Why It’s Hard to Break the Gnus

It's all about their efficient muscles.

A wildebeest
Radu Sigheti / Reuters

Scientists, on top of being good at their actual research, must also excel at fund-raising, mentorship, management, teaching, and public speaking. To that list, Alan Wilson must add marksmanship. For his latest project, he had to shoot fast-moving wildebeest with tranquilizer darts, while hanging out the side of an equally fast-moving helicopter. “It’s not easy,” says Wilson, who is a professor at the Royal Veterinary College, “but I’ve misspent my life in many ways and part of it was in the military.”

It helped that wildebeest—cow-like antelopes, also known as gnus—behave predictably. As the helicopter pilot flew toward them, they would always run away in a straight line. As the vehicle drew nearer, they would invariably bank under it, giving Wilson a clear shot. He managed to tag 20 wildebeest in May 2016, and he only missed around one in five shots. The main challenge was avoiding obstacles. “The two things you don’t want for a helicopter are to fly low and slow,” he says. “Typically, we had just two of us with a half-full fuel tank, so we could pull out of a turn or over a tree.”

It might seem odd to go to all this effort for wildebeest. They’re like the extras of the Serengeti. Scientists have largely ignored them. When documentary-makers film them, it’s usually because they’re being killed by lions, cheetahs, or crocodiles. They’re best known for their epic seasonal migrations. In an ecosystem that contains some of the world’s largest, tallest, fastest, and most formidable mammals, wildebeest don’t seem to be exceptional at much besides wandering around.

Except, as Wilson and his colleagues showed, they really are exceptional at that. By taking small biopsies from the front legs of the darted animals, the team found that wildebeest muscles are far more efficient than those of humans, cows, rabbits, or any other mammal that’s been measured thus far.

Almost two-thirds of the energy that’s put into them is converted into physical movement, while the rest is lost in the form of heat. “That is tremendous,” says Angela Horner from California State University at San Bernardino, who was not involved in the study. “It’s nearly three times as efficient as muscle in human athletes.” This efficiency, Wilson says, allows wildebeest to stride across hot, dry grasslands without overheating or dehydrating.

To see how far wildebeest actually walk, Wilson fitted the tranquilized individuals with tracking collars of his own design. Each contains a bevy of instruments that sense their bearers’ position, speed, and posture, as well as the surrounding temperature and humidity.

Wilson has used such collars to study cheetahs and wild dogs, and his results have busted myths about these animals that wormed their way into textbooks. The wildebeest were no exception. It’s commonly said that they have to drink water every day, but the collared individuals stayed away from the local river—the only water source available—for up to five days straight. “That was a surprise,” he says. “They’re much more resilient than we imagined.”

Their endurance is especially impressive because they live in “lion country, so they can’t walk around at night,” says Wilson. Instead, they must brave daytime temperatures that can reach scorching highs of 100 degrees Fahrenheit. They cope by strolling slowly, and, as the team found, by having very efficient muscles.

It is very hard to take a muscle biopsy in the field. The surgery itself removes just a thin sliver of tissue, and such procedures are simple and harmless. But mammalian muscle is “very tetchy,” Wilson says, and dies easily. To preserve the samples, he put each one in a bottle infused with 90 percent oxygen, cooled it to room temperature, and helicoptered it back to their camp.

There, Wilson’s colleague Nancy Curtin dissected individual muscle fibers from the biopsied tissue. She hooked these up to devices that could zap them with electricity, record the force of their contractions, and measure the heat they release to a thousandth of a degree. These methods were first developed a century ago, but they’re so finicky that they’ve only ever been done in a few species within carefully controlled lab settings. It was quite something to deploy them from a hut in the middle of the savanna.

On average, Curtin found that the muscles converted 63 percent of their energy into work—i.e., physical movement. For comparison, the equivalent figures are 42 percent for cows, 34 percent for mice, and 27 percent for rabbits. Higher efficiencies have only ever been recorded from tortoises—animals that are synonymous with slow and steady walking.

Walking produces heat, and the team estimated a wildebeest’s body temperature would rise by an intolerable 10 degrees over just 20 kilometers if it were unable to cool down. Shade can help, but migrating wildebeest can’t afford to dawdle. The only option is to sweat, which deprives them of around 3.1 liters of water a day. Wilson’s team calculated that if wildebeest muscles were as inefficient as those of cows, they’d lose 50 percent more water—4.7 liters daily. Their high-performing fibers allow them to go that much farther, freed from the tyranny of hydration—exactly what the data from the collars suggested.

That’s what makes this study unique, says Carolyn Eng from Brown University: It ties together measurements of single muscle fibers with data about entire animals, and free-living ones, no less. “It’s challenging to get these types of data from a wild population of a little-studied organism,” she says.

“It is a truly groundbreaking paper,” adds Robyn Hetem from the University of Witwatersrand. “Our understanding of muscle efficiency is mostly based on work done in the mid-1990s on mouse fibers, which convert only about 35 percent of energy into work.”

“The field had largely taken muscle to be that efficient and moved on,” says Natalie Holt from Northern Arizona University. For example, many scientists have put animals on treadmills and measured how much energy they spend to move a given distance. If that efficiency is greater than, say, 25 percent, researchers usually assume that the creatures must have some kind of energy-saving trick, like tendons that act as springs. “This has become central to our understanding of why certain [physiques] and ways of moving have evolved,” explains Holt. But if wildebeest muscles can be that much more efficient, maybe those assumptions should be reconsidered.

Indeed, wildebeest may not actually be that exceptional. In 2011, another group of researchers found that the muscles that humans engage when we splay our fingers are 68 percent efficient—a figure far higher than even athletes’ limb muscles. That result, Holt says, was more or less dismissed at the time as an anomaly rather than an exciting finding, especially since the team used a new technique to measure efficiency. But, again, given the wildebeest study, maybe it’s not an anomaly after all.

“While it’s cool to see such high muscle efficiency [in the wildebeest], and it definitely could be related to living in extreme environments,” Holt says, it could just be that we don’t know a lot about how efficient animal muscles can really be.