Abstract
Recent theory has overturned the assumption that accelerating returns from individual specialisation are required to favour the evolution of division of labour. Yanni et al., 2020, showed that topologically constrained groups, where cells cooperate with only direct neighbours such as for filaments or branching growths, can evolve a reproductive division of labour even with diminishing returns from individual specialisation. We develop a conceptual framework and specific models to investigate the factors that can favour the initial evolution of reproductive division of labour. We find that selection for division of labour in topologically constrained groups: (1) is not a single mechanism to favour division of labour-depending upon details of the group structure, division of labour can be favoured for different reasons; (2) always involves an efficiency benefit at the level of group fitness; and (3) requires a mechanism of coordination to determine which individuals perform which tasks. Given that such coordination must evolve prior to or concurrently with division of labour, this could limit the extent to which topological constraints favoured the initial evolution of division of labour. We conclude by suggesting experimental designs that could determine why division of labour is favoured in the natural world.
Highlights
Division of labour, where cooperating individuals specialise to carry out distinct tasks, plays a key role at all levels of biology (Bourke, 2011; Queller, 1997; Maynard Smith & Szathmáry, 1995; West et al, 2015)
Quantifying the shape of the returns from individual specialisation has been assumed to be a fundamental step in determining why division of labour was favoured in some species, but not others (Diard et al., 2013; Dragoš et al, 2018a; Flores & Herrero, 2010; Koufopanou, 2002; Mridha & Kummerli, 2021; Strassmann et al, 2000; Veening et al, 2008). 89 We first use the methodology developed by Rueffler et al (2012) to derive the general conditions that favour the initial evolution of reproductive division of labour between helpers and reproductives
We examine the specific case of reproductive division of labour between helpers and reproductives, where helpers are more cooperative, contributing to a higher viability for group members, and reproductives are less cooperative, contributing to higher individual fecundity. 112 We consider an initial population of clonal groups each containing n individuals, in which all individuals cooperate at the Evolutionarily Stable (ES) level (z∗), which is the level that cannot be outcompeted by a mutant strain that uses a different level of uniform cooperation across the group (Maynard Smith, 1982)
Summary
Division of labour, where cooperating individuals specialise to carry out distinct tasks, plays a key role at all levels of biology (Bourke, 2011; Queller, 1997; Maynard Smith & Szathmáry, 1995; West et al, 2015). Diminishing returns means that specialised individuals are inefficient, and earlier work suggested that division of labour could not be favoured in this situation (Figure 1A) (Cooper & West, 2018; Michod, 2006; Schiessl et al, 2019) This result has the potential to overturn our understanding of the factors that favour the evolution of division of labour. We finish by suggesting experimental designs for determining why division of labour has evolved in specific species
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