'Worm Porn'
Evolution of sperm
Some hermaphroditic Macrostomum lignano flatworms mate, then suck out unwanted sperm. These worms' sperm have bristles to help them stay in place.
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. 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. The team also examined the worms' sperm, the stylet (the organ used to deliver sperm), the antrum (the female sperm-receiving organ) and the evolutionary relationships among the worms. (These worms are equipped simultaneously with both male and female genitalia.) The implications of this research go beyond just the worms, and help explain why animal sperm come in so many shapes, according to Scott Pitnick, an evolutionary biologist at Syracuse University, who was not involved in the study. "When most people think of sperm, they think of a tadpole-looking thing," Pitnick said. "There is no such thing as a typical sperm cell when you look at sperm diversity throughout the animal kingdom. It is just unbelievable, the outrageous, dramatic forms that have evolved."
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