Sexual dimorphism in the second-to-fourth digit length ratio in green anoles, Anolis carolinensis (Squamata: Polychrotidae), from the southeastern United States

Abstract

Digit length ratios are organized during embryonic development and may show sexual dimorphism related to steroid exposure. The second-to-fourth digit length ratio (2D:4D) has received the most attention. In the present study, we measured 2D:4D of all four feet of adult male and female green anoles (Anolis carolinensis Voigt, 1832) to determine whether it is sexually dimorphic and whether results are repeatable across laboratories. Lizards were housed at Michigan State University (MSU) and Oklahoma State University (OSU), and one investigator at each institution used digital cali- pers to measure the 2D:4D of each foot. At both MSU and OSU, we found that males had a significantly larger 2D:4D on the back right foot than females did, and that no sex difference existed in either the back left or the front right foot. Fur- thermore, although no sex difference in the front left foot was found at MSU, the 2D:4D on this foot was larger in females at OSU. Our results demonstrate both sexual dimorphism in 2D:4D and repeatability between laboratories, but they also suggest the importance of verifying such repeatability if 2D:4D or any other digit length ratio is used as a potential indica- tor of the early steroid environment.