[On the reproducibility of transitory effects. The response ofDrosophila melanogaster to a deficient diet and to feeding with thymidine].

Administration of products from resistant grape-vines has been reported to lead to transitory abnormal effects in chickens. The induced abnormalities gradually disappear in later generations. In order to determine whether comparable effects could be obtained in other organisms,Drosophila melanogaster were fed 1) on a nutritionally deficient diet lacking yeast and 2) on a diet containing different concentrations of thymidine, a substance known to have mutagenic and teratogenic effects.In the first series, flies that had developed under normal conditions were placed on the deficient medium for oviposition. These normal flies reacted to the yeast-free deficient diet with a marked reduction in the rate of eggs laid within 48-72 hours after mating. A further reduction in egg-laying rate was observed in F1 flies, raised on the deficient medium and kept under the same conditions for oviposition.F1-males and females, grown on the deficient medium, but transferred to standard medium for egg-laying, showed some degree of rehabilitation with regard to laying-rate within 48-72 hours after mating. However, the number of eggs laid remained significantly below that of the controls.Significantly lower egg rates were also found in F2-flies raised on normal food that were descendents of P1-flies raised on a deficient diet, but whose F1-parents had been raised on normal food.However, if the total number of progeny from these flies was determined instead of the rate of oviposition within 48-72 hours after mating, the low egg rates turned out as a relative rather than an absolute effect. Judged by the number of individuals obtained, complete rehabilitation had taken place, experimental and control values being of the same order. The progeny of treated parents, however, even if raised on the standard diet showed a developmental delay of about 48 hours as compared to the controls. Differences between daily numbers of progeny produced by treated as compared to that of untreated parents, remained significant throughout the entire period of hatching.In a second series of experiments flies developing on food containing thymidine showed a great variety of abnormalities, sublethals and lethals. The frequency in the latter two categories increased markedly with increasing thymidine concentrations.In F1 lethals and sublethals were significantly more frequent among females than among males. Consequently the sex ratio of surviving adults was shifted considerably in favor of males.Further generations (F2-F6) were reared on normal food and checked for mutagenic and/or teratogenic after-effects. As a rule selection for F1 anomalies was not successful. Regardless of the parental phenotype selected in F1, a number (non-significant) of sporadic aberrations re-appeared, representing practically the whole array of abnormalities found in F1 adults. Hardly any abnormal flies were found among the controls.In one case the frequency of one of the wing anomalies could be temporarily increased by selection.Another wing anomaly turned out to be a true recessive mutation, its manifestation depending on at least one dominigene.The results support the hypothesis that transitory effects, followed by rehabilitation, are reproducible. Their relationship to comparable cases that have been reported is discussed.