|Typhlomys chapensis Osgood, 1932|
Panyutina, Kuznetsov, Volodin, et al., 2017.
The means of orientation is studied in the Vietnamese pygmy dormouse Typhlomys chapensis, a poorly known enigmatic semi-fossorial semi-arboreal rodent. Data on eye structure are presented, which prove that Typhlomys (translated as "the blind mouse") is incapable of object vision – the retina is folded and retains no more than 2 500 ganglion cells in the focal plane, and the optic nerve is subject to gliosis. Hence, Typhlomys has no other means for rapid long-range orientation among tree branches other than echolocation. Ultrasonic vocalization recordings at the frequency range of 50-100 kHz support this hypothesis. The vocalizations are represented by bouts of up to 7 more or less evenly-spaced and uniform frequency-modulated sweep-like pulses in rapid succession. Structurally, these sweeps are similar to frequency-modulated ultrasonic echolocation calls of some bat species, but they are too faint to be revealed with a common bat detector. When recording video simultaneously with the ultrasonic audio, a significantly greater pulse rate during locomotion compared to that of resting animals has been demonstrated. Our findings of locomotion-associated ultrasonic vocalization in a fast-climbing but weakly-sighted small mammal ecotype add support to the "echolocation-first theory" of pre-flight origin of echolocation in bats.
Key words: ultrasonic echolocation, locomotor behaviour, arboreal locomotion, reduced eyes, Typhlomys, Rodentia
|Figure 1 Vietnamese pygmy dormouse Typhlomys chapensis. Its reduced eyes are reflected in the generic name, which means “the blind mouse.”|
Concluding remarks. The major limitations of our study were the small number of live individuals to experiment with and the poor quality of dead specimens for histology. This is due to the extreme rarity of the Vietnamese pygmy dormouse, or "blind mouse" in nature. That is why our conclusions, though rather convincing, are still preliminary. Additional research is required to describe in detail the acoustic patterns of ultrasonic pulses and bouts in Typhlomys and to compare them with the known acoustics of bats and with non-echolocation ultrasonic calls of other rodents. A remaining question is the mechanism of signal production – is it located in the larynx? and is the animal entirely incapable to communicate in the human-audible range indeed? It will be of interest to investigate the degree of eye degeneration and development of echolocation in a closely related and very similar species, the Chinese pygmy dormouse – Typhlomys cinereus.
Aleksandra A. Panyutina, Alexander N. Kuznetsov, Ilya A. Volodin, Alexey V. Abramov and Irina B. Soldatova. 2017. A Blind Climber: The First Evidence of Ultrasonic Echolocation in Arboreal Mammals. Integrative Zoology. 12(2); 172–184. DOI: 10.1111/1749-4877.12249
Video: Blind mouse navigates like a bat sciencemag.org/news/2017/01/video-blind-mouse-navigates-bat
Blind climber science.sciencemag.org/content/355/6322/258.5
An echolocating dormouse could reveal the origins of one of nature's coolest superpowers http://po.st/YfQ1MK @SmithsonianMag
Rare rodent is the first tree-climbing mammal known to echolocate like a bat | MNN mnn.com/earth-matters/animals/stories/rare-rodent-first-tree-climbing-mammal-known-echolocate-bat