Correlation among Thermosensitive Period, Estradiol Response, and Gonad Differentiation in the Sea TurtleLepidochelys olivacea
ABSTRACT Reptile embryos with temperature sex determination have a thermosensitive period (TSP). The finding that exogenous estradiol (E2) overcomes the effect of male-promoting 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 ridleyLepidochelys 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 μg 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 female-promoting 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 thermosensitive 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.
- SourceAvailable from: Gonçalo M. Rosa[Show abstract] [Hide abstract]
ABSTRACT: In marine turtles, the sex of an individual is determined by temperatures experienced during embryonic development. Gonad histological observation is still the only reliable way to determine hatchling sex, hampering the study of reproduction and of the demographic consequences of context-dependent sex-ratios, a subject of interest in a warming planet. We investigated whether hatchling remains from predation by Ocypode cursor can be used to estimate sex-ratio trends in a green turtle rookery at Poilão, Guinea-Bissau (10°52′N, 15°43′W). Sex could be readily determined in 77 and 79% of the predated hatchlings in 2008 and 2009, respectively. By comparing hatchlings killed by crabs, hatchlings accidentally dying on the reefs, and live hatchlings, we show that ghost crabs select the smaller prey, but do not select according to hatchling sex, which is explained by the lack of hatchling size dimorphism in this population. The proportion of male hatchlings was 0.45 ± 0.06 and 0.15 ± 0.06 for early and late-season clutches, respectively, these differences most likely being explained by rainfall. Using leftovers from predation by crabs may be a good solution to non-invasively monitor broad trends in sex-ratios of sea turtles.Marine Biology 03/2012; 159(3):613-620. · 2.39 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The goal of this study was to test the effectiveness of analyzing sex hormone profiles to sex green sea turtle (Chelonia mydas) hatchlings. To assess the efficacy of this method, 200 eggs of C. mydas were incubated at five different temperatures, and a chemiluminescent immunoassay system was used to determine the sex hormone profiles (estrogen and testosterone) in the amniotic fluid (from eggshells) and plasma of a subset of C. mydas hatchlings. Results were compared to a standard histological technique and revealed that evaluating sex hormone profiles from amniotic fluid is an effective, noninvasive technique for determining hatchling gender.Chelonian Conservation and Biology 07/2011; · 0.70 Impact Factor