It can be lonely at the top. Snub-nosed monkeys live at a higher altitude than any other non-human primate – but they are also among the rarest of all primates.
The latest genomic analyses may help to explain exactly how they have adapted to life in the thin air found in their habitat and perhaps inform their conservation.
Snub-nosed monkeys were once fairly common across Asia, before climate and geological processes conspired against them. Mountain-building activity in the area associated with the formation of the Himalayas and the Tibetan plateau created physical barriers that isolated monkey populations from one another.
The deterioration of environmental conditions during the last ice age helped keep those populations apart.
By about 300,000 years ago, the monkeys had been isolated for so long that they had split into five distinct species. Golden, black and gray snub-nosed monkeys live in the mountainous forests of southern China, the Tonkin snub-nosed monkey inhabits northern Vietnam and the Myanmar snub-nosed monkey lives in Myanmar.
The black snub-nosed monkey has the highest elevational range of any non-human primate. It lives in a small corner of the Tibetan plateau at 3400 to 4600 metres above sea level.
Xuming Zhou and Ming Li at the Chinese Academy of Sciences, Beijing, and their colleagues, have looked at snub-nosed monkey DNA for clues to how the animals survive in these challenging conditions. The researchers studied the whole genomes of 38 individuals from four of the five snub-nosed monkey species.
Getting hold of the genetic samples was tough. “[The monkeys] are very rare and they are protected by law in China,” says Zhou.
The high-quality biological samples they needed for the analysis – from muscle, skin and blood – came mostly from individuals that had died of natural causes in the nature reserves of south-west China.
The study revealed variants of 19 genes that seemed to have been under positive selection since the black snub-nosed monkey diverged from the other species. They included one – ADAM9 – which is expressed at higher levels in some oxygen-starved cancer tumours.
The gene might be under selection in the monkeys because of the thin high-altitude air they are exposed to. A recent study found that ADAM9 also seems to be under selection in another high-altitude species, the Tibetan chicken.
Earlier this year another team found selection in the black snub-nosed monkey’s genes related to blood vessel formation, lung function and DNA repair, among others. These could also be helpful for life on the Tibetan plateau, where the air is thin and UV radiation more intense.
The monkeys have adapted to high-altitude living by changing their behaviour, too. “They hold together to sleep in the cold weather,” says Li. And, although they are primarily leaf-eating, “they capture some small mammals or birds to get meat to add energy”.
The monkeys also tend to spend more time on south-facing mountains at high altitudes in winter – perhaps because the snow is more likely to melt there and expose the vegetation that the monkeys eat.
Journal reference: Molecular Biology and Evolution, DOI: 10.1093/molbev/msw150
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