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Lauren Admire | 15 Feb 2010 21:00
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To Deter Predators, Dry Up and Fly Away

Bdelloid rotifers, the sex-spurning invertebrates I've described before, should have gone extinct a long time ago. When you avoid sexual reproduction, you become a part of what's known as the Red Queen Hypothesis: "If an organism stops having sex and crystallizes its genome, all of [its enemies] catch up with it evolutionarily and can quickly overwhelm it," states Paul Sherman, a Cornell professor of neurobiology and behavior.

Despite this threat, bdelloid rotifers have survived without sex for 30 million years and have produced nearly 450 different species worldwide. Compare that success story to the nematode - another asexual creature that's slated to go extinct in a mere hundred thousand years. So, what makes bdelloid rotifers so special? How have they managed to avoid the specter of extinction? They just dry up and just ride the winds, man.

Desiccation is a highly unappealing state for organisms. Cells depend on the constant ebb and flow of solutes, water and waste in order to survive. When an animal dries up, it mimics a simple kind of death: Metabolic procedures stop completely, the animal is completely and totally non-functioning. Think of it as a miniaturized form of cryostasis. Rotifers can only become desiccated when there is a lack of water in their environment - but when there is, they can use it as a form of protection. Otherwise, they're on their own.

To begin their study on the way rotifers thrive, Paul Sherman and Chris Wilson, lead author and Cornell doctorial candidate first wanted to see what kind of natural defenses rotifers had in an aqueous environment. The team introduced a thriving colony of bdelloid rotifers to their arch nemesis: fungi. Even the tiniest threat of fungi can destroy a colony of bdelloid rotifers within weeks. Since the environment was kept wet, the rotifers were not able to dessicate and were quickly decimated.

The next experiment tested rotifer defenses when the environmental conditions were dehydrated. Fungi can't withstand dehydration for too long, so the rotifers simply dessicated and waited out the dry spell. Once a freshwater source was reintroduced into the system, rotifers ingested the liquid, left their desiccated state and went about their merry, fungi-free lives.

The last experiment tested the rotifers within dehydrated conditions with wind available. When rotifers were placed inside a wind chamber, Wilson and Sherman found that the rotifers dried up and simply rode the wind away from the fungi to safer locales. After seven straight days of riding the wind, the fungi-free rotifer colonies were more established than colonies without the use of wind to aid in their great escape.

"These animals are essentially playing an evolutionary game of hide and seek," explains Sherman. "They can drift on the wind to colonize parasite-free habitat patches where they can reproduce rapidly and depart again before their enemies catch up. This effectively enables them to evade biotic enemies without sex, using mechanisms that no other known animals can duplicate."

However, there are still mysteries that need to be solved. Bdelloid rotifers may have the upper hand when their environment is dehydrated, but what if they're surrounded by water? How do they avoid parasites and fungi when their main mode of protection is rendered absolutely useless?

Sources: Science Daily, National Geographic, Science Mag

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