Study system and field sampling
The focal species for this study is Thoropa taophora, a
cycloramphid frog with a unique tolerance for coastal habitat that
allows a wide distribution across the coastal Atlantic Forest of São
Paulo State (36). Adult T. taophora frogs (n=175 total) were
sampled from each of ten study populations: seven island populations and
three coastal mainland populations (Fig. 1, Table 1). Genetic diversity
is lower in island T. taophora populations relative to coastal
mainland populations, both at neutral (microsatellite) loci (35) as well
as at the MHC IIB immunogenetic locus (17). To examine how host genetics
impact skin microbiome diversity, skin swab samples were taken from the
same individuals that were previously genotyped at MHC IIB (see Belasen
et al. 2019). Frogs were thoroughly washed with sterile (autoclaved)
distilled water and then swabbed on the ventral surface using standard
protocols that minimize cross-contamination (37). DNA was extracted from
swabs using a Qiagen DNeasy Blood and Tissue kit.