Spatial differences in genetic diversity and northward migration suggest genetic erosion along the boreal caribou southern range limit and continued range retraction

Abstract

With increasing human activities and associated landscape changes, distributions of terrestrial mammals become fragmented. These changes in distribution are often associated with reduced population sizes and loss of genetic connectivity and diversity (i.e., genetic erosion) which may further diminish a species' ability to respond to changing environmental conditions and lead to local population extinctions. We studied threatened boreal caribou (Rangifer tarandus caribou) populations across their distribution in Ontario/Manitoba (Canada) to assess changes in genetic diversity and connectivity in areas of high and low anthropogenic activity. Using data from >1,000 caribou and nine microsatellite loci, we assessed population genetic structure, genetic diversity, and recent migration rates using a combination of network and population genetic analyses. We used Bayesian clustering analyses to identify population genetic structure and explored spatial and temporal variation in those patterns by assembling networks based on RST and FST as historical and contemporary genetic edge distances, respectively. The Bayesian clustering analyses identified broad‐scale patterns of genetic structure and closely aligned with the RST network. The FST network revealed substantial contemporary genetic differentiation, particularly in areas presenting contemporary anthropogenic disturbances and habitat fragmentation. In general, relatively lower genetic diversity and greater genetic differentiation were detected along the southern range limit, differing from areas in the northern parts of the distribution. Moreover, estimation of migration rates suggested a northward movement of animals away from the southern range limit. The patterns of genetic erosion revealed in our study suggest ongoing range retraction of boreal caribou in central Canada.

Genomic islands of heterozygosity maintained across caribou populations despite inbreeding

“…It is made The copyright holder for this preprint this version posted December 30, 2020. ; https://doi.org/10.1101/2020.12.29.424772 doi: bioRxiv preprint were observed near the current southern edge of the boreal caribou range in Ignace, Ontario, suggesting recent isolation caused by range contraction. This result is congruent with the findings of a microsatellite study that suggested recent genetic erosion, a decrease in connectivity, and an increase in inbreeding along the southern continuous range edge of boreal caribou in Ontario and Manitoba (Thompson, Klütsch, Manseau, & Wilson, 2019). The second longest average ROH was observed on Michipicoten Island, Ontario, an isolated population that has experienced several recent bottlenecks (Bergerud et al, 2007;Fletcher, 2017).…”

Science to inform policy: Linking population dynamics to habitat for a threatened species in Canada

“…We did not consider immigration or emigration in this model because they are low among boreal caribou populations (e.g. Thompson, Klutsch, Manseau, & Wilson, 2019), nor did we consider age-dependent effects due to the lack of information to parameterize such effects for boreal caribou.…”

Genome-wide SNP analysis of three moose subspecies at the southern range limit in the contiguous United States

“…However, many of these studies focused on populations more latitudinally centered in each subspecies' range. Investigations of genetic patterns in species populations, including in North American ungulates, have generally found genetic diversity to be lower at the margins and greater towards the center of a species' range (Eckert et al 2008;Thompson et al 2019). This is often due to isolation by distance or inbreeding as a result of multiple biotic and abiotic factors (i.e.…”