Low levels of genetic heterozygosity in Hymenoptera

Abstract

IT has been suggested^1–4 that organisms with a haplodiploid sex determination system should have reduced genetic variability relative to diploid organisms. In haplodiploid systems such as in bees and wasps (Hymenoptera), unfertilised eggs develop into haploid males and fertilised eggs into diploid females. Thus the frequency with which alleles are exposed to selection in an effectively homozygous state is increased over comparable diploid species. A lower level of genetic variation would be expected for haplodiploid organisms, relative to diploid organisms, for that genetic variation which is not neutral and is expressed in the haploid sex. Thus, measurement of the level of genetic variability in haplodiploid species is of considerable interest in understanding the mechanisms responsible for maintaining the high levels of genetic polymorphism in diploid organisms^5,6. For this reason, we have measured the genetic variability in haplodiploid species using the combined techniques of electrophoresis and histochemical staining^7,8. As predicted by selection theory, we have shown that the Hymenoptera (haplodiploid organisms) have a lower level of genetic heterozygosity and a lower frequency of enzyme polymorphism than do diploid organisms.