Brain plasticity correlates with behavioral changes in ant queens

We addressed how brain plasticity underlies behavioral changes in ants . In all animals, long term behavioral changes are usually accompanied by neuronal modifications. Queen ants have a unique life-history among insects, because they undergo a rapid diminishment of their behavioral repertoire once they have mated and start a colony. To examine how brain plasticity underlies shifts in behavior, we compared the behavior and brain morphometrics of virgin queens, mated queens and older queens in two species of harvester ants. A behavioral transition occurs rapidly (within a day) after a queen mates. Virgin queens go towards the light, stay in open areas and will not dig, whereas mated queens show the opposite: strong aversion to light, seek cover and dig into the soil. After the colony founding stage, the behavior of a queen dwindles to mainly laying eggs, as workers take over brood care.

These behavioral changes coincide with morphological changes in the brain. The brains of mature queens are significantly smaller than those of virgin females at the time of their mating flight. A disproportionately large shrinkage occurs in the visual systems. The brain reduction appears to be adaptive as mated queens show reduced behavioral repertoires and live in the dark. In contrast to virgin females, they do not rely on vision and might increase their fitness by reducing metabolically costly neural tissue (Julian & Gronenberg 2002).