Regulation of Reproductive Rate by Intra-uterine Mortality in the Deer Mouse

Abstract

Under crowded conditions (four mating pairs per cage), pregnant female deer mice of a partially domesticated strain, Peromyscus maniculatus bairdii, showed increased resorption of implanted embryos, and therefore a 60 percent reduction ii effective natality, as compared with control females living at a populatto density of one pair per cage. No significant difference was found in the incidence of pregnancy or in the number of embryos implanted,but the adrenal glands of crowded females were enlarged by an average of 17 percent (by weight).