Role of ancient mammoths and horses as “ecological engineers” described

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Part of an illustration entitled <em>Pleistocene mirrored</em>, by Julius Csotonyi. 
Part of an illustration entitled Pleistocene mirrored, by Julius Csotonyi.

The important role once played by ancient mammoths, horses and bison in shaping the grassland environment in the northern reaches of North America is described in a recently published study.

Scientists, writing in the journal Nature Communications, have presented a 30,000-year DNA record of past environments, drawn from cored permafrost sediments extracted from the Klondike region of central Yukon.

Mere spoonsful of soil pulled from Canada’s permafrost have been analyzed, opening vast windows into ancient life in the Yukon, revealing rich new information and rewriting previous beliefs about the extinction dynamics, dates and survival of megafauna such as mammoths, horses and other long-lost life forms.

Researchers from McMaster University, the University of Alberta, the American Museum of Natural History and the Yukon government reconstructed the ancient ecosystems using tiny soil samples which contain billions of microscopic genomic sequences from animal and plant species.

They used DNA capture-enrichment technology developed at McMaster to isolate and rebuild, in remarkable detail, the fluctuating animal and plant communities at different time points during the Pleistocene-Holocene transition, an unstable climatic period 11,000-14,000 years ago when several large species such as mammoths, mastodons and sabre-toothed cats disappeared.

The analysis reveals that mammoths and horses were already in steep decline before the climatic instability, but they did not immediately disappear because of human overhunting as previously thought.

In fact, the DNA evidence shows that both the woolly mammoth and North American horse persisted until as recently as 5000 years ago, bringing them into the mid-Holocene, the interval beginning roughly 11,000 years ago that we live in today.

Evolutionary geneticist Hendrik Poinar was a lead author on the paper. He is the director of the McMaster Ancient DNA Centre. Photo: Georgia Kirkos
Evolutionary geneticist Hendrik Poinar was a lead author on the paper. He is the director of the McMaster Ancient DNA Centre. Photo: Georgia Kirkos

Through the early Holocene, the Yukon environment continued to experience massive change. Formerly rich grasslands — the “Mammoth Steppe” — were overrun with shrubs and mosses, species no longer held in check by large grazing herds of mammoths, horses and bison.

Today, grasslands do not prosper in northern North America, in part because there are no megafaunal “ecological engineers” to manage them.

“The rich data provides a unique window into the population dynamics of megafuana and nuances the discussion around their extinction through more subtle reconstructions of past ecosystems,” says evolutionary geneticist Hendrik Poinar, a lead author on the paper and director of the McMaster Ancient DNA Centre.

The work builds on previous research by McMaster scientists, who had determined woolly mammoths and the North American horse were likely present in the Yukon about 9700 years ago. Better techniques and further investigation have since refined the earlier analysis and pushed forward the date even closer to contemporary time.

“Now that we have these technologies, we realize how much life-history information is stored in permafrost,” explains Tyler Murchie, a postdoctoral researcher in McMaster’s Department of Anthropology and a lead author of the study.

Tyler Murchie: "Now that we have these technologies, we realize how much life-history information is stored in permafrost." Photo: Georgia Kirkos
Tyler Murchie: “Now that we have these technologies, we realize how much life-history information is stored in permafrost.” Photo: Georgia Kirkos

“The amount of genetic data in permafrost is quite enormous and really allows for a scale of ecosystem and evolutionary reconstruction that is unparalleled with other methods to date,” he says.

“Although mammoths are gone forever, horses are not,” says Ross MacPhee, of the American Museum of Natural History, another co-author.

“The horse that lived in the Yukon 5000 years ago is directly related to the horse species we have today, Equus caballus. Biologically, this makes the horse a native North American mammal, and it should be treated as such.”

The scientists stress the need to gather and archive more permafrost samples, which are at risk of being lost forever as the Arctic warms.

Tyler J. Murchie, Alistair J. Monteath, Matthew E. Mahony, George S. Long, Scott Cocker, Tara Sadoway, Emil Karpinski, Grant Zazula, Ross D. E. MacPhee, Duane Froese, Hendrik N. Poinar. Collapse of the mammoth-steppe in central Yukon as revealed by ancient environmental DNA. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-27439-6

Extraction of a core sample in the Yukon for analysis. Photo: Tyler Murchie
Extraction of a core sample in the Yukon for analysis. Photo: Tyler Murchie

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