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June 15, 2012

No country for young men (if you are an ant)

Fighting ant males scour the brood-chambers in search of emerging rivals, as speed kills: the older ones win fight for the queen • Cooperation between IST-Professor Sylvia Cremer and the University of Regensburg

Image of older ant attacking younger ant
Image of older ant attacking younger ant.

In a publication appearing in the open-access journal BMC Ecology on June 15, Professor Sylvia Cremer from the Institute of Science and Technology (IST) Austria, together with researchers from the University of Regensburg, describes the rivalry between male Cardiocondyla obscurior ants.

While most male ants court the queen peacefully and try to fly to the queen faster than their competitors during the mating flight, the nests of the small tropical ant C. obscurior are a regular site of murder. Wingless, aggressive males patrol the colony in a constant search for emerging young queens, with which they mate, or rivals, which they immediately attack. The ants’ mouth parts are good enough for grabbing, but not sufficient for biting. Therefore, they grab their opponent and mark him with a chemical substance, which causes worker ants to kill the marked ant.

The researchers could now show that newly emerged males hardly fight back and are helplessly vulnerable to the attacks of the old male. As the young never chemically mark the old, the worker ants always kill the newly emerged ant. But a different picture is seen after two days: then, the young male is on par with the old one and fierce battles with mutual chemical marking ensue, such that both males may be killed by worker ants.

It would therefore be a good strategy for young males to not reveal themselves as an emerging rival. This is done by their winged brothers, who are able to evade the aggression of the dominant wingless males by female mimicry (Cremer et al. 2002, Nature). In their current work, the researchers show that young wingless males lack this ability, as they already signal their identity shortly before emerging from the pupa. Interestingly, with few exceptions the old males wait with attacks until the rival emerges. They probably avoid committing the mistake of inadvertently killing a mating partner instead of a rival, as the chemical signals of pupae are not as reliably attributable to gender as is the case in emerged ants.

The constant production of wingless males helps the colony ensure that in case the dominant male dies, a new male is ready to replace him. As the killed wingless ants are use to feed the larvae, the costs for this strategy are kept low.

Sylvia Cremer is Professor at IST Austria and works on conflict and cooperation in ant colonies as well as cooperative health care, described recently in the journal PLoS Biology (PLoS Biol 10(4): e1001300; also see New York Times).


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