What’s the fastest repetitive muscular action you can do? Tap your fingers on a desk or blink your eyes 5 times a second? Now compare that to wingbeats of some flies up to 200 times a second! How do they do that?
It’s too fast for nerve impulses to arrive. It turns out that the flight muscles in those fast-beaters “self-excite”: their contraction sets them off again without needing a nerve impulse, which only stops or starts the process. This ”asynchronous” beating contrasts with synchronous beating driven by nerve impulses. Jeff Gau and colleagues looked at about 140 species of insects with wing beating rates from 30 to 200 beats per second. One question was, What are the differences in physiology of the wing and the body stiffness in slow- vs. fast-beaters? Another was, When did the differences evolve over the 400 million years of insect life? The third was, Can we make robotic flies that can shift between these modes?
The evolutionary question interested me most. They used DNA sequences to estimate the time in millions of years ago that various modern insects diverged from each other. It appears that the first insects had nerve-timed wing beats. The fast asynchronous style evolved soon… but some species of insects with the fast asynchronous style even mutated back to give rise to the “slow” beaters. What diversity!
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
