Intrauterine Position Effects on Anogenital Distance and Digit Ratio in Male and Female Mice
Anogenital distance (AGD) and the ratio of the second (index) to fourth (ring) digit lengths (2D:4D) are two widely used indicators of prenatal androgen exposure. The former is commonly used in rodent models, while the latter is principally used in human studies. We investigated variation in these two traits in C57BL/6J mice to test the hypothesis that variation in these two traits reflect a common underlying variable, presumably testosterone exposure. AGD is a sexually dimorphic trait used to sex young rodents. This distance typically increases and becomes more male-like in females pups when their uterine neighbors are male. 2D:4D is sexually dimorphic in a number of species, including humans and other great apes. Lower digit ratios may be associated with greater exposure to androgens during fetal development in humans. We found the expected sexual dimorphism in AGD, but no significant sex difference in 2D:4D, and no correlation between 2D:4D and AGD. Gestating next to males increased a pup’s 2D:4D ratio, but it had no effect on AGD. The lack of correlation between 2D:4D and AGDs in this mouse strain suggests that these two measures do not reflect a common influence of androgen exposure. The possible roles of temporal and localized effects of masculinization are discussed.
KeywordsIntrauterine position Digit ratio 2D:4D Anogenital distance Masculinization
Research funding by NSERC (Canada) Discovery Grant (249685) to PLH. AGDs were measured by AAB and RHY, 2D:4D by PAG and RHY, and Cesarean sections and gonadal inspections were performed by SP. We wish to thank Doug Wong-Wylie for graciously lending his stereoscope and camera, and Janelle Pakan for assistance in collecting the data. Thanks to John Manning, Dennis McFadden, and Norm Stacey for valuable discussion and comments on this manuscript, and to Clay Dickson, Andy Iwaniuk, Jodie Jawor, Jim Martin, Steve Phelps, Doug Wahlsten, and Karen Wendt for comments on earlier versions.
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