PARENT SESSION
Oral Session #36: Conservation of aquatic systems: Ecology and ecotoxicology. Presiding: R. Lathrop.
Tuesday, August 7, 2001. 1:00 PM to 5:15 PM. Hall of Ideas H.
A test for the effect of contaminants on the sexual development of free-living leopard frogs .
Edblom, Tara1, Karasov, William1, 1
ABSTRACT- The Green Bay and Fox River ecosystem in Wisconsin is polluted with polychlorinated biphenyls, heavy metals including mercury, lead, and cadmium and over 100 other organic contaminants. Many of these contaminants, including some PCBs, are putative endocrine disrupters that may affect sex determination and cause reproductive dysfunction in wildlife. We raised northern leopard frogs (Rana pipiens) in enclosures at field sites and evaluated their sexual development using histological (incidence of intersex individuals and percent males) and functional (serum vitellogenin) biomarkers. Among the sites, contaminants in sediments ranged for polychlorinated biphenyls from <0.025 to 3.7 mg/kg dry mass, for mercury from 0.029 to 0.84 mg/kg dry mass, and for cadmium from <0.4 to 1.2 mg/kg dry mass. Endpoints were measured in froglets at metamorphosis and 30-days post-metamorphosis. We did not observe any intersex froglets, but there was a strong trend for a difference in percent males among sites (F2,20 = 3.39; p = 0.054). A contaminated site had more males (69%) than did two reference sites (48.3 and 46.9%). The mean percent males for all egg clutches used (n=10) was 50.9%. An enzyme-linked immunosorbent assay was used to quantify vitellogenin in sera of 30-day post-metamorphic froglets. Vitellogenin was not detected in froglets from any site. Our results suggest that leopard frogs living at relatively more contaminated sites in this ecosystem may be subject to disruption in normal patterns of sexual development.
KEY WORDS: northern leopard frog, contaminants, sex ratio, vitellogenin