'Worm Porn' Sheds Light on Evolution of Sperm
Some hermaphroditic Macrostomum lignano flatworms copulate, then suck out unwanted sperm. These worms' sperm have bristles to help them stay in place. The sperm of related worms, which don't suck out sperm, have no bristles. In fact, the bristles seem to have disappeared twice, independently, when worms adopted the alternative mating strategy. This led researchers to conclude that sex shapes sperm, which are the most diverse type of animal cell.
Credit: Lukas Schärer

Watching hours upon hours of worms having sex (yes — essentially worm porn), has helped scientists figure out why some flatworms have simple, thin, squiggly sperm, while others sport larger sex cells with bristles and a feeler in the front.

The new findings shed light on the evolution of all animal sperm, the researchers said.

In the study, a team that included Lukas Schärer and his wife Dita Vizoso, both of the University of Basel in Switzerland, linked the evolutionary loss of the bristles — which they think keep the sperm lodged in the female reproductive tract — as well as the feelers, to the adoption of a new mating strategy that renders the bristles useless.

Schärer described the methodology that led to their discovery: "You take time-lapse movies and sit there and look at worms mating for some hours," Schärer said. [Video: Worm Sex & Sperm]

Some were more obliging than others, mating all the time, while other healthy specimens didn't get down to business when placed together, he said. [

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