Bat Bugs Evolved Fake Genitals to Avoid Sex Injuries

Anne Minard
for National Geographic News
September 25, 2007
For African bat bugs, the battle of the sexes is quite literally a violent struggle—and now it appears that the bugs are using gender-bending tactics to defend themselves.

Bat bugs are small, reddish-brown parasites related to bed bugs that suck the blood of bats and sometimes bite humans.

Researchers have long known that male bat bugs ignore females' conventional parts and instead use their sharp penises to stab the females' abdomens, injecting sperm directly into the bloodstream.

So the females evolved a defense: structures called paragenitals that guide a male's needle-like member into a spongy reservoir of immune cells.

But the females aren't the only ones in need of protection. Observers documented males performing the same injurious sexual acts on other males.

Now evolutionary biologist Klaus Reinhardt of the University of Sheffield in England has discovered that male bat bugs have developed their own versions of female paragenitals to avoid the assaults.

And some female bat bugs are mimicking the paragenitals of the more successful males to improve their defenses.

Reinhardt calls the interactions a "hotbed of deception" with no known analogies in the animal kingdom.

The results, based on studies of bat bugs from a cave in Kenya, are being prepared for publication in an upcoming issue of the journal the American Naturalist.

I Have a Headache?

This odd display of sexual evasion does not stop bat bugs from reproducing.

Some females have retained their own gender's version of the paragenitals, which presumably ensures that their defenses will occasionally be penetrated.

And even the best-defended females sporting the male versions sometimes end up injured and impregnated too.

The bugs exhibit a fantastic example of evolution at work, Reinhardt said, which is why he studies them.

Erik Svensson, an animal ecologist at Lund University in Sweden, called the bat bug findings important.

While male sexual differences within species have been well documented, he said, the females' physical responses have not.

Reinhardt added that it was "truly surprising" that males seemed to have copied females in the first place.

But, he added, "I suppose I never think of these things as shocking."

Spines and Twists

While African bat bugs might be one of the wildest examples, there are similar cases of apparent transexualism and even sexual sadism among other critters.

(Related: "Sex Tips for Animals—A Lighthearted Look at Mating" [September 12, 2002].)

The genitals of male seed beetles, for example, are spiny to help anchor the males inside the females as they work to impregnate them.

But the spines tend to damage females, so the females have developed tougher genitals. The males in turn keep getting spinier.

Seed-beetle researcher Göran Arnqvist, at Uppsala University in Sweden, said that the evolutionary advantage is competition between males. Tougher, spinier males are the ones most likely to pass on their genes.

As long as the spines don't get so extreme that they are sabotaging reproduction, the species won't lose out from the unusual technique, he said.

And in a literally twisted approach to sex, some species of duck seem to be going to great lengths to achieve reproductive control.

Patricia Brennan of Yale University and the University of Sheffield was part of a team that announced in May the discovery that some female ducks sport convoluted genitalia—dead-end sacs and clockwise coils—to prevent impregnation.

Male fowl, in turn, have been evolving to have longer phalluses.

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