Honesty is the best policy

24 February 2010

Queen ants who have to compete for dominance of a colony may act selfishly to promote their survival, but scientists have discovered that they are rigorously honest when declaring their status to potentially murderous workers.  The research, published today in Proceedings of the Royal Society B, may have interesting wider implications in terms of the evolution of cooperative behaviour.

In some ant species, several queen ants work together to begin a new colony, each raising broods of workers until there are enough ants to form a viable colony.  However, the worker ants cannot tolerate joint sovereignty and ultimately kill the queens until only one remains.  Luke Holman and his team based at the University of Copenhagen aimed to discover whether queen ants prepare for this attack in any way and if so, what the best strategy might be.

Workers tend to prefer to spare the lives of queens who produce larger broods, identifying the more productive queens via chemical signals.  However, productivity comes at a cost: producing a larger brood makes a queen weaker and less able to survive the onslaught of murderous workers when the time comes.   The researchers discovered that when placed in direct competition against each other, queens would always produce smaller broods and save their strength for the final battle against the observers.

This is a “selfish” strategy on the part of the queens because producing smaller broods will ultimately mean that the colony as a whole is weaker, although their individual chance for survival might be increased.  However, it also seems to be an inherently paradoxical behaviour: given that worker ants can readily identify unproductive individuals, it would seem that the additional strength gained by producing a smaller brood is likely to lose any selective advantage.

One way of getting round this would be for queen ants to produce smaller broods and then cheat the worker ants by producing a false chemical signal to fool them into thinking that they had been more productive than they appear.  However, the scientists found no sign of cheaters, suggesting that even in a potentially life-threatening situation, honesty is the best policy.  The research may even have significance beyond ant colonies – the question of how cooperation evolved is a hot topic and the authors suggest that “punishment and honest signalling may be universally important”.