If you own a birdbath, chances are you’re hosting one of evolutionary biology’s most puzzling enigmas: bdelloid rotifers. These microscopic invertebrates—widely distributed in mosses, creeks, ponds, and other freshwater repositories—abandoned sex perhaps 100 million years ago, yet have apparently diverged into nearly 400 species. Bdelloids (the “b” is silent) reproduce through parthenogenesis, which generates offspring with essentially the same genome as their mother from unfertilized eggs.

Bdelloid rotifers are egg laying microscopic invertebrates — widely distributed in mosses, streams and ponds — which have managed to diverge into nearly 400 species without a scintilla of sex… Now a new study, published today in the journal PLoS biology, has confirmed the worst fears of scientists: the rotifers do indeed present a major challenge to the assumption that sex is necessary for organisms to diversify into species.
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Rather than mixing up DNA, creatures like the bdelloid rotifers can evolve solely through the build-up of mutations that occur in the ‘cloning’ process when a new rotifer is born. The new study proves that these differences are not random and can help rotifers adapt to a different environment, such as the legs or chest of a water louse. Bdelloids can be found happily swimming around in a puddle in your garden, hot springs or in freezing ponds in the Antarctic.