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When flatworms can't find a mate, they self-fertilize

The method, dubbed "selfing," is an imperfect solution to solitude.

By
Brooks Hays
Pictured is a normally reproducing free-living flatworm, with two eyes in the front (left) and sperm in the back (right). Photo by Lukas Scharer/University of Basel
Pictured is a normally reproducing free-living flatworm, with two eyes in the front (left) and sperm in the back (right). Photo by Lukas Scharer/University of Basel

BASEL, Switzerland, July 1 (UPI) -- Being single can be a drag, even for the most simple of creatures. Humans have a variety of distractions to mask their sexual frustrations, but for flatworms, the drive to reproduce is everything.

When Macrostomum hystrix flatworms fail to find a mate, it's beyond devastating. Unwilling to accept their fate, single flatworms use a bizarre workaround to reproduce. They self-fertilize. The flatworms literally inject sperm into their own heads using a needle-like penis.

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It's sounds painful and disgusting, but for flatworms, it's better to take advantage of their hermaphroditic anatomy than to die childless.

The method, dubbed "selfing," isn't ideal. Their offspring, inbred, inevitably have issues.

"As far as we know, this is the first described example of hypodermic self-injection of sperm into the head," study author Steven Ramm, a researcher at the University of Basel, explained in a press release. "To us this sounds traumatic, but to these flatworms it may be their best bet if they cannot find a mate but still want to reproduce."

Because Macrostomum hystrix flatworms are transparent, their insides are easily observable. Researchers found that isolated worms tended to have more sperm in their heads than those kept in groups. Social flatworms possessed more sperm in the tails, the normal site of fertilization.

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Researchers shared their findings in the journal Proceedings of the Royal Society B.

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