For all the focus on the hourglass-shaped patch of scarlet skin that graces its otherwise furry chest like a superhero’s crest, the gelada monkey’s soaring habitat is what interests Nebraska’s Jay Storz and many of his fellow biologists.
Sometimes called the bleeding-heart monkey, the signature species resides only on the plateaus of the Ethiopian Highlands. There it dwells between 6,000 and 14,000-plus feet above sea level, catching sleep on cliffsides and staking its claim as the only primate to feast primarily on grass.
That high-altitude life naturally drew the attention of Storz, who’s devoted decades to studying the physiology of birds and mammals that evolved to survive on the scarce oxygen available at such dizzying heights. In pursuit of the species’ physiological secrets, Storz recently collaborated with an international team led by Arizona State University’s Noah Snyder-Mackler and Kenneth Chiou, who catalogued the entire DNA of the gelada monkey by sequencing its genome.
“Primate species have adapted to many diverse ways of life, but very few have successfully colonized extremely high-altitude environments,” said Storz, Willa Cather Professor of biological sciences.
The team suspected that the gelada monkey adapted to its low-oxygen existence, as so many high-elevation denizens have, via mutations to its hemoglobin: a protein that collects oxygen in the bloodstream, then delivers it to the tissues and organs that need it. Prior research from Storz and his colleagues has shown that high-altitude animals often boast hemoglobins that attract oxygen more efficiently than those flowing through the bloodstreams of their lowland counterparts. That stronger affinity for oxygen allows the owners of those hemoglobins to subsist on much less of it — in the most extreme cases, roughly one-third what’s available at sea level.
So when the ASU researchers discovered two substitutions in the molecular joints of gelada hemoglobin that were absent in other primates, the team expected those substitutions would correspond with better oxygen-snaring capabilities. To test what they considered a “slam dunk” hypothesis, they turned to Storz. After putting the gelada hemoglobin through its paces in his lab, though, Storz found that the protein attracted oxygen no better than that of humans or baboons.
“Patterns of DNA variation can suggest hypotheses about evolutionary adaptation, but those hypotheses have to be tested with functional experiments,” Storz said. “If your tests rule out one possible explanation, it forces you to keep searching until you find the right answer.”
The lack of modifications to hemoglobin function, Storz said, suggests that changes in other respiratory or metabolic traits may have allowed the species to tolerate the rarefied air of the Ethiopian Plateau. And the researchers did find that the famously marked chests of adult geladas are relatively larger than would be expected at sea level, suggesting that the animals have an enhanced lung capacity. If so, that larger surface area, and the corresponding increase in gas exchange, could compensate for the reduced oxygen availability.
Analyzing variation in the DNA sequences of wild geladas, meanwhile, revealed 103 genes whose mutations may have helped the primate adapt to its Ethiopian habitat. Those genes are already yielding new hypotheses that will continue to keep the team busy, Storz said.