Heath MacMillan CBC Radio Interview

Dr. Heath MacMillan was interviewed on Ottawa Morning on CBC Radio 1 on Monday the 21st of August 2017.

Hear the interview on CBC Ottawa Radio 1 here.

Read the CBC Article How freezing fruit flies helps us better understand a warming climate.

It’s fruit fly season in Canada. Last time you opened your compost bin it was like an explosion. Tiny dots with wings emerged and spread around your house. Now they annoy you every chance they get, and you think twice about whether or not to lift the lid again.

These common visitors to your kitchen are common for a reason: It’s August, so it’s warm and food is plentiful. Flies, like most insects, are poikilothermic ectotherms. This means that unlike us, their body temperature follows the temperature of the air surrounding them. When the air temperature is warm, (like today), the flies are happy, but a cold fly is a sad fly, and we are beginning to understand why. A new study suggests that fruit flies can’t tolerate low temperature for an interesting reason: their guts get leaky.

“Most fruit flies are chill susceptible”, says Heath MacMillan, an Assistant Professor in the Biology Department at Carleton University in Ottawa who led the study. “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.”

The MacMillan Lab at Carleton University studies the physiology of chill susceptible insects. “We know surprisingly little about the physiological mechanisms that set the limits of animal survival at high and low temperatures” says MacMillan. “With insect populations already responding to rapid climate change, there is an urgent need to understand how temperature impacts insects”. The research was published today in Scientific Reports.

One problem that insects face in the cold is that they 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 (called paracellular barriers), which normally act to effectively keep what’s inside the gut from getting into the rest of the animal’s body (and vice versa). Indeed, exposure to 0°C caused the guts of the flies to get leaky.

Insects, however, aren’t going to just sit around and suffer the consequences of getting cold. In fact, many insects, including fruit flies can become more cold tolerant if they are exposed to just a bit of chilling first. This process, called thermal acclimation, allows animals to adjust their physiology to the temperature of their environment, and thereby maximize their chances of survival. “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 Andrew Donini, the senior author of the study and an Associate Professor at York University in Toronto.  “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.

Kaylen Brzezinski, a graduate student in the Department of Biology at Carleton University working with MacMillan plans to take this research forward using locusts, an insect separated from fruit flies by over 300 million years of evolutionary time. Kaylen will examine whether locusts also have problems maintaining barriers in the cold and whether this problem is responsible for the loss of water and salt balance that is often seen in insects in the cold. The ultimate goal of this research is to understand how temperature sets critical limits to insect survival, because this information is critical to predicting and controlling the abundance of insect pests in a changing climate.

In the meantime, you can control the flies in your own home by emptying the compost bin regularly. “At room temperature, the fruit fly lifecycle takes around a week” says MacMillan, “so empty your bin regularly and you should avoid large numbers of flies calling it home.

The research was supported by the Natural Sciences and Engineering Research Council of Canada.

Dr. Heath MacMillan

Assistant Professor

Department of Biology

Carleton University


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