Gelada monkeys hold secrets of high altitude adaptation

Gelada monkeys are unique, living far above their baboon relatives in the Ethiopian highlands at elevations of 6,000 to 14,000 feet above sea level. Scientists wanted to look at how these monkeys survived at these elevations, and even thrived, peacefully grazing on mountain grasses. The question is especially interesting as geladas have lived at high elevation much longer than any human population. 

A team of experts from Arizona State University (ASU) led by Professor Noah Snyder-Mackler and postdoctoral researcher Kenneth Chiou set out to discover the genetic adaptations that allow the monkeys to live in the mountains. 

“Life at high altitude is very difficult. The air is colder and contains less oxygen,” said Snyder-Mackler. “Our team has studied geladas living in such extreme environments for over a decade, so we have a firsthand understanding of how challenging it can be to live at such heights over extended periods of time. Yet geladas have survived for much longer, making us wonder how exactly they have shifted their biology to adapt to their challenging environments.”

One of the first things the researchers checked was the gelada’s hemoglobin and right away they found changes in the molecular sequence of the gelada hemoglobin. At first, the researchers thought that the hemoglobin was modified to hold greater concentrations of oxygen. This idea was quickly challenged however when the scientists tested the oxygen concentration of gelada blood against that of baboons and humans, which all ended up being the same.  

“The absence of an elevated hemoglobin concentration in wild geladas living at high altitude suggests that they can still provide enough oxygen to tissues in spite of the reduced availability of oxygen,” explained Chiou. “There are a lot of other ways geladas could be physiologically compensating for low oxygen and these could entail many kinds of changes to respiratory or circulatory traits that affect oxygen transport.”

The scientists compared the chest sizes of geladas with baboons and found that indeed, geladas have bigger chests. The chests may be larger to hold larger lungs as an adaptation to high elevation (and thin air) living. This, the scientists explain, is similar to chest dimensional changes of people native to the Andes mountains, also seen as an adaptation to high elevation. It’s uncertain if the gelada chest size is due to genetics or from growing up at high elevation.  

Next, the scientists returned to their genetic analysis. After sequencing the gelada genetic code, the researchers found 103 genes that might have been selected for adaptation to highland life. Genes that were selected for include parallels to humans, such as genetic adaptations found in Tibetans, Ethiopians, Nepalese Sherpas and Bajau deep sea divers. However, a lot of the genes had no parallels. 

“While we found a lot of overlap between pathways under selection in geladas and human populations living at high altitudes, aside from notable examples listed above, few genes identified by our analysis were shared with candidate genes reported by studies of high-altitude human populations or other high-altitude primates,” said Chiou.

The experts did make another important discovery though. They found chromosomal differences between geladas in the northern and central areas. This suggests that they may actually be two separate species, unbeknownst to science.

“Given that chromosomal rearrangements tend to be associated with infertility–like mules, which are the hybrid offspring of a horse and a donkey, our findings suggest that geladas may encompass at least two distinct biological species,” said Chiou.

The accidental discovery has important conservation implications, if the geladas are actually two species, it means two smaller and potentially more vulnerable species. This possibility calls for more research into these unlikely mountain monkeys.  

The study is published in the journal Nature Ecology & Evolution.

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By Zach Fitzner, Earth.com Staff Writer