1. Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California-Davis, Davis, California 95616, USA
2. U.S. Geological Survey, Riverside, California 92507, USA
3. Department of Biology and Laboratory of Biomedical and Environmental Sciences, University of California-Los Angeles, Los Angeles, California 90024, USA
4. Present address: Division of Botany and Zoology, Australian National University, Canberra ACT 0200, Australia
5. Present address: Smithsonian Institution, National Zoological Park, Department of Zoological Research, 3001 Connecticut Ave., Washington, D.C. 20008, USA
6. Present address: Department of Zoology, Oklahoma State University, Stillwater, Oklahoma 74078, USA