The deadly amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), first appeared in the Sierra Nevada 30-50 years ago. Since then, it has invaded populations of the mountain yellow legged frogs Rana muscosa and Rana sierrae in a wave from west to east, leaving local extinction in its wake. Scattered populations of Rana sierrae survived, however, and persist with infection despite declines due to the disease. Now these populations are giving us clues to how a susceptible species of amphibians can survive a devastating disease, and we are using these clues to inform direct conservation actions and interventions that we hope will allow these endangered species to survive and rebound.
Results/Conclusions
Here we present evidence from two laboratory experiments that the mountain yellow legged frogs have a robust adaptive immune response to Bd that decays with time, but confers long-term protection to disease despite infection. We discuss the age-specific immune response to Bd, and compare experimental outcomes to individual frog disease data from natural populations—both those that have persisted with Bd, and those that have been extirpated. Finally, we use our time-series data to parameterize an existing model to demonstrate how the individual dynamics of immunity in mountain yellow legged frogs can drive population-level persistence or die-off from Bd.