Fluctuating asymmetry is nongenetically related to mating success in Drosophila buzzatii

To date, there is still no consensus on the real significance of fluctuating asymmetry (FA) in evolutionary biology. Some studies have established links between FA and Darwinian fitness, and in a number of cases intermediate heritabilities for FA have been reported. However, many claims have been raised against the generality of these findings. I therefore tested if FA of a sexually selected trait (wing length) is indeed related to male mating success in Drosophila buzzatii from field and laboratory samples and whether FA has detectable heritability. Single, unsuccessful males had greater asymmetry for wing length than their mating counterparts both in nature and under nonoptimal rearing environments, but the higher FA in single males is most likely due to a poorer average phenotypic condition because there was no evidence of a genetic basis for this trait. Further evidence of an increase in FA under larval food stress is suggested when comparing the magnitude of the FA levels between stressful and optimal environments. On methodological grounds, a linear model is suggested that allows directional asymmetry (DA) and any genetic variation of DA that may be present to be statistically eliminated from estimates of FA.