Intrasexual Signalling and Aggression in male rock agama, Psammophilus dorsalis

Abstract

Contests between males are costly, and hence animals have evolved signalling tactics which are modulated based on the level of threat that they encounter. I studied intrasexual competition in male Psammophilus dorsalis, or the Indian Rock Agama, in the field, by presenting model lizards representing different levels of threat in the home range of residents. There were two types of model presentations: 1) On a rock perch, where the lizards are usually found, and 2) On the ground, next to rock perch occupied by the males. Intruder at these two locations were expected to represent different threat levels. In addition, a PVC pipe was presented on the perch in order to verify that the models are indeed treated as intruders, and not as any novel object. Focal observations of these individuals were done prior to and after model presentation. I found that individuals do show a higher level of a few aggressive behaviours, namely lateral compression and gular extension to the intruder on the perch as compared to the novel object and to focal observations without intruders. However, there were no clear differences in behavioural responses to the models presented on the perch and on the ground, except that individuals came close to the model consistently more often when model was presented on perch. This study provides evidence that male Psammophilus dorsalis indeed defend their home ranges against intruders. But, the position of the intruder within the home range with respect to the rock perches does not seem to matter. To the best of our knowledge, this study provides the first instance of documentation of response of a tropical lizard to a simulated intruder in the field.