UC Berkeley

The fungal pathogen Batrachochytrium dendrobatidis, or Bd, has been a major driver of amphibian extinctions world wide. This dissertation investigates the effects of Bd on the mountain yellow legged frogs, Rana muscosa and Rana sierrae. These two species occur in the Sierra Nevada in California, and have under gone dramatic declines in part due to the invasion of Bd. Even before the invasion of Bd, populations of Rana muscosa/sierrae have faced habitat loss and fragmentation from introduced predators and habitat fragmentation. The fist chapter of this dissertation investigates how genetic diversity effects $R_0$, the threshold for invasion of a pathogen. I model the case where a naive population faces multiple disease, as well as a single population faced with invasion of a single disease. I also model the effect of overdominance and genetic diversity on R_0. In my second chapter, I use both models and simulations to investigate how genetic diversity effects the final size of an epidemic, and whether or not populations with higher genetic diversity maintain that diversity after an epidemic. In my third chapter, I present data on a series of experiments on how variation in the external source of Bd, or zoospore pool, affects the growth rate of Bd on its amphibian host, as well as host mortality. In my final chapter, I use microsatellite markers to measure genetic diversity in serveral populations of Rana muscosa and Rana sierrae, and test whether or not these populations have experienced historic bottlenecks.