Gray wolves survived Ice Age extinction event by changing their diets – which may help them cope with ongoing climate change

Zoe Landry @zoey_landry

Master’s student in Biology at Carleton University, soon to be PhD student at the University of Ottawa and member of the SAiVE Lab

Climate change is arguably one of the biggest issues that the Earth is currently facing. Ecosystems all over the world are being affected in different ways, with northern ecosystems being some of the most severely impacted. The Canadian Arctic is currently warming at nearly double the rate of the global average, which is drastically altering the Arctic environment. The effects of climate change will be felt long past our lifetimes, but how exactly climate change will impact northern species, some of which are not found anywhere else in the world, is unknown.

            An unparalleled tool for investigating the long-term responses of species to climate change is, fortunately, available in the form of the fossil record. In the Yukon Territory of Canada, there is a diverse array of fossils from the last Ice Age that provide an excellent opportunity to study the effects of climate change on ancient animals. The end of the Ice Age is characterized by a global shift in climate, with warming temperatures and melting glaciers, culminating in an extinction event where about 70% of large mammal genera died out in North America – similar to what we are seeing in the Canadian Arctic today. One of the most abundant fossil animals found in the Yukon is the gray wolf (Canis lupus), which to this day still calls the Yukon home. Ancient wolves managed to survive the extinction event at the end of the Ice Age, but how did they do so, when so many other species did not? Could wolves have changed aspects of their ecology, such as their diets, over time to cope with environmental changes?

Zoe Landry, lead author of the study, holds a 40,000-year-old gray wolf skull from the Yukon. Credit: Danielle Fraser, © Canadian Museum of Nature.

My colleagues and I set out to investigate these questions, using a combination of two different methods: dental microwear and stable isotope analyses in a recent paper. We studied both Ice Age and recent (circa 1960s) gray wolf specimens from the Canadian Museum of Nature, in Ottawa, Ontario, and the Beringia Interpretive Center (Yukon Government), in Whitehorse, Yukon. By comparing the dietary ecology of modern and ancient wolves, we can better understand how wolves responded to past climatic disturbances, and how they may respond at present and in the future.

Zoe Landry and Danielle Fraser prepare for sampling.

Dental microwear analysis

            Dental microwear analysis involves observing microscopic wear patterns on the surface of animal teeth. Through observations of these patterns, we can make inferences about the types of food an animal ate during the last few days to weeks prior to its life. There are two main types of dental wear: pits and scratches. Pits are small, circular features that are caused by an animal consuming hard food – in the case of carnivores, pits indicate that the animal was eating bones. Scratches are long, linear features that are generated when the teeth of carnivores slide against each other to slice meat from prey.

Our dental microwear analysis revealed very similar wear patterns between both the Ice Age wolves and the recent wolves, which indicated that both groups primarily consumed flesh. This is especially interesting, as previous studies had suggested that during the Ice Age, wolves were scavengers that fed on the remains of animals that other carnivores had killed. We can conclude that gray wolves have maintained their status as competitive hunters over thousands of years, and that actively taking down prey is an important aspect of wolf ecology that is unlikely to change even as their habitat does.

Top: Taking moulds of teeth; Bottom: SEM of tooth surface. Credit: Danielle Fraser

Stable isotope analysis

Stable isotope analyses were performed at the University of California, Merced, by Dr. Sora Kim and Dr. Robin B. Trayler. We analyzed the δ13C and δ15N values from both bone carbonates and collagen. There were minimal changes in the δ13C values between the two groups, which suggest that wolves have remained generalist predators that hunted a variety of large herbivores. There was a very clear difference in δ15N values between the Ice Age and recent wolves, which we determined to be driven by a change in the main prey species that the wolves were hunting.

Zoe sampling material for stable isotope analysis. Credit: Danielle Fraser

Based on diet modelling, we discovered that the primary prey of wolves during the Ice Age were horses (Equus sp.), with moderate contributions from other herbivores, such as caribou (Rangifer tarandus) and muskox (Ovibos moschatus). Obviously, there are not huge herds of wild horses in the Yukon today, as they were one of the species that went extinct in North America at the end of the Ice Age. Instead, gray wolves that inhabit the modern Yukon rely mainly on hunting caribou and moose (Alces alces) to fulfill their dietary needs. This shift from a diet composed largely of horse to one of caribou and moose indicate that the survival of wolves is not fixed on a single prey species. Rather, gray wolves are able to shift their diets from one species to another, and are capable of surviving significant climatic and environmental changes, provided that they have access to a sufficiently large population of large-bodied herbivores.

Implications for wolf conservation

            Our study revealed that gray wolves from the Yukon were able to survive the threat of extinction at the end of the Ice Age by changing their diets to target different prey species, and are very adaptable predators. The key to modern wolf survival is the survival of their current prey species, caribou and moose. Conservation efforts should focus on preserving these large herbivores, and ensuring that their populations remain healthy and at stable sizes as the Arctic environment changes. The continued survival of grey wolves in the Yukon is directly linked to these animals, which further demonstrates the important role of caribou and moose in the Canadian Arctic.

We acknowledge that the institutions at which this research took place are located on the traditional and unceded territories of the Algonquin, Anishnaabeg People, the Yokuts and Miwuk People, the Taa’an Kwächän and Kwanlin Dün People. We are grateful to the placer gold mining community and the Tr’ond¨ek Hw¨ech’in First Nation for their continued support and partnership with our research in the Klondike goldfields region; and the Vuntut Gwitchin First Nation for their collaboration with research in the Old Crow region. This research was funded by: Canadian Museum of Nature Research Activity Grant, and Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN-2018-05305), awarded to my supervisor, Dr. Danielle Fraser; and by funds of the Yukon Palaeontology Program of the Yukon Department of Tourism and Culture, contributed by Dr. Grant Zazula.

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