The evolution of mechanisms to divide labour in microorganisms

Abstract Division of labour, where cooperating individuals specialise to perform complementary tasks, plays a fundamental role at all levels of biological complexity, from genes to complex animal societies. Different labour-dividing species employ different mechanisms to determine how tasks are allocated between individuals, including coordinated, random, and genetic determination of phenotype (caste). It is not clear if this diversity is adaptive– arising because different mechanisms are favoured in different environments–or is merely the result of non-adaptive, historical artifacts of evolution. We use theoretical models to analyse the relative advantages of the two dominant mechanisms employed for reproductive division of labour in microorganisms: coordinated and random specialisation. We show that fully coordinated specialisation is more likely to evolve over random specialisation in well-mixed groups when: (i) social groups are small; (ii) cooperation has a greater relative impact on fitness (i.e., is more “essential”); and (iii) there is a relatively low metabolic cost to coordination. We find analogous results when we allow for spatial structure in a more mechanistic model of growing cyanobacteria filaments. More generally, our results show that the diversity in mechanisms to divide labour are likely to have arisen through the action of adaptation by natural selection, and not as an historical artifact of non-adaptive evolution.