The Bat That Became a Master Hunter by Chance

Biologists often point to a relentless tug-of-war between predators and their prey to explain why predators don’t wipe out their food source. Both sides are in a perpetual dance of adaptation, trying to outsmart one another.

This concept is notably evident in the relationship between bats and insects. About 50 million years ago, bats developed echolocation, allowing them to hunt in the dark. As a countermeasure, certain insects evolved ears sensitive to these ultrasonic sounds to dodge their winged adversaries.

Lasse Jakobsen, a bat specialist and associate professor at the University of Southern Denmark, along with his team, has delved deeper into this presumed evolutionary duel in a recent publication in Current Biology. Collaborating with researchers like Daniel Lewanzik and Holger R. Goerlitz from the Max Planck Institute for Biological Intelligence and John M. Ratcliffe and Erik Etzler from the University of Toronto, they’ve presented some intriguing findings.

Central to their research is the observation that certain bats, specifically the barbastelles (Barbastella barbastellus), have calls that are considerably softer—about 20 dB less—than their peers. This makes them virtually inaudible to many insects.

Jakobsen mentions that these bats are often seen as nature’s retort to the hearing adaptation of insects.

However, a closer look at the barbastelle’s lineage reveals an enigma. Most of its relatives aren’t airborne hunters but prefer to pick insects from surfaces like leaves or branches. Known as ‘gleaning bats’ in scientific circles, these relatives are inherently quieter than the airborne insect-hunting, or ‘hawking bats.’ Surprisingly, the barbastelle is categorized as a hawking bat.

Jakobsen theorizes that the barbastelle’s ancestors were likely gleaners, which would mean its quiet nature isn’t a strategic evolution against insect hearing.

He emphasizes that evolutionary paths aren’t always a matter of choice. As an analogy, he states that since mammals’ ancestors lacked feathers, they can’t sprout feathered wings; however, they’ve adapted by having skin extensions between their fingers for flight.

So, if the barbastelle’s silent hunting isn’t a result of this predator-prey tug-of-war, what’s the reason? Jakobsen believes it’s due to their gleaning lineage. They might be physically unable to produce louder calls, but this limitation has inadvertently given them an advantage in hunting certain nocturnal insects. These insects, like moths, beetles, and mosquitoes, can detect and avoid most bats but are caught off guard by the barbastelle’s subtle calls.

This inherent quietness can be traced back to the way bats produce sound. Most emit calls from their mouths, leading to louder sounds. In contrast, many gleaners vocalize through their noses, resulting in softer calls.

Consequently, Jakobsen concludes that the barbastelle’s soft calls aren’t a tactical evolution against insects but rather a byproduct of their ancestral lineage.

Interestingly, before the dawn of bats around 50 million years ago, nocturnal flying insects largely roamed the night skies unchallenged. Today, they face the nightly threat of these adept hunters.

Source: 10.1016/j.cub.2023.10.014

Image Credit: SHERRI AND BROCK FENTON