Intrasexual variability of a conspicuous social signal influences attack rate of lizard models in an experimental test

Abstract

Colorful sexual traits are shaped by the opposing pressures of natural and sexual selection. Although increased conspicuousness improves mating success, an individual bearing brighter sexual traits may pay direct costs in terms of detectability to predators. While it is well established that the mere presence of non-aposematic, conspicuous sexual traits influences predation risk, little empirical work has examined how within-sex variability in sexual trait coloration affects attack rates; of these studies, results are equivocal. We experimentally tested the hypothesis that, within a single sex, brighter sexually selected traits impose a greater survival risk. We created clay models resembling male water anoles (Anolis aquaticus) and manipulated the coloration (bright red vs. brown-orange) of their colorful sexual ornament, the dewlap. Models were placed and monitored within A. aquaticus habitat. Our results suggest that a more conspicuous dewlap coloration is a cause of increased attack: redder models were attacked more than twice as often as less red models. Although previous studies have found correlational relationships between conspicuous coloration and predation, or have demonstrated long-term evolutionary changes in sexual dichromatism caused by a change in predator regime, our results show direct, within-lifetime costs of conspicuous sexual coloration among individuals of the same sex. These findings correspond well with a contemporary understanding of the drivers of female choice for costly male traits. These results also suggest the need for additional study on the effects of predation on the evolution of intrasexual variation in colorful sexual traits.