Suicidal Punishment in the Ant Acromyrmex versicolor

Question: Foundress associations of the desert leaf-cutter ant Acromyrmex versicolor exhibit a single forager-foundress prior to worker eclosion. A prior specialized task, removing soil from the nest during excavation, allocates later forager risk. Experiment reveals that a queen refusing such prior assignment is not replaced by her cofoundresses; rather, these latter suicidally punish the shirker, leading to the colony’s demise (Rissing et al. 1996). Why do cofoundresses fail to replace a shirker when failure implies reproductive death? Method: We model cofoundress options as a game in asexual haploid strategies where self-preserving replacement of a shirking foundress exists as an alternative (Pollock et al. 2004). Embedding this game in the natural history of A. versicolor, we simulate populations for 500,000 years, with 100 replicates under various parameter sets, some deviating significantly from A. versicolor. Shirkers appear through mutation, with suicidal punishers and self preservers mutating one to the other. Results: Self preservation never outperforms suicidal punishment, although it can recur and drift upwards for some time. Whenever forager assignment is retained, suicidal punishment dominates. But stability is stochastic: forager assignment may endure in many-to-most runs, yet be lost in others. Generally, the greater the frequency of self preservers, the more likely assignment will be lost entirely in the long run. Task coordination endures through suicidal punishment.