Grizzly–polar bear hybrid

A grizzly–polar bear hybrid (also named grolar bear, pizzly bear,[1][2] grizzlar, or nanulak) is a rare ursid hybrid that has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid in nature was confirmed by testing the DNA of a unique-looking bear that had been shot near Sachs Harbour, Northwest Territories on Banks Island in the Canadian Arctic. The number of confirmed hybrids has since risen to eight, all of them descending from the same female polar bear.[3]

Grizzly–polar bear hybrid
Polar/brown bear hybrid at Osnabrück Zoo
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Tribe: Ursini
Genus: Ursus
Species:
U. maritimus × U. arctos
Polar/brown bear hybrid, Natural History Museum at Tring, Tring

Possible wild-bred polar bear-grizzly bear hybrids have been reported and shot in the past, but DNA tests were not available to verify the bears' ancestry.

Genetic analysis has revealed multiple instances of introgressive hybridization between bear species,[4][5][6] including introgression of polar bear DNA into brown bears during the Pleistocene ("grizzly bear" is a local common name for Ursus arctos whereas "brown bear" is used internationally and in science to refer to the species as a whole).[7]

Occurrences in the wild

With several suspected sightings and eight confirmed cases,[3] theories of how such hybrids might naturally occur have become more than hypothetical. Although these sister species often occupy adjacent regions, direct contact has not been the norm because polar bears hunt, breed and sometimes even make maternity dens on sea ice, where brown bears have an overwhelmingly terrestrial lifestyle.

2006 discovery

Jim Martell, a hunter from Idaho, reportedly shot a grizzly–polar bear hybrid near Sachs Harbour on Banks Island, Northwest Territories on April 16, 2006.[1][8] Martell, with his local guide, Roger Kuptana, had been hunting for polar bears,[9] and killed the animal believing it to be a normal polar bear. Officials took interest in the creature after noticing that while it had thick, creamy white fur typical of polar bears, it also had long claws, a humped back, a shallow face, and brown patches around its eyes, nose, back, and foot, which are all traits of grizzly bears. If the bear had been adjudicated to be a grizzly, the hunter would have faced a possible CAN$1,000 fine and up to a year in jail.[9]

A DNA test conducted by Wildlife Genetics International in British Columbia confirmed it was a hybrid, with a polar bear mother and a grizzly bear father. It is the first documented case in the wild,[3] though it was known that this hybrid was biologically possible and other ursid hybrids have been bred in zoos in the past.[10]

On May 8, 2006, the discovery of the grizzly-polar bear hybrid received increased attention when, soon after the story was announced, the comedy television show The Colbert Report light-heartedly named the new species as the number one threat to American Security.

Amidst much controversy, the bear has since been returned to Mr. Martell.[11][12]

Subsequent discoveries

On April 8, 2010, David Kuptana, an Inuvialuit hunter from the community of Ulukhaktok on Victoria Island shot what he thought was a polar bear. After inspecting the bear and having its DNA tested, it was discovered that the bear's mother was a grizzly-polar hybrid and the father was a grizzly bear. The bear possesses physical characteristics intermediate between grizzlies and polar bears, such as brown fur on its paws, long claws, and a grizzly-like head.

Between 2012 and 2014 another six hybrid bears were either killed by hunters or live-captured by biologists. Samples were collected from all six, and genetic analysis confirmed both their hybrid status and their family relationships.[3] The eight hybrids identified to date include four first generation (F1, 50:50) and four grizzly bear backcross individuals (75:25 grizzly:polar bear). A single F1 female was the mother of all four backcross individuals, and a single female polar bear was the mother of all four F1s, and thus the grandmother of all four backcross bears. Two male grizzlies mated with the female polar bear to give rise to the four F1s, with one grizzly bear apparently mating with the polar bear in two different years (two of the F1s are full siblings, but born three years apart). The same two male brown bears both mated with the F1 female to produce the four backcross individuals, with three litter mates being sired by one male and a single, older 3/4 grizzly bear coming from a mating between the F1 female and her father.

It is hard to know whether these events are a harbinger of the breakdown of a species barrier, or just an unusual anecdote, since all confirmed cases to date trace to the unusual mate choice of a single polar bear.

The Arviat bear

It was widely reported that a bear shot in 2016, near Arviat on the western shore of Hudson Bay, was a hybrid, with news agencies going so far as to describe this as an outcome of climate change.[13] This bear was light in colour, but 'blonde' grizzly bears are common on the Barren Grounds,[14] and the Arviat bear did not have other features characteristic of hybrids. The Arviat bear was subsequently confirmed by genetic analysis to be a pure brown bear.[15][16]

Range expansion of brown bears as a possible contributing factor

Although a grizzly bear was killed on Banks Island in 1951, it has until recently been rare for this species to stray far north of the coast of mainland Canada. In 1991 one or more grizzly bears were documented hunting seals and polar bears on the sea ice near Melville island, over 500 km from the mainland coast.[17] In 2003 and 2004 a geological team working on Melville Island obtained photographic and DNA evidence of a grizzly bear in the area.[18] Their report also collated information on several other sightings in the Canadian Arctic Archipelago.

Grizzly bears have apparently also been extending their range east across the Barren Grounds towards Hudson Bay, and south towards northern Saskatchewan and Manitoba.[19] Between 2003 and 2008 seven individuals were spotted in Wapusk National Park south of Churchill, Manitoba, an area used by polar bears for maternity dens and as a refuge during the ice-free season on Hudson Bay.[20][21]

Ancient hybridization

The genetic methods used to confirm the family relationships and ancestry of the hybrid bears from northern Canada date back to the early 1990s, and are not powerful enough to reveal ancient history. However, the newer methods of genomics analyze thousands of sites in the genome, allowing the history of individual fragments of chromosomes to be traced back to particular populations (or species in the case of hybridization). Genomic studies of brown bears and polar bears have revealed that gene flow from polar bears into brown bears, but not the other way around, was widespread in time and space during the Pleistocene.[7] Of particular note, the bears living on the islands of the Alexander Archipelago of southeast Alaska trace their maternally inherited mitochondrial DNA entirely to polar bears, but over 90% of their nuclear genome to brown bears. This appears to reflect a process in which a population of polar bears was left behind as the species retreated northwards at the end of the last ice age, with male brown bears subsequently introducing genes from the adjacent mainland, but female brown bears being generally unable or unwilling to swim across several km of open ocean to reach the islands (thus the lack of exchange of mitochondrial DNA).[22]

Such studies have not been limited to polar bears and brown bears, and it now appears that gene flow between species has been widespread during the evolution of the living species of bears.[23]

Naming
Possible hybridisation between different species of bear

Since the 2006 discovery placed the hybrid into the spotlight, the media have referred to this animal with several portmanteau names, such as pizzly bear, grolar bear,[24] and polizzly, but there is no consensus on the use of any one of these terms. Canadian wildlife officials have suggested calling the hybrid "nanulak", taken from the Inuit names for polar bear (nanuk) and grizzly bear (aklak).[25]

By one convention,[26] the name of the sire comes first in such combinations: the offspring of a male polar bear and a female grizzly would be the suggested nanulak or a "pizzly bear", while the offspring of a male grizzly and a female polar bear would be a "grolar bear" or possibly an aknuk.

Characteristics

Two grizzly–polar hybrid cubs (one female and one male) were born at Osnabrück Zoo in Osnabrück in 2004, and their physical traits are generally intermediate between the polar bear and the grizzly bear.[27] For example, their bodies are smaller than polar bears, but larger than grizzlies, while their heads fall between the broader grizzly head and the leaner polar bear head.[27] They have long necks like polar bears, but small shoulder humps like grizzlies.[27] The soles of their feet are partially covered in hair; polar bears have hair-covered soles, which act as insulation, and grizzlies have hairless soles.[27]

Similarly, the hair of the hybrids exhibits a pattern of hollowness, which blends the traits of polar bears and grizzlies. In cross-section, the hair of polar bears is hollow, while the hair of grizzlies is either solid or has small hollow regions.[27] This varies according to which part of the grizzly the hair is taken from.[27] In the hybrid male, the paw hair was solid, but the dark back hair was somewhat hollow, albeit with "smaller empty regions than found in polar bear hair".[27] The hair of the female hybrid, "contains a range of hollow regions".[27]

The hybrids demonstrated behavior more similar to polar bears than grizzlies. They stomped toys in a manner reminiscent of how polar bears break the ice, and hurled bags to the side "as polar bears may hurl prey".[27] Grizzlies given the same bags do not demonstrate this hurling behavior.[27] The hybrids were also observed lying down as polar bears do: on their bellies with rear legs splayed.[27]

References
  1. Mallet, James (2008). "Hybridization, ecological races and the nature of species: empirical evidence for the ease of speciation" (PDF). Phil. Trans. R. Soc. B. 363 (1506): 2971–2986. doi:10.1098/rstb.2008.0081. PMC 2607318. PMID 18579473.
  2. Barnosky, Anthony D. (2009). Island Press (ed.). Heatstroke: Nature in an Age of Global Warming. Island Press. p. 10. ISBN 978-1-59726-197-5. Pizzly Bear.
  3. Richardson, Evan; Branigan, Marsha; Paetkau, David; Pongracz, Jodie D. (May 31, 2017). "Recent Hybridization between a Polar Bear and Grizzly Bears in the Canadian Arctic". Arctic. 70 (2): 151–160. doi:10.14430/arctic4643.
  4. Kutschera, Verena E.; Bidon, Tobias; Hailer, Frank; Rodi, Julia L.; Fain, Steven R.; Janke, Axel (2014). "Bears in a Forest of Gene Trees: Phylogenetic Inference is Complicated by Incomplete Lineage Sorting and Gene Flow". Molecular Biology and Evolution. 31 (8): 2004–2017. doi:10.1093/molbev/msu186. PMC 4104321. PMID 24903145.
  5. Hailer, F.; Kutschera, V. E.; Hallstrom, B. M.; Klassert, D.; Fain, S. R.; Leonard, J. A.; Arnason, U.; Janke, A. (2012). "Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage". Science. 336 (6079): 344–347. Bibcode:2012Sci...336..344H. doi:10.1126/science.1216424. hdl:10261/58578. PMID 22517859. S2CID 12671275.
  6. Miller, W.; Schuster, S. C.; Welch, A. J.; Ratan, A.; Bedoya-Reina, O. C.; Zhao, F.; Kim, H. L.; Burhans, R. C.; Drautz, D. I.; Wittekindt, N. E.; Tomsho, L. P.; Ibarra-Laclette, E.; Herrera-Estrella, L.; Peacock, E.; Farley, S.; Sage, G. K.; Rode, K.; Obbard, M.; Montiel, R.; Bachmann, L.; Ingolfsson, O.; Aars, J.; Mailund, T.; Wiig, O.; Talbot, S. L.; Lindqvist, C. (2012). "Polar and brown bear genomes reveal ancient admixture and demographic footprints of past climate change". Proceedings of the National Academy of Sciences. 109 (36): E2382–E2390. doi:10.1073/pnas.1210506109. PMC 3437856. PMID 22826254.
  7. Shapiro, Beth; Green, Richard E.; Monaghan, Nigel; Malev, Alexander V.; Kisleika, Aliaksandr A.; Graim, Kiley; Edwards, Ceiridwen J.; Bradley, Daniel; Stirling, Ian (May 1, 2018). "Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age". Molecular Biology and Evolution. 35 (5): 1120–1129. doi:10.1093/molbev/msy018. PMID 29471451.
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  9. "Polar Bear / Grizzly Bear Crossbreed Hydrid". Blackbearheaven.com. Retrieved March 9, 2011.
  10. "Le "grolar", un nouvel ours témoin du réchauffement climatique". FIGARO (in French). March 28, 2014. Retrieved October 28, 2018.
  11. "Rare hybrid bear comes to Idaho...as a trophy". Associated Press. January 21, 2007. Archived from the original on September 27, 2007. Retrieved January 21, 2007.
  12. Wittmeyer, Alicia P.Q. (January 19, 2007) Rare hybrid bear coming to Reno hunting show. Tahoe Daily Tribune
  13. Milman, Oliver (May 18, 2016). "Pizzly or grolar bear: grizzly-polar hybrid is a new result of climate change". The Guardian. Retrieved January 23, 2019.
  14. "Grizzly Bear | NWT Species at Risk". www.nwtspeciesatrisk.ca. Retrieved January 23, 2019.
  15. "Exotic bear harvested in Nunavut was a blonde grizzly". Nunatsiaq News. June 22, 2016. Retrieved January 23, 2019.
  16. Barton, Katherine (June 21, 2016). "Grolar or pizzly? Nope, just a blond grizzly bear". CBC News. Retrieved January 29, 2019.
  17. Taylor, Mitch (1995). "Grizzly bear sightings in Viscount Melville Sound". Polar Bears: Proceedings of the Eleventh Working Meeting of the IUCN/SSC Polar Bear Specialist Group, 25 – 27 January 1993, Copenhagen, Denmark. Occasional Paper of the IUCN Species Survival Commission (SSC). 10: 191–192.
  18. Paetkau, D.; Furze, M.; England, J. H.; Doupé, J. P. (2007). "Most Northerly Observation of a Grizzly Bear (Ursus arctos) in Canada: Photographic and DNA Evidence from Melville Island, Northwest Territories". Arctic. 60 (3): 271–276. doi:10.14430/arctic219.
  19. "Grizzly bear (Ursus arctos): COSEWIC assessment and status report 2012". Environment and Climate Change, Canada. November 1, 2012. Retrieved January 23, 2019.
  20. Hedman, Daryll; Gormezano, Linda; Rockwell, Robert (2008). "Grizzly Bears, Ursus arctos , in Wapusk National Park, Northeastern Manitoba". The Canadian Field-Naturalist. 122 (4): 323–326. doi:10.22621/cfn.v122i4.639.
  21. Shapiro, Beth; Slatkin, Montgomery; Stirling, Ian; John, John St; Salamzade, Rauf; Ovsyanikov, Nikita; Jay, Flora; Stiller, Mathias; Fulton, Tara L. (March 14, 2013). "Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution". PLOS Genetics. 9 (3): e1003345. doi:10.1371/journal.pgen.1003345. PMC 3597504. PMID 23516372.
  22. Paetkau, David; Shields, Gerald F.; Strobeck, Curtis (1998). "Gene flow between insular, coastal and interior populations of brown bears in Alaska". Molecular Ecology. 7 (10): 1283–1292. doi:10.1046/j.1365-294x.1998.00440.x. PMID 9787441.
  23. Janke, Axel; Nilsson, Maria A.; Kolter, Lydia; Pfenninger, Markus; Bidon, Tobias; Lammers, Fritjof; Kumar, Vikas (April 19, 2017). "The evolutionary history of bears is characterized by gene flow across species". Scientific Reports. 7: 46487. Bibcode:2017NatSR...746487K. doi:10.1038/srep46487. PMC 5395953. PMID 28422140.
  24. "Hunter may have shot grolar bear – or was it pizzly?". Archived from the original on May 25, 2006. Retrieved May 12, 2006.CS1 maint: bot: original URL status unknown (link), CBC North, April 26, 2006.
  25. "Hybrid bear shot dead in Canada". BBC Science. May 13, 2006.
  26. Naming Conventions A semi-scientific reference for hybrid naming conventions, with specific examples of big-cat hybrids.
  27. Walker, Matt (October 30, 2009). "Polar bear plus grizzly equals?". BBC News Online. Retrieved October 30, 2009.
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