Theory suggests that a male in good condition at the end of the period of parental investment will outproduce a sister in similar condition, while she will outproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. As maternal condition declines from good to poor, the fetal sex ratio should decline from a high proportion of males to a high proportion of females. Data from 1525 domestic reindeer (Rangifer tarandus) in six different herds slaughtered during December and January in 1976 through 1979 do not support a relationship between the sex of the fetus and either the condition of the mother or her age.
Diabetic Embryopathy in C57BL/6J Mice: Altered Fetal Sex Ratio and Impact of the Splotch Allele
