House sparrow Passer domesticus survival is not associated with MHC-I diversity, but possibly with specific MHC-I alleles
Maria Karlsson, Julia Schroeder, Shinichi Nakagawa, Henrik G. Smith, Terry Burke, Helena Westerdahl
The MHC (Major Histocompatibility Complex) plays an important role in the immune system of vertebrates. MHC genes are extremely polymorphic and this variation is considered to be maintained by selection from pathogens. We investigate whether MHC diversity (number of different alleles per individual) affects the survival and recruitment of nestling house sparrows. We hypothesize that individuals with higher MHC diversity can recognize and combat a wider range of pathogens, and therefore are more likely to survive and recruit into the breeding population. Additionally, we hypothesize that specific MHC class I alleles (MHC-I) could be associated with survival and recruitment. We screened MHC-I genotypes in 518 house sparrow chicks hatched on Lundy Island but we found no evidence for a relationship between nestling survival, post-fledging survival or recruitment success with MHC diversity. Then we investigated effects of specific MHC-I alleles in 195 individuals from a single cohort. Twenty-one MHC-I alleles were tested for relationships with nestling survival, post-fledging survival and recruitment, and we detected associations with survival for three different alleles. This pattern was, however, not different to what would be expected from random, so we could not conclude that particular MHC-I alleles are associated with survival in house sparrows on Lundy Island. Nonetheless, one of these alleles (1105) showed both a tendency for a higher probability of surviving in nestlings, and a significant association with survival in fledglings. We envision that allele 1105 could be an interesting candidate gene for testing associations with survival in house sparrows in the future.