This article is from the WSSF 2015 AFRMA Rat & Mouse Tales news-magazine.

Did You Know?  Females in better body condition (i.e., more energy reserves in adipose tissue) produce a greater proportion of male offspring, as males would benefit more from increased parental investment.

Published in Science 1973; 179:90–92, Natural selection of parental ability to vary the sex ratio of offspring. Trivers RL, Willard DE.