Complete loss of MHC genetic diversity in the Common Hamster (Cricetus cricetus) population in The Netherlands. Consequences for conservation strategies

The Common Hamster (Cricetus cricetus L.) has suffered from changes in agricultural practices. In some Western European countries the populations have become so small and scattered that they are threatened with extinction. We studied the genetic diversity of mitochondrial and major histoincompatibility complex (MHC) loci in the few animals left in the South of the Netherlands and in three animals from the Alsace region in France, and compared it to the diversity in Dutch animals in the past (samples taken from stuffed animals in museum collections dating back to the period 1924-1956) and in a large present-day population from Czech Republic. For the mitochondrial cytochrome b gene, SNP mapping demonstrated a total of nine alleles among 14 Czech samples, of which one (possibly two) was present in the Dutch museum samples, and only one in the current Dutch animals. For the MHC genes, DQA exon 2 and 3 showed no variation, while 14 different alleles were found at DRB exon 2. The Czech population contained 13 different alleles in 15 animals sampled, and most animals were heterozygous (H_o = 0.80, H_e = 0.91). Therefore, the solitary living Hamster maintains, in nature, a large diversity at this MHC locus. The Dutch museum samples contained eight different alleles in 20 samples, and they were slightly less heterozygous (H_o = 0.60, H_e = 0.75). All but one of these alleles were also found in the Czech samples. In contrast, the present Dutch and French animals (a total of 16 samples) contained only one of these alleles, and all animals were genetically identical and homozygous. We conclude that the remaining animals have lost all diversity at this MHC locus. This is probably the result of a severe bottleneck, which may have been quite severe, reducing diversity in many loci. In addition, the remaining Dutch animals are partly derived from one family. These animals are now part of a breeding program. Options for restocking the genetic diversity are discussed.