HYBRID VIGOR AND MATERNAL ENVIRONMENT IN MICE .1. BODY AND BRAIN GROWTH

Ovarian grafting and surrogate fostering were used to manipulate the pre- and postnatal maternal environments, respectively, in order that the inbred mouse strains BALB/c and C57BL/6J and their reciprocal F1 hybrids experienced either an inbred or an F1 hybrid environment pre- and/or postnatally. Results revealed sizeable heterotic as well as maternal environmental effects on birth, weaning and 100-day body weights as well as on brain weight at 100 days. The maternal environmental effect on brain weight was mediated by its effect on body weight, but there was heterosis for brain weights even when body weight was taken into account. At birth and weaning, inbreds appeared to benefit more from the hybrid maternal environment than did hybrids, but we found no evidence of increased variability of inbreds compared to hybirds (homeostasis) within experimental conditions.