Bat wings are equipped with an unusual repertoire of very sensitive touch sensors, a new study in the journal Cell Reports has found.
The big brown bat (Eptesicus fuscus). Image credit: Angell Williams / CC BY 2.0.
The study shows that the sensors provide feedback to an animal during flight, and suggests that neurons in the bat brain respond to incoming airflow and touch signals, triggering rapid adjustments in wing position to optimize flight control.
“Until now no one had investigated the sensors on the bat’s wing, which allow it to serve as more than a propeller, a flipper, an airplane wing or any simple airfoil. These findings can inform more broadly how organisms use touch to guide movement,” said co-author Dr Cynthia Moss of the University of Maryland, College Park.
“This study provides evidence that the sense of touch plays a key role in the evolution of powered flight in mammals,” added co-author Dr Ellen Lumpkin of Columbia University.
“This research also lays the groundwork for understanding what sensory information bats use to perform such remarkable feats when flying through the air and catching insects. Humans cannot currently build aircrafts that match the agility of bats, so a better grasp of these processes could inspire new aircraft design and new sensors for monitoring airflow.”
Dr Moss, Dr Lumpkin and their colleagues studied the big brown bat (Eptesicus fuscus), a common species found throughout North America. Bats are the only mammals capable of true powered flight, able to reach speeds of 7 – 20 miles per hour, and with the sort of aerial maneuverability humans only wish they could engineer.
The scientists found that the evolutionary process that allowed bats to form wings resulted in unusual tactile circuitry that not only enhances control during flight, but also allows bats to use their wings to climb, cradle their young, and capture insects.
They discovered an array of sensory receptors in bat wings – a significant number of which are clustered at the base of tiny hairs that cover the appendages. Such placement of these touch cells, both lanceolate endings and Merkel cells, allows the bat, while flying, to sense changes in airflow as the air ruffles the hairs.
When the researchers stimulated these hairs with brief air puffs, neurons in the bat’s primary somatosensory cortex responded with precisely timed but sparse bursts of activity, suggesting this circuitry helped guide bats during fast, dynamic flight.
“While sensory cells located between the ‘fingers’ could respond to skin stretch and changes in wind direction, another set of receptors associated with hairs could be specialized for detecting turbulent airflow during flight,” explained Dr Sterbing-D’Angelo of the University of Maryland, College Park.
The scientists also found the innervation of bat wings to be unlike that of other mammalian forelimbs – a clue into how wings grew in bats during evolution.
“Our next steps will be following the sensory circuits in the wings all the way from the skin to the brain. In this study, we have identified individual components of these circuits, but next we would like to see how they are connected in the central nervous system,” Dr Moss said.
“An even bigger goal will be to understand how the bat integrates sensory information from the many receptors in the wing to create smooth, nimble flight.”
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Kara L. Marshall et al. Somatosensory Substrates of Flight Control in Bats. Cell Reports, published online April 30, 2015; doi: 10.1016/j.celrep.2015.04.001
