Hoisting the white flag of surrender? Color change in agonistic encounters between Achala copper lizard males (Pristidactylus achalensis)

Abstract

Sexual selection pressures play a significant role in driving the evolution of color, morphological, and behavioral traits that serve as signals to communicate fighting ability between opponents. In lizards, body and head size often predict the outcome of male-male contests, but these morphological signals are static during and after the contest. However, coloration and behaviors may be dynamic traits that change during interactions being a potential mechanism of continuous evaluation of current or future opponents. In this study, we examine the function of color change as a signal in agonistic interactions between males of the Achala copper lizard. Also, we examine the relationship between fighting ability and multiple traits, including body size, head size, behaviors, and coloration. Furthermore, we explore the variability of agonistic encounters between reproductive and non-reproductive periods. We performed dyadic trials between males to evaluate behavior and measure dorsal color before and after the trials. Results show that Pristidactylus achalensis can modify the lightness of their skin during intrasexual interaction, with winners displaying lighter colors than losers. We observed dramatic changes from very light green to totally dark coloration. Notably, color difference between competitors was distinguishable only after the trial, not before. Winners also displayed more push-up behaviors, predicting the outcome of the agonistic interactions. Additionally, we did not find differences in the behavioral repertoire between periods (reproductive vs non-reproductive). We suggest that push-up behavior and color change are essential signals that allow contenders to assess their opponent’s fighting ability from a distance without physical interaction and settle conflicts without escalating aggression.