Effect of Prolonged Coldness on Survival and Fertility of Drosophila melanogaster

The laboratory fruit fly, Drosophila melanogaster, is used widely in biological research, but the requirement to maintain stocks with a roughly biweekly generation time imposes substantial burdens of labor, potential cross-contamination and mutation accumulation. The purpose of this study was to assess the impact of prolonged cold stress or milder cooling on survivorship and fertility. The hypothesis was that cold storage would result in postponement of reproduction and a longer generation time. Flies of several genotypes were maintained continuously at 4-11 degrees C; recovery rates and subsequent yields of adult progeny were recorded. Adults and pupae of a relatively long-lived y w lineage were more resistant to severe cold stress than embryos and larvae. Adults exhibited minimal mortality up to at least 5 d at 4 degrees C, 20 d at 8 degrees C and 12 weeks at 11 degrees C. Reproduction did not occur at these temperatures, but progeny were obtained after recovery at 25 degrees C. At all temperatures, chilling caused a rapid, severe and progressive decrease in fertility during the first 2 d of recovery. The impact on fertility during the subsequent 2-4 d was much milder and it occurred only after prolonged incubation at low temperatures. The total reproductive output during the first 6 d of recovery was sufficient to replace the parental population after 12 weeks at 11 degrees C. Food spoilage had an unexpectedly low impact on survivorship and fertility, and the reproductive output of F1 progeny was not affected by storing parental flies at 11 degrees C for 8-10 weeks. In the case of w(1118) flies, replacement of the parents within 6 d of recovery was possible for up to 60 d at 11 degrees C. Among less fertile genotypes, replacement of the parents was possible within 18 d after 4-10 weeks at 11 degrees C. These results show that the 2-week maintenance interval of stocks of D. melanogaster can be extended 3-7 fold, at least for 1 generation, by storing adult flies at 11 degrees C.