Effects of methoxychlor on directional and fluctuating asymmetry of mandible characters in mice

Two kinds of asymmetries are common in bilateral characters: fluctuating asymmetry (FA), a type of nondirectional variation between left and right sides, and directional asymmetry (DA), in which one side is consistently larger than the other. FA has been extensively used as a measure of developmental instability and is presumed to increase as stress from toxins or other sources increases. In this paper we tested the hypothesis that exposure of pregnant female mice to two different dosage levels of methoxychlor (MXC), an insecticide derived from DDT, would increase FA in one or more of 10 mandible characters measured in the offspring of these females. The data showed that exposure of pregnant females to MXC produced no detectable effect on FA in their offspring, but at the higher dosage level (10 mu g/g body weight), did change FA to DA in one of the characters. MXC also had a significant effect on the mean size of five of the mandible dimensions, all of which were located primarily in the anterior portion of the mandible.