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Amy L. Reeder,¹ Marilyn O. Ruiz,² Allan Pessier,³ Lauren E. Brown,⁴ Jeffrey M. Levengood,⁵ Christopher A. Phillips,⁷ Matthew B. Wheeler,¹ Richard E. Warner,⁶ and Val R. Beasley⁵

¹Department of Animal Sciences, and ²Department of Veterinary Pathobiology, University of Illinois at Urbana-Champaign, Champaign, Illinois, USA; ³University of Illinois Zoological Pathology Program, Loyola University Medical Center, Maywood, Illinois, USA; ⁴Department of Biological Sciences, Illinois State University, Normal, Illinois, USA; ⁵Department of Veterinary Biosciences, and ⁶Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Champaign, Illinois, USA; ⁷Center for Biodiversity, Illinois Natural History Survey, Champaign, Illinois, USA

Abstract
Exposure to anthropogenic endocrine disruptors has been listed as one of several potential causes of amphibian declines in recent years. We examined gonads of 814 cricket frogs (Acris crepitans) collected in Illinois and deposited in museum collections to elucidate relationships between the decline of this species in Illinois and the spatial and temporal distribution of individuals with intersex gonads. Compared with the preorganochlorine era studied (1852-1929) , the percentage of intersex cricket frogs increased during the period of industrial growth and initial uses of polychlorinated biphenyls (PCBs) (1930-1945) , was highest during the greatest manufacture and use of p,p-dichlorodiphenyltrichloroethane (DDT) and PCBs (1946-1959) , began declining with the increase in public concern and environmental regulations that reduced and then prevented sales of DDT in the United States (1960-1979) , and continued to decline through the period of gradual reductions in environmental residues of organochlorine pesticides and PCBs in the midwestern United States (1980-2001) . The proportion of intersex individuals among those frogs was highest in the heavily industrialized and urbanized northeastern portion of Illinois, intermediate in the intensively farmed central and northwestern areas, and lowest in the less intensively managed and ecologically more diverse southern part of the state. Records of deposits of cricket frog specimens into museum collections indicate a marked reduction in numbers from northeastern Illinois in recent decades. These findings are consistent with the hypothesis that endocrine disruption contributed to the decline of cricket frogs in Illinois. Key words: Acris crepitans, amphibian, cricket frogs, endocrine disruption, environmental contaminants, Illinois, intersexuality. Environ Health Perspect 113:261-265 (2005) . doi:10.1289/ehp.7276 available via http://dx.doi.org/ [Online 7 December 2004]

Address correspondence to V.R. Beasley, Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, 2001 S. Lincoln Ave., Urbana, IL 61802 USA. Telephone: (217) 333-9360. Fax: (217) 244-1652. E-mail: val@uiuc.edu

We thank M. Post for technical assistance. We greatly appreciate the following individuals and their respective institutions for allowing us to examine cricket frogs in their natural history collections: H. Voris and A. Resetar, Field Museum of Natural History ; R. Axtell, Department of Biological Sciences, Southern Illinois University ; E. Moll, Department of Zoology, Eastern Illinois University ; R. Brandon, Department of Zoology, Southern Illinois University ; K. Cummings, Illinois Natural History Survey ; the Department of Biological Sciences, Illinois State University ; R.P. Reynolds and R. McDiarmid, National Museum of Natural History, Smithsonian Institution ; G. Thurow, Department of Biology, Western Illinois University ; J.R. Purdue and D. Bakken, Illinois State Museum ; G. Schneider, Museum of Zoology, University of Michigan ; R. Vasile, M. Hennen, and S. Sullivan, Chicago Academy of Sciences ; E. Censky, Carnegie Museum of Natural History ; J. Cadle, Academy of Natural Sciences ; and J.W. Wright, Natural History Museum of Los Angeles County.

Funding was provided by the John G. Shedd Aquarium through support from the Dr. Scholl Foundation.

The authors declare they have no competing financial interests.

Received 24 May 2004 ; accepted 7 December 2004.