The reason for the extinction of mammoths could be a "mutational explosion" - a sharp increase in the number of negative mutations in their DNA, provoked by a decrease in the number of these animals, scientists say in an article published in the journal PLOS Genetics.
“We were very surprised to find a huge number of deleterious mutations in mammoth genomes recently published by colleagues, and found a similar number of negative changes in the DNA of other mammoths from Wrangel Island. This rapid degeneration is broadly in line with what the theory predicts with a sharp decline in genetic diversity in the population,”said Rebekah Rogers of the University of California at Berkeley (USA).
Secrets of the megafauna
To date, there is no general opinion about the reasons for the extinction of the ice age megafauna. Some scientists believe that mammoths and woolly rhinoceroses have become extinct solely due to climate change, while other paleontologists hypothesize an equal "contribution" of man and climate to the extinction of giant animals in Asia and America.
Relatively recently, paleontologists have found in Siberia the "milk tusks" of several mammoths, the footprints on which unambiguously showed that hunters were involved in the extinction of these giants, who lived in Taimyr and Eastern Siberia. Also, geneticists found traces of degeneration in the DNA of the last mammoths of the Earth from Wrangel Island, and other scientists - hints that these animals could become extinct from thirst.
Rogers and her colleague Montgomery Slatkin became interested in the traces of degeneration in DNA, they decided to trace how quickly mutations in mammoth genes accumulated in the last few thousand years of their existence on Earth.
In this they were helped by new mammoth genomes published by colleagues. Some of the animals they studied lived during the heyday of mammoths in Yakutia, in the vicinity of Oymyakon, about 45 thousand years ago, and others - on Chukotka and on Wrangel Island in the last days of their existence on Earth, 4.3 thousand years ago.
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The secret threat of degeneration
Comparing the mammoth genomes with each other, as well as with the DNA of Indian elephants, scientists have counted all harmful mutations in them - sudden "breaks" of genes, genes with large distant sections of the genetic code and various minor damages. As it turned out, the genome of mammoths from Wrangel Island contained a disproportionate number of such mutations, which accumulated more than should have arisen in the course of the usual course of evolution.
The last mammoths of the Earth have thus lost many olfactory receptors, as well as genes associated with the synthesis of vitamins and other vital molecules. In addition, the hair of the animals became transparent due to the loss of the FOXQ1 gene. In addition, the mammoths had nearly 3,000 disrupted genes associated with reading DNA inside cells and producing protein molecules.
The features in the distribution of these mutations, according to Rogers and Slatkin, indicate that they appeared almost simultaneously in the genome of the last generations of Earth's mammoths. We can say that they have experienced a kind of "mutational explosion". This explosion, according to scientists, accelerated the degeneration of mammoths and led to their death at a time when the climate of Wrangel Island began to change. Interestingly, biologists have recorded traces of a similar accelerated degeneration in the genome of Indian elephants, whose numbers have declined in recent years.
This discovery will help uncover possible reasons for the extinction of mammoths, and also indicates that the survival of small groups of animals on islands and other isolated ecosystems is not enough to restore the population. A sharp reduction in their genetic diversity and the associated "mutational explosion" will not allow animals to recover after the appearance of suitable conditions for their life in other parts of the world, scientists conclude.
