Estrogenic exposure affects metamorphosis and alters ...



Title Estrogenic exposure affects metamorphosis and alters sex ratios in the northern leopard frog (Rana pipiens): Identifying critically vulnerable periods of development
Author(s) Natacha S. Hogan, Paula Duarte, Michael G. Wade, David R. S. Lean, Vance L. Trudeau
Journal General and Comparative Endocrinology
Date 2008
Volume 156
Issue 3
Start page 515
End page 523
Abstract During the transformation from larval tadpole to juvenile frog, there are critical periods of metamorphic development and sex differentiation that may be particularly sensitive to endocrine disruption. The aim of the present study was to identify sensitive developmental periods for estrogenic endocrine disruption in the northern leopard frog (Rana pipiens) using shirt, targeted exposures to the synthetic estrogen ethinylestradiol (EE2). Post-hatch tadpoles (Gosner stage 27) were exposed over five distinct periods of metamorphosis: early (stage 27-30), mid (stage 30-36), early and mid (stage 27-36), late (stage 3642), and the entire metamorphic period (chronic; stage 27-42). For each period, animals were sampled immediately following the EE2 exposure and at metamorphic climax (stage 42). The effects of EE2 on metamorphic development and sex differentiation were assessed through measures of length, weight, developmental stage, days to metamorphosis, sex ratios and incidence of gonadal intersex. Our results show that tadpoles exposed to EE2 during mid-metamorphosis were developmentally delayed immediately following exposure and took 2 weeks longer to reach metamorphic climax. In the unexposed groups, there was low proportion (0.15) of intersex tadpoles at stage 30 and gonads appeared to be morphologically distinct (male and female) in all individuals by stage 36. Tadpoles exposed early in development displayed a strong female-biased sex ratio compared to the controls. Moreover, these effects were also seen at metamorphic climax, approximately 2-3 months after the exposure period, demonstrating that transient early life-stage exposure to estrogen can induce effects on the reproductive organs that persist into the beginning of adult life-stages. (c) 2008 Elsevier Inc. All rights reserved.
DOI 10.1016/j.ygcen.2008.03.011 ER

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