Fluctuating thermal regimes extend longevity and maintain fecundity to increase colony shelf-life of Drosophila melanogaster

Authors: Melicher, Dacotah; WILSON, AMANDA - North Dakota State University; Yocum, George; Rinehart, Joe

Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2021
Publication Date: 5/2/2021
Citation: Melicher, D.M., Wilson, A.M., Yocum, G.D., Rinehart, J.P. 2021. Fluctuating thermal regimes extend longevity and maintain fecundity to increase colony shelf-life of Drosophila melanogaster. Journal of Thermal Biology. https://doi.org/10.1111/phen.12357.
DOI: https://doi.org/10.1111/phen.12357

Interpretive Summary: Fruit flies are a common species used for research and are often used as a safe stand-in for invasive insects, those that carry diseases, pest insects with high economic impact, and those that are hard to raise in a lab. They are also the most used for genetic modifications, which are expensive to produce and maintaining them also has a significant economic impact. Insects cannot control their body temperature and some grow slowly and live longer under cold temperatures, but they deteriorate over time under these conditions. By giving them brief pulses of warm temperature they are able to repair damage and live even longer than just cold temperatures would allow. We developed a protocol that allows fruit flies to live on average 10-times longer than they would under industry standard rearing conditions. This means that individual flies which normally live 2-3 weeks live several months without additional care. We test flies to see if they can still reproduce after long periods under our protocol of cold storage with a warm pulse. We find that after 60-80 days flies are still able to lay approximately as many fertile eggs as flies under industry standard rearing conditions. This has the potential to reduce the cost of labor and consumable materials at stock centers that maintain thousands of strains and tens of thousands of individual colonies. It also has the potential to aid researchers who wish to work with large numbers of flies but are limited by labor. We continue to refine our protocol to increase longevity and reduce costs of storage. This also shows us how insects are able to live under cold temperatures and survive winter seasons by using brief warm periods to repair damage.

Technical Abstract: Reduced temperatures increase longevity in cold-tolerant insects, but insects that are not cold-tolerant experience elevated mortality at constant low temperatures. Fluctuating thermal regimes (FTR) increase longevity in many insect species while slowing or delaying development and senescence. Under FTR insects are held at low temperature with a daily warm pulse of increased temperature. Drosophila melanogaster is an important model organism and considerable resources have been applied to developing transgenic strains that are preserved in continuous culture at stock centers. We measured the effect of FTR compared to constant temperature (CT) on the longevity and fecundity of adult D. melanogaster incubated at CT of 6°C and 22°C, and FTR that oscillates between 6°C and 22°C. We demonstrate a FTR that oscillates between the cold and warm constant temperatures greatly increases longevity with mean survival approximately seven times longer than CT and up to 241 days. We assessed the effects of FTR on male and female fecundity at 20 day intervals from 20 to 100 days. Under FTR male flies exhibited increased fecundity peaking at 80 days before dropping significantly at 100 days. Female fecundity declined steadily under FTR but remained at 53% of control after 60 days when no flies remained alive in either CT treatment. The reduction in female fecundity is likely a combination of the high cost of egg production and loss of fat stores over long incubation, while the increase in male fecundity remains unexplained. Offspring reared from each treatment group did not differ from control. We demonstrate that FTR extends generation time and after 80 days flies incubated under this protocol are capable of establishing new colonies. FTR can be used to further investigate the accumulation and mitigation of chill injury, and may be a valuable tool for reducing colony maintenance in stock centers.