Sheffield, United Kingdom. Comparisons of rats and mice with their distant relative, the marsupial, suggest that moveable whiskers were an important milestone in the evolution of mammals from reptiles.

Research suggests that the emergence of a new tactile sense based on moveable facial whiskers was an important step along the evolutionary path to modern mammals. This was an important complement to becoming warm-blooded, having an enlarged brain, and giving birth to live young.


Rodents like rats and mice move their whiskers back-and-forth at high speed and in varying ways to actively sense the environment around them in a behavior known as whisking. This allows the rodents to accurately determine the position, shape and texture of objects, make rapid and accurate decisions about objects, and then use the information to build environmental maps. Although humans no longer have moveable whiskers, they were a critical feature of our early mammalian ancestors."


Rat


House mouse


OpossumThe research team, led by Professor Tony Prescott from the Department of Psychology at the University of Sheffield, used high-speed digital video recording and automatic tracking. Their findings appear in the journal Philosophical Transactions of the Royal Society B: Biological Sciences and presented at the annual meeting of the Society for Neuroscience.



Tony Prescott, PhD, is Professor of Cognitive Neuroscience at the University of Sheffield. His research is concerned with understanding brain function using methods in the computational, neural, and behavioral sciences.

He Co-Directs the Adaptive Behaviour Research Group and is a Visiting Fellow at the Bristol Robotics Laboratory.When running in a straight line, rats and mice move their whiskers back-and-forth the same amount on both sides. However when turning, they bias their whisker movements in the direction of the turn, and when the whiskers on one side of the head contact an object, those on the opposite side sweep round to gather more information.

These active sensing strategies boost the information gained by the whiskers, helping the animals to better understand their world through touch.

In their latest research, the team showed that whisking like that of rodents, using these active sensing strategies, is also seen in a small South American marsupial - the grey short-tailed opossum. This animal has many similarities to an early mammal that would have lived more than 125 million years ago. That is around the same time that the evolutionary lines leading to modern rodents and marsupials diverged.

This evidence suggests that some of the first mammals may plausibly whisked like a modern mouse or rat, and that the appearance of moveable whiskers was pivotal in the evolution of mammals from reptiles.

The earliest mammals were nocturnal, and tree-living. To successfully move around and thrive in this challenging environment. they had to effectively integrate information from multiple senses — sight, sound, smell, and touch.

Facial whiskers provided mammals with a new tactile sense not available to reptiles that could help them to get around in the dark.

In addition to continuing to investigate the similarities and differences between rodents and marsupials, the team is also using these insights from biological whisker sensing to develop animal-like robots that can use artificial whiskers to navigate without vision. These robots could have applications in search-and-rescue, particularly in environments, such as disaster sites, where vision is compromised by smoke or dust.

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