January 2010, Volume 8, Issue 1

Bats in the News

Unraveling Echolocation


One of the most fascinating of bats’ adaptations is echolocation, the biosonar that lets most bats not only navigate but capture such elusive prey as fast-flying insects as small as mosquitoes in total darkness. But, Scientific American reports, “human researchers are still in the dark about many of the precise biological and evolutionary mechanisms that make this skill possible.” Now, however, scientists are tapping the latest technology to cast new light on how bats “see” in the dark.
 
Echolocation in bats basically involves emitting a series of sounds like beeps or clicks, then collecting and analyzing the echoes that bounce back from obstacles or prey. Most, but not all, bat species use echolocation.
 
At the University of Western Ontario in Canada, scientists used a microcomputed tomography (micro-CT) scanner to create precise images of the inner ear of both echolocating and non-echolocating bats, Scientific American’s Katherine Harmon writes. The micro-CT is a very high-resolution version of the large medical CTs most of us are familiar with, and the nondestructive imaging can reveal precise details previously available only by dissection. The team examined bat specimens on loan from the Royal Ontario Museum in Toronto.
 
The detailed 3-D images from 26 species revealed that bats that use the typical form of echolocation, which relies on sound produced by the larynx (the voice box), had a unique feature in their skeletal structures, the magazine says. Among those bats, the researchers reported in the online edition of Nature, a common mammalian bone called the “stylohyal” bone physically connects the larynx to the ear (tympanic) bone.
 
That was an unexpected result, Brock Fenton, the study’s senior author and a BCI science advisor, told Harmon. He said the only previous work on this part of bat anatomy was done in the 1930s and ’40s, before scientists were aware of echolocation.
 
The researchers said it is not clear just why this feature is present only in echolocating bats, but it might help them perceive the outgoing signal and perhaps dampen vibrations “to prevent the bat from deafening itself with the sound it produces, which can be more than 100 times louder than the reflected echoes,” Scientific American says. It could also aid in comparing the outgoing and incoming signals.
 
The magazine quotes the researchers as saying their new data will “reopen basic questions about the timing and the origin of flight and echolocation in the early evolution of bats.” Fenton said that means that fossil bats with the stylohyal connecting to the tympanic bone apparently were able to echolocate.
 
The oldest known fossilized bat, Onychonycteris finneyi, which was found in Wyoming in 2003, had primitive wings but was described as incapable of echolocation. That conclusion was said to resolve the question of which came first in bat evolution: flight or echolocation. Echolocation-first was favored by many experts until the Wyoming fossil was reported. However, Scientific American writes, Fenton said the fossil appears to have the stylohyal-tympanic connection, “hinting that echolocation and flight might have evolved at the same time, after all.” (He notes that the “main fossil is flattened, making it difficult to confirm the connection.”)
 
Combining echolocation and flight into a hunting strategy, the magazine quotes Fenton as saying, “would have meant early bats were ‘exploding a new niche,’ because they would have been able to hunt bugs at night that birds and other creatures could not track.”

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