Feather chemicals contain information about the major histocompatibility complex in a highly scented seabird

Mate choice informed by the immune genes of the Major Histocompatibility Complex (MHC) may provide fitness benefits including offspring with increased immunocompetence. Olfactory cues are considered the primary mechanism organisms use to evaluate the MHC of potential mates, yet this idea has received limited attention in birds. Motivated by a finding of MHC-dependent mate choice in the Leach’s storm-petrel (Oceanodroma leucorhoa), we examined whether the chemical profiles of this highly scented seabird contain information about MHC genes. Whereas previous studies in birds examined non-volatile compounds, we used gas chromatography-mass spectrometry to measure the volatile compounds emitted from feathers that potentially serve as olfactory infochemicals about MHC and coupled this with locus-specific genotyping of MHC IIB genes. We found that feather chemicals reflected individual MHC diversity through interactions with sex and breeding status. Furthermore, similarity in MHC genotype was correlated with similarity in chemical profiles within female-female and male-female dyads. We provide the first evidence that volatile chemicals from bird feathers can encode information about MHC. Our findings suggest that olfaction likely aids MHC-based mate choice in this species, and highlight a role for chemicals in mediating genetic mate choice in birds where this mode of communication has been largely overlooked.

Methods
We gathered blood samples and feather samples from 60 Leach’s storm-petrels (Oceanodroma leucorhoa) breeding on Bon Portage Island in Nova Scotia, Canada.

We extracted DNA from the blood samples and used PCR-based cloning and sequencing to determine the MHC class IIB genotypes of individuals.

We identified and quantified the volatile chemicals associated with the feather samples using headspace gas-chromatography mass-spectrometry to describe the chemical profiles of individuals.

We used the resulting data to test whether information about MHC genotype is reflected in the scent of Leach’s storm-petrel plumage.

Detailed methods about how the data were generated can be found in the corresponding publication.