Sonic Genitals: A Bizarre Defense in the Moth vs Bat War

For as long as experts have been researching how bats hunt, they have also seen that some moths have the unique ability to jam honing sonar. Among hawkmoths, for instance, the sonic calls of bats are apparently disrupted by dissonant signals coming from the insects' genitals. Now, researchers think they have determined the evolutionary roots of this unusual defensive adaptation.

According to Akito Kawahara, the assistant curator of Lepidoptera (moths and butterflies), at the Florida Museum of Natural History at the University of Florida, moths and bats have been in a biological arms race for over 65 million years. This race traditionally centers around flight, misdirection, and above all else, sonar. Bats have even developed strategies for competing with one another by interfering with a neighbor's sonar (you can read more about that here).

Until now, it had remained unclear how exactly sonar jamming had developed in moths. After all, it's hard to imagine what kind of insane circumstance could have led a moth's private parts to become weapons in a sound-based arms race.

"Before now people thought ultrasound usage in insects was very restricted to certain groups, but it looks much more complex than that," Kawahara said in a recent statement.

The researcher and his colleagues recently spent their time observing and collecting hawkmoth specimens from 70 sites in 32 countries. More than 700 moths were then involved in both field and lab-side experiments to help the team better understand their sonar-jamming capabilities. After testing the response of 124 species of hawkmoths, researchers found that nearly half generated ultrasonic sounds with their genitalia. (Scroll to read on...)

Looking to the fossil record (primarily amber samples), Kawahara's team then built a rough tree that maps out hawkmoth evolution. They determined that the first hawkmoth that produced ultrasonic sound likely arose in the late Oligocene period about 26 million years ago. Interestingly, they were unrelated to the tiger moth variety - once thought to be the only species of moth capable of sonar jamming. However, tiger moths produce ultrasonic sound using tymbals - a vibrating membrane located on the thorax, rather than their genitals.

"Our evolutionary tree demonstrates that sonar jamming and the ability to hear bat attack calls evolved twice during the Miocene after the radiation of insectivorous bats," Kawahara said.

Still, the fact that both species developed the defense around the same time suggests that there may have been a leap in sonar technique on the bat side - a change that would have prompted hasty natural selection in the predator-prey arms war. The adaptation could have even been a response to the arrival of other ultrasonic predators as well, such as sound sensitive rodents, shrews and primates. Put under such pressures, it's not as difficult to imagine that a species would take advantage of any change to survive, even the unexpected (but rather lucky) development of strange, sonic genitals.

"This is just the beginning - we are trying to chip away at what goes on with nocturnal insect biodiversity," Kawahara said.

The results of the team's work were published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

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