Aleksandra A. Panyutina
By Sandrine Ceurstemont
A rare rodent isn’t just blind as a bat: it may navigate like one too. The tree-climbing Vietnamese pygmy dormouse seems to make ultrasonic calls to guide its motion. If that’s confirmed, it would be the first arboreal mammal known to use echolocation.
Apart from bats, dolphins, whales, rats and shrews – which use calls in the audible range – few mammals echolocate as vision is usually more efficient. But Aleksandra Panyutina at the Russian Academy of Sciences in Moscow and her team thought the dormouse was a good candidate. They had access to two of these seldom-studied, mainly nocturnal rodents at the Moscow zoo, where keepers had noticed that they were able to climb with remarkable agility despite poor eyesight. They also have big, bat-like ears. “We suspected that they use echolocation,” says Panyutina.
To find out, the team first confirmed the rodent’s poor vision by analysing the preserved eyes of dead individuals. Then, the two zoo dormice were filmed in cages filled with branches (pictured below).
Aleksandra A. Panyutina
The soundtrack revealed that they often produced a series of quick, ultrasonic pulses similar in structure to bat echolocation calls but much quieter. Syncing the video and audio showed that they typically made sounds while moving, suggesting that the sounds are for navigation.
Gareth Jones, a bat researcher at the University of Bristol in the UK, thinks the results are interesting although further work is needed. “It is important to determine whether the mice can hear echoes from the calls,” he says.
Read more: Human bat uses echoes and sounds to see the world
Panyutina and her colleagues are not sure whether the rodent is producing sounds from its larynx or elsewhere. In addition, the experiments were not performed in darkness and didn’t test if the call rate changes on approaching an obstacle, says Eran Amichai from Tel Aviv University, who studies bat echolocation.
However, if the dormouse is indeed echolocating, it could help solve an age-old question in bat evolution: whether flight or echolocation came first. There is some evidence that bats gained the ability to echolocate very early on, although fossils suggest at least one early bat species seems to have lacked the ability. New examples of echolocation in land mammals could help support the theory that it evolved prior to flight.
“It is conceivable that the terrestrial ancestors of echolocating bats used echolocation in a similar way,” says Jones – although he points out that bats are not closely related to rodents, so the dormice would have gained their ability to echolocate independently rather than from an ancestor common to them and bats.
Journal reference: Integrative Zoology, DOI: 10.1111/1749-4877.12249
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