Landscape Structure and Hierarchical Genetic Diversity in the Brook Charr, Salvelinus Fontinalis

Abstract

Explaining the extent, causes, and consequences of biotic distributions in space is fundamental to our understanding of how species evolve and cope with particular environments. Yet, identifying extrinsic barriers to migration imposed by landscape structure and predicting their impacts on intraspecific genetic diversity remains a major challenge in population biology. In this study, 30 populations (771 individuals) of brook charr (Salvelinus fontinalis, Salmonidae) representing six major river drainages from Maine, USA, were characterized at six microsatellite loci to quantify the role of landscape features, such as habitat size, altitude, contemporary and historical connectivity, in shaping genetic diversity at three spatial scales: within lakes, within river drainages, and among river drainages. Within-population expected heterozygosity was negatively correlated with altitude, whereas no significant correlation was observed with lake size. Conversely, the extent of heterozygote deficiency within lakes was negatively associated with habitat size. The hierarchical analysis of genetic variance revealed that the extent of among-drainage differentiation was unexpectedly low relative to the pronounced population structuring within drainage. Geographically proximate St. John and Penobscot River drainages were characterized by opposite effects of altitude and geographic distance in shaping the pattern of population differentiation within drainages. The geographic pattern of differentiation among drainages could not be accounted for either by an isolation by distance or by a stepwise range expansion model. Overall, this study provided evidence for the role of contemporary landscape features in shaping the observed pattern of genetic diversity at smaller geographic scales (within and among populations within river drainage). On a broader geographic scale, contemporary landscape structure appeared to be only a minor factor determining the observed pattern of genetic structuring among drainages. These results add to the increasing evidence for nonequilibrium conditions between drift and migration in a wide array of animal taxa. The development of more realistic theoretical descriptions of nonequilibrium population structure thus appears to be important to better understand the relative influence of historical and ecological factors in shaping genetic variation in young habitats, such as recently deglaciated areas.

Microsatellite genetic differentiation among populations of the Trinidadian guppy

“…For example, upstream populations tended to have less genetic variability than the corresponding downstream population (Table 1). This pattern is consistent with studies in other fishes, including mosquitofish, Gambusia holbrooki (Hernandez-Martich and Smith, 1990); brown trout, Salmo trutta (Hamilton et al, 1989) and brook charr, Salvelinus fontinalis (Castric et al, 2001). The pattern probably reflects more pronounced founder effects and smaller population sizes associated with upstream populations as well as lower immigration due to unidirectional downstream gene flow (Shaw et al, , 1994Crispo et al, 2006).…”

“…The first involves topographical features including water connectivity and barriers that can affect contemporary dispersal (Castric et al, 2001;Crispo et al, 2006;Caldera and Bolnick, 2008). The second involves adaptive divergence under variable selection pressures whereby dispersers or hybrids tend to have lower fitness than residents and gene flow between ecological environments can thus be impeded (Lu and Bernatchez, 1999;Ogden and Thorpe, 2002;Rundle, 2002;reviewed by Schluter, 2000;Hendry, 2004).…”

The Maintenance of Genetic Variation Due to Asymmetric Gene Flow in Dendritic Metapopulations

“…Previous research using this experimental design found predictable patterns of genetic variation of fish and invertebrate species in watersheds on the basis of their ability to ascend stream gradients and migrate over long distances (Monaghan et al 2002;Whiteley et al 2004;de Kerckhove 2005). Another promising approach would be the study of the same organism in different landscape arrangements (e.g., Castric et al 2001). …”

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)

“…Furthermore, although suitable Arctic char habitat has not been quantified directly in both systems, Roux et al (2011b) suggest that Brock Lake has low productivity and relatively limited fish habitat potential primarily because of its small size (2.5 km ). This situation has implications for Arctic char carrying capacity, and several studies have documented associations between habitat size and population size (Frankham, 1996;Hänfling and Brandl, 1998;Castric et al, 2001). Although abundance estimates are not available for the Brock system, Roux et al (2011b) suggested, on the basis of low catch-per-unit-effort (CPUE), that the population is likely very small.…”