Sexually selected traits vary over a latitudinal gradient in green anole lizards ( <i>Anolis carolinensis</i> )

Abstract Species frequently exhibit ecogeographical trends such that phenotypes in different populations vary according to local conditions along a geographical cline or gradient. Latitudinal gradients for traits such as body size and shape are thought to be driven by variation in environmental temperature, but we currently lack an understanding of how such variation affects both sexual size dimorphism and the expression of secondary sexual traits. We measured sexual size dimorphism and the relative size of dewlap area, bite force, and head morphology in four populations of green anole (Anolis carolinensis) lizards spanning a latitudinal gradient in the eastern United States. We found that while populations at lower latitudes exhibit greater sexual size dimorphism than those further from the equator, the relative expression of secondary sexual traits did not consistently follow this pattern, with bite force and dewlap area exhibiting negative and positive relationships with latitude, respectively. We also found that bite force and head shape are decoupled in male green anoles at both the highest and lowest latitudes, suggesting that other selective forces are acting on head morphology in these populations as well.