A gull species recognizes mhc-ii diversity and dissimilarity using odor cues

The major histocompatibility complex (MHC) plays a crucial role in resistance to parasite, and is thus often suggested to be an important force driving social interactions, including mating preference, in vertebrates. However, the phenotypic cues used by individuals to assess the MHC characteristics of conspecifics is generally unknown. Here we used behavioral tests to investigate whether, in black-legged kittiwakes, females use odor cues to distinguish male MHC-II diversity and MHC-II dissimilarity. We found that females took less time to peck at the odor sample when it came from a male with high MHC-II dissimilarity. They also took less time to peck at an odor sample coming from a male with high or low MHC-II diversity compared to intermediate MHC-II diversity. However, this result is due to the single individual who has only one MHC-II allele. When excluding this individual, females took less time to peck at an odor sample coming from a male with high MHC-II diversity. Altogether, our study adds evidence for olfactory recognition of MHC characteristics in birds, but further studies are required to determine whether kittiwakes use this ability to optimize fitness