Geographic variation in male agonistic display among three populations of the lizard Amphibolurus muricatus: the role of habitat structure, predation risk and temperature

Signal diversification is often the product of sexual or natural selection and may be accompanied by genetic differentiation or reflect a plastic response to environmental variables. Visual displays of lizards performed during communication with conspecifics can be affected by a multitude of factors including habitat light and habitat structure, predators, and the thermal environment. Widely-ranging species occupying different habitat types and environmental conditions including predator type and density are predicted to exhibit greater variation in signal form and function.This geographic variation can manifest itself in differences in communication and even population-level aggression and dominance. I use an agamid lizard from Australia, the Jacky dragon (Amphibolurus muricatus) to: 1) examine geographic variation of intrinsic features such as genetic structure, morphology, performance capacities, body temperature and signaling behaviour; 2) determine the variation of extrinsic factors such as the characteristics of the habitats, predation risk and ambient temperature experienced by these populations; and 3) establish the relationships between intrinsic and extrinsic factors and the repercussions for the communicative system of the species. I sampled three populations (Yarratt State Forest, Royal National Park and Cann River State Forest) across the range of the species (at least 280 km apart) and collected data in the field on morphological traits and body temperatures of lizards, as well as the structure and complexity of the habitat. I also performed lab experiments to record the variation in signaling behaviour, performance capacities and preferred body temperature of animals. I found that individuals from two more closely-related populations were alsomore similar in morphology and field body temperatures than lizards from a third, more distant population. All three populations differed in performance capacities and characteristics of the signaling behaviour. Variation in visual displays and habitat use was unrelated to habitat structure and complexity. Predation risk and thermal environment were highly variable along the distribution of the Jacky dragon and both factors have an effect on the properties of the signaling behaviour. No significant differences in aggression were found during intra- and inter-population contests, although one population seemed to be dominant over the others and different rules among populations seemed to govern the outcome of contests. I argue that display variation might be a consequence of behavioural plasticity and that, despite difference in genetic structure, morphology and behaviour, the species retains a communicative cohesion.