By Kendrick Marr and Richard Hebda
For many years, the idea that an enormous ice sheet covered all of B.C. during the last ice age, ending 15,000 years ago, has been widely accepted, but recent advances in DNA sequencing of animals and plants are challenging this idea.
Some species may have persisted in previously unsuspected locations in northern B.C. The technique uses the same approach that traces the migration of humans.
According to the prevailing viewpoint, after the ice sheet melted, plants recolonized B..C as suitable habitats became available. Warmth requiring species must have migrated from south of B.C. But where did the cold-adapted, high mountain species come from? Some survived in ice-free portions of Yukon and Alaska and some survived south of the ice sheet, but were there areas that were not covered by ice within the borders of B.C.?
If ice-free areas did exist within B.C. during the last ice age, then hardy tundra species may have been present. In 2001 we began collecting tissue of 10 tundra species from throughout B.C. To place B.C. in its proper context we obtained samples from other parts of the northern hemisphere assisted by botanists in the U.S., Yukon, Asia and Europe.
In 2010, a Walton Innovation Fund grant gave us the opportunity to collect samples from southern Siberia. In 2011 and 2012 we made collections from eastern Russia and Alaska, supported by the October Hill Foundation. These locations occur along the likely migration route of tundra species, connecting the mountains of Central Asia and western North America, via the Arctic.
In this type of study, small sections of DNA are sequenced from many individuals of the same species to reveal the order of the four chemical bases, commonly abbreviated as A, T, G and C. When a cell divides, its DNA is copied and the daughter cells receive the full complement of DNA.
Occasionally errors (mutations) occur, e.g. an A might be replaced by a T, C or G.
Descendants of an individual in whom a mutation occurs bear that same mutation. Individuals that bear the same DNA sequence belong to the same genetic type or lineage. Over time, as plants migrate, different lineages often occur in different regions. We work together with a colleague at the University of Victoria.
The first species we analyzed, mountain sorrel revealed some populations survived the last ice age in Alaska, some in the western U.S. and, contrary to expectations, some appear to have survived within the borders of northern B.C.
Survival in B.C. was demonstrated by two genetic types that occur only in B.C., and were not found north or south of our province. Some populations in B.C. include individuals that are the descendants of plants that migrated from the north and from the south.
Not surprisingly, populations from eastern Russia and from Alaska have similar genetic types as would be expected, because a broad expanse of land connected eastern Asia to western North America when sea levels were low. Populations from eastern Russia differ from those in southern Siberia, suggesting a barrier to migration.
Surprisingly, few genetic types occur in the Arctic, an indication that the species spread there relatively recently.
The migration patterns revealed by this study could not have been predicted without genetic analysis. They raise important questions about the origin of B.C.’s plant and animal species and bring into question the concept of a province-smothering ice sheet at the end of the ice age.
Our goal is to analyze additional species to illuminate more widely the origin of the flora of the northern hemisphere.
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Dr. Kendrick Marr is curator of botany and Dr. Richard Hebda is curator of botany and earth history at the Royal B.C. Museum.