Geographic influences on fine-scale, hierarchical population structure in northern Canadian populations of anadromous Arctic Char (Salvelinus alpinus)

Abstract

Assessments of fine-scale population structure in natural populations are important for understanding aspects of ecology, life history variation and evolutionary history and can provide novel insights into resource management. Although Arctic char, Salvelinus alpinus, represent one of the most culturally and commercially important salmonids in the Canadian Arctic, fine-scale assessments of genetic structure in northern populations of this species are rare. In this study, we assessed population structure in anadromous Arctic char from Cumberland Sound in Canada's Nunavut territory using 18 microsatellite loci. Specifically, we aimed at identifying potential habitat and landscape/geographic features influencing genetic variation and population structure and resolving potential barriers to gene flow. Overall population structure was moderate (global F ST and Jost's D of 0.042 and 0.236 respectively) and significant among all sampling locations. Habitat and landscape/geographic features, with the exception of fluvial (shoreline) distance, appeared to have little influence on genetic variation and population structure. Bayesian clustering revealed a hierarchical model of population structure, in which the 14 sampling locations were nested within two distinct clusters corresponding to the north and south shores of Cumberland Sound. Both isolation-by-distance analysis and calculations of mean dispersal distance suggest dispersal and gene flow is highest among proximate locations. Finally, several putative barriers to gene flow were identified and one, a putative barrier separating north and south Cumberland Sound, was consistent with the hierarchical STRUC-TURE results. Our results suggest that the current river-specific management of commercially harvested Arctic char is appropriate. Overall, we provide further insights into the evolution of genetic variation and population structure in iteroparous, Arctic salmonids.

Genetic Stock Identification and Relative Contribution of Arctic Char (<i>Salvelinus alpinus</i>) from the Hornaday and Brock Rivers to Subsistence Fisheries in Darnley Bay, Northwest Territories + Supplementary Appendix Tables S1 to S4 (See Article Tools)

“…Our study represents the first assessment of genetic stock structure in Arctic char from the Darnley Bay region of the Northwest Territories, focusing on the two river systems contributing to an important fishery for the community of Paulatuk. Overall, this study revealed significant genetic structure between the baseline sampling locations assessed, similar to that which has been reported in other areas of the Canadian Arctic (Moore et al, 2013;Harris et al, 2014). We did, however, find elevated levels of genetic divergence that were greater than expected on the basis of geographic distance alone (e.g., the ~6 km fluvial distance between the LAKE-A and LAKE-B samples), which suggests the existence of differing life history variants (e.g., landlocked or freshwater-resident) of Arctic char in the Hornaday River system, as discussed below.…”

“…For example, values of F ST between our LAKE-A or LAKE-B samples and known anadromous samples ranged from 0.141 to 0.204, which is magnitudes higher than values in comparisons between known anadromous samples used in this study and in other anadromous stocks of Arctic char from other regions in the Canadian North (Moore et al, 2013;Harris et al, 2014, in press). For example, pairwise estimates of F ST among samples of anadromous Arctic char from Cumberland Sound averaged ~0.02-0.04 (Moore et al, 2013;Harris et al, 2014) and in the Cambridge Bay region of Nunavut, estimates were even lower (~0.01-0.02, Harris et al, in press). Additionally Bayesian clustering and DAPC analyses clearly highlight the divergence of the LAKE-A and LAKE-B samples from known anadromous or coastal samples.…”

“…Electro-fishing was not practical on the main stem of the Hornaday River given the size and depth of the river and the gradient of the banks. Juvenile char were targeted because they are highly unlikely to be strays, as might be expected from anadromous adults (Moore et al, 2013;Harris et al, 2014). When possible, we collected juveniles from multiple locations within the lake or from streams.…”

“…The results indicate that future management could be designed around the small-scale genetic differences among baseline stocks at the scale of the river system (i.e., Hornaday and Brock Rivers). A similar management technique for Arctic char has been proposed in Cumberland Sound (see Harris et al, 2014). Moreover, Dempson and Kristofferson (1987) have proposed the idea of "local stock complexes," which recognizes that a fishery may be harvesting fish from a number of river systems.…”

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

“…Within and among populations of freshwater and anadromous salmonids (salmon, trout, char, and their relatives), for example, the hydrology of aquatic habitats can impact the movement of individuals and thus dispersal and subsequent gene flow (Guy et al 2008;Whiteley et al 2010). Hydrological features such as stream connectivity and complexity (Taylor et al 2011, physical barriers to dispersal (Hänfling and Weetman 2006;Gomez-Uchida et al 2009), and the physical distance between occupied habitats (Koizumi et al 2006a;Harris et al 2014) have all been shown to impact biological connectivity.…”