A study on insects by Uppsala University scientists have shed new light on the injuries that the males' mating organs cause in females.
The researchers suggest that such injuries are the side effects of the benefits the males reap from their mating organs.
"One especially tricky case involves species where the males have mating organs that are supplied with hooks, barbs, and flukes that cause internal injuries in females during mating. This is extremely common among insects, but it also occurs in many other animal groups," says Professor Goran Arnqvist, at the Department of Ecology and Evolution.
Writing about their work in the journal Current Biology, the researchers revealed that they studied seed beetles and their mating behaviour.
Goran says that the males' mating organ, which is rather similar to a medieval spiked club, causes severe wounds in females during mating.
However, since it is never a good idea for a male merely to injure a female, the researchers have assumed that these structures serve another purpose, and that the injury is an unfortunate side effect.
"Females' injuries as such do not benefit the male she mated with. It has been suggested rather that the injuries are a side effect of other benefits the males reap from the barbs. Now, for the first time, we are able to show that this is the case," says Arnqvist.
Despite such costs, females mate with multiple males.
"We also show that males with long barbs cause more severe injuries to females, but also that these males have a greater rate of fertilization success," says Arnqvist.
The barbs are thus extremely important to males in their competition to be able to fertilize an egg, and when females mate with two males, it is more often the male with the longer barbs that fertilizes her eggs.