After mating, males in numerous species from insects to rodents often seal a female's genital tract with what biologists term a "copulatory plug," a mass that was believed to block the female's vulva so that she cannot mate with other males. But that plug may actually have nothing to do with competition among males. It may simply be a gift, a box of chocolates, if you will, to the lady. In today's issue of Frontiers in Zoology, researchers report that the gelatinous mass which a male nematode worms deposit in a female's vulva at the end of copulation (right) seems to help her produce eggs and prevents the entry of harmful pathogens. Still, the gift isn't totally selfless: It may help the male, too, by keeping his sperm inside the female.
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