The genetic diversity of narwhals is strikingly low compared to other Arctic creatures and many less successful species, scientists have revealed.
Researchers who sequenced their genome are surprised the trait appears to be having for no impact on their survival, as they continue to thrive.
It’s contrary to what is usually the case in biology, where low genetic variation often causes a species to struggle in numbers.
The narwhal’s case shows persistently low diversity and throws into question the popular notion that a narrow gene pool is associated with negative consequences.
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The genetic diversity of narwhals (pictured) are strikingly low compared to other Arctic creatures and many less successful species
Scientists have ruled out inbreeding as a cause of the Narwhal’s low genetic diversity, or a sudden event that could have reduced their genetic population to a small representation.
Whatever the cause, the trait has likely persisted for tens or hundreds of thousands of years.
While researchers still don’t have the answers, they have suggested it could have something to do with the onset of the last Ice Age, roughly 115,000 years ago.
The event may have created an habitat so ideal for the significantly smaller population narwhals that it allowed them to rapidly multiply as well as protect them.
‘Narwhals’ long-term low genetic diversity may have allowed them to evolve different mechanisms to cope with their limited genome,’ said Dr Michael Vincent Westbury, a postdoctoral researcher at the Natural History Museum of Denmark.
Scientists who have sequenced their genome says the trait is surprisingly not impacting on their survival, as they continue to thrive
A lack of genetic diversity in any species is linked to low survivability as it makes species more vulnerable to disease and environmental pressures.
Geneticists studying Narwhal mitochondrial DNA and micro-satellites observed the trait across a number of narwhal populations which are mostly in the Arctic where they are one of three whale species.
They are now considered globally ‘abundant’, recently estimated at roughly 170,000 in numbers and removing them from the International Union for Conservation of Nature (IUCN) Red List status for ‘Near Threatened’ to ‘Least Concern’ in 2018.
This is surprising compared to other Arctic dwelling marine mammal which has significantly greater genetic diversity but only numbers around 1,800 in total.
The trait is contrary to what is usually the case in biology – that low genetic variation often cause a species to struggle in numbers. Map of the narwhal distribution range based on International Union for Conservation of Nature distribution data comparing genome-wide diversity of 16 Mammalian Species
Narwhals are one of three whale species found only in the Arctic and are well-known for their horn-like tusk protruding from their forehead.
They are mainly found in the Arctic and current estimates have put their numbers at roughly 170,000.
Even the panda has greater genetic diversity in comparison, yet their numbers are merely one hundredth of that of the Narwhals.
Dr Eline Lorenzen, an associate professor and curator at the Natural History Museum of Denmark and an author on the study said: ‘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.
‘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.
The narwhal’s case has thrown into question the notion that narrow gene pool is always associated with negative evolutionary consequences
‘Equating those two doesn’t seem to be quite as simple as previously thought.’
‘However, the species is still considered vulnerable to changing climates due to its high specialisation and restricted Arctic distribution.’
‘We assembled and annotated a genome from a narwhal from West Greenland.’
‘We find relatively low diversity at the genomic scale and show that this did not arise by recent inbreeding, but rather has been stable over an extended evolutionary timescale.’
We also find that the current large global abundance most likely reflects a recent rapid expansion from a much smaller founding population.
Moving forward, the authors are interested in exploring whether this unexpected finding in narwhals is present in other species as well.
