Lizards can recognize opponents using variation in morphological and behavioural cues

Within-species discrimination is a prerequisite for social behaviour. This phenomenon is well established with acoustic and chemical cues. In contrast, there are few studies of visual cues, despite their widespread occurrence and potential to mediate discrimination. We conducted video playback experiments, using a lizard Amphibolurus muricatus, to test for discrimination based on visual information. Captive males were shown a different video sequence of the same stimulus lizard every day for four days. They were then tested in probe trials with either a sequence of the same male, or a matched sequence of a different male. First, we presented footage of live males performing aggressive push-up displays. These stimuli reproduced both morphological and behavioral cues. We then investigated the role of morphological cues by presenting clips of inactive lizards. Finally, we tested for individual distinctiveness in displays using a 3-D computer model of a lizard performing displays from two exemplar males. Subjects could perceive differences between the two individuals in all three series, as indicated by elevated levels of chemosensory behavior in the unfamiliar probe trials.