Flies, like most insects, are poikilothermic ectotherms. This means that unlike us, their body temperature follows the temperature of the surrounding air. When it is warm, flies are happy; a cold fly is a sad fly, and we are beginning to understand why. New research conducted in the Faculty of Science at York University suggests that fruit flies can’t tolerate low temperature for an interesting reason: their guts get leaky.
Common fruit fly, Drosophila melanogaster (image: Heath MacMillan, York University)
“Most fruit flies are chill susceptible,” said Heath MacMillan, who is now based at Carleton University, but led the study as a Banting Postdoctoral Fellow working with Professors Andrew Donini and Scott Kelly in the Department of Biology. “That means that unlike some insects that can survive or avoid freezing solid in the cold, they simply cannot take it, and instead die at relatively mild low temperatures.”
Graduate students Gil Yerushalmi, who is supervised by Donini, and Sima Jonusaite, who is co-supervised by Donini and Kelly, were also authors on the study, which was published in Nature Scientific Reports.
In the cold, insects struggle to keep salts and water from accumulating in their gut, and this loss of balance can trigger cell death. If these injuries are severe enough, the insect cannot survive. The researchers used fruit flies to examine whether this loss of balance was related to a problem regulating the barriers between cells in the gut. Indeed, exposure to a temperature of 0 C caused the guts of the flies to get leaky. However, exposing the flies to just a bit of chilling first led them to be more cold tolerant.
“If we first exposed the flies to 10 C to acclimate, their cold tolerance improved, and they were also better able to maintain the barriers in their gut tissues,” said Donini. “These changes were specifically associated with changes in proteins that we already know are structural components of these barriers.”
The researchers plan to use this information to examine specifically how these proteins are contributing to insect survival in the cold. The ultimate goal is to better understand how temperature sets critical limits to insect survival, which has implications for controlling insect pests in a period of climate change.