Joseph Mathieu, August 12, 2021
Photo credit: Fangliang Xu
Carleton University professor of biology Heath MacMillan has spent most of his career understanding why insects live or die in low temperatures. Specifically, he’s been researching the thermal limits of fruit flies since studying biology at Western University.
Heath MacMillan, Professor of Biology at Carleton University
“I was amazed how little was known in this area,” he says. “It just seemed like such a big field to play and explore.”
All living things have a certain temperature range in which they can survive. As soon as they reach their thermal limit when the temperature drops, their nerves, muscles and motor skills no longer function as well. Injuries occur which, if worsened, lead to death.
Why, where and how this happens are fundamentally interesting questions for MacMillan. It’s also important to know that insect populations and their distribution change rapidly in response to climate change. Understanding what sets the temperature limits in insects can enable researchers to make better predictions about which insects will survive, thrive, or die in our changing climate.
Close up of the head of a fruit fly
For many insects, the cause of these problems lies in their kidney system. When insects catch a cold, their kidney system no longer works so well and they lose their water and salt balance. This leads to an increase in the amount of potassium in their blood (called a hemolymph in the insect world), which leads to the death of cells.
“We have a lot of knowledge about the physiology of this process and know that these limits are very different in nature,” says MacMillan. “This project will begin to study some of the genetic and molecular mechanisms that could cause these differences that we see between and within different species of insects.”
The specific cellular signals that regulate the functioning of the renal system at low temperatures are unknown. That’s why MacMillan will lead an Early Researcher Award (ERA)-funded research team to find out how insects physiologically adapt to cold.
Little is currently known about how microRNAs – small RNA molecules that bind to mRNA from other genes and suppress them – contribute to the physiology and mechanisms of low-temperature biology. By exposing the common fruit fly (Drosophila melanogaster) to cold, MacMillan and his team will use molecular biology and machine learning to determine whether certain microRNAs are activated. In this way they can reasonably deduce which genes help the insects against the cold.
The project is characterized by collaboration with other Carleton researchers and faculties. Kyle Biggar, who worked with microRNAs in amphibians and molds at low temperatures, and Jim Green from the Department of Systems and Computer Engineering previously used machine learning to predict what types of targets microRNAs would have in the cold.
An Aedes aegypti mosquito
MacMillan wants to use what he can learn from the fruit fly – an ideal model for understanding biology – to apply it to another flying insect: the mosquito Aedes aegypti. Responsible for transmitting various diseases such as Zika virus, dengue fever, and yellow fever in tropical and subtropical regions, Aedes aegypti has become increasingly common in the United States and was recently registered in Windsor, Ontario.
Although it’s a different species of fly, mosquitoes have microRNAs similar to fruit flies. “In general, microRNAs that have a specific function have a similar function in other closely related species,” says MacMillan.
Although this mosquito does not transmit disease to Canada on its way north, it is in Canadians’ interests to find ways to control insects that are invading new areas due to climate change. If MacMillan’s research can determine the insect genes that respond to cold, then that knowledge could one day help control insect populations.
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