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 °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 °C, 20 d at 8 °C and 12 weeks at 11 °C. Reproduction did not occur at these temperatures, but progeny were obtained after recovery at 25 °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 °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 °C for 8-10 weeks. In the case of w1118 flies, replacement of the parents within 6 d of recovery was possible for up to 60 d at 11 °C. Among less fertile genotypes, replacement of the parents was possible within 18 d after 4-10 weeks at 11 °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 °C

Fertility (<i>w</i>¹¹¹⁸) After Housing Flies at 11°C <i>vs</i>. 25°C (10–40 d).

<p>*SS = sum of squares. **df = degrees of freedom.</p

Fertility (<i>w</i>¹¹¹⁸) After Housing Flies at 11°C (0–84 d).

<p>*SS = sum of squares. **df = degrees of freedom.</p

Fertility of adult <i>w</i>¹¹¹⁸ flies after recovery from incubation at 11°C.

<p>Within 1 d after eclosion, groups of 3 females and 3 males were crossed and placed immediately at 11°C for 0–84 d. Unmated flies were housed at 25°C for 10–40 d, and then crossed. All flies were then provided with fresh vials for 3 successive broods at 25°C, each of 2 d duration. Results for all broods (mean ± S.D.) are numbers of adult F1 progeny per original parental fly (total progeny divided by 6). n = 4 vials per time point, except n = 8 at 0 weeks and n = 5 at 12 weeks. (A) 11°C. (B) 25°C. (C) Sums of progeny per parent from all 3 broods at 11°C or 25°C. The horizontal bar in (C) represents the threshold for stock replacement, i.e. 1.0 fully eclosed F1 adult per parental fly after 6 d.</p

Fertility (<i>y w</i>) After Recovery from 8°C Cold Stress (2–14 d) With or Without Food.

<p>*SS = sum of squares. **df = degrees of freedom.</p><p>***Housing was in polypropylene vials with food, or polystyrene vials with or without food.</p

Fertility (<i>y w</i>) After 8 Weeks at 11°C on Different Media.

<p>*SS = sum of squares. **df = degrees of freedom.</p

Fertility (<i>y w</i>) After 8 Weeks at 11°C – Condition I.

<p>*SS = sum of squares. **df = degrees of freedom.</p

Media for 11°C: <i>y w</i> Experiment 2.

<p>*Am°unts are fold differences in comparison with the standard medium containing 1.875 g/L methyl-4-hydroxybenzoate (dissolved in 15 mL ethanol/L).</p

F1 Fertility (<i>y w</i>) After Housing Parents at 11°C for 8 Weeks on Different Media.

<p>*SS = sum of squares. **df = degrees of freedom.</p

Fertility (TM3, <i>ry</i>^RK<i>Sb</i>¹<i>Ser</i>¹/TM6B, <i>Tb</i>¹) After Housing Flies at 11°C (0–12 Weeks).

<p>*SS = sum of squares. **df = degrees of freedom.</p