Climate change may hinder the adaptation of the world's fastest-evolving moss

The world’s oldest moss has seen three mass extinctions — but may not survive climate change.

The genus Takakia has the highest number of fast-evolving genes of any moss, researchers report August 9 in Cell. A decade-long study of Takakia in the Himalayas shows that the moss is well-adapted to its high-altitude home, with resistance to extreme cold and intense ultraviolet light. But no matter how fast it can tweak its genes, the scientists found, rapidly rising temperatures in the region were associated with a decrease in the moss’s range — a faster decrease than any of the mosses around it.

Takakia consists of just two species of moss. While they can be found individually in the United States and Japan, both species occur together only on the Tibetan Plateau in the Himalayas. The two are unlike any other plant in the world. The evolutionary shoot containing Takakia branched off the other bryophytes — mosses, liverworts and hornworts — around 390 million years ago.

“The evolutionary position of Takakia in plants is like that of platypus in mammals,” says Yikun He, a plant geneticist at the Capital Normal University in Beijing. Just as the platypus has a lot of strange, not-quite-mammal traits — like egg-laying and a beak — Takakia has a bunch of features that make it not quite like other plants, such as featherlike leaves and a lack of pores for controlling the flow of oxygen and carbon dioxide.

“It looks very different from other mosses,” says Ralf Reski, a plant biotechnologist at the University of Freiburg in Germany. “For a long time, it was unclear if it was a moss.”

To learn more about mysterious Takakia, Reski, He and their colleagues set up a long-term study in the Tibetan Plateau, more than 4,000 meters above sea level.

Over 11 years, the researchers collected samples, analyzed genomes, collected data on the surrounding ecosystem and compared modern specimens with fossils from 165 million years ago. The team also had to evacuate several students due to altitude sickness. The field sites were accessible only in August and September, and even then, “the climate is unpredictable, and one day may experience spring, summer, autumn and winter,” He says.

Humans might have had a tough time, but the moss was comfortable in its high-altitude home. That’s due in part to its genes. While Takakia sports a genome whose length is average for a bryophyte — just over 27,400 genes — it has the largest known number of fast-evolving genes of any moss, liverwort or hornwort, the researchers found.

Takakia needed that speed when the Himalayas began to rise 65 million years ago. As the mountains stretched toward the sky, the mosses on them were exposed to lower temperatures and higher amounts of ultraviolet light. They had to adapt. And adapt Takakia did.

The new study showed the moss’s ability to withstand solar radiation. When the researchers exposed Takakia to a high amount of UV light, it was unharmed, while comparison mosses began to die within 72 hours. The hardy moss produces “high amounts of metabolites like flavonoids and polyunsaturated fatty acids to protect against radiation,” Reski says. It also sports genes to enable more efficient DNA repair — essential protection against harmful rays.

Takakia also adapted to the extreme cold. It can go dormant for eight months of the year while under snow, and gets all of its growth and reproduction done, He says, “in the precious three-to-four-month light window period.”

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All of these features evolved from about 50 million years ago to the present, the study showed, without ever changing the moss’s physical appearance compared with fossils of Takakia from about 165 million years ago.

But this relatively speedy evolution doesn’t seem to be fast enough to help the moss adapt to climate change (SN: 3/10/22).

During the 11 years of the study, Reski, He and their colleagues documented an average increase in temperature of about four-tenths of a degree Celsius in the region. Meanwhile, the coverage of Takakia in their sample population decreased by about 1.6 percent per year — faster than four other local mosses.

The researchers predict that by the end of the 21st century, suitable conditions for Takakia will be limited to only 1,000 to 1,500 square kilometers around the world. By that time, the researchers suspect, the world’s oldest moss could be extinct.

Others are more optimistic about the fate of this tough little moss. There are populations in other places, says evolutionary biologist S. Blair Hedges. So while the Tibetan Plateau may eventually be Takakia-free, he hopes the moss can make it elsewhere.

What’s more, “it’s fantastic to see all these different things known about a single [genus], from the fossil record all the way up to the complete genome,” says Hedges, of Temple University in Philadelphia.

In the meantime, He, Reski and their colleagues are cultivating Takakia populations and transplanting them to other regions in Tibet in the hopes of giving old moss a new lease on life. “Takakia saw the dinosaurs come and go. It saw us humans coming,” Reski says. “Now we can learn something about resilience and extinction from this tiny moss.”

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