Competing females strategically combine signals and physical aggression differently from males in a polygynous tropical lizard

Abstract

Intrasexual competition, the intense competition between individuals of the same sex, is a strong evolutionary force that is well known to select for elaborate and spectacular traits in males. In contrast, female-female competition is poorly understood. Although historically expected to be weak, evidence for female-female competition is fast accumulating. Yet, systematic studies of such competition are rare. Here, we frame and test for a strategy of competition in females in a wild population of a classically polygynous lizard, Psammophilus dorsalis. We used models of female P. dorsalis to simulate a gradient in perceived competitor threat to individually tagged, wild females on their territories, and comprehensively measured their signalling and aggression responses. Similar experiments were performed with males. Our results clearly demonstrate a complex, threat-sensitive strategy of direct competition among females in this species with conventional sex roles. Females systematically escalate their use of diverse signals along a gradient in threat and show surprisingly high levels of physical aggression. Comparisons with the responses of males to simulated threats reveal distinct sex differences in competition strategies that match theoretical expectations derived from life history. Using these findings, we argue that female-female competition may be complex but cryptic, requiring experimental manipulations to uncover.