Biogeography and Restoration Strategy of North American Wolverine

North American wolverine (Gulo gulo luscus) consist of a metapopulation that requires steep and remote alpine environments with deep snowpack and talus fields, referred to as primary habitat (1, 2). Each wolverine home range is large (2). Therefore, long-distance dispersals are necessary to mix the gene pool (2). Connectivity between alpine habitat is important and can be considered islands in a matrix of forest (secondary habitat), low lying valleys and urban infrastructure (2). North American wolverine historical range included western alpine states: Colorado, California, Utah, Idaho, Montana, Wyoming and Washington (2).

Sometime between the turn of the 20th century and the Great Depression, the North American wolverine population tanked (1). With the exception of Utah, documented evidence suggests wolverine recolonized these states (1). One individual from the Rocky Mountains dispersed to California 86 years post extirpation (2). Five subspecies in the circumpolar species are recognized in addition to the North American subspecies (ITIS 2018). To understand migration and dispersal of North America wolverine, two studies were considered. The first study by McKelvey et al.

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2014, discusses the relationship between phylogeny and biogeography in the species. The second by Packila, Riley and Spence 2017, is a case study of one individual wolverine.

Biogeography and Phylogeny of North American Wolverine

The authors sampled museum specimens for mitochondrial DNA (mDNA) dating back to the turn of the century 20th compared to extant populations to confirm if North American wolverine was really extirpated from western USA, and to find genetically appropriate source populations for future reintroduction (1). The authors considered all published genotypes from a total of 741 individual wolverines, with a focus on a set of alleles (haplotype) (1).

The oldest specimen in the study dates back to 1870, which was from Colorado (1). Haplotypes included in the study were from North America, Mongolia, Asia, Eurasia, and Scandinavia (1). Eight haplotypes are in North American populations: A, Cali1 (widely distributed in North America, including in Colorado, originated in Asia), O (widely distributed in North America, including in Colorado), Cali2, F, I, C (northern Cascades and southern British Columbia), and Z-25 (eastern Canada) (1).

Pleistocene wolverine specimens are from Colorado, Wyoming and Idaho, Utah, Nebraska and Nevada, when primary habitat was more contiguous across those states (1). Around that time, its believed that two disjunct isolated populations existed in North America, separated by glaciers, one in the north by the Bering land-bridge, the other in the lower 48 (1). DNA comparing Asian wolverine populations with North America populations show that haplotype H is the common link (1). Cali1, which probably diverged first due to glacial retreat, and Z_25 are most closely related to Asian wolverine haplotypes (1). Within North America, population are closely related with haplotype A as the common link between all, dating back to approximately 10,000 to 100,000 years, and the dominating alleles (83% of haplotypes sampled) (1).

However, the haplotype changed between historic and extant wolverine populations in North America. Other studies argue that during the Holocene, glacial retreat and vegetation cover type changed from tundra and boreal forest to arid montane forest, shrub and grassland, and this caused genetic isolation of wolverine in the western US (1). For instance, Cali2 diverged from Cali1 due to vicariance resulting from Holocene climate change (1).

The haplotype diversity indicates that wolverine in North America exhibit gene pool exchange and connectivity between most populations (1). The genetic evidence supports that up to the Holocene, dispersal between primary and secondary habitat occurred (1). For example, the Northern Cascade population migrated from Canada, based on haplotype C distribution (1). In contrast, Alaska and Canada have vast expanses of contiguous primary and secondary habitat with fewer barriers to movement and dispersal (1). However, those haplotypes are geographically localized, thus there is limited gene flow within the Alaska and Canadian groups (1). This runs counter to classic biogeography concepts which suggest that physical barriers can limit gene flow (Lomolino et al. 2010). In sum, the authors state that reintroduction efforts should strive for genetic diversity over selection from one source gene pool, but that behavioral acclimation to mountainous terrain is important (1).

Long-Distance Dispersal in Extant Populations

In a 2009 Greater Yellowstone telemetry study where 9 wolverines were captured and tracked, a juvenile male wolverine (M56) with a GPS collar and an implanted radio transmitter, dispersed from the Absaroka Range. M56 travelled to the Wind River Range, across the southern Wyoming cold desert (non-habitat), to the Elk Mountains, down the Laramie Range, across I-80, and dispersed to a home range he created between the Mosquito Range and Mummy Range in Colorado 90 years after extirpation (2). In April 2016, M56 was shot in Alexander, North Dakota after 200 years of extirpation (2).

Generally, 200 km from center of natal is considered wolverine home range, dispersal occurs in March, and at an average age of 13 months (2). For all 9 dispersed radio-collared wolverines in the study, based on average daily rate between straight-line distances from radio-transmitted locations, >15km distances indicated travelling movement, and ≤15km was classified as resting (2). M56 traveled 710 km, at a minimum, mainly in primary alpine habitat. His average movement was 8.3 km per day, his average daily dispersal travels was 33.5 km/day (2). During rest hours, he moved 2.9 km/day on average (2). A little over half his time was spent in primary wolverine habitat. Barriers M56 successfully navigated included: 8 highways and one interstate, human occupied housing subdivisions, and non-habitat. M56 crossed I-80 between midnight and 0400, ran from moving vehicles and changed course when encountering loose dogs and human housing (2).

Conclusion

The success of future dispersal and migration of North American wolverine and reintroduction efforts into historic ranges will depend upon genetic diversity and phylogenetic relationships of wolverines, as well as modern day geographic barriers and future climatic changes. Island biogeography principles will have a stronger influence on wolverine dispersal, migration and gene flow as primary habitat in alpine and boreal forested environments change.

References:

1. Integrated Taxonomic Information System. 2018. Available: https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=622033#null Retrieved: June 22, 2018

2. Lomolino, M.V., Riddle, B.R., Whittaker, R.J., and Brown, J.H. 2010. Biogeography, Fourth Edition. Sineauer Associates, Inc. Sunderland, MA.