16S V4 raw read count data; 16S reads metadata; new MHC class II allele sequences

Pathogen-mediated selection at the major histocompatibility complex (MHC) is thought to promote MHC-based mate choice in vertebrates. Mounting evidence implicates odour in conveying MHC genotype, but the underlying mechanisms remain uncertain. MHC effects on odour may be mediated by odour-producing symbiotic microbes whose community structure is shaped by MHC genotype. In birds, preen oil is the primary source of body odour and similarity at MHC predicts similarity in preen oil composition. Hypothesizing that this relationship is mediated by symbiotic microbes, we characterized MHC genotype, preen gland microbial communities, and preen oil chemistry of song sparrows (Melospiza melodia). Consistent with the microbial mediation hypothesis, pairwise similarity at MHC predicted similarity in preen gland microbiota. Overall microbial similarity did not predict chemical similarity of preen oil, counter to this hypothesis. However, permutation testing identified a maximally predictive set of m...