Data from: Effectiveness of antifungal treatments during chytridiomycosis epizootics in populations of an endangered frog

The recently-emerged amphibian chytrid fungus Batrachochytrium
dendrobatidis (Bd) has had an unprecedented impact on global amphibian
populations, and highlights the urgent need to develop effective
mitigation strategies. We conducted in-situ antifungal treatment
experiments in wild populations of the endangered mountain yellow-legged
frog during or immediately after Bd-caused mass die-off events. The
objective of treatments was to reduce Bd infection intensity
("load") and in doing so alter frog-Bd dynamics and increase the
probability of frog population persistence despite ongoing Bd infection.
Experiments included treatment of early life stages (tadpoles and
subadults) with the antifungal drug itraconazole, treatment of adults with
itraconazole, and augmentation of the skin microbiome of subadults with
Janthinobacterium lividum, a commensal bacterium with antifungal
properties. All itraconazole treatments caused immediate reductions in Bd
load, and produced longer-term effects that differed between life stages.
In experiments focused on early life stages, Bd load was reduced in the
two months immediately following treatment and was associated with
increased survival of subadults. However, Bd load and frog survival
returned to pre-treatment levels in less than one year, and treatment had
no effect on population persistence. In adults, treatment reduced Bd load
and increased frog survival over the entire three-year post-treatment
period, consistent with frogs having developed an effective adaptive
immune response against Bd. Despite this protracted period of reduced
impacts of Bd on adults, recruitment into the adult population was limited
and the population eventually declined to near-extirpation. In the
microbiome augmentation experiment, exposure of subadults to a solution of
J. lividum increased concentrations of this potentially protective
bacterium on frogs. However, concentrations declined to baseline levels
within one month and did not have a protective effect against Bd
infection. Collectively, these results indicate that our mitigation
efforts were ineffective in causing long-term changes in frog-Bd dynamics
and increasing population persistence, due largely to the inability of
early life stages to mount an effective immune response against Bd. This
results in repeated recruitment failure and a low probability of
population persistence in the face of ongoing Bd infection.