The prenatal environment affects offspring phenotype later
in life, and there is increasing recognition that these
effects may differ between males and females. In placental
mammals, it has been hypothesized that male and female
fetuses follow different strategies, whereby
in the face of adversity males take a riskier
approach to prioritize growth (but risk short-term
survival), whereas females are more responsive to
challenges, reducing growth to increase survival. However,
the evidence in support of this hypothesis is mixed at
best. Furthermore, this research often suffers from a lack
of robust statistical testing, whereby authors test the
sexes separately, rather than explicitly testing the
statistical interaction between sex and early-life
environment (Chin
and Christians 2015). This can result in frequent
false positives, explaining the lack of repeatability in
sex-dependent effects (Christians
et al 2021). Furthermore, much of the literature
uses prenatal challenges (e.g., maternal high-fat diet)
that would not have been encountered in the animal’s
evolutionary past; these responses to adversity are
therefore not necessarily adaptive. We are focusing on
evolutionarily-relevant adversities and outcomes for which
sex-dependent strategies might be expected, including
maternal and paternal low protein diets, maternal stress
and advanced maternal age. In addition, we are examining
the mechanisms underlying sex-dependent responses, i.e.,
whether they are due to chromosomal complement (XX vs XY)
and/or gonadal sex. A better understanding of the
molecular mechanisms will shed light on the evolutionary
basis of sex differences.
