The vast majority of woolly mammoths went extinct at the end of the last ice age, but small, isolated populations managed to hold out for a little while longer. New research uncovers the extent to which at least one of these final mammoths suffered due to its many mutations.
Diabetes, developmental disorders, male infertility, and even the inability to smell flowers are at least some of the health problems experienced by one of the last mammoths to grace this good Earth, according to research published today in Genome Biology and Evolution. The new paper, co-authored by evolutionary biologist Vincent Lynch from the University at Buffalo, highlights the dramatic extent to which inbreeding likely affected the final populations of woolly mammoths, who were trapped on small islands in the northern Atlantic.
Woolly mammoths roamed the Pleistocene landscape for hundreds of thousands of years, inhabiting a territory that practically encircled the planet. As successful and well-adapted as they were to cold climates, however, their long reign eventually came to an end—an extinction process that transpired across two phases.
Between 15,000 and 10,000 years ago, as the Pleistocene transitioned to the Holocene, all continental populations of woolly mammoths disappeared. The end of the ice age and associated loss of habitat played a critical role in their demise, but other factors, such as human predation, may have contributed as well.
But a pair of relict populations managed to survive, at least for a little while.
Woolly mammoths on St. Paul Island lasted until around 5,600 years ago, while mammoths on Wrangel Island finally expired around 4,000 years ago. Rising seas left the mammals stranded on these islands, which proved to be as much a blessing as a curse. The tiny, isolated populations suffered from a lack of genetic diversity, leading to a host of problems associated with inbreeding.
That these proboscideans suffered from deleterious mutations is not a huge surprise. In 2017, a study co-authored by Rebekah Rogers from the University of North Carolina identified a host of genetic glitches in woolly mammoths from Wrangel Island, including an inordinate amount of deleted and non-functional genes, disrupted gene sequences, retrogenes, and an unhealthy abundance of premature termination codons, which normally identify the end of genetic translations, among other problems.
The new research is unique in that it demonstrates the functional consequences of specific genetic mutations, which scientists call alleles.
“What we did that was different [from previous studies] was try to determine if mutations in the Wrangel Island mammoth genome changed the way genes functioned, which we did by resurrecting some of those genes,” explained Lynch to Gizmodo.
“We could then test the functions of those genes in the lab—and it turns out all the mutations we tested changed how Wrangel Island mammoth genes functioned, and in ways that are expected to be pretty bad,” said Lynch, whose team included scientists from the University of Chicago, Northwestern University, University of Virginia, University of Vienna, and Penn State.
As Lynch noted, he and his colleagues reconstructed the genome of a single Wrangel Island woolly mammoth. The DNA from two continental mammoths, both of whom lived when mammoths were abundant, and three Asian elephants were used as comparative references. After detecting a batch of genetic mutations unique to Wrangel mammoths, the scientists tested synthesized versions of these alleles in mice to assess normal gene function—a test these genes subsequently failed.
Rogers, author of the 2017 study on Wrangel Island mammoths, said she “loved” the new paper. “With mammoths, all the living animals are long gone. We cannot directly observe the impacts mutations have on animals. We can computationally identify mutations, and come up with ideas of how the animals might have been affected. This paper takes those ideas and tests them in mice. If we put a mutation from mammoths into mice, how bad is it? How does it affect the actual animal?”
The scientists identified several “deleterious mutations that are predicted to cause diverse behavioral and developmental defects,” wrote the authors in the study. These included disruptions to genes associated with neurological developmental defects (including a dangerous condition known as hydrolethalus syndrome), diabetes, reduced male fertility, and strangely, an inability to “detect floral scents,” according to the paper. In other words, this Wrangell mammoth had lost the ability to smell the flowers.
Interestingly, similar loss of olfactory function has been documented in dolphins and whales, but their ability to smell slowly withered away due to their transition to aquatic environments (whales and dolphins are descended from four-legged terrestrial mammals).
In terms of how this impaired smelling ability might have affected the mutated mammoth, Lynch said it “could smell things, just not floral scents,” adding that it’s “also remarkable given just how important smell is to elephants—they have thousands of genes for detecting various odors, which is way more than other mammals.”
Lynch said the new research has plenty of overlap with previous studies and that recent papers on the subject are “really complimentary.” Together, these efforts are painting a progressively clearer picture of what happened on Wrangel Island.
“We found that mutations changed the function of mammoth genes in ways that likely caused disease,” said Lynch. “Previous genetic studies have suggested that—but not demonstrated it—and found that the population of mammoths on Wrangel Island was small and getting smaller all the time, which led to lots of inbreeding among distant relatives. That kind of thing usually leads to an accumulation of genetic defects and disease, which certainly didn’t help the population escape extinction and probably contributed to extinction.”
Lynch is obviously conscious of the fact that his team’s research describes the genetic constitution of a lone Wrangel woolly mammoth, but the study suggests “at least one Wrangel Island mammoth may have suffered adverse consequences from reduced population size and isolation,” as they wrote in the paper. Analyses of other Wrangel mammoth DNA would be helpful, as it would show if these problems were widespread. Analysis of DNA from the St. Paul Island mammoths would show if they endured similar genetic meltdowns.
“I’d love to get both!” said Lynch. “There are some people attempting it; the fossils are not uncommon, but getting preserved DNA is the tricky bit,” he told Gizmodo.
Given what we already know about the DNA of these final holdouts, however, these findings are likely indicative of problems faced by many of the last mammoths. As research from last year found, the habitat at Wrangel Island was perfectly livable when these mammoths finally disappeared, but their weakened genetic condition made them vulnerable to other threats.
The final mammoths on Wrangel Island outlasted their continental cousins by roughly 6,000 years. Sadly, however, this isolation appears to have taken a terrible toll on the creatures caught at the very end of their species.