Bug sexual warfare drives gender bender
African bat bugs have two types of female genitalia.
Scientists trawling through remote caves of eastern Africa have stumbled on a strange example of sexual warfare. In the world of African bat bugs, they have found, males have learned to imitate females to reduce the trauma of sexual encounters. And females are retaliating by imitating the males.
The result, bizarrely, is two types of female genitalia. Some female bat bugs look feminine, but others look like males.
For the African bat bug — a small, reddish-brown parasite that feeds off bat blood, but can also bite humans — mating is a dangerous thing. Males pierce the sides of prospective mates to inseminate them, which can do harm to the recipient. And it's not just the females who are in danger; males sometimes attack other males too.
In response, male and female bugs have developed a distinctive structure to help reduce the trauma of a sexual attack — an extra genital funnel that is easier for the hypodermic probe to enter. This encourages the piercing to always happen in the same place, reducing the sites of injury and guiding the probe straight into a bucket of immune cells that help to reduce the impact of the injury.
The problem for males is that this structure also makes them appear more feminine, and so more prone to being sexually attacked in the first place. To signal their maleness, they have adopted a differently shaped funnel, which is more open and exposed. This successfully reduces the frequency of male-male encounters, the researchers found.
Love hurts, love scars, love wounds
The battle of the sexes doesn't end there. Some females have also embraced this new shape to lower their sex appeal and reduce the number of traumatic encounters that result in dark scars resembling human scabs. Researchers investigating this strange sexual adaptation observed that females with the more open form of genitalia suffer fewer mating scars than those with the standard closed form.
The bat bug provides a rare example of an animal that maintains a number of distinct female genital types. "The importance of female sexual polymorphisms has long been overlooked," says Erik Svensson of Lund University in Sweden, a biologist who studies sexual conflict.
Why some females maintain the closed genitalia remains unclear. "A trade-off may exist between reduced costs of mating but also decreased reproductive output," says Klaus Reinhardt of the University of Sheffield, UK, who led the study and reports the findings in an upcoming edition of the American Naturalist. For these females, perhaps it's a stark choice between dressing as a male, or dressing their wounds.