The evolution of mechanisms to divide labour in microorganisms 1

The evolution of mechanisms to divide labour in microorganisms 1 Guy Alexander Cooper*1,2, Ming Liu2, Jorge Peña3, and Stuart Andrew West2 2 1St. John’s College, Oxford, OX1 3JP, United Kingdom 3 2Department of Zoology, University of Oxford, Oxford, OX1 3SZ, United Kingdom 4 3Institute for Advanced Study in Toulouse, University of Toulouse Capitole, Toulouse, 5 31080 Cedex 6, France 6 7 Abstract 8 Division of labour, where cooperating individuals specialise to perform complementary 9 tasks, plays a fundamental role at all levels of biological complexity, from genes to 10 complex animal societies. Different labour-dividing species employ different mechanisms 11 to determine how tasks are allocated between individuals, including coordinated, random, 12 and genetic determination of phenotype (caste). It is not clear if this diversity is adaptive— 13 arising because different mechanisms are favoured in different environments—or is 14 merely the result of non-adaptive, historical artifacts of evolution. We use theoretical 15 models to analyse the relative advantages of the two dominant mechanisms employed 16 for reproductive division of labour in microorganisms: coordinated and random 17 specialisation. We show that fully coordinated specialisation is more likely to evolve over 18 random specialisation in well-mixed groups when: (i) social groups are small; (ii) 19 cooperation has a greater relative impact on fitness (i.e., is more “essential”); and (iii) 20 there is a relatively low metabolic cost to coordination. We find analogous results when 21 we allow for spatial structure in a more mechanistic model of growing cyanobacteria 22