Persistence of mountain yellow-legged frog populations infected with the amphibian chytrid fungus

Background/Question/Methods
Chytridiomycosis, caused by the fugal pathogen, Batrachochytrium dendrobatidis (Bd) has been called the "worst infectious disease ever recorded among vertebrates" because of its broad species range and the severe impacts it has had on amphibians, in many cases leading to population extinctions. Since it was first identified in the late 1990’s, Bd has been found in virtually every region where researchers have searched and has been implicated in dramatic declines in amphibian populations. In California's Sierra Nevada we have documented numerous cases of extinctions of local populations of frogs in the mountain yellow-legged frog species complex (Rana muscosa and Rana sierrae). In some areas, however, mountain yellow-legged frog populations are apparently persisting despite the presence of Bd. Here we present the results of a four-year mark-recapture study of R. sierrae in Bd-infected, but persistent, populations.

Results/Conclusions
We show that adult frogs at these sites are surviving within and between years, despite being infected with the fungus. Adults at these persistent sites have relatively low fungal loads, and individuals are losing and gaining the infection through time. We discuss the implications of these results in terms of host-pathogen models.