Recent Hybridization between a Polar Bear and Grizzly Bears in the Canadian Arctic

Abstract

Grizzly bears have recently become more common on the Arctic Islands in the Inuvialuit Settlement Region, concurrently with a period of environmental change. Over the last decade, grizzly bear – polar bear hybrids have been confirmed within this region, triggering extensive discussion and speculation regarding the impact of hybridization on the parent species. Through harvests, sightings, and captures, we document an increase in the presence of grizzly bears and combine field observations of hybrids with genetic analysis and parentage analysis to identify four first-generation (F1) hybrids and four offspring of F1 hybrids and grizzly bears (backcross-to-grizzly-bear individuals). We trace these eight hybrid individuals to a single female polar bear who mated with two grizzly bears. We sampled one of her mates on the sea ice in the High Arctic and deduced the genotype of the other from his five offspring. The two male grizzly bears are sires of both the F1 generation and the backcross-to-grizzly-bear generation. So what initially appeared to be a sudden spate of hybridization in the western Canadian Arctic originated with the unusual mating between three non-hybrid parents. The breakdown of species barriers may start with atypical mating preferences of select individuals; however, the story we present can be traced to a single female polar bear who, along with three of her known F1 offspring, has been killed.

Genomic Evidence of Widespread Admixture from Polar Bears into Brown Bears during the Last Ice Age

“…Admixture between brown bears and polar bears has also been observed in the presentday Canadian Arctic (DoupŽ et al 2007;Pongracz et al 2017) and has been attributed to climateinduced overlap between the two species (Kelly et al 2010). Together, these data reveal the ongoing and dynamic nature of gene flow between brown bears and polar bears, as well as the important role that consequent habitat redistribution plays in facilitating admixture.…”

Genomic evidence of globally widespread admixture from polar bears into brown bears during the last ice age

“…Admixture between brown bears and polar bears has also been observed in the present-day Canadian Arctic (Doupé et al 2007;Pongracz et al 2017) and has been attributed to climate-induced overlap between the two species (Kelly et al 2010).…”

Novel range overlap of three ursids in the Canadian subarctic

“…However, the delta is distant from concentrated terrestrial food sources such as snow goose (Chen caerulescens) colonies (Iles et al 2013) and forage plants are sparse at that time of year. Alternatively, that bear may simply have been traveling through, possibly towards the still-frozen bay for either feeding or mating opportunities (Taylor 1995;Pongracz et al 2017). Better understanding of grizzly bear ecology in this region should be a high scientific and conservation priority.…”

“…Hybridization between polar and grizzly bears is possible in and offshore from Wapusk National Park due to the range overlap there. Very little is known about the ecology or behaviour of such hybrid individuals (Pongracz et al 2017) so close study of any hybrid individuals' ecology would be important. Consequently, we recommend that range overlap of these three ursid species in Wapusk National Park not be viewed as a threat to any of them, but rather as an ecological response to environmental change that needs to be further examined through a holistic, dynamic, and non-equilibrium ecological perspective.…”

“…Type of interaction, species involved, and citations black bear grizzly bear polar bear spatial and temporal niche partitioning by grizzly and black bears, grizzlies dominant (Aune 1994;MacHutchon et al 1998;Schwartz et al 2010) − + n/i competitive exclusion of female and subadult grizzly bears from habitat dominated by black bears (Mattson et al 2005) + − n/i predation by grizzlies on black bears (Mattson et al 1992) − + n/i predation by grizzlies on polar bears (Taylor 1995) n/i + − competition between grizzly and polar bears for terrestrial food sources, grizzlies dominant (Miller et al 2015) n/i + − non-aggressive sharing of terrestrial food sources by polar and black bears (Lemelin et al 2010) 0 n/i 0 polar bear-grizzly bear hybridization (Pongracz et al 2017) n/i 0 0…”