| Agriculture Alters Gonadal Form and Function in the Toad Bufo marinus Krista A. McCoy,1,2 Lauriel J. Bortnick,2 Chelsey M. Campbell,2 Heather J. Hamlin,2 Louis J. Guillette Jr.,1,2 and Colette M. St. Mary1,2 1School of Natural Resources and Environment, and 2Department of Zoology, University of Florida, Gainesville, Florida, USA Abstract
Background: Many agricultural contaminants disrupt endocrine systems of wildlife. However, evidence of endocrine disruption in wild amphibians living in agricultural areas has been controversial. Typically, studies on the effects of pollutants on wildlife attempt to compare polluted with unpolluted sites. Objectives: We took a novel approach to address this question by explicitly quantifying the relationship between gonadal abnormalities and habitats characterized by differing degrees of agricultural activity. Methods: We quantified the occurrence of gonadal abnormalities and measures of gonadal function in at least 20 giant toads (Bufo marinus) from each of five sites that occur along a gradient of increasing agricultural land use from 0 to 97%. Results: The number of abnormalities and frequency of intersex gonads increased with agriculture in a dose-dependent fashion. These gonadal abnormalities were associated with altered gonadal function. Testosterone, but not 17β-estradiol, concentrations were altered and secondary sexual traits were either feminized (increased skin mottling) or demasculinized (reduced forearm width and nuptial pad number) in intersex toads. Based on the end points we examined, female morphology and physiology did not differ across sites. However, males from agricultural areas had hormone concentrations and secondary sexual traits that were intermediate between intersex toads and nonagricultural male toads. Skin coloration at the most agricultural site was not sexually dimorphic ; males had female coloration. Conclusions: Steroid hormone concentrations and secondary sexual traits correlate with reproductive activity and success, so affected toads likely have reduced reproductive success. These reproductive abnormalities could certainly contribute to amphibian population declines occurring in areas exposed to agricultural contaminants. Key words: amphibians, endocrine disruption, intersex, pesticides, secondary sexual traits. Environ Health Perspect 116:1526–1532 (2008) . doi:10.1289/ehp.11536 available via http://dx.doi.org/ [Online 3 July 2008]
Address correspondence to K.A. McCoy, Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002 USA. Telephone: 507-6-461-0821. E-mail: kristam@bu.edu We thank M. McCoy, L. Babonis, and R. Harris for constructive feedback on the manuscript and A. Amick, P. Barnes Jr., M. Fromowitz, M. McCoy, M. Rehrer, V. Bender, K. Hopkins, and H. Wineman for help with field collections. This work was supported in part by grants from the National Institute of Environmental Health Sciences (R21 ES014053) to L.J.G. and the Rewald, Olowo, Society for Integrative and Comparative Biology, and Sigma Xi grants in aid of research and the University of Florida Institute of Food and Agricultural Sciences Women's Club Fellowship to K.A.M. The funding sources had no influence in the study design ; collection, analysis, interpretation of data ; or writing of the paper. The authors declare they have no competing financial interests. Received 3 April 2008 ; accepted 3 July 2008.
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