Temperature shock during development fails to increase the fluctuating asymmetry of a sexual trait in stalk-eyed flies

The fluctuating asymmetry (FA) of bilateral traits is claimed to be a gener al indicator of environmental stress. Exaggerated sexual ornaments are thou ght to show elevated levels of FA and a greater response to stress than oth er traits. Previous work with stalk-eyed flies (Cyrtodiopsis dalmanni) has shown that the FA of the sexual trait (male rye stalks), wing length and wi ng width were unaffected by a continually applied food stress. Here we test ed whether a transient stress (24-h heat shock at 31 degreesC during develo pment affected the FA of these traits. A second experiment tested the combi ned stresses of transient heat shock at 31 degreesC: with continuous exposu re to desiccation. In each experiment, temperature shock reduced the trait size, confirming that the treatments were stressful. However, stress had Il o effect on the FA of individual traits, or the FA summed across all traits . Exposure to the combined stresses significantly elevated mortality and re duced trait size compared to the single-stress regime. However, FA did nor differ significantly between flies front the two experiments. We found no e vidence that FA in sexual and non-sexual traits reflects transient stress d uring the development of C. dalmanni.