Sex differences in the gut microbiota of healthy mice. (A) Observed species. (B) Shannon index. (C) The percentages of the microbial composition at the phylum level. (D) Classification based on PCA using the gut microbiome at the phylum level. (E) Classification based on PCA using the gut microbiome at the genus level. (F) Relative abundance of the microbial composition at the genus level. Pairwise comparisons were analyzed using Student's t test with a Bonferroni adjustment. M, male; F, female. Significance level: *, P < 0.05; **, P < 0.01; ***, P < 0.001.