Slave ants kill their masters' offsprings to take revenge

Researchers from the Johannes Gutenberg University Mainz (JGU) in Germany found that enslaved worker ants kill the offspring of their oppressors to improve the chances of survival for their neighbouring relatives.

Ant researcher Professor Dr Susanne Foitzik first observed this "slave rebellion" phenomenon in 2009.

In her latest findings, however, this behaviour appeared to be a widespread characteristic that was not limited to isolated occurrences.

In fact, in three different populations in the US states of West Virginia, New York, and Ohio, enslaved Temnothorax longispinosus workers have been observed to neglect and kill the offspring of their Protomognathus americanus slavemakers rather than care for them.

 

As a result, an average of only 45 per cent of the parasite's offspring survived. This presumably reduces the strength of the parasites in the area and thereby increases the chances of survival for the neighbouring colonies populated by the slave ants' relatives.

From the perspective of evolutionary history, the American slave-making ant Protomognathus americanus is an old social parasite that is entirely dependent on other ant species for its survival.

Slave workers have to care for the brood in parasite nests, bring food to their masters and feed them, and even defend the nest.

These ants become slaves when workers from the slave-making ant colony attack the nests of the host species Temnothorax longispinosus, kill the adult ants, and steal the brood.

Back in the masters' nest, which can be located in hollow acorns, nutshells, or twigs, the brood care behaviour of the emerging slave workers is exploited to the advantage of the slavemaker species.

The team found that the enslaved worker ants feed and clean the larvae, thereby raising the offspring of their social parasite - but only up to a certain point.

"Probably at first the slaves cannot tell that the larvae belong to another species," Foitzik said in a statement.

As a result, 95 per cent of the brood survives the larval stage. But the situation changes as soon as the larvae pupate.

"The pupae, which already look like ants, bear chemical cues on their cuticles that can apparently be detected. We have been able to show that a high fraction of the slavemaker pupae are killed by slave workers," Foitzik said.