Tropical birds develop 'superfast' wing muscles for mating, not flying

April 12, 2016, eLife
Adult male red-capped manakin, which produces wing claps by rapidly retracting its wings toward its body. Credit: Matthew Fuxjager

Studies in a group of tropical birds have revealed one of the fastest limb muscles on record for any animal with a backbone. The muscle, which can move the wing at more than twice the speeds required for flying, has evolved in association with extravagant courtship displays that involve rapid limb movements, according to a paper to be published in the journal eLife.

The 'superfast' wing movements of male red-capped and golden-crowned manakins are undetectable to the human eye, and are about six to eight times faster than the 8-hertz (Hz) speed at which a sprinter, such as Olympian athlete Usain Bolt, moves their legs through the air in a 100-metre run.

"The discovery of the superfast wing in these birds paves the way for further studies into what has to change, or what can change, in a muscle to make it drive faster movements," says first author Matthew Fuxjager, from Wake Forest University.

"This could be important for developing therapies for motor disorders, particularly those characterized by decreases in muscle performance that result from diseases such as cancer and HIV."

Many different species perform rapid limb movements as part of their courtship displays, from certain birds running across lake surfaces, to the unusual boxing displays of hares in March.

However, because is limited by trade-offs between speed and force, it is unclear how animals develop the ability to generate both the swift movements involved in showy physical displays and the force needed to drive these movements.

High-speed video of a golden-collared manakin performing a roll-snap. Credit: Barney Schlinger. As published in: Fuxjager, M.J., Longpre, K.M., Chew, J.G, Fusani, L. and Schlinger, B.A. (2013). Peripheral androgen receptors sustain the acrobatics and fine motor skill of elaborate male courtship. Endocrinology, 154: 3168-3177.)

To address this question, Fuxjager and his team compared the twitch speeds of forelimb muscles from wild-caught golden-collared and red-capped manakins to those of three other related species: the blue-crowned manakin, the dusky antbird, and the house wren.

"Of the species studied, the golden-collared and red-capped manakins produce exceptionally rapid wing movements as part of their acrobatic courtship displays," Fuxjager explains.

"For example, the golden-collared manakins perform 'roll-snaps', whereby they hit their wings together above the back at around 60 Hz to produce a loud mechanical sound. Likewise, red-capped manakins produce a similar wing sonation called a 'clap', in which the wings are extended slightly above the body and immediately retracted back to the sides in quick succession, at around 45 Hz."

To explain these birds' abilities to move their limbs rapidly during courtship performances, the researchers investigated the differences in muscle contraction speeds by comparing the half-relaxation frequency among the five different species. This represents the frequency at which each wing muscle is stimulated to contract, while still being able to relax to half their length following stimulation, thereby showing an accurate measure of how quickly they can contract.

For two of the three wing muscles, the half-relaxation frequencies averaged around 50 Hz and were indistinguishable among species. By contrast, the frequency measures in the main muscle that retracts the humerus were significantly higher in both the golden-collared and red-capped manakins. Estimates of their half-relaxation frequencies in this muscle were exceptionally high, and the frequencies between the two birds were indistinguishable.

These results show that only the golden-collared and red-capped manakins have evolved superfast contractile movements in their main humeral retractor muscle. The other two muscles that generate the majority of aerodynamic force for flight are no different from those of other birds, suggesting that they have been preserved to produce the strength needed for flying.

The team also found that the humeral retractor muscle in golden-collared and red-capped manakins is more than capable of driving the natural wing oscillations that make up their impressive displays.

Taken together, the results suggest that muscle-specific adaptations in contractile speed allow certain birds to avoid the trade-off between muscular speed and force, thereby using their forelimbs for both rapid gestural displays and powered locomotion.

"Further studies could now explore how this one muscle can create such superfast wing movements and whether male hormones, such as testosterone, play a role in regulating the muscle's speed," Fuxjager adds.

"If we discover whether steroids regulate the muscle's ability to contract at superfast speed, we would be uncovering how hormones can 'turn on' or 'turn off' its extraordinary ability. This would open the door to understanding how rapid limb movements are regulated in accordance with the animals' reproductive environment."

Explore further: Testosterone key to new bird bang theory

More information: Matthew J Fuxjager et al. Select forelimb muscles have evolved superfast contractile speed to support acrobatic social displays, eLife (2016). DOI: 10.7554/eLife.13544

Related Stories

Testosterone key to new bird bang theory

April 22, 2015

New research from a Wake Forest University biologist who studies animal behavior suggests that evolution is hard at work when it comes to the acrobatic courtship dances of a tropical bird species.

Acrobatic birds aren't as energetic as they look

December 19, 2013

In research published this week in Proceedings of the Royal Society B scientists have found that the acrobatic courtship displays of male golden-collared manakins are less energetically costly than they appear.

How the bat got its buzz: Superfast muscles in mammals

September 29, 2011

As nocturnal animals, bats rely echolocation to navigate and hunt prey. By bouncing sound waves off objects, including the bugs that are their main diet, bats can produce an accurate representation of their environment in ...

Small birds' vision: Not so sharp but superfast

March 18, 2016

One may expect a creature that darts around its habitat to be capable of perceiving rapid changes as well. Yet birds are famed more for their good visual acuity. Joint research by Uppsala University, Stockholm University ...

Recommended for you

Cells lacking nuclei struggle to move in 3-D environments

January 20, 2018

University of North Carolina Lineberger Comprehensive Cancer Center researchers have revealed new details of how the physical properties of the nucleus influence how cells can move around different environments - such as ...

Microbial communities demonstrate high turnover

January 19, 2018

When Mark Twain famously said "If you don't like the weather in New England, just wait a few minutes," he probably didn't anticipate MIT researchers would apply his remark to their microbial research. But a new study does ...

Hot weather is bad news for bird sperm

January 19, 2018

A new study led by Macquarie University and spanning Sydney and Oslo has shown that exposure to extreme temperatures, such as those experienced during heatwave conditions, significantly reduces sperm quality in zebra finches, ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.