Heritability of size but not symmetry in a sexually selected trait chosen by female earwigs.

The heritability of fitness-related traits remains an area of contention in evolutionary biology. despite theoretical arguments for little additive genetic variance in fitness-related traits, significant heritabilities in secondary sexual traits are an increasingly reported phenomenon. Some evidence suggests that fluctuating asymmetry (FA) in secondary sexual traits may reflect the genetic quality of the trait bearer. Consequently, females in search of 'good genes' should pay attention to ornament symmetry. If FA does reflect genetic quality which females can assess, an additive genetic component would be expected. Using sib analysis, we found that the length of the sexually selected forceps of male European earwigs (Forfcula auricularia) have significant levels of additive genetic variance. However, using both sib analysis and an estimate derived from the genetic and phenotypic correlations of the left and right sides, we found no evidence for additive genetic variance in forceps FA. These results thus provide evidence that female preferences for exaggerated secondary sexual traits can influence trait expression in offspring.