Dominance hierarchy limits resilience in the endangered queenless ant Dinoponera lucida

Abstract

Division of labour is an important factor of social insect ecological success. However, the specific mechanisms associated with division of labour differ widely between species. Often, social groups have to cope with severe perturbations and resume normal functioning as quickly as possible. How well they do so depends on the behavioural mechanisms involved and on species life-history traits. Here, we studied the division of labour in D. lucida, a threatened species of native Brazilian queenless ants with small colony sizes, to assess whether colonies facing a drastic perturbation of the established task allocation are resilient, and through which potential mechanisms. We first separated the colonies into two sub-colonies, one with the foragers and the other with the nurses. As this is an important modification of colony structure, we expected workers to respond quickly by switching tasks. Our experiment showed that, contrary to our hypotheses, workers showed little plasticity in switching tasks, and colonies did show very limited resilience. Foragers, when isolated from nurses, show a certain plasticity in their behavioural repertoire, performing both tasks (foraging and nursing). However, groups of nurses facing the absence of foragers kept almost exclusively to nursing tasks. Only a few performed episodic outside activities. When workers were returned to their original colonies, foragers switched back to foraging. However, the effect of the manipulation could still be observed 20 days after reintroduction, with workers showing lower general activity, ingesting larvae and reproductive workers losing their dominance. Considering our current knowledge about the regulation of both division of labour and reproductive hierarchies in Dinoponera and other ponerine ants, we propose that this lack of resilience is due to the reproductive conflict between nurses, which delays behavioural maturation and reduces motivation to engage in outside tasks. The existence of individual strategies thus imposes severe costs on group functioning. This could be an additional issue when considering the conservation of this endangered species.