Maternal Effects on Body Size of Large Insular Peromyscus maniculatus: Evidence from Embryo Transfer Experiments

Abstract

Adult Peromyscus maniculatus gambelii from mainland California are significantly smaller than P. m. santacruzae from Santa Cruz Island, California, whether they are captured in the wild or raised from birth in captivity. The two subspecies also differ significantly in weight as neonates. Results from the experimental transfer of 4-day old P. m. gambelii embryos into P. m. santacruzae foster mothers demonstrate that the average neonatal weight of P. m. gambelii offspring increases significantly if they are borne and delivered by P. m. santacruzae foster mothers. This apparent prenatal non-genetic maternal influence on neonatal body size does not appear to be caused by differences in gestation period or average litter size, or by a genetic bias in the donor sample. Although the transferred offspring were large at birth, and were nursed by the large P. m. santacruzae foster mothers, they were relatively small (equivalent to other P. m. gambelii) at maturity. The results of our experimental studies are concordant with predictions from quantitative genetic studies on laboratory mice.