Pronghorn antelope are the fastest animals in North America, accelerating from zero to 40 mph in seconds.
The speed in their long delicate legs is an adaptation from a pre-Ice Age existence, when they had to outrun fierce predators that roamed the grasslands – lions bigger than those on the African Savannah, American cheetahs, wild dogs and fleet-footed bears.
“It was a fearsome environment,” said University of Idaho professor John Byers, who once raced a pronghorn in his pickup truck, clocking it at speeds of 45 mph over two miles of bumpy prairie. “That’s why they can run so fast.”
Byers, an animal behavioralist, has spent 20 years studying pronghorns in Montana’s National Bison Range. Through his research, he learned that females select males with the top running speeds, endurance and agility to breed with, to produce the fastest offspring.
Twelve percent of pronghorn males sire 80 percent of the fawns. Speed is still an important attribute for pronghorns. It helps the youngsters evade coyotes.
Through his work over two decades, Byers used genetic testing to develop family histories for the 120-member pronghorn herd on the National Bison Range. Now he plans to use the data to answer another pressing question: Does the herd have a mechanism to avoid inbreeding?
Pronghorns were introduced to the fenced-in range in the 1950s. Despite limited introduction of new animals, the herd maintains a diverse genetic base. That makes Byers wonder whether something in the pronghorns’ mate selection process guards against inbreeding.
The National Science Foundation recently awarded Byers a four-year grant of $600,000 to study the question. It’s groundbreaking work, according to Samuel Scheiner, program director for the foundation’s Environmental Biology Division, which deals with evolutionary processes.
“One of the big concerns about managing wildlife species is that the landscape has become fragmented due to conversion of land into human use,” Scheiner said.
Populations that once roamed vast landscapes are confined to small patches of habitat. As pockets of animals become isolated, their genetic diversity tends to diminish, weakening the population.
“After a while, everybody’s related to everyone else,” Scheiner said. “John’s study would be one of the first to really demonstrate if females, in choosing their mates, can avoid that.”
It’s a question that fascinates Byers, who can identify animals in the herd by sight.
“We already know what the fitness benefit of choosing a hot male is,” said Byers, noting that offspring born to more vigorous males have higher survival rates.
Now he’ll use genetic testing to research whether females avoid mating with cousins or siblings, even if close male relatives have the desirable trait of stamina for long-distance treks across the prairie.
Byers chose to study pronghorns on the bison range because they’re accustomed to vehicles. He and his graduate students can get relatively close to the animals.
“After a while, it was like looking at human faces,” Byers said. “We could say, ‘That’s Bertha.’ ”
He started noticing that females spent a lot of time moving between harems during breeding season. The males that sired the most offspring also were the most successful in the grueling tasks of keeping flighty females bunched together in groups and warding off challenges from other males.
Their fawns, in turn, developed faster and were less likely to be killed by coyotes.
In his 2003 book, “Built for Speed: A Year in the Life of a Pronghorn,” Byers describes pronghorns’ allure.
The animals, he writes, have a “four-chopsticks-in-a- bratwurst” body type. Slender legs attach to stocky upper bodies, increasing the velocity of pronghorns’ gaits.
Byers includes funny descriptions of graduate students chasing fawns; scientific explanations of the blood flows that give pronghorns the stamina to maintain high speeds for long distances; and calorie counts for pronghorn milk. (Twice the energy value of cow milk, 2 ½ times the energy value of human milk.)
Watching a coyote trying to sneak up on a group of adults is comical, Byers said. When the coyote gets close enough, the pronghorns simply turn and float away across the prairie.
Pronghorns, he wrote, “are survivors from another world … running machines that in today’s environment blow the competition away.”
Click here to comment on this story »