Meeting Abstract
Ant colonies are distributed systems that are regulated in a non-hierarchical manner. Without a central authority, individuals inform their decisions by comparing information in local cues to a set of inherent behavioral rules. Collectively, many individual behavioral decisions lead to changes in colony behavior including the decision to be aggressive with neighboring colonies. Pavement ants (Tetramorium caespitum ) form conspicuous wars with neighboring colonies in which thousands of ants participate. Wars last for many hours and few workers die in the process as fighting is ritualized. A worker will decide to fight if 1) it has had a recent history of interactions with nestmates and 2) detects a mismatch in nestmate recognition cues on the cuticle of a non-nestmate ant. We present evidence showing how tactile and chemical cues and social context – isolation, nestmate interaction, or fighting non-nestmates – affect levels of the brain monoamines serotonin (5-HT), octopamine, and dopamine in pavement ant brains. Interactions with nestmate ants prior to meeting a non-nestmate opponent elevate 5-HT and octopamine levels in a worker’s brain. If levels of 5-HT and octopamine are above a threshold when the ant detects non-nestmate chemical cues, it is likely to fight the opponent. Pharmacologically increasing brain levels of 5-HT and serotonin make it more likely that an ant will fight an opponent, even if that ant had not recently interacted with nestmate ants. Dopamine levels are elevated during fighting. Our results provide correlational and causal evidence that changes in octopamine and serotonin in the brains of individuals contribute to the collective-decision to be aggressive whereas dopamine levels correspond specifically to physical fighting.
