| Endocrine disruptors are exogenous chemicals proposed to mediate actions of endogenous hormones. Studies in this dissertation address the identification of appropriate physiological endpoints for assessing endocrine disruptor effects in anurans. In vivo assays were used to address species-specificity at physiological endpoints,; The African reed frog, Hyperolius argus displays estrogen-dependent secondary sex coloration, and the pesticide, o,p′DDT, mimics estrogen effects. In chapter two, I compared the effects of o,p ′DDT and five other DDT congeners to the effects of estradiol (E2) using in vivo color changes in juvenile H. argus. Ortho-para DDT congeners (o,p′DDT, o,p′DDE and o,p′DDD) and E 2 prematurely induced adult female coloration patterns in juveniles. Hence, the H. argus color induction assay has potential to detect xenobiotic estrogens, and represents the first assessment of non-steroidal chemical effects in this species.; In chapter three, I evaluated the feasibility of using color morphology in H. argus as tool for identifying estrogenic compounds. In a double-blind survey, scientists and volunteers consistently differentiated E2-treated from non-E2 treated H. argus.; In chapter four, I used H. argus to evaluate estrogenicity in plant-derived compounds. Chapter four represents the first assessment of phytoestrogen effects in amphibians. Relative activities of equol, formononetin and daidzein were one to three orders of magnitude lower than E2-activity. Genistein naringenin, quercetin, biochanin A showed activity close to or below detection limits. The low phytoestrogen activities observed here were largely consistent with previously relative activities reported in mammalian studies.; Larval estrogen exposure in the African clawed frog Xenopus laevis produces female gonadal morphology. In chapter five, gonadal differentiation was used as a physiological endpoint to compare effects of o,p′ DDT and its non-estrogenic congener (p,p′DDT) to effects of E2. In vivo larval exposure to a thousand-fold range of o,p′DDT and p,p′ DDT doses did not affect sex ratios.; In chapter six, I evaluated the laryngeal morphology of metamorphic Pacific tree frogs (Hyla regilla) as a physiological endpoint to test larval androgen exposure. Chapter six represents the first characterization of laryngeal morphology in H. regilla. Larynges were not sexually dimorphic at metamorphosis. Exposure to DHT increased arytenoid cartilage size but did not affect muscle (dilator laryngis or constrictor laryngis) morphology. |
