayed extensive seasonal fluctuation, cycling from high levels to low levels several times over the course of the sampling period. Springtime-associated changes in total lipids were primarily due to diminution of triacylglycerols. Plasma T 4 titers in the age 0 + fish also showed substantial seasonal variation with multiple peaks noted over the course of the sampling period. Changes in plasma T 4 were highly correlated with liver total lipid; seasonal high plasma T 4 levels were observed at the time of maximum lipid depletion. In age 1 + fish, plasma T 4 displayed a single peak in coincidence with elevated plasma cortisol levels. Plasma sSS-25 levels in age 1 + fish, measured during smoltification for the first time, also displayed seasonal variation; levels underwent changes generally opposite to those of T 4 in early spring. Dramatic increases in plasma T 4 were displayed by both age classes of fish when transferred from spring-fed hatchery water to lake water. Our results suggest that land-locked chinook salmon may experience multiple parr-smolt episodes during freshwater development and that springtime-associated and thyroid hormone-correlated lipid depletion occurs in the absence of the fishs exposure to seawater.

Seasonal changes in gonadal steroids of a monogamous versus a polyandrous shorebird.

We examined the relationship between circulating levels of gonadal steroids (testosterone, progesterone, and estradiol) and breeding behavior in semipalmated sandpipers (Calidris pusilla) and red-necked phalaropes (Phalaropus lobatus) breeding sympatrically at La Pérouse Bay, 40 km east of Churchill, Manitoba. Semipalmated sandpipers are territorial and monogamous. Both parents incubate equally. Red-necked phalaropes are nonterritorial and polyandrous. Only male phalaropes care for eggs and young. Gonadal steroid hormone profiles were not reversed in the sex-role-reversed species. There was little difference in testosterone profiles between males of the territorial and nonterritorial species.