Lonely flatworms inject sperm into their own heads

Lukas Schaärer/Flickr/Creative Commons

Lonely flatworms inject sperm into their own heads

All you single people: If you think dating is a headache, consider the lengths that some hermaphroditic flatworms will go to in the name of reproduction. In the absence of mating opportunities, hermaphroditic flatworms such as Macrostomum hystrix self-fertilize by stabbing themselves in the head with their penile appendage and injecting sperm, report biologists from the University of Basel in Switzerland today in the Proceedings of the Royal Society B. To understand the creatures’ reproductive habits, they compared isolated flatworms with flatworms living in groups of three and used a light microscope to note where in the body cavity sperm was present—a feat made easier thanks to the worms’ transparent skin. Worms in isolation had received less sperm than their social counterparts, but the majority of the male gametes were clustered in the head region.  The triplet worms, on the other hand, received more sperm in their bodies (where the ovaries are located), and in the tail. The researchers suspect that the head penetration is necessary simply because the worms can’t fold tightly enough to get their penile appendage any closer to the ovaries. The sperm then presumably swim through the body cavity to the ovaries where development of a hatchling can begin. As convenient as it might sound to forego the headaches of courting a mate, the team points out that self-fertilization comes at a cost: the isolated worms produced fewer hatchlings with lower survival rates.