Abstract
North American martens are forest dependent, influenced by human activity, and climate vulnerable. They have long been managed and harvested throughout their range as the American marten (Martes americana). Recent work has expanded evidence for the original description of two species in North America — M. americana and the Pacific Coast marten, M. caurina — but the geographic boundary between these groups has not been described in detail. From 2010 to 2016 we deployed 734 multi-taxa winter bait stations across a 53,474 km2 study area spanning seven mountain ranges within the anticipated contact zone along the border of Canada and the United States. We collected marten hair samples and developed genotypes for 15 polymorphic microsatellite loci for 235 individuals, and 493 base-pair sequences of the mtDNA gene COI for 175 of those individuals. Both nuclear and mitochondrial genetic structure identified a sharp break across the Clark Fork Valley, United States with M. americana and M. caurina occurring north and south of the break, respectively. We estimated global effective population size (Ne) for each mountain range, clinal genetic neighborhood sizes (NS), calculated observed (Ho) and expected (He) heterozygosity, fixation index (FST), and clinal measures of allelic richness (Ar), Ho, and inbreeding coefficient (FIS). Despite substantial genetic structure, we detected hybridization along the fracture zone with both contemporary (nuclear DNA) and historic (mtDNA) gene flow. Marten populations in our study area are highly structured and the break across the fracture zone being the largest documented in North America (FST range 0.21–0.34, mean = 0.27). With the exception of the Coeur d’Alene Mountains, marten were well distributed across higher elevation portions of our sampling area. Clinal NS values were variable suggesting substantial heterogeneity in marten density and movement. For both M. americana and M. caurina, elevationaly dependent gene flow and high genetic population structure suggest that connectivity corridors will be important to ensuring long-term population persistence. Our study is an example of how a combination of global and clinal molecular data analyses can provide important information for natural resource management.
Highlights
MATERIALS AND METHODSNorth American marten (Martes spp.) are a group for which genetic data are changing the understanding of how populations and lineages are structured across large landscapes (e.g., Colella et al, 2019) and provide an important example of how genetic data can inform wildlife management
The strength of the genetic break that we identified shows that historical connectivity across the Clark Fork Valley has been low enough to produce more or less complete demographic independence: the trajectory of these populations will depend to a much greater extent on local birth and death than on immigration or emigration across the Clark Fork Valley
On this basis we suggest that these populations, which we identify as M. americana and M. caurina, should be treated as separate entities for monitoring programs and management decisions such as developing harvest recommendations
Summary
North American marten (Martes spp.) are a group for which genetic data are changing the understanding of how populations and lineages are structured across large landscapes (e.g., Colella et al, 2019) and provide an important example of how genetic data can inform wildlife management. Some authors continued to refer to two separate groups of marten in North America (Dawson and Cook, 2012), marten were subsequently considered, and managed, under the single species umbrella of M. americana (Colella et al, 2019). Analysis of widely spaced samples from western North America supports the longstanding notion (Wright, 1946) that there is a broad area of contact in the Inland Pacific Northwest including portions of British Columbia, Idaho, Montana, and Washington (Colella et al, 2019)
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