Tag Archives: evolution

The greater wax moth (Galleria mellonella) is locked into a high-frequency, evolutionary battle with the bats that prey upon them. Bats emit ultrasonic for the purpose of echolocation, sending out sounds at frequencies as high as 212 kHz. Now scientists have discovered that not only can the great wax moth hear the bats’ echolocation calls, but the moths can hear even higher frequency sounds, up to 300 kHz. The research team from the University of Strathclyde in Glasgow, Scotland report their findings in Biology Letters.

Such auditory sensitivity is “unprecedented,” the scientists write. No known bat produces sounds at that high a frequency, so why the moth evolved to hear such sounds is a bit of a mystery. But the researchers suspect that the super-hearing helps the moths avoid predators or communicate with each other, perhaps in courtship.

“The use of ultrasound in air is extremely difficult as such high frequency signals are quickly weakened in air,” the lead researcher James Windmill said in a statement. “It’s not entirely clear how the moths have developed to be able to hear at such a high frequency, but it is possible that they have had to improve the communication between each other to avoid capture from their natural predator – the bat – which use similar sounds.”

Image courtesy of Sarefo via Wikimedia Commons

Evolution works pretty fast sometimes. Biologists Charles Brown of the University of Tulsa in Oklahoma and Mary Bomberger Brown of the University of Nebraska-Lincoln have found that over a period of just 30 years, the cliff swallows (Petrochelidon pyrrhonota) of southwestern Nebraska evolved shorter wingspans that help them avoid getting hit by cars. Their study appears in Current Biology.

The discovery is a byproduct of a long-term study of the social behavior of the swallows, which nest in colonies beneath horizontal overhangs. They attach their gourd-shaped mud nests to sites like highway bridges, overpasses, and the concrete beneath railroad tracks.

In the 30 years of their study, the researchers drove the same roads, year after year, to check on the birds, stopping to pick up dead swallows whenever they found them. But they found something intriguing: The swallow population as a whole increased over that time, but the number of birds that became roadkill fell. In addition, the birds that got hit by cars had longer wings, on average, than the population as a whole, and the difference in wing length became more pronounced over time.

Factors like weather, changes in the prey population, or learning could explain either the difference in wing length or the decline in roadkill, but not both. Instead, the researchers say that natural selection likely favors birds that have a wing morphology that allows them to escape ongoing vehicles.

“Longer wings have lower wing loading and do not allow as vertical a take-off as shorter, more rounded wings,” the researchers write. “Thus, individuals sitting on a road, as cliff swallows often do, who are able to fly upward more vertically may be better able to avoid or more effectively pivot away from an oncoming vehicle.”

Image credit: Current Biology, Brown et al.