Variation in MHC genotypes in two populations of house sparrow (Passer domesticus) with different population histories


  • Funded by the Functional Genomics programme of the Norwegian Research Council, grant no. 191847/V40 from the Norwegian Research Council, and Centre for Conservation Biology, Norwegian University of Science and Technology.

Åsa Alexandra Borg, Centre for Conservation Biology, Department of Biology, Realfagbygget, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. Tel: +47 73596285; Fax: +47 73596100; E-mail:


Small populations are likely to have a low genetic ability for disease resistance due to loss of genetic variation through inbreeding and genetic drift. In vertebrates, the highest genetic diversity of the immune system is located at genes within the major histocompatibility complex (MHC). Interestingly, parasite-mediated selection is thought to potentially maintain variation at MHC loci even in populations that are monomorphic at other loci. Therefore, general loss of genetic variation in the genome may not necessarily be associated with low variation at MHC loci. We evaluated inter- and intrapopulation variation in MHC genotypes between an inbred (Aldra) and a relatively outbred population (Hestmannøy) of house sparrows (Passer domesticus) in a metapopulation at Helgeland, Norway. Genomic (gDNA) and transcribed (cDNA) alleles of functional MHC class I and IIB loci, along with neutral noncoding microsatellite markers, were analyzed to obtain relevant estimates of genetic variation. We found lower allelic richness in microsatellites in the inbred population, but high genetic variation in MHC class I and IIB loci in both populations. This suggests that also the inbred population could be under balancing selection to maintain genetic variation for pathogen resistance.