High MHC gene copy number maintains diversity despite homozygosity in a Critically Endangered single‐island endemic bird, but no evidence of MHC‐based mate choice

Abstract

Islands have intrinsic geographic characteristics (isolation, small area) that contribute to exacerbated genetic threats to insular species. Isolation can make gene exchange difficult, which, coupled to the often small size of island populations, can increase these risks (Ferreira et al., 2016; Frankham, 1998). One striking example of the genetic threats to insular species is that of the last woolly mammoth Mammuthus primigenius population, where 300 individuals surviving on Wrangel Island are thought to have ultimately disappeared

Editorial 2021

“…In a From the Cover article, Stervander et al. (2020) examined the diversity of major histocompatibility complex class I (MHC‐I) genes in one such critically endangered songbird. Surprisingly, the authors did not find an effect of MHC‐I diversity on mate choice or survival.…”

“…Instead, despite low population‐level diversity of MHC‐I genes, Stervander et al. (2020) show that the multicopy nature of MHC‐I allows for the maintenance of high levels of within‐individual allelic diversity. As MacDougall‐Shackleton (2020) points out, these results demonstrate how gene duplication events can have important long‐term evolutionary consequences.…”

Many loci make light work: High individual diversity despite low population diversity and random mating at class I MHC in a Critically Endangered island songbird

“…One of the authors, M. de L. Brooke, monitored a large fraction of the Raso lark population for survivorship and mate choice over a 15‐year period. Stervander et al (2020) then related these variables to the birds’ genotype at class I MHC, whose gene products bind and present intracellular antigens, including those from avian malaria ( Plasmodium spp.) and other haematozoan parasites.…”

“…Whatever the answers to these questions, the findings by Stervander et al. (2020) are exciting and important from both conservation and theoretical perspectives. First, high levels of genetic diversity at these keystone immune loci apparently achieved through duplication increasing gene copy number rather than through disassortative mating maintaining within‐locus polymorphism, may help to buffer Raso larks from future environmental change.…”

“…Stervander et al. (2020) used an ingenious approach to infer multilocus haplotypes: they identified certain combinations of alleles that always, or almost always, occurred together, and they identified a bimodal distribution of read ratios corresponding to the homozygous versus heterozygous state of multilocus haplotypes. This approach allowed the researchers to disambiguate the effects of variation in copy number from those of variation in zygosity.…”