Statistical analysis
To correct the differences in the number of reads, all samples were subsampled to the level of the smallest number of reads found in the samples. Bray-Curtis dissimilarities between all sample pairs were calculated using a Hellinger-transformed ASVs abundance matrix, and visualized using non-metric multidimensional scaling (NMDS). A nonparametric multivariate test (Permutational Multivariate Analysis of Variance, which is called ‘PERMANOVA’) was used to test for differences in bacterial community structure between the two groups of the muskox using PRIMER 6 and PERMANOVA+ (Clarke & Tobutt., 2003).
Age group (fixed with two levels; adult and calf) was considered as a fixed component, and p-values were obtained using 999 permutations. We used the 3 indices to estimate the bacterial diversity and compared the diversity values between two groups of the muskox by age with t test and Fligner-Killeen test. Rarefaction curve, stable isotopes analysis results were generated using R packages (version 4.0.5, http://www.R-project.org).
Bacterial functional abundances were inferred using PICRUSt2 v.2.3.0b (Douglas et al., 2020), and the predicted microbial functions (KEGG orthologs) were visualized with Principal Coordinates Analysis (PCoA) plot.