The brisk increase in warming rates in the Arctic is bringing rapid shifts in range for plants and animals across the region’s tree of life. Researchers say those changes can lead species that normally wouldn’t encounter each other to interbreed, creating new hybrid populations.
Now, scientists have presented the first evidence of large-scale hybridization that appears to have been driven by climate change. In a paper published this month in the journal Science Advances, researchers report that a hybrid Atlantic puffin population on the remote Norwegian island of Bjornoya seems to have emerged in a period coinciding with the onset of a faster pace of global warming.
The hybrid puffins likely arose from the breeding between two subspecies within the past 100 or so years, coinciding with the onset of the 20th-century warming pattern, the study concludes. Strikingly, the hybridization occurred after a subspecies migrated southward, not poleward toward cooler temperatures, as might have been expected, a finding that highlights the complexity of the changes underway in the Arctic ecosystem.
Additional analysis also shows a significant loss of genetic diversity in the populations studied, an alarming development for the prospective health of Arctic puffins, the researchers write.
“Both the timing of the hybridization as well as the genomic erosion really provide this compelling evidence that the last few years have been tremendously impactful on the Arctic communities,” said Oliver Kersten, the paper’s lead author and a postdoctoral researcher in genomics and marine ecology at the University of Oslo. The findings also underline the importance of analyzing both modern and historical DNA data, he added.
Atlantic puffins, affectionately dubbed the “clowns of the sea,” are distinctive seabirds known for black and white feathers and a vibrant multicolored bill. They live and breed across the North Atlantic and Arctic oceans. Globally, the bird is considered “vulnerable” to extinction, but in Europe, it has been listed as fully endangered since 2015.
The state of puffin populations worldwide is complex. Some of the bird colonies do relatively well; others are plummeting because virtually no chicks, or pufflings, survive to adulthood. Rost, one of three Norwegian islands whose populations were examined for the study, used to be the world’s largest breeding colony, boasting 2.8 million adult puffins. It has lost 80 percent of its breeding pairs over the past four decades, the scientists report.
“Twenty years ago, when you were on Rost and you looked at the sky, everything was covered in puffins,” Kersten said. “It must have been this really, really extremely fascinating site.”
Today, the local puffin population is estimated at just 208,500. “You can clearly see a difference,” the researcher said.
Within the Atlantic puffin species are three officially defined subspecies that look largely the same yet vary somewhat in size as well as genetic makeup. The genetic differences are believed to have emerged after the species were separated as a result of environmental factors—probably glacial cycles in past millennia.
Kersten was also the lead author of a 2021 paper that was the first to examine a comprehensive set of puffin genomes. When analyzing the data from different populations, researchers noticed the hybrid population on Bjornoya.
The study published this month focused on three puffin nesting colonies. The subspecies that is largest in physical size nests on the island of Spitsbergen, and the intermediate-size subspecies in Rost. Bjornoya, with its hybrid population, lies between Rost and Spitsbergen. Examining the DNA sequences of the puffins in the hybrid population, researchers knew which parts came from which of the other two subspecies.
The length of the DNA sequences in the hybrid genomes was relatively long, indicating that hybridization occurred relatively recently. (With each generation born after an initial interbreeding, the sequences grow shorter.) As a result, the researchers estimated that hybridization occurred between 82 and 295 years ago.
In considering the evolutionary history of a species, arriving at such a specific date range is considered remarkable. But the researchers wanted to further narrow the window for when the initial hybridization occurred, so they turned to museum specimens for more DNA information.