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Friday, October 12, 2012

Revenge of the ant slaves


Some species of ants will raid the nests of rival ants, kill or drive off the adults and carry the babies back to their own nests. Once imprisoned in the conquerors’ nest, the baby ants are put to work caring for their new ruling class. Enslaving ants in this way is a form of ‘brood parasitism’. You may be more familiar with this term as it relates to cuckoos laying their eggs in other birds’ nests. Just as the host birds rear young that is not their own, so too must the enslaved host ants rear unrelated parasitic ants.

File:Protomognathus americanus casent0003235 profile 1.jpg

File:Temnothorax longispinosus casent0104819 profile 1.jpg

Top: Parasitic slave-maker Protomognathus americanus
Bottom: Enslaved Temnothorax longispinosus
Photo by April Noble
Both pictures courtesy of AntWeb.org.

Slave-making ants are well equipped for warfare with their fellow ants, but not so well prepared to care for themselves. In some cases, their nests are entirely dependent on the foraging and caretaking abilities of their enslaved conquests. To some degree, this puts them at the mercy of their slaves. According to Tobias Pamminger and his colleagues from the Gutenberg University of Mainz and the Ludwig Maximilian University of Munich, the slaves can rebel by refusing to care for their ‘masters’.

In fact, the researchers found that only half as many pupae in the slave makers’ nests survive as pupae in undisturbed host nests. In other words, host workers make perfectly capable nurses when it suits them, but make little effort to rear the parasitic offspring of their slavers. They may neglect those young or even actively slaughter them.

What’s interesting about this is that the enslaved workers can gain no direct benefit from their ‘slave rebellion’. They can never escape and they can never reproduce. On the other hand, their fellow hosts do benefit if the slaver nest is weakened. By decreasing the number of parasitic slave makers, the enslaved hosts could be protecting other members of their species from the same fate. Apparently, this form of ‘kin selection’ is enough to make the slave rebellion trait a widespread phenomenon.

Tobias Pamminger, Annette Leingartner, Alexandra Achenbach, Isabelle Kleeberg, Pleuni Pennings, & Susanne Foitzik (2012). Geographic distribution of the anti-parasite trait ‘‘slave rebellion’’ Evolutionary Ecology DOI: 10.1007/s10682-012-9584-0