When a male African bat bug wants to mate, the insect, which sucks the blood of bats, simply stabs his sharp penile prong into the abdomen of one of his female counterparts, no consent necessary. To protect themselves from this so-called traumatic insemination, lady bat bugs have evolved extra genitalia. Now a study finds that these genitalia can take two forms--one of which helps the female disguise herself as a male. The findings bring the battle of the sexes to a whole new level, say evolutionary biologists.
Traumatic insemination is an extreme example of sexual conflict, a kind of intraspecies warfare that arises when one sex's reproductive attempts harm the other sex. In the bat bugs, the female develops a specialized abdominal organ with covered cavities to receive the male's sperm and minimize damage to the rest of her body. But it gets more bizarre. Because the sexes look alike--and homosexual mating attempts are common--the males develop an organ similar to the defensive female genitalia. But, unlike the females, they leave the organ's cavities open, apparently to maintain some distinction. Scientists have suggested that such sexual conflict and the evolution it forces can ultimately lead to speciation, but others disagree.
Michael Siva-Jothy, an evolutionary biologist at the University of Sheffield, U.K., and his colleagues wanted to better understand the bat bugs' battle of the sexes, so they collected the insects from a remote cave in East Africa and dissected them. Surprisingly, the scientists found that some females impersonate males, having open cavities on their specialized genitalia, whereas others maintain the typical closed form. "Members of this group don't do anything normal," Siva-Jothy says. From a tally of scars on the females, it appears that individuals with open cavities were pierced by males less often than were those with closed cavities, researchers report in the December issue of The American Naturalist. That suggests that females mimic males that already look like females to avoid sexual harassment. But not all females chose this protection; 16% maintained a closed form. "Here you have an unusual system where female genitalia are diverging," Siva-Jothy says. "If this goes on long enough, it may well result in two new species."
The study shows that sexual conflict can drive diversity in genital structure, says Locke Rowe, an evolutionist at the University of Toronto in Canada. But speciation would require that some male bat bugs evolve to prefer reproducing with one female form while other males evolve to prefer reproducing with the other female form, he adds; whether that happens "remains to be seen."