The larvae of an African fly survive severe droughts by essentially turning into candy drops, biologists have shown. The research might lead to new ways of preserving blood for transfusions or even entire organs for transplants.
Some invertebrates, when severely dehydrated, go into a state of suspended animation in which their metabolisms completely cease. When conditions are right, the critters come back to life. The larvae of the African fly Polypedilum vanderplanki scrounge a living by eating detritus at the bottom of rain puddles but can survive up to 17 years of drought waiting for the next abundant rains.
Most other animals known to freeze-dry are microscopic, such as sea monkeys (brine shrimp) and water bears (tardigrades). Biologists have known for years that a sugar called trehalose plays a crucial role in the survival tactics of several of these species. During desiccation, trehalose replaces water in the cellular fluids and is presumed to turn into a glassy state, much like melted sugar will solidify into candy drops. The glassy sugar would keep cellular structures from falling apart.
That’s indeed what happens in P. vanderplanki, researchers have now shown. “This is the first direct evidence” for a glassy state in any animal, says Takashi Okuda of Japan’s National Institute of Agrobiological Sciences in Tsukuba.
Okuda and his collaborators collected P. vanderplanki—which looks more like a mosquito than a fly—in Malawi, Burkina Faso, and Nigeria. After years of attempts, the team was able to get the insects to reproduce in the lab, providing an ongoing supply of larvae.
Infrared imaging of desiccated larvae showed that trehalose is uniformly distributed throughout their bodies. And when the researchers turned the temperature up, they noticed a peak in the larvae’s heat absorption at around 70 degrees Celsius. The peak was characteristic of a phase transition at which solid sugars begin to melt, demonstrating that the sugar had been in a glassy state, Okuda says.
In another experiment, the researchers detected telltale signs of trehalose molecules bonding with the double-layer lipid membranes that envelop cells. Trehalose had thus replaced water in its role of stabilizing the membranes. The results appear in the April 1 Proceedings of the National Academy of Sciences.
“This adds significantly to the evidence” that the insect turns to glass, says biologist Jim Clegg of the University of California, Davis.
Okuda says he and others would like to steal P. vanderplanki’s secret to learn, for example, how to keep transfusion blood in a dried form. The main challenge, he says, is to get trehalose to penetrate the membranes of red and white blood cells. Eventually, the technique could be used to preserve entire organs.
And could humans some day freeze-dry themselves alive with a shot of trehalose—perhaps to survive long trips to other stars? That’s a long shot, Okuda says, but “theoretically, I think it’s possible.”
For now, it’s P. vanderplanki that’s traveling in space: Okuda and his collaborators have sent dried larvae to be hung outside the International Space Station, to see how they fare.