Genetic relatedness in primitively eusocial wasps

Social insects are characterized by indirect reproduction, in which most individuals achieve genetic success by helping to rear the offspring of colony mates. The evolution of such systems is expected to be sensitive to the genetic relatedness of colony mates. In general, reproductive altruism evolves most easily when relatedness is high, although it could be maintained under regimes of low relatedness after morphologically distinct castes have evolved^1,2. Most social insects belong to the order Hymenoptera, and are therefore haplodiploid (males haploid, females diploid); this genetic system may favour the evolution of altruism because it makes rearing a full sister (r Combining double low line 3/4) genetically more valuable than rearing one's own offspring (r Combining double low line 1/2) (refs 1-3). Here we report new estimates of relatedness from 14 species of polistine wasps lacking morphological castes. Female colony mates are often not full sisters and therefore seldom realize the full advantage made possible by haplodiploidy. But relatedness is always fairly high, in striking contrast to the situation in some species with morphological castes.