Microsatellite and mtDNA analysis of lake trout, Salvelinus namaycush, from Great Bear Lake, Northwest Territories: impacts of historical and contemporary evolutionary forces on Arctic ecosystems

Abstract

Resolving the genetic population structure of species inhabiting pristine, high latitude ecosystems can provide novel insights into the post-glacial, evolutionary processes shaping the distribution of contemporary genetic variation. In this study, we assayed genetic variation in lake trout (Salvelinus namaycush) from Great Bear Lake (GBL), NT and one population outside of this lake (Sandy Lake, NT) at 11 microsatellite loci and the mtDNA control region (d-loop). Overall, population subdivision was low, but significant (global FST θ = 0.025), and pairwise comparisons indicated that significance was heavily influenced by comparisons between GBL localities and Sandy Lake. Our data indicate that there is no obvious genetic structure among the various basins within GBL (global FST = 0.002) despite the large geographic distances between sampling areas. We found evidence of low levels of contemporary gene flow among arms within GBL, but not between Sandy Lake and GBL. Coalescent analyses suggested that some historical gene flow occurred among arms within GBL and between GBL and Sandy Lake. It appears, therefore, that contemporary (ongoing dispersal and gene flow) and historical (historical gene flow and large founding and present-day effective population sizes) factors contribute to the lack of neutral genetic structure in GBL. Overall, our results illustrate the importance of history (e.g., post-glacial colonization) and contemporary dispersal ecology in shaping genetic population structure of Arctic faunas and provide a better understanding of the evolutionary ecology of long-lived salmonids in pristine, interconnected habitats.

Hierarchical population structure and genetic diversity of lake trout (Salvelinus namaycush) in a dendritic system in Northern Labrador

“…The first by Northrup, Connor & Taylor () estimated F ST values among lake trout populations from a broad geographic area spanning the Yukon, British Columbia and the North West Territories and found that values ranged from 0.014 for two connected lakes of the same catchment to 0.616 for two lakes located in different catchments (separated by 780 km) that probably belong to different glacial lineages. The second study found no structure among lake trout collected from different basins within one of the largest freshwater ecosystems in Canada, the Great Bear Lake in the North West Territories (Harris et al ., ). Population structure could not be identified despite very large distances separating sampling locations within the lake.…”

Evolution and origin of sympatric shallow-water morphotypes of Lake Trout, Salvelinus namaycush, in Canada’s Great Bear Lake

“…MtDNA data collection methods are described in Harris et al (2013). Briefly, the left domain of the control region (d-loop) was amplified with primers tPro2 (Brunner et al, 2001) and ARCH1 (Alekseyev et al, 2009).…”

“…We performed STRUCTURE analyses for two data sets: (1) one consisting of all samples; and (2) one containing only the GBL samples. Given the limited genetic structure that has previously been resolved among Lake Trout from GBL (Harris et al, 2013), we used the LOCPRIOR option in STRUCTURE for the latter analysis to enhance the likelihood of detecting existent population structure in this system (detailed by Hubisz et al, 2009). To avoid biasing the analysis toward the clustering by morph or arm, LOCPRIOR information was included at the sample level (that is, including 13 distinct entities in our LOCPRIOR information and the 13 localities represent various positions within arms).…”

“…If the latter is the case, then a second fundamental hypothesis concerns the geographic origin of the ecotypes (that is, whether they evolved in allopatry and now exist in sympatry following secondary contact or whether they evolved in sympatry). Testing these hypotheses with molecular markers, however, can often be challenging if processes such as contemporary gene flow after secondary contact is influencing population structure (Lu et al, 2001;Turgeon and Bernatchez, 2001), or if historical gene flow before isolation contributes to a blurring of population structure (Harris and Taylor, 2010;Harris et al, 2013).…”

Life-history characteristics and landscape attributes as drivers of genetic variation, gene flow, and fine-scale population structure in northern Dolly Varden (Salvelinus malma malma) in Canada

“…If connectivity is not restricted and gene flow between populations is pervasive, then differentiation should be relatively low (Als et al 2011;Harris et al 2013). Furthermore, when absolute barriers to gene flow are absent, and if populations are in a state of migration-drift equilibrium (Hutchison and Templeton 1999), noticeable patterns of isolation-by-distance (IBD; Wright 1943) should be apparent in stream-dwelling and anadromous salmonids (e.g., Koizumi et al 2006a;Primmer et al 2006).…”