New diseases are emerging at an increasing rate, and in numerous cases are having devastating effects on wildlife species. The amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) causes the disease chytridiomycosis that since its emergence has resulted in the extinction or serious decline of hundreds of amphibian species worldwide. In California?s Sierra Nevada, chytridiomycosis has caused the near-extinction of the once-common mountain yellow-legged frog. During summer 2012, the largest remaining mountain yellow-legged frog population will suffer a die-off event caused by the recent arrival of Bd in the area. In mountain yellow-legged frog populations the arrival of Bd in a previously uninfected population typically results in frog population extinction, and the goal of the proposed study is to change the outcome to long-term frog population persistence. This disease intervention will take the form of a field experiment implemented during the Bd-caused frog die-off. In this experiment the effectiveness of two treatments, (1) an antifungal drug, and (2) the augmentation of antifungal bacteria that occur naturally on frog skin, will be assessed at the scale of an entire frog population. This experiment will also provide an opportunity to describe the mechanisms underlying treatment effectiveness, including the role of the frog immune system, the microbial community present on the skin of frogs, and rapid evolution in frogs. Based on results from previous laboratory and small-scale field trials it is expected that antifungal drug and bacterial augmentation treatments will increase frog survival relative to frogs that are left untreated. Results from the proposed study will have important implications for conservation efforts aimed at wildlife species worldwide that are threatened by emerging diseases (e.g., amphibians, bats, apes). The study will also provide training opportunities for undergraduate and graduate students, with every effort made to include those from underrepresented groups to the maximum extent possible.
Amphibians around the world are disappearing at an alarming rate. Many recent declines have been caused by a deadly chytrid fungus called Batrachochytrium dendrobatidis (Bd). Bd has recently spread around the world and currently infects hundreds of amphibian species. In the Sierra Nevada Mountains of California, Bd has had a devastating effect on the mountain yellow-legged frog (Rana muscosa and Rana sierrae). Hundreds of mountain yellow-legged frog populations have already disappeared and many of the last remaining populations are threatened. The major goals of this project were to determine whether 1) mountain yellow-legged frogs have an immune response that could protect them from Bd and 2) interventions could be used to save the remaining frog populations once they are infected with Bd. Results suggest that these susceptible frogs do not have a robust immune response against Bd. In addition, thus far there is no evidence that the two different intervention options considered (treatment with an antifungal drug and augmentation of a bacterial species that produces a natural anti-fungal) can protect populations from extinction. The findings help explain why mountain yellow-legged frogs are highly susceptible to Bd. Further these results underscore the importance of coordinated monitoring efforts to track emerging infectious diseases and measures to preventing the invasion of pathogens to new geographic regions where wildlife are highly vulnerable. In addition to scientific research, this project also provided education about biodiversity and conservation to local public elementary school children through an outreach event called "Save the Frogs Day".
