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Endocrine Disruption in Amphibians : Developmental Effects of Ethynylestradiol and Clotrimazole on the Reproductive System

Amphibian populations are declining world-wide and one of the suggested reasons is environmental pollutants. Studies of long-term effects on the reproductive system in frogs following larval exposure to environmental pollutants are scarce. It is therefore important to develop methods to study developmental reproductive toxicity in amphibians. In this thesis the usefulness of Xenopus tropicalis (the West African clawed frog) as a model species for a test system was investigated. Effects on the reproductive system after larval exposure to the pharmaceuticals ethynylestradiol (EE2) and clotrimazole were evaluated. The susceptibility to EE2 exposure was compared between the model species and a wild species, the European common frog (Rana temporaria). Larval exposure to EE2 caused female-biased sex ratios in both examined frog species, indicating male-to-female sex-reversal. In adult Xenopus tropicalis, male frogs that were not sex-reversed had reduced fertility and decreased amount of mature spermatozoa in the seminiferous tubules. The proportion of frogs with ovaries but lacking oviducts increased with increasing EE2-concentrations. A female frog without oviducts is sterile. The development of ovaries in sex-reversed male frogs was implied to be similar to control females. The combination of a reduced number of males, due to sex-reversal, and impaired fertility could have severe effects on frog populations. Larval exposure to clotrimazole modulated aromatase activity in gonads and brain in Xenopus tropicalis. Brain aromatase activity was decreased at the time for gonadal differentiation and gonadal aromatase activity was increased at metamorphosis. The findings in this thesis indicate that reproduction in wild frogs might be impaired by estrogenic compounds in the environment. The results combined with the short generation time supports the use of Xenopus tropicalis as a model species when evaluating long term effects of endocrine disruptors on the reproductive system in amphibians.

Identiferoai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-9209
Date January 2008
CreatorsGyllenhammar, Irina
PublisherUppsala universitet, Ekotoxikologi, Uppsala : Acta Universitatis Upsaliensis
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text
Formatapplication/pdf
Rightsinfo:eu-repo/semantics/openAccess
RelationDigital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 545

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