Walk out your back door and take a look around. What do you see? If you’re a city dweller, you likely see cars, concrete, and construction. If you’re a rural resident, maybe forests, farms, and firewood. But whatever your surroundings, try to imagine what they looked like 50,000 years ago. Were they similar or drastically different? Scientists have been asking this exact question about the Arctic tundra. Specifically, they want to learn about the evolution of Arctic vegetation, and if the plants that make up the vast northern plains have changed over the past tens of thousands of years.
You may think of the Arctic as a landscape frozen in time, but its biodiversity has undergone major shifts over the millennia—remember, it wasn’t that long ago that colossal creatures, like woolly mammoths, roamed the Far North. Luckily the details of these ecological shifts, like much of the Arctic’s natural history, are preserved within ancient DNA found deep in the permafrost.
Given enough time, just about everything in the Arctic worms its way into the permafrost. This means that the DNA trapped inside permafrost is a genetic hodgepodge, originating from a diversity of sources, such as the toothy and bony remains of long-dead animals, decomposed plants, miscellaneous microbes, and even prehistoric poop and age-old urine deposits.
Recently, to better understand prehistoric northern landscapes, an international team of researchers isolated DNA from hundreds of permafrost samples taken from twenty-one sites across the Alaskan, European, and Siberian Arctic. Carbon dating showed that the sediment samples range from a few hundred to over fifty thousand years old, but the coolest findings came from the DNA sequences within the frozen dirt.
After sequencing huge amounts of permafrost DNA and digitally sifting through millions of genes, the scientists were able to tease out the genetic information that came from plants. They then used these data to piece together a history of the different plant species that populated the Arctic over a fifty-thousand year period.The results of this analysis, which were published in the journal Nature, suggest that there was a surprisingly large amount of plant diversity in the ancient Arctic, slightly more diversity, in fact, than the contemporary Arctic environment. What’s more, the types of plants found in the Arctic have changed considerably over time.
For example, if you travelled back in time fifty millennia and landed in the Arctic, you would probably spot lots of wildflowers and other types of herbaceous vascular plants (things commonly referred to as forbs) spread across dry steppes. But fast-forward to the present-day Arctic and you’ll find more woody plants and grasses scattered across wet tundra. The researchers believe that the forbs declined from the Far North around fifteen thousand years ago,and at around the same time there was a slow transition from a relatively dry to a more moist tundra environment.
I know what you’re thinking: Is there really much of a difference between forbs and grasses? Well, if you are a ten-thousand-pound woolly mammoth,there is a big difference. Wildflowers, and forbs in general, pack a lot of protein and are more nutrient-rich and more easily digested than grasses. Thus, if you’re a prodigious woolly beast wanting to put on and keep on weight, forbs are likely a better bet than grasses.
The researchers argue that the decline in forbs might be associated with the extinction of ice-age beasts. To explore this hypothesis further, they explored the stomach contents of ancient woolly mammoth, woolly rhino, bison, and horse specimens from Siberia and Alaska, some of which are estimated to be fifty-five thousand years old. Sure enough, they found an abundance of forbs within the tummies of these ice-age giants, supporting the view that the disappearance of the large woolly mammals that once grazed the northern steppes is linked to the decline of forbs from the Arctic.
This study is a testament to how innovations in DNA sequencing technologies are transforming how we do science. Ten years ago it would have been inconceivable for a relatively small team of researchers to sequence and analyze DNA from hundreds of samples of permafrost. One can’t help but wonder what new genetic techniques the next decade will bring—techniques that will not only help the health sciences and the fight against disease,but will change the way we view the history and evolution of life on Earth.
David Smith is an assistant professor in the Biology Department at Western University. You can find him online at www.arrogantgenome.com.