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 ge netic variance in fitness-related traits, significant heritabilities in sec ondary sexual traits are an increasingly reported phenomenon. Some evidence suggests that fluctuating asymmetry (FA) in secondary sexual traits may re flect the genetic quality of the trait bearer. Consequently, females in sea rch of 'good genes' should pay attention to ornament symmetry. If FA does r eflect genetic quality which females can assess, an additive genetic compon ent would be expected. Using sib analysis, we found that the length of the sexually selected forceps of male European earwigs (Forfcula auricularia) h ave significant levels of additive genetic variance. However, using both si b analysis and an estimate derived from the genetic and phenotypic correlat ions of the left and right sides, we found no evidence for additive genetic variance in forceps FA. These results thus provide evidence that female pr eferences for exaggerated secondary sexual traits can influence trait expre ssion in offspring.