Resource sharing is sufficient for the emergence of division of labour

Abstract

Division of labour occurs in a broad range of organisms. Yet, how division of labour can emerge in the absence of pre-existing interindividual differences is poorly understood. Using a simple but realistic model, we show that in a group of initially identical individuals, division of labour emerges spontaneously if returning foragers share part of their resources with other group members. In the absence of resource sharing, individuals follow an activity schedule of alternating between foraging and other tasks. If non-foraging individuals are fed by other individuals, their alternating activity schedule becomes interrupted, leading to task specialisation and the emergence of division of labour. Furthermore, nutritional differences between individuals reinforce division of labour. Such differences can be caused by increased metabolic rates during foraging or by dominance interactions during resource sharing. Our model proposes a plausible mechanism for the self-organised emergence of division of labour in animal groups of initially identical individuals. This mechanism could also play a role for the emergence of division of labour during the major evolutionary transitions to eusociality and multicellularity.

Fig. 1. Task switching and four resource sharing scenarios.

a Our model assumes that individuals can switch (solid arrows) between two states: foraging (green) and nursing (blue). While foraging, individuals retrieve resources (black dots) from the environment and store these resources in a temporary storage organ (grey circle). As long as resources are in the storage organ, they can in principle be shared with other individuals. Once they are integrated into the individual’s body (green dots in foraging individuals; blue dots in nursing individuals) they contribute to the individual’s nutrition level and can no longer be shared. As foraging is triggered by a low nutrition level, foraging individuals have on average lower nutrition levels than nursing individuals. b Four resource sharing scenarios considered in our study: (1) No sharing: Resources are not shared; foraging individuals consume all resources themselves. (2) Equal sharing: Foraging individuals share the collected resources equally between themselves and a nursing individual. (3) Dominance-based sharing: Each individual has a pre-assigned dominance value and resources are shared in relation to these dominance values: The dominant individual obtains a larger proportion of the collected resources. (4) Nutrition-based sharing: As in (3), but now the dominance level of an individual is not pre-assigned and constant, but proportional to the individual’s nutrition level.

Fig. 2. Division of labour and nutrition levels of nursing and foraging individuals under no resource sharing and equal sharing.

a No sharing. In the absence of resource sharing, D = −1 which indicates that individuals alternate between nursing and foraging. As foraging is triggered by a decline in the nutrition level, nursing individuals have a higher nutrition level than foragers. b Equal sharing. If foraging individuals share their collected resources equally with nursing individuals, D ≈ 0.6 which represents an intermediate level of division of labour. Each grey dot (left panel) is the division of labour metric from a replicate simulation (n = 20). Blue (nursing) and green (foraging) dots (right panel) represent the nutrition levels of all individuals at the end of all replicate simulations.

Fig. 3. Division of labour when the metabolic costs of foraging and nursing differ.

a If metabolic rates during nursing are lower relative to foraging, division of labour is reinforced. Conversely, division of labour is weaker when metabolic rates during nursing are higher than during foraging. b As their metabolic rates become lower, the nutrition level of nursing individuals deviates more strongly from those of foraging individuals. For graphical conventions, see Fig. 2.

Fig. 4. Division of labour, nutrition level and dominance of nursing and foraging individuals.

a1 Dominance-based sharing. Division of labour reaches maximal levels of D = 1. Nursing and foraging individuals exhibit a bimodal distribution of nutrition levels. a2 Nutrition levels of individuals diverge over simulation time, depending on the individual’s dominance. b1 Nutrition-based sharing. Division of labour again reaches maximal levels of D = 1, and nutrition levels exhibit a bimodal distribution. b2 Nutrition levels of individuals diverge over simulation time. a1 + b1 For graphical conventions, see Fig. 2. a2 + b2 Each line shows the nutrition level of an individual over the first 20% of simulation time from a representative replicate simulation, coloured according to the individual’s dominance value if dominance values were pre-assigned.

Fig. 5. Effect of group size on division of labour in the equal sharing scenario.

Division of labour emerges irrespective of group size. Each dot shows the division-of-labour metric from a replicate simulation per group size (n = 10).