To avoid parasites, some fruit flies sacrifice sleep

That's the waking nightmare one species of Australian fruit fly must contend with each night as hungry mites stalk and attach themselves like a tick while the fly is sleeping in the fruit orchards and rainforests of Queensland.

Biologists at the University of Cincinnati examined the benefits and costs of avoiding these parasites in a study published in the Nature journal Biological Timing and Sleep.

It may sound trivial, but the parasite Gamasodes queenslandicus poses a potentially deadly threat to fruit flies, UC professor and study co-author Michal Polak said.

"If they have too many mites, they can get ripped apart. It's very detrimental to them," Polak said.

He captured wild flies in Queensland and bred 16 generations in his UC biology lab, selecting only males that were able to survive a night's close exposure to the mites unscathed.

"At night when the flies are quiet and sleeping, they become a good target for the mites," Polak said.

But the flies that were adroit at evading the mites' efforts to latch on at night did so at the expense of losing valuable sleep. The energy and sleeplessness this effort requires has consequences of its own, said UC Professor Joshua Benoit, the study's lead author.

This is not the first study to observe behavioral adjustments in animals exposed to external parasites. Researchers have found that parasitism also affects the sleep patterns of bats and birds.

UC biologists examined changes in gene expression relating to the flies' metabolism in the mite-resistance population. Mite-resistant flies were more prone to starvation and leaned more on their nutrient reserves than other flies, they found.

These hypervigilant flies were more active, slept less and consumed more oxygen at night.

"When we measured it, we found that more than 30 metabolism genes were differently expressed in these flies suggesting they were burning their energy a little faster than you'd expect," Benoit said.

"Sleep in all higher animals is important," Benoit said. "Usually, over a long period of time, you can observe detrimental effects where sleep-deprived animals are not as healthy and start making poor choices. Their behavior is impacted."

Ironically, Benoit said, sleep is usually beneficial to animals infected with internal parasites such as those that cause malaria.

Polak said once fruit flies are bitten by mites, their immune system kicks into high gear. Parasitized flies often have less mating success and quickly deplete their fat reserves.

"The mites cause a massive up-regulation or down-regulation of hundreds of genes. These defense mechanisms can be very costly to the fly," he said. "So it behooves the fly to avoid getting parasitized in the first place."