Variations of Drosophila in relation to its environment VII

Does Drosophila change its characters during dark life? (1)

Abstract

1. Drosophila melanogaster, Oregon RS strain, was segregated into 6 independent strains, of which 3 strains were reared under normal daylight conditions (the light series) and the remaining 3 strains were cultured in continuous darkness (the dark series). Both sets were cultured in Pearl's medium at a temperature maintained at 25°C.
2. At intervals of a few generations or of several tens of generations the photic reactions of the flies were tested. Flies of the dark series which were to be tested were reared for one generation from the egg stage in the normal daylight condition (Fig. 1). This report is concerned with the results obtained during 108 generations.
3. Ten males or females, 2 or 3 days after emergence, were put into a test tube (Fig. 2) and dark adapted. Twenty minutes later, the flies were gathered at one end of the tube and the test tube was illuminated longitudinally from the opposite end by a parallel light source. The flies began to move toward the light source, and the numbers of individuals, passing across the line marked at the center of the test tube, were counted every 15 seconds during 1 minute. In this report the number passing across during the first 30 seconds was taken as an index of the degree of “phototaxis+photokinesis”. This counting was repeated three times with the same materials.
The said light source was then extinguished and a diffused light source which illuminated from the side of the test tube was switched on. The number of individuals moving within 1 minute across three lines, marked at equal intervals on the test tube, was counted. The numbers thus obtained were taken as an index of the degree of “photokinesis”. This counting was also repeated three times with the same materials.
These sets of experiments were repeated twice for each strain with males and females respectively. (refer to Fig. 2).
4. Both male and female flies which were cultured in continuous darkness reacted more vigorously or sensitively to sudden illumination than those cultured under normal daylight conditions (Tab. 1-6). The photokinetic response in the males and the phototaxic response in the females seemed to be chieflv responsible for the difference in behavior.
5. Differences of behavior in the “photokinesis+phototaxis” experiments were so delicate as to be almost negligible after the flies had been subjected to light for 2 to 3 minutes.
6. These results seem to be consistent with the data published by F. Payne in 1911, although he did not draw the correct conclusions from his data (Tab. 7).