Landscape-scale evaluation of genetic structure among barrier-isolated populations of coastal cutthroat trout,Oncorhynchus clarkii clarkii

Abstract

Relationships among landscape structure, stochastic disturbance, and genetic diversity were assessed by examining interactions between watershed-scale environmental factors and genetic diversity of coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) in 27 barrier-isolated watersheds from western Oregon, USA. Headwater populations of coastal cutthroat trout were genetically differentiated (mean FST = 0.33) using data from seven microsatellite loci (2232 individuals), but intrapopulation microsatellite genetic diversity (mean number of alleles per locus = 5, mean He = 0.60) was only moderate. Genetic diversity of coastal cutthroat trout was greater (P = 0.02) in the Coast Range ecoregion (mean alleles = 47) than in the Cascades ecoregion (mean alleles = 30), and differences coincided with indices of regional within-watershed complexity and connectivity. Furthermore, regional patterns of diversity evident from isolation-by-distance plots suggested that retention of within-population genetic diversity in the Coast Range ecoregion is higher than that in the Cascades, where genetic drift is the dominant factor influencing genetic patterns. Thus, it appears that physical landscape features have influenced genetic patterns in these populations isolated from short-term immigration.

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

“…Importantly, knowledge of population connectivity, lifehistory variability, and the degree of natal homing is crucial for understanding the distribution of genetic variation and the evolution of genetic population structure (Taylor et al 2011;Moore et al 2013;Seymour et al 2013). 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.…”

“…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). Alternatively, when barriers that deter or restrict migration exist, notable population structure has been well documented between adjacent and geographically proximate populations separated by these features (e.g., Guy et al 2008;Whiteley et al 2010). These factors may also promote asymmetrical dispersal and gene flow due to the restriction of movement that is facilitated by natural (e.g., waterfalls and cascades) or human-made dispersal barriers (e.g., dams and weirs; Crispo et al 2006;Hänfling and Weetman 2006).…”

Genetic variation and effective population size in isolated populations of coastal cutthroat trout

“…Isolated populations above stream barriers are similar to those on islands, in that they may be threatened by loss of genetic variation and inbreeding (Wang et al 2001;Novinger and Rahel 2003). Genetic effects of stream barriers have been observed to include loss of genetic diversity in and increased genetic differentiation of above-barrier populations (Angers et al 1999;Bouza et al 1999;Carlsson and Nilsson 1999;Costello et al 2003;Taylor et al 2003;Wofford et al 2005;Neville et al 2006;Guy et al 2008). However, important questions remain about fundamental evolutionary processes associated with population isolation in above-barrier populations.…”

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

“…For instance, natural habitat features such as waterfalls Whiteley et al 2010), stream gradient (Cook et al 2011), spawning area size (Dillane et al 2008), lake characteristics (e.g., lake size, perimeter, depth, Caldera and Bolnick 2008;Tamkee et al 2010), river distance/ length (e.g., distance of sampling location from marine habitats, Dionne et al 2008;Perrier et al 2011) and stream order (e.g., Tamkee et al 2010) and complexity (Guy et al 2008) can play important roles in shaping both the distribution of genetic variation and population structure in freshwater fishes. Additionally, evidence for aquatic environmental variables such as temperature (Dionne et al 2008;Leclerc et al 2008) and salinity (McCairns and Bernatchez 2008) that influence population structure are becoming more common.…”