Hormone levels in yolk decline throughout development in the red-eared slider turtle (Trachemys scripta elegans) (original) (raw)
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Maternally derived yolk hormones vary in follicles of the painted turtle, Chrysemys picta
Journal of …, 2002
The transfer of hormones from a female to her o¡spring is known to occur in egg laying vertebrates, and the potential for these early, maternally derived hormones to in£uence sex determination in reptiles with temperature-dependent sex determination is intriguing. In the present study, we examine variation in the concentrations of progesterone, testosterone, and estradiol among three follicle size classes within a female painted turtle (Chrysemys picta) and among females across four periods that span the pre-to post-nesting season. Females were collected, and both follicles and shelled eggs (when present) were harvested for hormone analysis. Progesterone levels did not vary seasonally. However, the concentration of progesterone did vary among and within follicle classes, and was primarily dependent upon ovulatory state: Recently ovulated follicles (as yolks within shelled eggs) contained signi¢cantly more progesterone than unovulated follicles. Concentrations of testosterone were low and did not vary either among size classes or across the season. Estradiol levels decreased with increasing follicle size and were higher later in the nesting season.Thus, hormone concentrations varied among follicle sizes and states but in patterns that di¡ered among hormones.This variation has the potential to in£uence sex determination.
Biology of Reproduction, 1999
Incubation temperature determines gonadal sex in the redeared slider turtle, Trachemys scripta. However, little is known about the long-term effects of incubation temperature on traits other than gonadal sex in this species. To investigate the hypothesis that incubation temperature (independent of gonadal sex) influences sex steroid levels after hatching, we incubated eggs of the red-eared slider turtle at three temperatures (26, 28.6, and 31؇C). We then measured plasma levels of dihydrotestosterone, estradiol, progesterone, and testosterone in 6-wkold males from 26؇C and 28.6؇C eggs, and in 6-wk-old females from 28.6؇C and 31؇C eggs. We found that dihydrotestosterone levels were not influenced by incubation temperature or gonadal sex. However, progesterone levels were significantly higher in males from 26؇C eggs than in males from 28.6؇C eggs. In contrast, testosterone levels did not differ between males from 26؇C versus males from 28.6؇C eggs, but they were significantly higher in females from 28.6؇C than in females from 31؇C eggs. Progesterone and testosterone levels did not differ between males and females from 28.6؇C eggs. Temperature also influenced estradiol levels in both sexes, but the effects were enigmatic. We conclude that incubation temperature has lasting effects on sex steroid levels even after hatching.
Embryonic sex steroid hormones accumulate in the eggshell of loggerhead sea turtle (Caretta caretta
Steroids hormones such as estradiol-17b (E2) and testosterone (T) are involved in gonadal differentiation of oviparous animals with temperature-dependent sex determination (TSD), and are greatly distributed. This hypothesizes that these embryonic steroid hormones probably accumulate in the eggshell throughout blood or/and chorioallantoic fluid in sea turtle species with TSD, producing females at higher temperature. To demonstrate this hypothesis, concentrations of E2 and T in the blood plasma from the hatchling loggerhead sea turtle (Caretta caretta) and in their eggshells were measured by radioimmunoassay. In the present study we propose that both concentrations of E2 and T in the blood plasma are correlated with amounts of these sex steroids in the eggshell. Moreover, contents of E2 in the eggshell showed a significant positive correlation with mean incubation temperatures during a thermosensitive period in the experimental nests, whereas T contents in the eggshell did not. Taken together, these findings indicated that embryonic E2 and T that accumulated in the eggshell can be extracted and measured. Furthermore, the present study suggested that contents of E2 in the eggshell may differ between male and female, and monitoring of these steroids is a useful method to identify the sex of loggerhead sea turtle hatchling.
General and Comparative Endocrinology, 1997
Reptile embryos with temperature sex determination have a thermosensitive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of malepromoting temperature led to the idea that temperature may regulate estrogen concentration in the gonad during TSP. Since interspecific variations in TSP and in the effect of exogenous E2 exist, we undertook a study in the olive ridley Lepidochelys olivacea. Four parameters were correlated: the TSP (time dimension), the thermosensitive stages (rate of development), gonad development (histological aspect), and the estradiol response. Two kinds of experiments were performed: (1) Eggs were shifted once, at different stages of development, from a male-promoting temperature to a female-temperature (or vice versa) for the remainder of development. (2) Eggs at male-promoting temperature were treated once with 6 or 12 mg of estradiol (E2) at various times of incubation. Sex ratio was established around hatching in each experimental series. We found that the temporal dimension of the TSP was around 7 days (Days 20-27 of incubation) at a male-promoting or a female-promoting temperature. The rate of development of the whole embryo and gonadal growth was faster at femalepromoting temperature than at male-promoting temperature. Formation of the genital ridge began at stage 21-22 and histological differentiation of the gonads occurred around stage 26-27. Although these stages coincided with the TSP, at male-promoting temperature the thermo-sensitive stages occurred earlier (from stages 20-21 to stages 23-24) than at female-promoting temperature (from stages 23-24 to stages 26-27). Thus, at male promoting-temperature, sex was determined in embryos with incipient or undifferentiated gonads. In contrast, E2 treatment continued to feminize the gonads of embryos at a male-promoting temperature beyond the TSP up to stage 25-26, but the E2-induced ovaries were significantly smaller than temperature-induced ovaries. It is suggested that the doses of E2 used were higher than the concentration of endogenous E2 required for normal sex determination. The lack of correlation between sex determination and gonad differentiation suggests that irreversible molecular processes underlying sex determination occur earlier at male-than at female-promoting temperature. Results suggest that the male sex may be the default state and that the female condition must be imposed upon it. r 1997 Academic Press Sexual differentiation of the gonads is dependent on incubation temperature in five sea turtle species: Eretmochelys imbricata , Lepidochelys olivacea Caretta caretta Mrosovsky, 1980, 1982), Chelonia mydas Limpus, 1980, Morreale et al., 1982), and Dermochelys coriacea . Pivotal temperatures (temperature during incubation at constant temperature which gives 50% individuals of each sexual
Synergism between temperature and estradiol: A common pathway in turtle sex determination?
Journal of Experimental Zoology, 1991
In many reptiles, the temperature at which the eggs are incubated determines the sex of the hatchlings. Administration of estradiol will counteract the masculinizing effects of a male-producing temperature, resulting in female hatchlings. To address whether temperature and estrogen are biologically equivalent, two experiments were conducted with the red-eared slider turtle, Trachemys scripta. In the first experiment, varying dosages of estrogen were administered at Stage 17 (the middle of the temperature-sensitive window) to eggs maintained at two temperatures, 26°C (which normally produces all males) and 28.2"C (which produces mostly males but lies at the threshold of the transition from male-to female-producing temperatures). Results indicate that estrogen and temperature exert a synergistic effect on sex determination. In the second experiment, estrogen was administered at different stages of embryonic development. The results indicate an estrogen-sensitive period ranging from Stage 14 through Stage 21, a period similar to the temperature-sensitive period for this species. The results of these experiments are consistent with the hypothesis that temperature and estradiol act in a common pathway in temperature-dependent sex determination.
General and comparative …, 1996
triol treatment also resulted in cranially hypertrophied In many turtles the temperature during the middle of oviducts at all incubation temperatures in a dose-depenincubation determines the gonadal sex of the hatchling. dent manner, whereas animals treated with estradiol-Sex steroid hormones have been implicated in tempera-17b and estrone had normal oviducts. These results supture-dependent sex determination in the red-eared slider port the hypothesis that estrogens are involved in the turtle, Trachemys scripta; nonaromatizable androgens final common pathway of female sex determination in are involved in male sex determination and estrogens this species. ᭧ 1996 Academic Press, Inc. and aromatizable androgens in female sex determination. Administration of exogenous estradiol-17b to eggs incubating at a temperature that normally produces only In many reptiles gonadal sex is determined by the males can overcome the effect of temperature and result temperature of the incubating egg, a process known as in all offspring being female. Further, estradiol-17b and temperature-dependent sex determination (TSD). In the incubation temperature synergize to produce a greater red-eared slider turtle (Trachemys scripta), incubation of feminizing effect at intermediate incubation temperaeggs at relatively low temperatures (e.g., 20 -28.6Њ) retures that produce mixed sex ratios. This study demonsults in only male hatchlings, whereas relatively high strates that, in the red-eared slider, there is a complex temperatures (e.g., 29.6 -35Њ) results in only female interaction between incubation temperature, different hatchlings; when eggs are incubated at temperatures estrogens, and the dosage effect of each hormone. There intermediate to these, varying sex ratios are produced are changes in potency of different estrogens with incu- . Sex steroid hormones appear to be bation temperature such that estriol is more potent than the physiological equivalent of incubation temperature estrone and estradiol-17b at 26Њ (an all-male producing and both male-and female-producing incubation temincubation temperature), estrone and estriol are equipoperatures and exogenous steroids exert their effects tent to each other and more potent than estradiol-17b at during the mid-trimester of development (Crews et al., . Estrogens and aromatizable biased sex ratio), and estradiol-17b is more potent than androgens induce female sex determination, whereas estrone and estriol at 29Њ (an incubation temperature nonaromatizable androgens induce male sex determithat produced equal numbers of males and females).
Concentrations of steroid hormones in layers and biopsies of chelonian egg yolks
General and Comparative …, 2001
The actions of circulating hormones, although relatively well understood for adults, are largely unknown for their developing embryos. Transfer of maternal hormones to the egg is known to occur in oviparous species, and recently the presence of hormonally heterogeneous yolk layers has been described in two avian species. To investigate the possibility of a similar phenomenon occurring in chelonian species, egg yolk layers were analyzed in the painted turtle (Chrysemys picta marginata) and the redeared slider turtle (Trachemys scripta elegans), two species that exhibit temperature-dependent sex determination. There was a similar pattern of hormonally heterogeneous yolk layers in both species: concentrations of progesterone and testosterone were significantly higher in the external yolk layer while concentrations of 17-estradiol were significantly higher in the intermediate and internal layers. This pattern of hormone deposition concurs with previously published studies of plasma hormone profiles from females of temperate-zone turtle species. Yolks of freshly laid eggs were also sampled using a biopsy technique to examine the concordance of early yolk hormone concentrations and offspring sex. No relationship was found between yolk hormone concentrations and individual offspring sex. Previous work showing that maternally derived yolk estradiol concentrations are correlated with female-biased sex ratios was, however, replicated. These findings suggest that off-spring sex is influenced, in part, by the maternal hormone environment.
Sexual Development, 2007
ER ␣ and AR levels spike at the female-producing temperature while ovarian sex is determined, but none of the receptors exhibited sexually dimorphic localization within the gonad prior to morphological differentiation. All three receptors respond differentially to sex-reversing treatments. When shifted to female-producing temperatures, embryos maintain ER ␣ and AR expression while ER  is reduced. When shifted to male-producing temperatures, medullary expression of all three receptors is reduced. Feminization via es tradiol (E 2 ) treatment at a male-producing temperature profoundly changed the expression patterns for all three receptors. ER ␣ and ER  redirected to the cortex in E 2 -created ovaries, while AR medullary expression was transiently reduced. Although warmer incubation temperature and estrogen result in the same endpoint (ovarian development), our results indicate different steroid signaling patterns between temperature-and estrogen-induced feminization.
Seminars in Cell & Developmental Biology, 2009
The developmental processes underlying gonadal differentiation are conserved across vertebrates, but the triggers initiating these trajectories are extremely variable. The red-eared slider turtle (Trachemys scripta elegans) exhibits temperature-dependent sex determination (TSD), a system where incubation temperature during a temperature-sensitive period of development determines offspring sex. However, gonadal sex is sensitive to both temperature and hormones during this period -particularly estrogen. We present a model for temperature-based differences in aromatase expression as a critical step in ovarian determination. Localized estrogen production facilitates ovarian development while inhibiting male-specific gene expression. At male-producing temperatures aromatase is not upregulated, thereby allowing testis development.
Differentiation, 1993
Gonadal differentiation associated with estrogen-induced female sex determination was examined in a turtle with temperature-dependent sex determination, and was compared to ovarian differentiation at a female-producing temperature. Freshly ladi eggs of the red-eared slider, Trachemys scripta, were incubated at a male-producing temperature (26 degrees C) and were experimentally manipulated at one of three embryonic stages: stage 15, 17, or 20 (i.e. early, midway, or late in the temperature-sensitive and estrogen-sensitive periods). At those developmental stages, groups of eggs were either: (1) treated with a control solution (95% ethanol) and placed back at the male-producing temperature, (2) treated with 10 micrograms of estradiol-17 beta and placed back at the male-producing temperature, or (3) shifted to a female-producing temperature (31 degrees C). Additionally, a control group of freshly laid eggs was continually incubated at 31 degrees C throughout embryonic development. To examine morphological events occurring after the treatments, a subset of embryos from each group was examined at the time of the treatment and at 1-2 stage intervals following the treatments. The results indicate that estradiol-17 beta as well as female-producing temperature may ensure female sex determination by facilitating medullary cord regression. Further, the results reveal a chronology of differentiation in which medullary cord regression temporally precedes cortical proliferation.