Differences in Aggressive Behavior between Two Throat Color Morphs in a Lizard, Urosaurus ornatus

In a population of Urosaurus ornatus in New Mexico, males are polymorphic for throat color. Two relatively abundant morphs occur, one with a green central spot on the throat and a second with an orange throat. Tests in an outdoor enclosure indicated that green males are more likely to dominate similarly sized orange males than is expected by chance. Trials in which color was altered by painting indicated that this difference was related to the perception of an opponent's throat color. Experiments in which tethered males were introduced into the proximity of free males showed that orange residents are more likely to attack intruders than are green residents, perhaps because intruders display more often to orange residents than to green. Some tethered intruders even dominated orange residents. Orange males observed in natural encounters were more likely to be of above average size than were similarly observed green males.