Superfast bat muscles? You bet!
Echolocation is a bat's greatest tool, helping it navigate and hunt for prey. Bouncing sound waves off objects allows bats to generate an accurate representation of their environment in total darkness. A Danish-US team of scientists sheds new light on why the bat has the ability to do what it does. Presented in the journal Science, they identified how 'superfast' muscles are the key to this ability. Researchers at the University of Southern Denmark and the University of Pennsylvania in the United States showed how superfast muscles can contract around 100 times faster than typical body muscles. These muscles are also 20 times faster than the fastest human muscles, the muscles that control eye movement. 'Superfast muscles were previously known only from the sound-producing organs of rattlesnakes, birds and several fish,' explains Professor Coen Elemans of the University of Southern Denmark, the lead author of the study. 'Now we have discovered them in mammals for the first time, suggesting that these muscles - once thought extraordinary - are more common than previously believed.' According to the researchers, echolocation is different to vision because it only gives bats a snapshot of their environment with each call and echo, while vision is a relatively continuous stream of information about the world. Echolocation forces bats to make quick successions of calls. While on the hunt to find prey, bats must get fast updates on their victims' positions - it is a challenge because flying insects move around in various directions. When it's crunch time, bats generate a 'terminal buzz', making up to 190 calls per second. 'Bat researchers assumed that the muscles that control this behaviour must be pretty fast, but there was no understanding of how they worked,' explains Andrew Mead, a graduate student at the Department of Biology in Penn's School of Arts and Science. 'Research on superfast muscles is just a world apart from what they do. This study represents many worlds coming together: the muscle world, that bio-acoustics and echolocation world and the bat behavioural world.' The team assessed the performance of the bats' vocal muscles by attaching one between a motor and a force sensor and electrically stimulating it to flex. When the motor was stationary, a single electric pulse permitted the researchers to calculate the time that bat muscle took to twitch, or to contract and relax. 'The twitch gives us a sense of the time it takes for a muscle cell to go through all the steps, all the chemical reactions, necessary to exert force and to relax again,' Mr Mead points out. 'The faster the muscle, the shorter the twitch. These muscles could go through all the motions in less than a hundredth of a second.' The team, however, modified the length of the muscle while it was contracting, in order to determine how much hard the muscle was working inside the bat. The muscle lengthened and shortened at a controllable rate when the motor was running. While the muscle was being stretched, the researchers stimulated the muscle to contract in order to see if the muscle pulled on the motor harder than the motor pulled on the muscle. And to determine if the muscle was really of the superfast type, the team increased the speed of the motor to more than 100 oscillations per second. 'You're always limited to how many twitches you can do in a given period of time,' Mr Mead says. 'If you keep on increasing the frequency, doing twitch after twitch, you get to the point where the twitches begin to build on top of each other and the muscle doesn't fully turn off. We went to the highest cycling frequency where we still had evidence that the muscle was turning on and off.' Says Professor Elemans: 'We determined the power the muscles can deliver, much like how you measure a car's performance. We were surprised to see that bats have the superfast muscle type and can power movements up to 190 times per second, but also that it is actually the muscles that limit the maximum call rate during the buzz.' Adds Mr Mead: 'You can think of it like a car engine. It can be tuned to be efficient, or tuned to be powerful depending on what you want it to do. It turns out that bats trade off a lot of force to be able to get these rapid oscillations. In a way it's like an engine that's been tuned for extremely high RPM.'For more information, please visit: University of Southern Denmark:http://www.sdu.dk/?sc_lang=enScience:http://www.sciencemag.org/
Countries
Denmark, United States