Male animals can be greedy about paternity. They have evolved a ton of different strategies to help them monopolize a female’s eggs. Beating up rivals is a general favourite. Some species use long bouts of sex to keep females away from new mates. Still others stop up female genitals with gooey plugs or bits of broken male genitalia.
None of these strategies are perfect: females may sneak off to find other mates on the side, bigger males may come along to displace a determined lover, or new males may scrub out the physical barriers that lay in their path. But a team of zoologists led by the University of Greifswald’s Gabriele Uhl have found that at least one Eastern European orb weaving spider has evolved a way to make sure all his mate’s eggs belong to him alone. He breaks her genitals so she can never mate again.
Male Larinia jeskovi slip sperm into their mates with a specialised limb called a pedipalp; its flaps and projections put the palp in the right position inside the female and pump sperm into her body. Uhl’s team found that each time a male stuck his pedipalp into his mate, one section of the limb sawed away at her genitals. After a few passes, one V-shaped part of her external genitalia (called the scapus) simply broke right off.
After the scapus is gone, the females are perfectly willing to mate with other males, but those males can’t grab on to transfer sperm. The boys have the right key, but they’re trying to stick it into a broken lock.
It’s not clear how having broken genitalia affects a female’s health over the long term, but it’s a common condition: by the end of the breeding season, most mature females from the wild have a broken scapus. One thing is certain: all of her babies will have just one daddy.
Images from Mouginot et al. 2015