Wolverene (Gulo gulo)

We report a chromosomal-level genome assembly of a male North American wolverine (Gulo gulo luscus) from the Kugluktuk region of Nunavut, Canada. The genome was assembled directly from long-reads, comprising: 758 contigs with a contig N50 of 36.6 Mb; contig L50 of 20; base count of 2.39 Gb; and a near complete representation (99.98%) of the BUSCO 5.2.2 set of 9,226 genes. A presumptive chromosomal-level assembly was generated by scaffolding against two chromosomal-level Mustelidae reference genomes, the ermine and the Eurasian river otter, to derive a final scaffold N50 of 144.0 Mb and a scaffold L50 of 7. We annotated a comprehensive set of genes that have been associated with models of aggressive behavior, a trait which the wolverine is purported to have in the popular literature. To support an integrated, genomics-based wildlife management strategy at a time of environmental disruption from climate change, we annotated the principal genes of the innate immune system to provide a resource to study the wolverine’s susceptibility to new infectious and parasitic diseases. As a resource, we annotated genes involved in the modality of infection by the coronaviruses, an important class of viral pathogens of growing concern as shown by the recent spillover infections by severe acute respiratory syndrome coronavirus-2 to naïve wildlife. Tabulation of heterozygous single nucleotide variants in our specimen revealed a heterozygosity level of 0.065%, indicating a relatively diverse genetic pool that would serve as a baseline for the genomics-based conservation of the wolverine, a rare cold-adapted carnivore now under threat.

Wolverines (Gulo gulo) were nearly eliminated from the contiguous U.S. by the mid-1920s, when they began to naturally recolonize portions of their historical range. Currently, the Greater Yellowstone Ecosystem in Wyoming represents the southernmost distribution. Using remote cameras, we detected two female wolverines in 2016 and 2017 in Wyoming, originally captured as juveniles. At nearly 11 and 12 y old, both were documented in the same areas where they appeared to set up home ranges previously, suggesting continued residency. The presence of long-lived females near the southern boundary of recolonization is important to the persistence of residents as well as population expansion. However, nearest habitat to the south is ≥130 km across open land atypical of wolverine habitat. Connectivity between island-like patches of habitat will be critical to continued recolonization, although active restorations may still be needed in areas unlikely to receive females through natural dispersal.

Abstract
Background

Reliable estimates of population status are a pre-requisite for informed wildlife management. However, abundance estimates can be challenging to obtain, especially for species that are highly mobile, rare and elusive. For nearly two decades, management agencies in Norway and Sweden have been monitoring populations of three large carnivores – brown bear (Ursus ursus), wolf (Canis lupus), and wolverine (Gulo gulo) – using non-invasive genetic sampling (NGS). DNA extracted from fæces, urine, and hair can be used to identify the species, sex, and individual from which each sample originated. Samples thus become evidence of the presence of an individual carnivore in space and time. Project RovQuant was initiated in 2017 with the objective to develop statistical methods that allow a comprehensive assessment of population status and dynamics using NGS data and other sources of information collected by the national monitoring programs in Sweden and Norway.

Approach

We developed a Bayesian open-population spatial capture-recapture (OPSCR) model that, using a combination of NGS and recoveries of dead carnivores, jointly estimates 1) the spatial variability in the probability of genetic detection, 2) the spatial distribution and interannual movements of individuals and 3) population size and dynamics. We fitted this model to the extensive individual-based monitoring data for bears, wolverines, and wolves, which had been compiled in the Scandinavian large carnivore database Rovbase 3.0 between 2012 and 2019.

Results

The OPSCR model yielded annual density maps both total and jurisdiction-specific population sizes for each species. The estimated number of bears for April 1, 2018 was 2 757 (95% credible interval, CrI: 2 636 – 2 877), of which 2 615 (CrI: 2 499-2 732) were located in Sweden and 142 (CrI: 124-162) in Norway. The estimated number of wolverines for December 1, 2018 was 1 035 (CrI: 985 – 1 088), of which 660 (CrI: 619-703) were located in Sweden and 375 (CrI: 353-397) in Norway. The estimated number of wolves for October 1, 2018 was 375 wolves (CrI: 352 – 402), of which 297 (CrI: 274-322) were located in Sweden and 79 (CrI: 72-86) in Norway. In addition to density and abundance estimates, the OPSCR models also yielded estimates of survival, recruitment, and space use parameters for each species. Six additional tasks linked to the development of OPSCR model were implemented as either prerequisite technical developments or to address persistent challenges in monitoring and management of large carnivores in Scandinavia. Although this report focuses on the main results from the OPSCR model, findings related to these additional tasks are briefly described as well.

Conclusions

The unique Scandinavian data set combined with a novel OPSCR model allowed RovQuant to quantify the population status of three large carnivore species at an unprecedented spatial scale (up to 593 000 km2). The approach used here has several advantages over proxy-based approaches for obtaining estimates of population size. The OPSCR model directly estimates annual abundance from NGS and dead recovery data while accounting for spatial and temporal variation in detection probability of individuals. The resulting estimates are spatially explicit, allowing extraction of abundance estimates and associated measures of uncertainty for any spatial extent desired by the user (e.g. management unit). Annual cause-specific mortality and recruitment are also estimated, which are both useful metrics of the population’s status and trajectory. Importantly, this approach efficiently exploits the data (NGS and dead recoveries) currently collected annually by Swedish and Norwegian management authorities at the population level.

Although the OPSCR model has been extensively tested, it constitutes a novel approach and is still under development. The ability of the model to produce trustworthy estimates relies on several statistical assumptions and on the suitability of the input data. For example, although the model was able to produce annual density maps and abundance estimates for bears throughout Scandinavia, the current patchy sampling for this species in Sweden means that confidence in the reliability of the results for bear is substantially lower than for the other two species. We discuss the strengths and limitations of our approach and suggest areas for further study and development in order to increase the reliability of the OPSCR model and the cost-efficiency of large carnivore monitoring in Scandinavia.

Compilation of this document was initiated by the Norwegian Environment Agencyin order to establish recommended protocols for capture, chemical immobilization, anesthesia and radio tagging of free-ranging brown bears (Ursus arctos), gray wolves (Canis lupus), wolverines (Gulo gulo) and Eurasian lynx (Lynx lynx). In addition, procedures to ensure proper sampling of biological materials for management, research and banking purposes have been included. The current protocols are based on nearly 4,000 captures of free-ranging brown bears, wolves, wolverines and lynx carried out from 1984 through 2017in Scandinavia. Some of the results have been published as peer reviewed papers, conference presentations, theses, and reports. However, a large amount of data are still on file and will be published in the future. In addition, comprehensive literature reviews have been carried out in order to include pertinent information from other sources.Earlier versions of these protocols were approved by all ongoing research projects on brown bears, wolves, wolverines and lynx in Scandinavia.We thank the project leaders, researchers, and field technicians for their cooperative efforts

Within the predator guild, wolverines (Gulo gulo(L., 1758)) have evolved as generalist predators and scavengers on prey killed by other predators. The recovery of wolves (Canis lupusL., 1758) in the boreal forests of southern Norway during the late 1990s may have triggered consequent recolonization by wolverines through increased carcass avail-ability. We investigated winter foraging behavior of wolverines in the boreal forest with regard to wolf, lynx (Lynx lynx(L., 1758)), and red fox (Vulpes vulpes(L., 1758)) presence. We followed 55 wolverine tracks in the snow from at least nine individuals for a total of 237 km during the winters of 2003–2004. We documented 19 moose (Alces alces(L.,1758)) and 4 bird carcasses, and no successful hunts. Wolverines did not follow guild species trails directly to carcasses; however, they did change their movement patterns after red fox encounters. While wolverines were more active at higher elevations, the probability of encountering a wolf was higher at lower elevations, suggesting a spatial separation between wolverines and wolves. Although wolverines seem to depend on wolf for carrion during winter, they did not use wolf trails to find carcasses. This may indicate that wolverines reduce risk of intra guild predation by avoiding direct confrontation with wolves.