The common fruit fly is a pest to many, and friend to few. But for geneticists, fruit flies are the key to a wealth of information about human disease, genetics, and cell biology, offering a look at one of the most common physiological changes in the animal kingdom, hibernation.
“What we were interested in doing was to find a gene or genes involved in insect diapause-essentially insect hibernation,” said Marla Sokolowski, a professor at UTM’s department of biology, and the principal investigator of a new study on the genetic cause of diapause, working with her former PhD student Karen Williams.
Diapause, like mammalian hibernation, is triggered by shorter days and lower temperatures. Little is known about the behaviour of wild flies in diapause, or whether it affects male flies, so researchers gauge its presence by examining the female fly ovary, which will suspend its development in diapause. The research pinpoints a single gene with a determining influence on fruit-fly diapause.
“Once you find a gene for this trait, you can understand the mechanisms for how the gene acts…and the evolution of it,” said Sokolowski.
This finding challenges the prevailing polygenic (‘many-gene’) model for the creation of a complex behaviour, suggesting that all the genes affect behaviour equally. The identification of a single gene as largely responsible for diapause-more than any other genes-is part of the growing body of research disputing the polygenic model.
“[Hibernation is] a means to cope with stress,” said Sokolowski. “And it’s a common thing that animals do. They’re able to slow down their reproductive [system] or development under stressful conditions.”
Using fruit flies from Windsor and Florida, the researchers found that the gene is involved in insulin signaling. The gene’s mammalian counterpart may play the same role, suggesting that the processes involved in insulin, fat storage, and conserving energy are linked to hibernation.
“This means of dealing with stress, [arrested development], is evolutionarily conserved,” said Sokolowski. Whether bear, worm, or fly, adapting to live with the cold or a scarcity of food is a process that may have appeared very early in evolution, and may have stayed with higher organisms including humans.
The gene in humans is potentially linked to seasonal affected disorder (SAD). Predominately found in women, SAD causes excessive eating and less physical activity in the fall. Come spring, SAD patients eat less and become more active. For unknown reasons, SAD patients are more responsive to day length than is normal in humans. Because of these similarities to hibernation, Sokolowski is collaborating with researchers at the Centre for Addiction and Mental Health to sequence the DNA of individuals with SAD in hopes of finding a genetic basis for the disorder.
The finding has many implications for human diseases. Over-wintering female mosquitoes have been found to carry pathogens like West Nile virus. Because of the close genetic similarities between fruit flies and mosquitoes, the ability to genetically control mosquito populations by rendering them unable to survive the winter would be a valuable tool in stopping the West Nile virus.
