Polar bear photo on left, grizzly bear photo on right

Photo: © Daniel J. Cox/Natural Exposures

Hybridization Extremely Rare Between Grizzly and Polar Bears, Study Finds



13 Jun 2024

Genome analysis of over 800 polar and grizzly bears reveals no new hybrids and confirms the eight previously-known “grolar bears”

Bozeman, Montana and Winnipeg, Canada — June 13, 2024 — Researchers from Environment and Climate Change Canada, Polar Bears International, University of Manitoba, MacEwan University, Government of Northwest Territories, and San Diego Zoo Wildlife Alliance today published “Development of an 8K SNP chip to assess adaptive diversity and hybridization in polar bears” in the Conservation Genetics Resources journal. This is the first-ever large-scale analysis of how often hybrids of polar and grizzly bears exist in the wild, made possible by developing an innovative SNP genetic sequencing chip, which is a new tool to analyze samples from polar and grizzly bears. This report analyzed 371 historic polar bear and 440 historic grizzly bear samples from across Canada, Alaska, and Greenland and confirmed that only the eight already-known are hybrids, thus underscoring the rarity of hybridization. 

Range expansion, facilitates hybridization of two large carnivores: “Polar bears evolved from grizzly bears several hundred thousand years ago and although gene flow has occurred between the two species in the past, it appears that recent hybridization is restricted to a small group of polar bears and brown bears in the western Arctic,” says co-author Evan Richardson, Research Scientist at Environment and Climate Change Canada, adding, “This study develops a new genomic toolset to rapidly detect hybrids and indicates that contemporary hybridization is not a conservation concern.” 

Hybridization, increasing but rare: This report answers the question of, “How many polar-grizzly bear hybrids are there?” which responds to an expectation that the numbers of polar-grizzly hybrids were increasing. Out of 819 wild grizzly and polar bears across Canada, Alaska, and Greenland, encompassing four subpopulations, this report found that only eight hybrids exist, or 1% of the samples. This report analyzed samples of polar bears, grizzly bears, and known hybrids collected between 1975 and 2015, with the first hybrid not appearing until 2006. While it is a rare occurrence, it is a recent one, suggesting hybridization is a result of warming temperatures causing their habitats to increasingly overlap. 

“We were surprised to find no new cases of polar-grizzly hybrids despite speculation of increasing numbers,” says co-author Dr. Ruth Rivkin, postdoctoral research fellow with Polar Bears International, University of Manitoba, and the San Diego Zoo Wildlife Alliance, “We’re proud that this new chip allows rapid identification of polar-grizzly bear hybrids, which will be an important tool as the climate warms and polar and grizzly bears come increasingly into contact.”

A grizzly-polar bear hybrid at Osnabrück Zoo.

Photo: Corradox

A grizzly-polar bear hybrid at Osnabrück Zoo.

About hybrids (also known as pizzly bears or grolar bears): Hybrids of grizzly and polar bears are often referred to as grolar or pizzly bears depending on the paternal lineage, i.e., a grolar bear when the father is a grizzly bear, and a pizzly bear when the father is a polar bear. This study confirms the existence of eight known grolar bears in the wild as the descendants of one female polar bear. Hybridization is only possible in areas where grizzly and polar bear distributions overlap (thus excluding regions like the high Arctic). Hybridization is uncommon but expected to increase as climate change pushes grizzly bears northward, increasingly into polar bear territories, but hybrids are still ill-suited to adapt to the changing Arctic

“This report underscores that hybridization is remarkably rare, and that hybridization is not an adaptive capability of polar bears,” says Geoff York, senior director of research and policy at Polar Bears International, who was not involved in the report. “The report introduces a new tool for wildlife managers to use as they evolve their strategies due to a warming climate and changing ecosystems.” 

Technological breakthrough: This research developed the new 8K genotyping chip, called the Ursus maritimus V2 SNP chip, which is a genetic tool used to analyze polar bear samples in a lab. It reads the genetic samples, allowing rapid and reliable genome analysis, and spots polar bear-grizzly hybrids with 100% accuracy. The Ursus maritimus V2 SNP chip is a result of years of development through the Genomics Research and Development Initiative STAGE funding by Environment and Climate Change Canada. The authors had access to long-term, robust polar bear data from Canadian government and territorial monitoring programs, which have been collecting data since 1966, and which were critical to the research and Ursus maritimus V2 SNP chip development. This chip is an important tool for wildlife managers, scientists, policymakers, and conservationists to identify hybrid bears and further enable their protection and more effective wildlife management. 

“Our newly developed technology allows rapid and accurate consideration of over 8,000 genetic markers in polar bears,” notes lead author Dr. Joshua Miller, Assistant Professor, Biological Sciences, MacEwan University, adding “This will allow for the assessment and monitoring of genetic diversity, which is a key part of a species' ability to survive changing environmental conditions.”

About Environment and Climate Change Canada
ECCC is the lead federal department for a wide range of environmental issues, including taking action on clean growth and climate change. The Department is also engaged in activities aimed at preventing and managing pollution, conserving nature, and predicting weather and environmental conditions. 

About MacEwan University
Founded in 1971, MacEwan University inspires its students with a powerful combination of academic excellence and personal learning experiences. Offering more than 90 programs including undergraduate degrees, applied degrees, diplomas, certificates, continuing education, and corporate training, the university provides a transformative education in a creative, collaborative, and supportive learning environment where creativity and innovation thrive. Located in Edmonton, Alberta Canada, MacEwan University offers a unique student experience that opens up diverse pathways for achievement and growth.

About the University of Manitoba 
The University of Manitoba is recognized as Western Canada's first university, with more than 29,000 students, 5,000 academic staff, 3,900 support staff, and more than 188,000 alumni. It is part of the U15, ranking among Canada’s top research-intensive universities, and is Manitoba’s only medical-doctoral post-secondary institution. The University provides exceptional liberal arts, science, and professional programs of study, inspiring undergraduate and post-graduate students to positively impact their communities as globally engaged citizens. UM campuses are located on the original lands of Anishinaabeg, Ininiwak, Anisininewuk, Dakota Oyate, and Dene, and on the National Homeland of the Red River Métis. We respect the Treaties that were made on these territories, we acknowledge the harms and mistakes of the past, and we dedicate ourselves to move forward in partnership with Indigenous communities in a spirit of Reconciliation and collaboration. For more information, please visit umanitoba.ca. 

About San Diego Zoo Wildlife Alliance
San Diego Zoo Wildlife Alliance, a nonprofit conservation leader, inspires passion for nature and collaboration for a healthier world. The Alliance supports innovative conservation science through global partnerships. Through wildlife care, science expertise and collaboration, more than 44 endangered species have been reintroduced to native habitats. Annually, the Alliance reaches over 1 billion people, in person at the San Diego Zoo and San Diego Zoo Safari Park, and virtually in 150 countries through media channels, including San Diego Zoo Wildlife Explorers television programming in children’s hospitals in 14 countries. Wildlife Allies—members, donors, and guests—make success possible.

About Polar Bears International
Polar Bears International’s mission is to conserve polar bears and the sea ice they depend on. We also work to inspire people to care about the Arctic, the threats to its future, and the connection between this fragile ecosystem and our global climate. Polar Bears International is the only nonprofit organization dedicated solely to wild polar bears and Arctic sea ice, and its staff includes scientists who study wild polar bears. The organization is a recognized leader in polar bear conservation. For more information, visit www.polarbearsinternational.org.

Media Contacts
Annie Edwards, for Polar Bears International
T: +44 07307 139782

Melissa Hourigan, for Polar Bears International
T: +1 720-608-1919