The woolly mammoths on Wrangel Island, descended from a very small initial population, maintained themselves for 6,000 years despite genetic obstacles. Their sudden disappearance remains a mystery, providing lessons for contemporary conservation efforts. Credit: Beth Zaiken
Genetic analysis of the last woolly mammoths on Wrangel Island has revealed a population that managed to survive for 6,000 years despite rough sex and low genetic diversity.
Originally coming from no more than eight individuals, this group expanded to 200-300 members. While genetic issues did not directly cause their extinction, it remains unclear what ultimately led to their demise. The study provides insights into how such populations can inform current conservation strategies for the endangered species today.
Ten thousand years ago, the final population of woolly mammoths was isolated on Wrangel Island, located off the coast of Siberia, due to the rising sea level that separated the mountainous island from the mainland. New genomic research shows that this isolated population, which lived on the island for the next 6,000 years, began with no more than eight individuals and expanded to between 200 and 300 within 20 generations. Published in the magazine Cell On June 27, the study shows that Wrangel Island mammoths showed signs of inbreeding and low genetic diversity, but these factors alone do not account for their mysterious and final extinction.
Continental Siberian Tusk. Credit: Love Dalen
Reassessing extinction theories
“We can now confidently reject the idea that the population was simply too small and that they were doomed to extinction for genetic reasons,” says senior author Love Dalén, an evolutionary geneticist at the Center for Paleogenetics, a joint collaboration between the Museum Swedish. of Natural History and Stockholm University. “That means it was probably just a random event that killed them off, and if that random event hadn’t happened, then we’d still have mammoths today.”
I love Dale. Credit: Ian Watts
Insights into current conservation efforts
In addition to shedding light on woolly mammoth population dynamics, this analysis of Wrangel Island mammoths can help inform conservation strategies for today’s endangered animals.
“Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens genetically when a species goes through a population bottleneck, because they mirror the fate of many populations today,” says first author Marianne Dehasque. Center for Paleogenetics.
Marianne Dehasque works in the Ancient DNA Laboratory. Credit: Love Dalen
Genetic challenges and sustainable inheritance
To understand the genomic consequences of the Wrangel Island Strait on the mammoth population, the team analyzed the genomes of 21 woolly mammoths—14 from Wrangel Island and 7 from the mainland population that preceded the Strait. In total, the samples covered the last 50,000 years of the woolly mammoth’s existence, providing a window into how the mammoth’s genetic diversity changed over time.
Compared to their mainland ancestors, the genomes of Wrangel Island mammoths showed signs of inbreeding and low genetic diversity. In addition to overall low genetic diversity, they showed reduced diversity in the major histocompatibility complex, a group of genes known to play a critical role in the vertebrate immune response.
Tusk of Wrangel Island. Credit: Love Dalen
Long-Term Genetic Effects and Future Research
The researchers showed that the genetic diversity of the population continued to decline during the 6,000 years that the mammoths inhabited Wrangel Island, albeit at a very slow rate, suggesting that the population size was stable until the end. And although the island’s mammoth population gradually accumulated moderately harmful mutations during its 6,000-year stay, the researchers showed that the population was slowly clearing out the most harmful mutations.
“If an individual has an extremely deleterious mutation, it’s essentially not viable, so those mutations gradually disappeared from the population over time, but on the other hand, we see that mammoths were accumulating mildly deleterious mutations almost until they disappeared.” says Dehasque. “It is important that today’s conservation programs keep in mind that it is not enough for the population to grow back to a good size; you also have to monitor it actively and genetically because these genomic effects can last for more than 6000 years.
The last mystery of the disappearance of woolly mammoths
Although the mammoth genomes analyzed in this study span a large span of time, they do not include the last 300 years of the species’ existence. However, researchers have discovered fossils from the late mammoth period and plan to perform genomic sequencing in the future.
“What happened at the end is still a mystery – we don’t know why they disappeared after being more or less fine for 6,000 years, but we think it was something unexpected,” says Dalén. “I would say there is still hope of understanding why they disappeared, but no promises.”
Reference: “Temporal dynamics of pre-extinction woolly mammoth genome erosion” 27 Jun 2024, Cell.
DOI: 10.1016/j.cell.2024.05.033