Environmental versus genetic influences on fluctuating asymmetry in the house fly, Musca domestica

The causes of fluctuating asymmetry (FA) are poorly understood, yet it has been widely used as a measure of fitness. Many studies have demonstrated that individuals with low FA are preferred as mates, and it has been argued that this is because FA provides an indicator of genetic quality. However, the relative importance of genes versus environment in determining the level of FA shown by an organism is currently the subject of much controversy. As yet there is no clear consensus as to whether FA generally has a heritable component and if so how large this might be, or indeed if it is sensible to generalize at all. In Musca domestica flies with low wing length FA have beeen found to enjoy higher mating success. In order to interpret this finding we assess whether wing length FA in this species is heritable, and also how it is influenced by environmental stresses induced by temperature and crowding. We also examine whether offspring viability is related to parental FA. We found that wing length FA in M. domestica had no detectable heritable components, and parental FA did not influence offspring viability. FA was influenced by rearing temperature, with flies exhibiting highest FA at the lowest rearing temperature (15°C). Larval survival rate was greatest, and the resulting adults largest, at the intermediate rearing temperature (25°C) compared to higher or lower temperatures, suggesting that 25°C is close to the optimum for the development of M. domestica. Adult size appears to provide a better indicator of stress during development than does wing FA. These results are discussed in relation to the utility of FA as a tool for use in evolutionary studies.