Despite Lack of Genetic Diversity, Narwhals Thrive – for Now

(CN) – Danish researchers have now added narwhals to the list of more than 250 animal species with sequenced genomes, and their findings tell us an interesting story about the genetics of these unicorns of the sea.

Narwhals, with distinctive horn-like tusks protruding from their foreheads, live year round in Arctic waters and show long-term low genetic diversity despite an abundant population according to research published in the journal iScience on Wednesday. The diversity phenomenon in Narwhals appears to be unique to the species as even their closest relative, the beluga, have higher levels of genomic diversity similar to that of many other Arctic species.

Scientists say a species displaying low genetic diversity would typically be heading toward extinction given that less DNA variation means fewer of the animals would be able to adapt to major changes, such as loss of sea ice due to climate change. Compared to other Arctic marine mammals now showing declines, Narwhal populations still number in the hundreds of thousands – but researchers warn they are not out danger from human activities in the Arctic.

“There’s this notion that in order to survive and be resilient to changes, you need to have high genetic diversity, but then you have this species that for the past million years has had low genetic diversity and it’s still around – and is actually relatively abundant,” said Eline Lorenzen, an associate professor and curator at the Natural History Museum of Denmark, in a statement.

The population estimate of 170,000 narwhals was enough to change their International Union for Conservation of Nature Red List status from “Near Threatened” to “Least Concern” last year.

Pod of narwhals, northern Canada, August 2005. Image courtesy of Kristin Laidre.

“This shows us that just looking at the number of individuals isn’t indicative of the genomic diversity levels of a species, but also looking at the genomic diversity levels isn’t indicative of the number of individuals. Equating those two doesn’t seem to be quite as simple as previously thought,” Lorenzen said.

Inbreeding or bottleneck events that force a species to rebuild their numbers with the limited remaining members after a large population die-off usually cause the dearth of genetic diversity. For Narwhals neither explains their DNA sequencing.

“Narwhals’ long-term low genetic diversity may have allowed them to evolve different mechanisms to cope with their limited genome,” said Lorenzen’s co-author and museum colleague Michael Vincent Westbury in a statement.

Lorenzen and Westbury hypothesize the onset of the last glacial period, roughly 115,000 years ago, created an ideal habitat for a considerably smaller population of narwhals who were able to use it to thrive and proliferate. However, because the species is distinctly confined to an Arctic locale now undergoing dramatic changes from a warming climate, they may not continue to be so lucky.

“Our study can’t comment on whether narwhals will be able to adapt, or if they have the plasticity to be resilient in these rapid changes,” Lorenzen said. “But what we can say is that they have had this low genetic diversity for a really long time and they’re still around.”

While Denmark’s waters aren’t actually home to the tusk-headed whales, they are of historic significance to the Danish people who traded the tusks as unicorn horns during the Viking period. Today narwhals are a highly prized hunting product in Greenland.

“Narwhals are culturally important to Danish national history,” Lorenzen said, noting even the coronation chair of Danish King Frederik the 3rd from 1640 is made of narwhal tusks.

“Their prevalence in Danish culture represents a long-lasting friendship between Greenland and Denmark.”  

This unexpected finding leads the researchers to question whether other species could have similar low diversity numbers. Future research plans include conducting genomic analyses of a variety of Arctic species, both terrestrial and marine, in further their understanding and for comparisons.

“This study shows that, as new data becomes available, we can question these commonly perceived notions that genetic diversity predicts the survivability of a species,” Westbury said. “Ultimately, this analysis is just one step of a lot of work to come.”

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