Abstract
In bacteria and other microorganisms, the cells within a population often show extreme phenotypic variation. Different species use different mechanisms to determine how distinct phenotypes are allocated between individuals, including coordinated, random, and genetic determination. However, it is not clear if this diversity in mechanisms is adaptive—arising because different mechanisms are favoured in different environments—or is merely the result of non-adaptive artifacts of evolution. We use theoretical models to analyse the relative advantages of the two dominant mechanisms to divide labour between reproductives and helpers in microorganisms. We show that coordinated specialisation is more likely to evolve over random specialisation in well-mixed groups when: (i) social groups are small; (ii) helping is more “essential”; and (iii) there is a low metabolic cost to coordination. We find analogous results when we allow for spatial structure with a more detailed model of cellular filaments. More generally, this work shows how diversity in the mechanisms to produce phenotypic heterogeneity could have arisen as adaptations to different environments.
Highlights
In bacteria and other microorganisms, the cells within a population often show extreme phenotypic variation
It is with the reproductive division of labour that these three very different mechanisms have been observed in different species and for which there is an absence of evolutionary explanations[2,3,23,24,30]
We test the robustness of our results by examining several alternate models for different biological scenarios (Supplementary Methods A–C) and by developing a more detailed model of growing cyanobacteria filaments that include the effects of within-group spatial structure
Summary
In bacteria and other microorganisms, the cells within a population often show extreme phenotypic variation. The focus in that literature is on a different question—how different proximate mechanisms can produce coordinated specialisation—rather than the broader question of whether coordinated specialisation should be favoured over random specialisation or genetic control in the first place. It is with the reproductive division of labour that these three very different mechanisms have been observed in different species and for which there is an absence of evolutionary explanations[2,3,23,24,30]. While the form of cooperation and life histories of microbes share many similarities, they vary in factors that could influence the evolution of division of labour, such as social group size[31,32]
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