Using environmental DNA for early detection of amphibian chytrid fungus Batrachochytrium dendrobatidis prior to a ranid die-off

Amphibian chytridiomycosis caused by the fungus Batrachochytrium dendrobatidis (Bd) is an emerging infectious disease that has been associated with mass mortality and extinctions of amphibians worldwide. Environmental DNA (eDNA) techniques have been used to detect the presence of Bd in the environment, but not to detect Bd prior to an amphibian die-off. We collected eDNA using filtered water samples from 13 lakes across Sequoia Kings Canyon National Park. Seven of those sites had populations of mountain yellow-legged frogs, an amphibian highly susceptible to chytridiomycosis, and 3 of those populations experienced a Bd related die-off 1 mo post-eDNA sampling. We detected Bd in eDNA samples that were collected 1 mo prior to the observed Bd-caused die-off at all 3 sites affected by Bd, and we did not detect Bd at the other sites where no die-off was observed. Our study indicates the potential to use eDNA techniques for early detection of Bd in the environment.