Worms Do It
"One has to be specific about what one means by sex," says biologist Lukas Schärer of the University of Basel, Switzerland. In this case, Schärer is discussing hermaphrodites doing it in the 69 position -- in other words, copulating flatworms. Schärer, the lead author of a new study on the intercourse habits and sperm design of flatworms, is an authority on the subject, having studied the behavior of a particular species, Macrostomum lignano, over the past decade. Discovered in 1995 and so far found only on Mediterranean beaches, M. lignano individuals are transparent, making it easy to observe their inner workings through a microscope, and every specimen has both testes and ovaries. To mate, partners insert their male genitalia into each other’s female opening and inject sperm. Both worms then double over and appear to attempt to suck their partner’s sperm back out. Schärer says there are several possible explanations for this, all of which require an understanding of what sex means for an organism that is both male and female.
At its most basic, being male means producing small gametes (sperm), while being female means producing large ones (eggs). For creatures that do both, the question is how much to invest in each product. Maleness is, in a sense, parasitic -- a male’s goal being to exploit the body of another to further his own genetic goals. Indeed, in M. lignano, due to the worms’ post-conjugal sucking behavior, successful sperm seem to have evolved hook and bristle shapes to help them hang on inside the vaginal opening.
But why the sucking in the first place? Schärer says it could be a worm’s attempt to rid itself of the sperm it was forced to accept in exchange for delivering its own. On the other hand, the worms could just be vacuuming out water that got in during copulation. Researchers have also identified other flatworm species that don’t reciprocally mate or suck but rather stab each other with needle-like organs to deliver sperm. Studying flatworms of both persuasions may help scientists understand what social and environmental factors determined how and why the species adapted the way they did.
But let’s be honest: Part of what’s so interesting about observing M. lignano sex is imagining what it’s like for the creatures engaged in it. "How does a hermaphrodite feel?" Schärer asks. "Is it driven by male urges? Is it driven by female urges? Does it even feel them as different parts of itself, or is it just one feeling?"
Speculate to the extent you feel comfortable.
