The ontogeny of cross-sex genetic correlations: an analysis of patterns.

The independent evolution of males and females is typically constrained by shared genetic variance. Despite substantial research, we still know little about the evolution of cross-sex genetic covariance and its standardized measure, the cross-sex genetic correlation (r(MF)). In particular, it is unclear if r(MF) tend to vary with age. We compiled 28 traits for which ontogenetic trends in r(MF) were documented. Decreases in r(MF) with age were observed significantly more often than increases and the mean effect size for the relationship between r(MF) and age was large and negative. This suggests that sexual dimorphism (SD) may typically evolve more readily for phenotypes expressed later in ontogeny and that evolutionary inferences related to the evolution of SD should be limited to the ontogenetic stage at which r(MF) was estimated. Knowledge about ontogenetic variation in r(MF) should help improving our understanding of evolutionary patterns related to SD and the resolution of intralocus sexual conflicts.