1. Environmental Studies Program, San Francisco State University, 1600 Holloway Avenue, San Francisco CA 94132, Section of Evolution and Ecology, and Center for Population Biology, University of California, Davis, California 95616, Office of Laboratory Animal Care, Northwest Animal Facility, University of California, Berkeley, California 94720-7150, Departments of Microbiology and Immunology and of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, Department of Biochemistry,...