Memory of opponents is more potent than visual sign stimuli after social hierarchy has been established

During agonistic interactions between male Anolis carolinensis, perception of a visual sign stimulus (darkened eyespots) not only inhibits aggression and promotes initial attainment of dominant social status, but also evokes distinct neuroenclocrine responses in each opponent. This study was designed to examine the effect of eyespot manipulation on behavior and social rank during a second interaction between opponents that had previously established a natural dyadic social hierarchy. Prior to a second interaction, eyespots of familiar size-matched combatants were manipulated to reverse information conveyed by this visual signal. Eyespots on the previously dominant male were masked with green paint to indicate low aggression and social status. Previously subordinate males had their eyespots permanently marked with black paint to convey high aggression and status. Opponents were then re-paired for a second 10 min interaction following either I or 3 clays of separation. Aggression was generally decreased and social status between pairs remained reasonably consistent. Unlike rapidly activated monoaminergic activity that occurs following the initial pairing, most brain areas sampled were not affected when animals were re-introduced, regardless of visual signal reversal or length of separation between interactions. However in males with normal eyespot color, dominant males had reduced serotonergic activity in CA(3) and raphe, while subordinate males exhibited elevated CA3 dopaminergic activity. Reversing eyespot color also reversed serotonergic activity in raphe and dopaminergic activity in CA3 after 3 days of separation. The results suggest that males remember previous opponents, and respond appropriately to their previous social rank in spite of eyespot color. (C) 2007 Elsevier B.V. All rights reserved.