Bourgeois queens and high stakes games in the ant Aphaenogaster senilis

Thibaud Monnin,Adam L Cronin

doi:10.1186/1742-9994-6-24

Abstract

BackgroundMany animals face some form of conflict over reproductive opportunities. Queen selection in social insect colonies represents a high-stakes conflict where competition occurs among multiple queens for a few or a single reproductive role(s). The outcome of the contest is critical to the fitness of all colony individuals as most are sterile, and thus represents a conflict at multiple levels. Aphaenogaster senilis is a monogynous, monandrous, fission performing ant, in which queen selection occurs during colony fission and when replacement queens are produced to overcome orphaning. First-born queens are usually behaviourally dominant over subsequent queens, and eventually inherit the colony. We investigated the importance of physical dominance in queen selection in orphaned groups by manipulating the fighting ability of first-born queens via mandibular ablation.ResultsFirst emerged queens were heavier than second emerged queens, performed almost all aggression, were behaviourally dominant 92% of the time, and prevailed in 76% of groups after co-existing for 16 days on average. Mandibular ablation had no effect on queen behaviour or contest outcome.ConclusionAggression is probably ritualised and contests are decided by workers based on relative queen fertility. First-born queens thus have an inherent advantage over second-born queens as they have more time to develop ovaries. Subordinates never retaliated against aggression from dominants and this lack of retaliation can be interpreted as a form of bourgeois strategy as dominants were almost always first-born. However, the lack of alternative reproductive options makes not-fighting effectively a form of suicide. High relatedness between full-sister queens means that subordinates may be better off sacrificing themselves than risking injury to both queens by fighting.

Highlights

Many animals face some form of conflict over reproductive opportunities
Therein lies a conflict of interest at multiple levels: whereas colony level selection will favour rapid emplacement of a high quality queen, individual level selection acting on workers can select for behaviour that favours closely related queens, while queens are presumably under selection to fight among themselves [2,3]
Queen selection occurs in three main contexts in social insect colonies: i) after worker emergence in pleometrotic assemblages [4], ii) associated with colony division by dependent colony founding [3,5], and iii) during emergency queen replacement [3,6,7]

Summary

Introduction

Queen selection in social insect colonies represents a high-stakes conflict where competition occurs among multiple queens for a few or a single reproductive role(s). This conflict is centred on the queen because she is the sole reproductive in a colony of potentially thousands of individuals: workers cannot (or do not) reproduce themselves and only gain fitness indirectly. Unrestrained direct conflict between queens may be unfavourable because it entails the risk of both queens being injured or killed [9], potentially leading to colony failure This is true during emergency queen replacement because the supply of brood that can be reared into new queens is limited to that laid by the previous queen, so that colonies can ill afford losing new queens. When queens are equivalent or there is no information available to workers with respect to queen quality or relatedness, they should select for rapid resumption of laying activity by favouring first eclosing queens, as occurs in army ants [26]

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