Phototactic responses along a gradient of light intensities for the sibling speciesDrosophila melanogaster andDrosophila simulans

The phototactic responses of four recently collected isofemale strains ofDrosophila melanogaster andDrosophila simulans were measured in a light gradient from 590 to 10 lux. High light intensities were preferred by most flies, but a small proportion of flies preferred the lowest light intensity. Based on the strains tested,D. simulans showed greater phototaxis thanD. melanogaster, and within each species variability was found. The niche breadth ofD. melanogaster appears likely to be greater than that ofD. simulans for phototaxis in the light gradient. These results are in general qualitative agreement with earlier results published on dispersal activities from the same populations.