The effect of three ecological stresses on variation of morphological traits in Drosophila melanogaster

The effect of temperature, nutrition, and density stresses on phenotypic an d genetic variation in morphological traits (thorax length, wing length, nu mber of sternopleural and abdominal bristles, and number of arista branches ) was examined in Drosophila melanogaster. In addition, the effect of stres s on developmental stability measured as fluctuation asymmetry of bilateral traits was analyzed. All of the stresses were shown to increase phenotypic variation and fluctuating asymmetry of bilateral traits. Genetic variation of morphometric traits estimated using the isofemale line technique was hi gher under stressful than under normal conditions. Biotic and abiotic stres ses were similar in their effect on phenotypic and genetic variation. The e ffect of stress on variability of morphometric traits was generally higher than on that of meristic traits. Possible causes of the increase of genetic variation under stress are discussed.