Global Bd Meta-analysis
We conducted a meta-analysis to standardize and compare results across multiple experiments to draw broadly applicable conclusions regarding the effects of distance and host taxa on the outcomes of Bd infections. We used a subset of the data published in Sauer et al.(Sauer et al. 2020), restricting the database to metamorphic/juvenile amphibians for consistency. This refined database included 23 amphibian species from 7 families and 22 Bd strains (Database S1). Host species and strains were collected from North and Central America and Europe (See Supplemental Information for more details regarding data collection). The final database consists of 84 effect sizes from 26 Bd studies.
We analyzed the database using a mixed-effects meta-analysis to determine the effect of distance (log-linear Euclidean distance between the collection location of the host and Bd strain; log10(km)) and host taxonomic group (superfamily, four-level categorical variable) on host mortality (blme package) (Chunget al. 2013). Mortality was measured using log odds ratios from Sauer et al . (2020) (where a log odds ratio significantly greater than zero represents greater mortality in the Bd-exposed than control group). We controlled for log10-transformed Bd zoospore dose by including it as a fixed effect and accounted for between-study random effects as well as non-independence among Bd strains by including Bd strain and host species as random intercepts in our models. For the full list of host species included in the meta-analysis, and more details regarding effect sizes, see Supplemental Methods and Table S5 for summary information. Model prediction plots were made using the predict function and the original conditions of the datasets.