The role of body size in competition and mate choice in an agamid with female-biased size dimorphism

Competition and mate choice are fundamentally important components of social systems. We investigated intra-sexual competition and inter-sexual competition (mate choice) in Rankinia diemensis, an agamid lizard with female-biased size dimorphism. We examined intra-sexual interactions during contests and mate choice in relation to body size for both males and females. In male-male competition trials, proportions of two display types differed depending on body size, with more tail flicks produced by bigger males, and more hand-waves displayed by smaller males. These behaviours hold particular biological significance for agamid lizards; tail-flicks convey aggressiveness and, therefore, dominance, while hand-waves often denote submissiveness. In female-female competition trials, a greater difference in body size between the two conspecifics resulted in the larger female directing more pushes towards the smaller female. This female competition may be important in the social system and could be involved in resource defence. We found no indication of size-based mate choice for males or females. This suggests mate preferences may not be based on body size in this species. This may be linked to female-biased size dimorphism in this species, but it also supports previous studies that have failed to demonstrate female choice in reptiles. © 2007 Brill Academic Publishers.