Results
The laboratory experiment revealed that geographic distance between the
host and Bd collection locations, a metric for host-pathogen novelty
(hereafter, distance), was negatively associated with host mortality
(β = -0.06, SE = ±0.03, z = -2.10, p = 0.04; Figure
2A & Table S3), Bd prevalence (β = -0.53, SE = ±0.23, z =
-2.33, p = 0.02, Table S5), and pathogen abundance on the host
(β = -0.03, SE = ±0.02, z = -2.01, p <
0.05, Figure S1 & Table S4). Distance was also negatively associated
with host mortality in the global-scale meta-analysis (while accounting
for among-study variance, Bd strain, and host taxonomic group; β= -0.77, SE = ±0.25, t = -3.05, p < 0.01;
Figures 2B & Table S4).
While local host-pathogen interactions generally result in worse
outcomes for hosts, there was substantial variation among host-pathogen
outcomes. We found significant variation in mortality, infection
success, and pathogen load among Bd strains (main effect of strain
identity on mortality: χ2 = 61.05, p< 0.001; prevalence: χ2 = 56.98, p< 0.001; pathogen load: χ2 = 351.65,p < 0.001; Figure 3 & S2). Specifically, when
averaging across host species, Bd from Louisiana was most deadly, most
likely to cause infection, and produced the highest infection burdens
(Figure 3 & S2). We also found significant variation in mortality,
prevalence, and pathogen load among host species (main effect of host on
mortality: χ2 = 136.22, p < 0.001;
prevalence: χ2 = 9.95, p = 0.04; and pathogen
load = χ2 = 12.36, p = 0.01; Figures 3 & S2).
Specifically, when averaging across Bd strains, toads from Arizona and
Tennessee had the highest mortality and infection prevalence (Figure
S2). Consistent with the experimental results, in the meta-analysis, we
found significant variation in mortality among taxonomic groups with
Bufonoidea species being especially susceptible to Bd-induced mortality
(χ2 = 29.92, p < 0.001; Figure 3).
Importantly, we compared fits of all models from the experiment with and
without the inclusion of a two-way interaction between host and Bd
identity and determined that models without the interaction fit better
and thus did not include the interaction term in any model (ΔAIC
>7). This means that the main effects of host and Bd strain
are more important than any potentially idiosyncratic interactions
between these two factors. Finally, our log-likelihood ratio test of
proportional hazard model fits from the laboratory experiment revealed
that host species accounted for the most variation in the model
(χ2 = 140.91, df = 4, p <
0.001), followed by Bd strain (χ2 = 60.22, df =
5, p < 0.001) and distance (χ2 =
4.19, df = 1, p = 0.0406).