The Environmental Contaminant DDE Fails to Influence the Outcome of Sexual Differentiation in the Marine Turtle Chelonia mydas

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The National Institute of Environmental Health Sciences (NIEHS) and Brogan & Partners are collaborating with JSTOR to digitize, preserve and extend access to Environmental Health Perspectives. In many turtles, the temperature experienced during the middle of egg incubation determines the sex of the offspring. The implication of steroid sex hormones as the proximate trigger for sex determination opens the possibility that endocrine-disrupting contaminants may also influence the outcome of sexual differentiation. In this study we investigate the potential effects of DDE (a common DDT metabolite) on sexual differentiation of Chelonia mydas (green sea turtle). Four clutches of eggs collected from Heron Island, Queensland, Australia, were treated with DDE at the beginning of the thermosensitive period for sexual determination. An incubation temperature of 28?C or less produces male hatchlings in this species, whereas 30?C or more produces female hatchlings. Dosed eggs were consequently incubated at two temperatures (27.6?C and 30.4?C) on the upper and lower boundaries of the sex determination threshold for this species. DDE, ranging from 3.3 to 66.5 pug, was dissolved in 5, 10, and 25 pl ethanol and applied to eggshells above the embryo. Less than 2.5 ng/g DDE was present in eggs prior to dosing. Approximately 34% of the applied DDE was absorbed in the eggs, but only approximately 8% of applied DDE was found in embryos. Thus, treated eggs, corrected for background DDE, had up to 543 ng/g DDE. The sex ratio at these doses did not differ from what would be expected on consideration of temperature alone. Incubation time, hatching success, incidence of body deformities, hatching size, and weight were also within the limits of healthy developed hatchlings. This indicates that the eggs of C. mydas in the wild with concentrations of DDE less than 543 ng/g should produce hatchlings with relatively high hatching success, survival rate, and normally differentiated gonads.

Turtle sex determination assay: Mass balance and responses to 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin and 3,3′,4,4′,5‐pentachlorobiphenyl

“…In this study, application of hydrophobic and extremely adsorptive compounds such as TCDD and PCB‐126 resulted in transfers of only a few percent of the chemical (4 and 10%, respectively), comparable with those of estradiol‐17β. Using ethanol as the carrier solvent, a much greater transfer efficiency for p,p ′‐dichlorodiphenyldichloroethylene of 34% was reported in a recent sexual differentiation study of green sea turtle eggs ( Chelonia mydas ) [19]. Though ethanol has previously been used as a carrier in studies with natural and synthetic estrogens and with hydroxy‐PCBs (with previously mentioned transfer efficiencies), acetone was selected as the carrier solvent for this work because of the limited solubility of the chemicals in ethanol.…”

“…Dosing solutions of TCDD (Don Tillitt, U.S. Geological Survey, Columbia, MO) and of PCB-126 (AccuStandard, New Haven, CT, USA) in acetone were made by solvent exchange and dilution of stock solutions prepared from neat materials dissolved in dichloromethane. Ethanol, used in previous studies [15,17,19], was not used as the carrier solvent in this study because of the limited solubilities of the two compounds at the desired dosing concentrations.…”

“…Developmental abnormalities have occurred in eggs and hatchlings of common snapping turtles ( Chelydra serpentina serpentina ) exposed via environmental PHH contamination [18]. However, another suspected hormonally active agent, p,p′ ‐dichlorodiphenyldichloroethylene, failed to influence the outcome of sexual differentiation in the green sea turtle ( Chelonia mydas ) [19].…”

Topical dose delivery in the reptilian egg treatment model

“…Muller et al [56] reported that 14 d after topical treatment, percentage transfer of topically applied DDE, dieldrin, and chlordane from a dimethyl sulfoxide carrier into the contents (albumin, yolk, and embryo) of American alligator eggs was very low (0.0–5.5%), highly variable, and did not correlate with applied dose. Podreka et al [57] treated green sea turtle eggs with various concentrations of DDE dissolved in 5, 10, or 20 μl of 95% ethanol and found that approximately 34% of the applied dose (regardless of concentration or volume) transferred into the total contents of the egg, with 8% found inside the embryo. These authors incubated eggs for 34 d, more than twice the incubation time used by Gale et al [53] or Muller et al [56], which may have allowed for greater chemical transfer over time.…”

Endocrine Disruption of Reproduction in Reptiles

“…Temperature, dosage, and the synergistic or additive activities of EDCs provide a complicated matrix of effects that makes comparisons across species difficult to predict. Milnes et al (2005) reported that no sex reversal could be demonstrated in response to p,p'-DDE treatment when eggs were incubated at 33 C (an all-male temperature) but almost complete sex reversal to females occurred at the intermediate temperature of 32 C. In contrast to the alligator, p,p'-DDE does not sex reverse embryos of the sea turtle Chelonia mydas (Podreka, Georges, Maher, & Limpus, 1998) but does sex reverse at least one species of freshwater turtle, the red-eared slider (Willingham & Crews, 1999), further complicating our understanding and highlighting a complex species diversity in response to p,p'-DDE exposure. Competitive binding assays have demonstrated partial binding of o,p'-DDE, p,p'-DDE, trans-nonachlor, p,p'-DDD and various PCBs with the alligator uterine ER (Vonier et al, 1996).…”