Small, freshwater invertebrates called bdelloid rotifers have long puzzled and fascinated evolutionary scientists. These unusual, asexual organisms have managed to survive and avoid disease for at least 30 million years without sexual reproduction. Now according to the Cornell Chronicle, researchers are unlocking their secrets for the first time.
One of the advantages of sexual reproduction is that it mixes up the genes for each new generation, allowing populations of organisms to adapt quickly to changes in their environment and to fend off relentlessly evolving parasites and pathogens. But since rotifers have forsaken sex, they should have been driven to extinction by disease long ago. Instead, they have defied natural selection by proliferating into more than 450 species.
Their secret? Rotifers, it turns out, are the ultimate biological Houdinis. They are capable of cheating death and escaping disease — essentially surviving without sex — by shriveling up and blowing away. Since harmful parasites and fungi can't survive dehydration like the rotifers can, the dried-up tricksters make a clean getaway.
"These animals are essentially playing an evolutionary game of hide and seek," said Paul Sherman, Cornell professor of neurobiology and behavior. "They can drift on the wind to colonize parasite-free habitat patches where they 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."
The study was performed by infecting populations of rotifers with deadly fungi, allowing them to dry out, then placing them in a wind chamber. To the surprise of scientists, the rotifers were able to disperse without the fungi and establish parasite-free populations.
In fact, it took only seven days on the wind for the rotifers to establish the same number of fungus-free populations that took three weeks to establish without wind, demonstrating that the key to their survival without sex is likely that rotifers blow around.
"It also helps answer one of the deepest puzzles in evolutionary biology — why sex is nearly ubiquitous," said Chris Wilson, lead author of the study.