Secrets of Survival and Mysterious Extinction on Wrangel Island

Genetic analysis of the last woolly mammoths on Wrangel Island has revealed a population that managed to survive for 6,000 years despite heavy inbreeding and low genetic diversity.

Initially, the group consisted of just eight individuals, but has since 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 offers insights into how such groups can inform current conservation strategies for endangered species. Class today.

Ten thousand years ago, the last woolly mammoth population on Wrangel Island, off the coast of Siberia, was isolated by rising sea levels that separated the mountainous island from the mainland. New genomic research suggests that this isolated population, which lived on the island for the next 6,000 years, began with just eight individuals and expanded to between 200 and 300 individuals within 20 generations. Published in the journal cell On June 27, the study showed that the Wrangel Island mammoths showed signs of inbreeding and low genetic diversity, but these factors alone do not explain their eventual mysterious extinction.

Siberian porcupine tusk. Copyright: Love Dalen

Re-evaluating extinction theories

“We can now reject the idea that the population was very small and that they were doomed to extinction for genetic reasons,” says Love Dalén, the study’s lead author and an evolutionary geneticist at the Centre for Palaeogenetics, a joint project of the Swedish Museum of Natural History and Stockholm University. “This means that it was probably just a random event that killed them off. If this random event had not happened, we would still have mammoths today.”

I love Dalin. Copyright: Ian Watts

Insights into current conservation efforts

In addition to shedding light on woolly mammoth population dynamics, this analysis of the Wrangel Island mammoth may help inform conservation strategies for today’s endangered animals.

“Mammoths are an excellent model for understanding the ongoing biodiversity crisis and what happens from a genetic standpoint when a species goes through a population bottleneck because they mirror the fate of many populations today,” says first author Marianne Dehascq, of the Center for Paleogenomics.

Marianne Dehasek works in the ancient DNA lab. Photo credit: Love Dalen

Genetic Challenges and Lasting Legacy

To understand the genomic consequences of the Wrangel Island bottleneck on mammoth populations, the team analyzed the genomes of 21 woolly mammoths—14 from Wrangel Island and 7 from pre-bottleneck populations. In total, the samples spanned the past 50,000 years of woolly mammoth existence, providing a window into how mammoth genetic diversity has changed over time.

Compared to their mainland ancestors, the Wrangel Island mammoth genomes showed signs of inbreeding and reduced genetic diversity. In addition to lower overall genetic diversity, they showed reduced diversity in the major histocompatibility complex, a set of genes known to play a critical role in vertebrate immune responses.

Wrangel Island Fang. Copyright: Love Dalen

Long-term genetic effects and future research

The researchers showed that the population’s genetic diversity continued to decline throughout 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. Although the island’s mammoth population gradually accumulated somewhat harmful mutations throughout its 6,000-year existence, the researchers showed that the population was slowly shedding the most harmful mutations.

“If an individual has a very deleterious mutation, it’s basically not sustainable, so these mutations gradually disappear from the population over time, but on the other hand, we see that mammoths were accumulating fairly deleterious mutations until they were almost extinct,” says Dehasc. “It’s important for current conservation programs to keep in mind that it’s not enough to bring the population back to a decent size; you also have to actively monitor it genetically because these genomic effects can persist for more than 6,000 years.”

The final mystery behind the extinction of the woolly mammoth

Although the mammoth genomes analyzed in this study span a long time span, they do not include the last 300 years of the species’ existence. However, the researchers have discovered fossils from the last period of the mammoth’s life and plan to sequence the genome in the future.

“What happened in the end is still a bit of a mystery — we don’t know why they went extinct after being pretty good for 6,000 years, but we think it happened suddenly,” Dalen says. “I would say there’s hope of finding out why they went extinct, but there are no promises.”

Reference: “Temporal Dynamics of Woolly Mammoth Genome Erosion Prior to Extinction” June 27, 2024, cell.
DOI: 10.1016/j.cell.2024.05.033