Experimental evidence that host species composition alters host-pathogen dynamics in a ranavirus-amphibian assemblage

Losses in biodiversity can alter disease risk through changes in host species composition. Host species vary in pathogen susceptibility and competence. Yet how changes in diversity alter host-pathogen dynamics remains unclear in many systems, particularly with respect to generalist pathogens. Amphibians are experiencing worldwide population declines linked to generalist pathogens, such as ranavirus, and thus represent an ideal group to investigate how host species composition affects disease risk. We conducted experiments where individuals in the laboratory and assemblages of three amphibian species (Pacific tree frogs, Pseudacris regilla; Cascades frogs, Rana cascadae; and Western toads, Anaxyrus boreas) or just A. boreas alone in outdoor mesocosms were exposed to ranavirus as larvae. In laboratory experiment, we observed low survival and high viral loads in P. regilla compared to the other species suggesting that this species was highly susceptible to the pathogen. In the mesocosm exp...