Stress intensity and developmental stability: An experiment in Drosophila melanogaster

The developmental stability of organisms is affected by stress and can be measured in bilateral traits by means of the fluctuating asymmetry (FA). Here we test experimentally the effect of two stressful environmental factors: habitat quality (three levels of food availability) and population density (three levels) on productivity, wing size, and wing FA in Drosophila melanogaster using a two-way factorial design. We expected fluctuating asymmetry to increase monotonically with stress. Individual productivity and wing length were significantly smaller in the poor habitat only. Population density only affected wing length in interaction with food availability. FA was affected by habitat quality, with the highest FA observed in the intermediate habitat quality, while we expected the highest FA in the poorest environment. We suggest that two mechanisms acting simultaneously may be involved according to the intensity of the stress: the balance of the energetic trade-off between development and reproduction may be acting for low stress, and developmental selection may become more efficient for stronger stress, thus hampering our capacity to detect any effect of stress on developmental stability.