2,3,7,8-Tetrachlorodibenzo-p-Dioxin Affects Size and Shape, But Not Asymmetry, of Mandibles in Mice

Fluctuating asymmetry (FA), the random differences between the left and right sides of a bilaterally symmetrical character, is often purported to be a sensitive measure of developmental instability particularly in populations exposed to environmental stressors. As the level of developmental instability increases, often too does the level of FA. In this study we tested the hypothesis that exposure of pregnant mice to low doses of 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) would increase the level of FA in the mandibles of their offspring. We used ten landmark coordinates around the mandible to create a single size variable (centroid size) and 20 Procrustes shape variables. These were used to test for effects of dioxin on mandible size and shape and their asymmetries. We found no detectable effect of TCDD on levels of FA in either size or shape of the mandible, but TCDD did produce a significant decrease in mandible size, and a significant effect on the overall shape.