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 have demonstrated that indiv iduals 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 relat ive importance of genes versus environment in determining the level of FA s hown by an organism is currently the subject of much controversy. As yet th ere is no clear consensus as to whether FA generally has a heritable compon ent and if so how large this might be, or indeed if it is sensible to gener alize at all. In Musca domestica flies with low wing length FA have been fo und to enjoy higher mating success. In order to interpret this finding we a ssess whether wing length FA in this species is inheritable, and also how i t is influenced by environmental stresses induced by temperature and crowdi ng. We also examine whether offspring viability is related to parental FA. We found that wing length FA in M. domestica had no detectable heritable co mponents, and parental FA did not influence offspring viability. FA was inf luenced by rearing temperature, with flies exhibiting highest FA at the low est rearing temperature (15 degrees C). Larval survival rate was greatest, and the resulting adults largest, at the intermediate rearing temperature ( 25 degrees C) compared to higher of lower temperatures, suggesting that 25 degrees C is close to the optimum for the development than does wing FA. Th ese results are discussed in relation to the unity of FA as a tool for use in evolutionary studies. (C) 2000 The Linnean Society of London.