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 rig ht 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 instabil ity 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-tetrachlo rdibenzo-p-dioxin (TCDD) would increase the level of FA in the mandibles of their offspring. We used ten landmark coordinates around the mandible to c reate a single size variable (centroid size) and 20 Procrustes shape variab les. These were used to test for effects of dioxin on mandible size and sha pe and their asymmetries. We found no detectable effect of TCDD on levels o f FA in either size or shape of the mandible, but TCDD did produce a signif icant decrease in mandible size, and a significant effect on the overall sh ape.