BRANDT, Y.; ALLEN, J.R.; Indiana University, Bloomington; University of Colorado, Boulder: Individual Distinctiveness of Pushup Displays

Individual recognition modifies many social interactions, like aggression, territoriality, and sexual behaviors. Neighbor-stranger discrimination is known in several lizard species, but the signals that allow lizards to recognize social partners remain unknown. Any signal that promotes recognition must be individually distinctive, stable through time and resistant to changes in physiological state. Pushups, which consist of rapid vertical movements of the head and trunk, are steroetyped species-typical displays performed by iguanian lizards in a variety of social contexts. This study examined whether the pushup displays of side-blotched lizards (Uta stansburiana) meet the requirements of recognition signals. To minimizing confounding sources of variation in pushup structure the analysis was limited to adult males that were collected within a localized population and to displays elicited under controlled conditions. Well-rested subjects were individually stimulated to perform a series of pushups in an experimental arena containing a mirror. Subjects were stimulated to display again on the following day, immediately after running on a motorized treadmill. The duration and the relative height of display sub-units exhibited repeatable differences between individuals. These variables allowed displays to be assigned to the correct individuals by discriminant function analysis at rates much higher than expected by chance, establishing that pushups are individually distinctive. Pushups were assigned successfully both within and between days, demonstrating that pushup structure is maintained through time and is resistant to fatigue. Our results show that pushups are a tenable substrate for social recognition, but whether pushups are indeed used to perform recognition tasks awaits confirmation with playback experiments.