It would appear that ants that are kept as slaves by more powerful species aren't as helpless as they might appear. New research from Gutenberg University Mainz in Germany shows that enslaved ants conduct their own form of civil disobedience, by neglecting and killing the offspring of their oppressors. And by doing so, the ants may be preventing their comrades outside the nest from being enslaved themselves.
This discovery was made by ant researcher Susanne Foitzik who started to observe this behavior back in 2009. But what she has since discovered is that this is not an isolated trick limited to one species; over the course of her studies, Foitzik has observed at least three different ant populations in which these acts of rebellion occur. It would appear, therefore, that it may be a fairly common way for enslaved ants to fight back.
Ants such as Temnothorax longispinosusbecome enslaved when workers from the slave-making ant colony, Protomognathus americanus, attack their nests. The parasitic master ants kill the adults of the subjugated population, and steal their offspring. Once back at their nest, the master ants force the new generation to feed and clean their larvae, thus compelling them to raise the offspring of their oppressors (what's called "brood parasitism").
At least up until a certain point — but it would appear that the enslaved ants have evolved a fairly potent countermeasure.
Foitzik observed that 95% of the brood survives the larval stage — but things change dramatically once the larvae starts to pupate. At this point, the pupae give off a chemical signature that the enslaved ant recognizes as being foreign. In turn, the slave ants ignore and even outright kill the baby ants by tearing them apart — as much as 65% of them (normally, 15% don't survive). Foitzik's research even showed some survival rates that were as low as 27%.
Clearly, the slave ants are making a difference — and at no benefit to themselves. But their free relatives back home (as much as it can be said that ants are "free") are clearly benefiting from their enslaved brethren working behind the front lines. And in fact, slavemaker colonies damaged by slave sabotage have been observed to grow slower and smaller slave-making colonies, while conducting fewer and less destructive slave raids.
What's particularly fascinating about this discovery is that the enslaved ants are not the ones passing the "destroy enemy pupae" genes to the next generation. Instead, this characteristic is arising and being reenforced among the free ants.
This research was financed since October 2011 by the project "The evolution of resistance and virulence in structured populations" funded by the German Research Foundation.
The entire study can be read at Evolutionary Ecology.