Different Evolutionary Conditions for Worker and Soldier Castes: Genetic Systems Explaining Caste Distribution among Eusocial Insects
According to N. Yamamura, the differences between worker and soldier castes of social insects have not been addressed sufficiently. He suggests that the evolution of worker and soldier castes must be considered in terms of different trade-offs, “specifically, the different relations between benefits and costs of sterility.” According to this, an individual becomes a sterile helping worker if there is a higher genetic gain for growing its siblings than the costs of losing its own offspring. Soldiers (also sterile) should occur if the sacrifice of their own life is connected with the survival of related family members, and therefore “genetically compensated”. According to Yamamura’s theory is the distribution of castes in eusocial insects explainable by differences in their genetic systems, when applying these different conditions for evolution of sterility (aphids, parasitic wasps: asexual and therefore with only soldiers; termites: diploidy and therefore dominantly soldiers; ants, wasps and bees: male-haploidy and therefore with mainly workers).