Reduced major histocompatibility complex class II polymorphism in a hunter-managed isolated Iberian red deer population

Abstract

The major histocompatibility complex (MHC) contains the most variable functionalgenes described in vertebrates. Individuals from natural populations dealconstantly with a diverse range of pathogens and the polymorphism at MHC lociis what determines the diversity of foreign antigens that the host immune systemcan recognize. Polymorphism at individual loci may result in variable MHC classII (MHC-II) haplotypes. We characterized for the first time, the allelic diversity atthe second DRB locus of the MHC-II in the Iberian red deer Cervus elaphushispanicus. The studied population was sampled from a fenced estate that has beenmanaged for hunting purposes and may provide information of the effect of gamemanagement on the genetic diversity of this species. Deer presented high levels ofvariation at MHC-II DRB-2 with 18 different alleles detected in 94 individuals.However, a significant heterozygous deficiency was found for MHC-II DRB-2locus (92.5% of individuals only amplified one allele), whereas genotype frequenciesat three neutral microsatellite loci were according to Hardy–Weinbergequilibrium, with heterozygosity over 50%. The analysis of control Iberian reddeer from different geographic locations identified two expressed DRB-2 loci witha high degree of heterozygosis. The annual diversity index of MHC-II DRB-2alleles significantly decreased along the 16-year study period, which was confirmedwith losses in microsatellite markers. Although we cannot exclude positive nonassortativemating and/or substructured breeding (Wahlund effect) within ourreference population, such unexpected apparent homozygosity at MHC DRB-2loci is suggestive of null alleles occurring at our population. The observed patterncould be the result of a founder effect in this recently established population.Nonetheless, the loss of MHC-II DRB-2 allele diversity could reflect the effects ofinbreeding in this fenced population managed for hunting. These findings supportthe importance of immunogenetic studies to assess management decisions,especially in isolated ungulate populations.