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
microbial taxa that best reflect MHC genotype, and another set of taxa
that best predict preen oil chemical composition. The relative strengths
of relationships between MHC and microbes, microbes and preen oil, and MHC
and preen oil suggest that MHC may affect host odour both directly and
indirectly. Thus, birds may assess MHC genotypes based on both
host-associated and microbially-mediated odours.