Dynamic dichromatism and effects of high temperatures on male coloration plasticity in an ectotherm model

Climate change is increasing the temperatures of wild environments, but the impacts on evolutionary ecological processes, such as sexual selection, are still under-studied. In ectotermic tetrapods, male coloration is a pivotal trait in social contexts. During the reproductive season, males can enhance the dichromatic coloration of certain body regions. However, it is unknown how reproductive dichromatism might interact with the increasing temperatures that cause body temperatures to fall within the upper range of preferred temperatures. We hypothesize that sexual dichromatism could be dynamic, i.e. show changes, being reinforced during the reproductive period of the species. However, high temperatures associated with climate change could disrupt reproductive colour patterns by inducing plastic changes. We test this in the social lizard species Tropidurus spinulosus in a laboratory setting by applying three thermal treatments: one reproducing current thermal conditions and two simulating scenarios of climate change. Our results highlight that male coloration is enhanced during the reproductive season in key body regions for social displays. At the preferred temperature of the species, males could darken their ventral coloration; however, no such change was observed at high temperatures. Therefore, increasing temperatures could impact the capacity of males to adjust their coloration plastically during the reproductive season.