Differences in levels of xanthine dehydrogenase activity between inbred and outbred strains of Drosophila melanogaster.

Levels of activity of xanthine dehydrogenase in homogenates of individual flies were measured by fluorometry for three inbred strains and two large, randomly breeding, laboratory populations of Drosophila melanogaster. The patterns of activity during the first five days following eclosion differed significantly between the inbred strains and the randomly breeding populations. In the latter, the levels rise from day 0 to day 2, then fall through day 4; in the former, the levels rise continuously throughout the period. The variances within days calculated on the logarithms of the observations are constant for the large populations, but show significant variability within and between the inbred strains. These differences parallel earlier observations on time of development and probability of embryonic success in the same strains. All these results suggest more effective regulatory mechanisms in the randomly breeding populations.