It's no pain, no gain in the cutthroat world of seed beetle sex: Males with the longest and spiniest genitalia propagate their genes better than their less endowed rivals, a new study says.
The males' sexual organs have barbs and spikes that resemble medieval torture instruments, said study co-author Göran Arnqvist, an evolutionary biologist at Sweden's Uppsala University.
"They literally injure females internally in their copulatory duct. They're pretty mean," Arnqvist said.
(View pictures of these bizarre beetle genitalia.)
Several species, especially among insects, are known to physically harm their mates in reproduction, but scientists aren't sure why these traits evolved.
The new research offers the first proof that dangerous genitalia in males can represent a reproductive advantage.
The resulting wounds in the females, however, are likely just an "unfortunate side effect" of the strategy, Arnqvist said, and do not provide a reproductive benefit.
(Related: "Beetles Are Thirsty for Sex.")
Anchored
Arnqvist and Uppsala colleague Cosima Hotzy drew from 13 distinct populations of beetles—from California to Yemen—and one control group from Nigeria, the males of which were sterilized.
Virgin females were mated with both virgin males and sterilized males from the control group.
After examining the males' genitalia under a microscope, the researchers discovered that the males with the most damaging sexual organs fertilized more eggs, the scientists will report in the March 10 issue of the journal Current Biology.
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