The development of tetrapod digits is directed by the Homeobox (Hox) genes. The expression of Hox genes is influenced by exposure to endogenous sex steroids during development so that prenatal exposure to estrogens and androgens positively influences the lengths of digits 2 (2D) and 4 (4D), respectively. Because of this, Manning (2002) predicted that male tetrapods should have smaller 2D:4D than that of females because males are exposed to higher levels of androgens during development. We measured digits in green anolis lizards (Anolis carolinensis) to (a) test Manning's prediction; (b) compare our results with those of other studies of digit ratios in reptiles and birds to test the phylogenetic constraint hypothesis, which argues that the digit ratios of reptiles and birds should be more similar to each other than either taxa is to mammals because the patterns have been conserved in living diapsids; and (c) compare our results with those of another study of digit ratio in anoles (Chang et al., 2006). We did not detect evidence of sexual dimorphism in 2D:4D. Our results did not support either Manning's prediction or the phylogenetic constraint hypothesis. Furthermore, our results did not match those found in Chang et al. (2006), suggesting that digit ratios in anolis lizards may not be reliable indicators of prenatal exposure to hormones.
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