Selection for class II Mhc heterozygosity by parasites in subterranean mole rats

Mhc organization and polymorphism have previously been studied in the four chromosomal species of the Spalax ehrenbergi superspecies in Israel, serologically, and at the DNA, RFLP and sequence levels of class I and class II genes. Here we demonstrate that the observed heterozygosity of Mhc class II genes P alpha 1 with 11 alleles, and Q beta, with at least 14 alleles, is positively and significantly correlated with infectivities of ectoparasites (gamasid mites) and endoparasites (helminths). Mhc heterozygosity is highest in the most infected area, which is in the most humid-warm region of the superspecies range, or where two zoogeographic regions overlap. We conclude that the evolutionary forces responsible for the Mhc class II two-gene polymorphisms include selection for increased heterozygosity as a defense strategy against ecto- and endoparasite infections.