What do a hummingbird and chicken have in common?

Brandy Velten (doctoral student) and Dr. Kenneth Welch (Comparative Physiologist) from the University of Toronto wanted to know whether birds with very different speeds at which they flaps their wings (i.e. wingbeat frequencies) had correspondingly varying types of myosin proteins in their muscles. Their findings were published in the American Journal of Physiology last month.

In their study they compared ruby-throated hummingbirds and zebra finches which reportedly have some of the highest wingbeat frequencies (20-60Hz). As you can imagine, their flight muscles are made up of almost exclusively of muscle fibers that contract very fast (i.e. fast twitch). Whereas a chicken's breast muscle (i.e. pectoralis) is composed of mostly slow-twitch muscle fibers that are more important in controlling things like posture. Myosin heavy chain (MHC) is very important in regulating the ability for a muscle to contract (for a review of myosin, see the video at the end of this post). The type of MHC varies depending on whether a muscle is mainly slow or fast twitch. It was these variations in the MHC protein that this study explored in the following birds:

Ruby-throated hummingbirds (Archilochus colubris)

Image of Ruby-throated hummingbird from Wikimedia Commons. Image of Ruby-throated hummingbird from Wikimedia Commons.

Zebra Finches (Taeniopugia guttata)

Image of zebra finches from Wikimedia commons. Image of zebra finches from Wikimedia commons.

Because some collectors nearby left behind the carcass of a juvenile yellow-bellied sapsucker (Sphyrapicus varius) and an adult house sparrow (Passer domesticus), these species were included as well since their wingbeats are not as fast, which made for a nice comparison.

What they found was really interesting. Even though each of these species had varying wingbeat frequencies, the pectoralis and supracoracoideus flight muscles of these birds had only one type of MHC protein, which turned out to be the same fast type that is found in chicken pectoralis muscles, not exactly a bird setting any records with its flying abilities. What these findings mean is that this particular MHC protein is important for general powered flight. Therefore, the structural properties of the MHC protein or other proteins that it interacts with may be more important in determining whether a bird can be an extraordinary flyer like a hummingbird or an occasional short distance "flyer" like a chicken.

Comic from: www.cartoonstock.com Comic from: www.cartoonstock.com

For a review on muscle contraction and what in the world myosin is, check out this YouTube video:

Velten BP, Welch KC. Myosin heavy-chain isoforms in the flight and leg muscles of hummingbirds and zebra finches. Am J Physiol Regul Integr Comp Physiol. 306: R845–R851, 2014. doi:10.1152/ajpregu.00041.2014


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