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article imageNew study shows the last mammoths suffered from 'gene meltdown'

By Karen Graham     Mar 3, 2017 in Science
Woolly mammoths were once the most populous large animals in Siberia, Alaska, and parts of North America. However, a warming climate and human predation led to their extinction on the mainland about 10,000 years ago, with the exception of Wrangel Island.
Wrangel Island is located in the Arctic Ocean between the Chukchi Sea and the East Siberian Sea and covers an area of about 7,600 square kilometers (2,900 square miles). The distance to the closest point on the island is 60 kilometers (37 miles) to the East, so it is rather isolated.
Nearly all of the island is a protected nature sanctuary governed by Russia's Ministry of Natural Resources and Environment, and for very good reason. Wrangel Island may have been the last place on earth where mammoths survived out of reach from humans up until 3,700 years ago.
Rebekah Rogers, an evolutionary geneticist at the University of North Carolina sort of put this amazing survival into context with our history here on Earth - "So the pyramids have been built, they've started to grow tea in China, and civilization had formed, and here are these mammoths no one knew was there, for the longest period of time.
Wrangel Island has the earliest sunrise in the world. (Русский: Остров Врангеля...
Wrangel Island has the earliest sunrise in the world. (Русский: Остров Врангеля, Иультинский район).
Boris Solovyev
"And then people finally found this island around 3,700 years ago, around the time they went extinct," she was quoted as saying by Scientific American. But did humans wipe out the last remaining stronghold of these great herbivores, or was it something else?
The last remaining mammoths begin to die out
In a study published in the journal PLOS Genetics on March 2, Rogers and Montgomery Slatkin at the University of California, Berkeley compared the complete genome of a 45,000-year-old mammoth from the Siberian mainland at Oimyakon with the genome of a Wrangel Island mammoth 4,300 years ago.
Mutations identified in mammoth genomes.
Mutations identified in mammoth genomes.
PLOS Nature
The genetic sequences were made available by Love Dalén at the Swedish Museum of Natural History in Stockholm. “As I looked at the sequence data,” says Rogers, “it became very clear that the Wrangel mammoth had an excess of what looked like bad mutations.”
Many of the mutations in the DNA are only visible to a geneticist. Sequencing showed the DNA was riddled with deletions along with an abundance of sequences called "stop codons." These tell a cell when to stop transcribing a particular section of DNA, among other changes. Imagine a stop light that stays on red without ever changing. This is sort of what happened to the Wrangel Island mammoth's DNA.
Mutations occurred when a codon that was supposed to specify an amino acid changed to a stop codon instead. This resulted in a protein that was shorter than normal because it was unable to finish adding all the necessary amino acids. But Rogers says that some of the genetic changes were probably visible in the behavior and appearance of the mammoth.
The function of the genes relating to urinary proteins and the mammoth's sense of smell were shut down. These two genes are important in today's elephants because they function in eliciting mating behaviors or the signalling of social status. Rogers and Slatkin say the mammoth's appearance was probably even more obvious.
Ice mummy of the six-to-eight-month old wooly mammoth baby named Dima in situ near Kirgiljach River ...
Ice mummy of the six-to-eight-month old wooly mammoth baby named Dima in situ near Kirgiljach River in northeast Siberia. Dated to 37,000 B.C.
A.V. Lozhkin - US National Oceanic & Atmospheric Administration (NOAA)
The researchers suggest that a mutation in a part of the genome called FOXQ1 would have given the mammoths a "satin" coat, with fur that is the same color but translucent and shiny. With only about 300 mammoths estimated to have been on Wrangler Island 4,000 years ago, the scientists conclude it wasn't a matter of inbreeding that led to their demise.
Why finding the answer to the demise of the mammoths is so important
What did happen was that the population was simply small,” Rogers says, and “under these circumstances, any mammoth was better than no mammoth at all, so natural selection did not operate in the usual way." But this allowed unhelpful mutations to proliferate, following a phenomenon called "nearly neutral genome evolution."
In other words, “Bad mutations that would normally be weeded out weren’t removed from the population because of reduced competition,” says Rogers. Paleontologist Ross MacPhee of the American Museum of Natural History in New York City says the research highlights just how far the study of ancient genomes has come.
MacPhee adds, “Isolation and reducing population size have long been recognized as important factors causing endangerment." But interestingly, the genetic mutations in the Wrangler Island Mammoths took place after the species had been wiped out on the mainland. So this knowledge opens the door to further study using additional mammoth DNA from other times and parts of the mammoths’ enormous range.
African elephants (Loxodonta africana) are the largest land animals on Earth and are considered a vu...
African elephants (Loxodonta africana) are the largest land animals on Earth and are considered a vulnerable species due to habitat loss and illegal hunting for their ivory tusks
Anna Zieminski, AFP/File
And here's something to think about - MacPhee adds, the study “is maybe telling us something very important about what happens in populations already under severe threat because of diminished range and numbers."
This study suggests that maybe human hunting, climate change or any other external factor wasn't the only thing responsible for wiping out those last remaining mammoths. But what was the final element that drove the species to extinction? The answer is something we need to find out because it could have implications for endangered species today.
More about Woolly mammoth, wrangel island, isolated population, gene mutations, Natural selection
 
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