Bacterial composition was significantly influenced by host
species, with subtler inter-island differences more pronounced in island
spotted skunks compared to island foxes
Both Bray-Curtis Dissimilarity and the Jaccard Index were significantly
predicted by species, island, their interaction, and sequencing plate
(adonis: Table 1). Across both beta diversity measures, species
explained the largest proportion of the variance in the dataset, with
24.0% for Bray-Curtis and 19.1% for Jaccard. Principal coordinate
plots mirrored this result (Figure 3 A-B), with separation by species
clearly evident along PC1, which explained 24.70% of the variation for
Bray-Curtis and 20.49% of the variation for Jaccard. Further
examination Bray-Curtis Dissimilarity revealed separation between foxes
by an unknown variable along PC2 (which explained 6.388% of the
variation) and between skunks by island along PC3 (which explained
6.188% of the variation; Figure S2). Using Jaccard Distances, we
observed separation between skunks by island along PC2 (which explained
5.985% of the variation) and between sequencing plates along PC3 (which
explained 4.176% of the variation; Figure S2).
Given the strong influence of species on bacterial community structure,
we created subsets of the data by species to look for finer-scale
intraspecific differentiation between island populations. Within island
spotted skunks (Figure 3 C-D), bacterial abundance and presence were
significantly predicted by island (adonis: Bray-Curtis, F =10.936,R2 =0.159, df =1, p= 0.001; Jaccard,F =10.386, R2 =0.146, df =1,p= 0.001) and sequencing plate (adonis: Bray-Curtis,F =2.967, R2 =0.086, df =2,p= 0.001; Jaccard, F =4.460,R2 =0.125, df =2, p= 0.001). We
observed similar patterns in island foxes (Figure 3 E-F), although
island (adonis: Bray-Curtis, F =3.625,R2 = 0.063, df =1, p= 0.001;
Jaccard, F =3.379, R2 =0.056, df =1,p= 0.001) and sequencing plate (adonis: Bray-Curtis,F =1.934, R2 =0.067, df =2,p= 0.002; Jaccard, F =3.254,R2 =0.109, df =2, p= 0.001)
explained lower proportions of variation.