The Evolution of Temporal Polyethism

Abstract

Temporal polyethism is a method of division of labor exhibited by many eusocial insect colonies, where the type of task an individual attempts is correlated with its age. The evolutionary pressures that give rise to this widely-observed pattern are still not fully known. The long generation times of eusocial insects combined with the complications associated with performing artificial selection experiments on colonies of organisms makes this topic challenging to investigate using organic systems. In this thesis, we use digital evolution to explore whether temporal polyethism may result from pressures to preserve colony members in the face of varying degrees of risk associated with different tasks. Specifically, we require a colony of digital organisms to repeatedly perform a set of tasks in order for the colony to replicate. When we associate the two different tasks with different lethality risks, we observe that the digital organisms evolve to perform the less risky tasks earlier in their life and more risky tasks later in life, regardless of the order in which the tasks were performed by the ancestor organism. In trials with three tasks, evolution produces a genome in which the tasks are reordered such that the mean age of completion of the riskiest task is later in life in the majority of the trials. These results demonstrate that pressures resulting from the relative riskiness of various tasks is sufficient to favor the evolution of temporal polyethism. Our preliminary results indicate that when there are competing pressures of lethality risks associated with tasks versus task-switching costs (a penalty to transition between tasks) to organisms, we see that temporal polyethism is still favored as a division-of-labor strategy.