A "mutational meltdown" among woolly mammoths meant the last of the species were likely left with a weird, translucent satin coat, scientists have discovered. By analysing a 4,300-year-old fossil and comparing it to a 45,000-year-old sample found on the mainland, the team was able to see how the species had changed in the millennia before it went extinct.
Woolly mammoths thrived during the last ice age, being found across the globe. However, as the ice retreated, so too did they. After being pushed further and further north, they were eventually isolated on Wrangel Island, with around 300 remaining.
Rebekah L Rogers and Montgomery Slatkin, from the University of California, Berkeley, have now looked at previously completed genome sequences of two mammoths that lived tens of thousands of years apart. Specifically, they looked at the mutations that had taken place and what impact that would have had on the dwindling population.
Findings showed the Wrangel Island population had changed significantly – for the worse: "We observe an excess of detrimental mutations, consistent with genomic meltdown in woolly mammoths on Wrangel Island just prior to extinction," they wrote in the journal PLOS One.
They found an excess of premature stop codons – or nonsense mutations – that can lead to genetic disease. Examples of nonsense mutations in humans include cystic fibrosis and Duchenne
Another finding was that the Wrangel mammoth had loss-of-function mutations in a large number of olfactory receptors (related to smell) – a finding the scientists believe might be because of the mammoth living on an island rather than the mainland. "Wrangel Island had different flora compared to the mainland, with peat and sedges rather than grasslands that characterised the mainland," they wrote.
"The island also lacked large predators present on the mainland. It is possible that island habitats created new selective pressures that resulted in selection against some olfactory receptors."
Finally the team found loss-of-function mutations at the locus of FOXQ1. This, they said, could have resulted in the mammoth having a translucent, satin coat. When FOXQ1 is knocked out in mice, they develop a satin coat with translucent fur but normal pigmentation.
"If the phenotype in elephantids matches the phenotype exhibited in mice, this mammoth would have translucent hairs and a shiny satin coat, caused by two independently formed knock-out alleles at the same locus," the scientists said, adding that while gene functions are conserved across mammals, there is "no guarantee" there would be the same across species.
Love Dalen, Professor of Evolutionary Genetics at the Swedish Museum of Natural History, sequenced the genomes of the two mammoths. Commenting on the latest study, he told IBTimes UK: "I think it seems pretty convincing that this particular mammoth had a dysfunctional variant in a gene that probably had an effect on its fur colour. That these genetic changes would have had any effect on the health of this individual is very speculative, but it's certainly possible.
"But the overall results of the study suggests that this mammoth likely was not doing so well, and that it probably had some problems caused by the large excess of deleterious genetic variants it had."