Effects of prenatal litter size in inbred mice on morphometric characters with different developmental patterns

Prenatal litter size effects were assessed in two inbred, cross-fostered strains of house mice (A/J and C57BL/10J) in order to see whether they differed among morphometric characters with different developmental histories. Three characters were used: body size, which exhibits both prenatal and postnatal development; the width of the second mandibular molar (M2), which exhibits mostly prenatal development; and the width of the third mandibular molar (M3), which exhibits all postnatal development. Prenatal litter size regressions differed significantly between fostered and non-fostered groups for each of the three characters in at least one of the two inbred strains, and as hypothesized, tended to be more negative in sign for the M2 versus the M3. Prenatal litter size differences accounted for 19% of the total variation in body size, but just 5% in both molar widths. Prenatal litter size also significantly affected the covariation among the characters, and in a direction consistent with their developmental histories. It was concluded that prenatal litter size can significantly affect a number of morphometric characters and that the magnitude and nature of these effects may be related to the developmental patterns of the characters.