Pathogen growth rate
At the time of collection in early hibernation, 88.89% (n=40) of individuals from Persisting 1 (Cold + Dry) had detectable P. destructans from swab samples, as did 97.78% (n=44) from Persisting 2 (Cold + Wet). All cages in each site had at least one infected bat at the beginning of the experiment. Additionally, at the time of collection, bats captured in Persisting 1 (Cold + Wet) had higher pathogen loads than bats that originated in Persisting 2 (Cold + Dry) (generalized linear model with gamma error distribution and log link function: β = 1.371 ± 0.428 SE, p = 0.002; Supplemental Fig. 3).
Over the course of the experiment, the highest on-host pathogen growth rates were recorded in the previously extirpated site (Warm + Wet), which was at least 4° C warmer than either of the two persisting sites, on average. Pathogen growth rates in Persisting 2 (Cold + Wet) were slightly higher than in Persisting 1 (Cold + Dry), likely attributable to the 1° C warmer and more humid conditions in the former. We also detected an interactive effect of origin site (the site from which bats were collected at the beginning of the experiment) and translocation site on the pathogen growth rate, such that within the previously extirpated site (Warm + Wet), bats originating in Persisting 2 (Cold + Wet) had lower pathogen growth rates than bats that originated in Persisting 1 (Cold + Dry) (Fig. 2; Supplemental Table 1). Correspondingly, we detected an interactive effect of average roosting temperature and origin site on pathogen growth rate (Fig. 2; Supplemental Table 2). Across all bats, the pathogen growth rate increased with average roosting temperature, consistent with the sensitivity of P. destructans to ambient thermal conditions24,66. However, due to the effect of origin site, the estimated relationship between average roosting temperature and pathogen growth rate was positive for bats that originated in Persisting 1 (Cold + Dry) but did not increase for bats that originated in Persisting 2 (Cold + Wet) (Fig. 2). Interestingly, we observed a decrease in pathogen loads on five bats in Persisting 1 (Cold + Dry), four in Persisting 2 (Cold + Wet), and one in Extirpated (Warm + Wet).