A study lifts the veil on the evolutionary origins of the tundra, a vast Arctic biome shaped by falling temperatures and rising grounds.
Grasslands dotted with dwarf trees, soaked soils bordered by birch trees overgrown with moss, rocks topped with lichens… Contrary to what one might think, mountain peaks are not just Arctic-like spaces, cold islands where hardy plants have taken refuge, but could well be the place of origin of the northern hemisphere’s polar flora. According to the article Evolutionary history of Arctic flora, published in Nature Communications this week, the majority of plants in the Arctic are believed to have descended from ancestors in the high mountains on the edge of the low-lying plains of the western American Arctic.
While our primate ancestors (Hominidae) were evolving 10 million years ago, plants of the genus Pleuropogon were colonising the Arctic Circle. The genus Artemisia, which originated in the Mediterranean, has also been identified as one of the earliest founders of today’s tundra. In Svalbard, for example, the archipelago’s flora is adapted to take root in waterlogged, nutrient-poor soils, dispersing via seeds and rhizome fragments, and also has Alpine and European origins.
The international team conducting the investigation used the genomes of 3,626 species of flowering plants, spanning 10 orders and 16 families of the tree of life, as well as species from the Arctic and other regions. By aligning fragments of common genetic codes and observing their variants, it is possible to trace the evolutionary history of species in time and space, one in relation to another, much like the observation of texts handed down by copyist monks, whose spelling or the appearance of changes according to version would signpost an era or a place.
They discovered that the Arctic tundra was formed by successive waves of colonization and diversification, during which plants gained ground or evolved in situ. The researchers inventoried 131 events, 105 of which correspond to colonization and 26 to diversification.
Vegetation evolution in the Arctic towards today’s tundra coincides with a period of climatic transition. After some twenty million years of stability and a short period of warming, our planet underwent a cooling phase. The Arctic would have gone from a warm, humid to drier, colder climate to that which we know today. At the same time, changes in landforms resulted in a more complex landscape, due to plate tectonics. Alaska, Greenland and Svalbard, once flat, became mountainous.
“The cooling and retreat of forests has created new habitats available for colonization by plants, particularly herbaceous species capable of tolerating or adapting to harsh environmental conditions,” tells us Dr. Wei Wang of the Botanical Institute of the Chinese Academy of Science
Around 7 million years ago, the tundra landscape we know today probably already existed. Until then, the scientific community estimated its appearance at between 3 and 2 million years before our era. The colonization and diversification of Arctic flora accelerated under the effect of falling temperatures, until the Arctic climate geographically isolated certain species and slowed the evolutionary speed of Arctic flora.
In their article, the authors highlight the importance of preserving the American Arctic, with its 36,500 islands and mountain ranges bordering the Arctic Circle. Invaluable assets in the colonization dynamics and diversification of the flora around the Arctic Circle, these areas offer a variety of microclimates that encourage the emergence of new versions of the same plant, which could take advantage and spread beyond the Arctic Circle.
Camille Lin, PolarJournal
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