The proposed research investigates how disease emerges in populations of salamanders in Arizona, is transmitted among individuals in populations, spreads across populations in a region, and finally, via natural selection, may alter salamander life history. Three hypotheses will be tested. Within a habitat, animals, soil, or water harbor viruses and environmental changes initiate infections by stimulating pathogen growth or weakening host salamanders. Alternatively, salamanders in a habitat are susceptible and disease is introduced from elsewhere. Experiments and field observations will evaluate the roles of salamanders, invertebrates, cows, birds, or humans as possible reservoirs of disease or vectors dispersing virus. Finally, disease selects against cannibalism, accounting for regional variation in salamander life history. The virus-vector-tiger salamander system is ideal for testing models in disease ecology. Arizona populations are well-studied, the principal viral pathogen is known, infections are frequent, and all habitats for one endangered subspecies where disease is common can be sampled. In the last fifteen years some species of amphibians have declined steadily, even to extinction, and pathogens are a possible cause. This research will advance our understanding of pathogens as a factor in amphibian declines; a key example of the general loss of biodiversity. Proposed experiments and observations incorporate experts in ecology, evolution, pathology, virology, and molecular genetics. Vertically-integrated field and laboratory experiments will untangle complex interactions from molecular genetics to population biology to test general models of disease ecology.
