Parasitic ants alter how captive ants recognize nest mates

Highly social ants, bees and wasps employ sophisticated recognition systems to identify colony members and deny foreign individuals access to their nest. Ants use chemical signals, called cuticular hydrocarbons, to determine nest membership, but some parasitic ants can break the recognition code and live unopposed within a host colony. In this study, the authors examine the influence of the socially parasitic slave-making ant, Polyergus breviceps on the nest mate recognition system of its slaves, Formica altipetens by comparing the chemical, genetic, and behavioral characteristics of enslaved and free-living Formica ant colonies collected in Arizona. Slave-making ants in the genus Polyergus depend on their host, Formica, for nest maintenance, brood care, and foraging.

The authors found that enslaved Formica colonies were more genetically and chemically diverse than their free-living counterparts. The researchers think these differences are likely caused by seasonal raids to steal pupa from several adjacent host colonies.

"When free-living Formica ants are kidnapped into the Polyergus colony, they enter a society that [comprises] kidnapped ants from many other Formica colonies. Here, we show that this rich social environment alters the behaviors displayed by the enslaved ants," said Neil Tsutsui.

The different social environments of enslaved and free-living Formica also appear to affect their recognition behaviors: enslaved Formica workers were less aggressive towards non-nest mates than were free-living Formica. Future studies are needed to understand the underlying mechanisms, but the authors suggest their findings indicate that parasitism by P. breviceps alters both the chemical and genetic context in which their hosts develop, leading to changes in how they recognize nest mates.