Enslaved worker ants fight back through acts of sabotage

Illustration for article titled Enslaved worker ants fight back through acts of sabotage

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.

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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 longispinosus become 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").

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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.

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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.

Image: Dr. Morley Read/Shutterstock.

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DISCUSSION

bluehinter
bluehinter

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.

[Puts on evolutionary biologist wizard's hat]

Ahem. While learned behavior is certainly possible, I wouldn't completely exclude genetic causes, or at least a genetic predisposition towards this behavior.

When talking about genetics and evolutionary adaptation, it is vitally important to understand that all evolution cares about is the survival of genes rather than the survival of individual organism. Genetic traits can be passed along directly from parent to child or indirectly through the process of "gene altruism" aka. inclusive fitness.

To put it in simple mathematical terms— If my self-sacrifice saves the life of my brother/sister (who shares the exact same percentage of genes with me as my own offspring, 50%) or my niece/nephew, (who shares the exact same percentage of genes as my own off grandchild, 25%) then that trait stands a pretty good chance of being passed along to subsequent generations, even if I'm not the one doing the passing.

This is something that proponents of intelligent design often don't understand, when ranting about bombardier beetles and exploding carpenter ants. It is perfectly logical for genetic traits to arise which don't necessarily benefit the poor creature destined to "take one for the team," but do benefit the rest of the species, provided it increases the survival chances of other individuals who share that same genetic trait.

One of the reasons why we see so much of this self-sacrifice behavior in haplodiploid species like ants, wasps, and bees is because sisters are more closely related to each other (75%) than to their offspring (50%).

Therefore, assuming there is a genetic predisposition towards "if slave, then rebel," killing off the brood of your oppressors would definitely reinforce the inclusive fitness of that particular gene, by making sure your sisters back home experienced fewer and/or less damaging slave raids than neighboring colonies which might not share these same genes.

Mind you, I'm not saying this is the mechanism by which this skill is passed along, (creatures like ants and bees have certainly proven to be excellent communicators), just that it certainly could be.

The only way to tell for sure would be to compare the genetic structure of ants who rebel with similar ants who don't rebel, try to determine the chromosomal variance between the two, and if we find something which seems to be the "on switch" for this kind of behavior, see what happens when we switch it off.

Not that things are usually that simple, especially when dealing with complex behaviors. For example: There could be a gene sequence for "destroy enemy pupae," and another one for smelling the difference between "good ants" and "bad ants," but turning off either would have the same result of not rebelling against your ant oppressors.

[/ biology rant]