Opponent recognition in male green anoles, Anolis carolinensis

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Male green anoles convey territorial ownership to rivals through use of stereotyped aggressive displays, with intrasexual interactions often escalating to physical combat. In the laboratory, losers of such interactions significantly reduce their aggressive behaviour when interacting with the same opponent 7 days later. In the current study, we examined whether this behavioural modification is a function of opponent recognition. Pairs of size-matched male A. carolinensis were allowed to interact for 2 h. Following this, subjects were separated for varying intervals, and then participated in a second interaction with either the same or an unfamiliar opponent. Losers of the first interaction significantly reduced their total aggressive behaviour when re-paired with the same opponent after a 3-day interval but not after a 10-day interval between the first and second interaction. However, losers of the first interaction failed to show reduced aggression during their second interaction when paired 3 or 10 days later with an unfamiliar opponent. Therefore, A. carolinensis appear to learn information specific to their opponent during an initial agonistic interaction, with the salience of this information declining when the interval between interactions increases. Males also showed low levels of chemosensory taste behaviour during agonistic interactions, suggesting that opponent recognition does not rely on chemoreception. Similarities between our results and findings from other vertebrate species suggest that the motivation to behave aggressively during social interactions can be influenced by opponent recognition rather than by previous experience of social defeat alone.