Evol Ecol Res 14: 951-971 (2012)     Full PDF if your library subscribes.

Suicidal punishment in the ant Acromyrmex versicolor

Gregory B. Pollock1, Antonio Cabrales2, Steven W. Rissing3 and Kenneth G. Binmore4

1KALX, LLC, USA,  2Departamento de Economa, Universidad Carlos III de Madrid, Madrid, Spain, 3Department of Evolution, Ecology and Organismic Biology, The Ohio State University, Columbus, Ohio, USA and  4Department of Economics, University College London, London, UK

Correspondence: K.G. Binmore, Department of Economics, University College London, London WC1E 6BT, UK. E-mail: k.binmore@ucl.ac.uk


Background: Several queens of the desert leaf-cutter ant Acromyrmex versicolor often establish nests in common. Before the emergence of workers, a single founding queen undertakes the risky but necessary task of foraging on behalf of the whole colony. The queen who previously took on the specialized task of removing soil from the nest during excavation usually also acts as the forager. Rissing et al. (1996) revealed that a queen that refuses the foraging task in such circumstances is not replaced by her cofoundresses. Shirking on the part of the nominated forager is therefore punished in a manner that results in the colony’s demise.

Question: How is such suicidal punishment to be explained?

Methods: We model cofoundress options as a game in asexual haploid strategies where self-preserving replacement of a shirking foundress exists as an alternative to the observed behaviour (Pollock et al., 2004). Embedding this game in the natural history of A. versicolor, we simulate populations for 500,000 years with various mutation regimes and parameter sets, the latter sometimes deviating significantly from A. versicolor. We follow the simulations with a formal game-theoretic analysis.

Results: In our simulations, stability is stochastic. However, there is a parameter range in which self-preservation never outperforms suicidal punishment, although the former can recur and drift upwards for some time. We conclude that suicidal punishment survives because it sustains the efficient coordination mechanism by means of which the foraging queen is chosen. Our formal game-theoretic analysis supports that conclusion.

Keywords: Acromyrmex versicolor, coordination mechanism, group selection, pleiotropy, self-preservation, stochastic stability, subgame perfection, suicidal punishment, viscous dispersal.

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