Is isolation by adaptation driving genetic divergence among proximate Dolly Varden char populations?

Abstract

Numerous studies of population genetics in salmonids and other anadromous fishes have revealed that population structure is generally organized into geographic hierarchies (isolation by distance), but significant structure can exist in proximate populations due to varying selective pressures (isolation by adaptation). In Chignik Lakes, Alaska, anadromous Dolly Varden char (Salvelinus malma) spawn in nearly all accessible streams throughout the watershed, including those draining directly to an estuary, Chignik Lagoon, into larger rivers, and into lakes. Collections of Dolly Varden fry from 13 streams throughout the system revealed low levels of population structure among streams emptying into freshwater. However, much stronger genetic differentiation was detected between streams emptying into freshwater and streams flowing directly into estuarine environments. This fine-scale reproductive isolation without any physical barriers to migration is likely driven by differences in selection pressures across freshwater and estuarine environments. Estuary tributaries had fewer larger, older juveniles, suggesting an alternative life history of smolting and migration to the marine environment at a much smaller size than occurs in the other populations. Therefore, genetic data were consistent with a scenario where isolation by adaptation occurs between populations of Dolly Varden in the study system, and ecological data suggest that this isolation may partially be a result of a novel Dolly Varden life history of seawater tolerance at a smaller size than previously recognized.

Phylogeography of a salmonid fish, masu salmon Oncorhynchus masou subspecies‐complex, with disjunct distributions across the temperate northern Pacific

“…Isolation‐by‐distance population genetic structure was found in the O. m. masou populations, as has frequently been found in other anadromous salmonids (e.g. Bond, Crane, Larson, & Quinn, ; Hansen, Fraser, Meier, & Mensberg, ; Yamamoto, Morita, & Sahashi, ). Most O. m. masou populations exhibit a diverse array of migration strategies, and include migrant and non‐migrant individuals within populations.…”

Water level influences migratory patterns of anadromous brown trout in small streams

“…In addition, a part of the reported strays may just spend time in foreign watercourses, to feed or avoid adverse environmental conditions (King, Hillman, Elsmere, Stockley, & Stevens, 2016). This parallels the isolation-by-distance effect reported from salmonid studies elsewhere (Bond, Crane, Larson, & Quinn, 2014;Campos, Posada, Caballero, & Moran, 2007;Hansen & Mensberg, 1998). This parallels the isolation-by-distance effect reported from salmonid studies elsewhere (Bond, Crane, Larson, & Quinn, 2014;Campos, Posada, Caballero, & Moran, 2007;Hansen & Mensberg, 1998).…”

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

“…The lack of gene flow (in at least the upstream direction) as well as the general decline in stream and habitat size and likely smaller effective population sizes in above-waterfall populations has probably contributed to increased divergence between proximate isolated and nonisolated populations (Whiteley et al 2010). Furthermore, natural selection acting in divergent directions, as a result of unique selective pressures operating in different environments (if above-and below-waterfall habitats differ substantially), may also be contributing to the elevated degree of divergence (Langerhans et al 2007;Bond et al 2014).…”

“…Given the marked variation in its life history, demography, and habitats (e.g., COSEWIC 2010; Mochnacz et al 2010), northern Dolly Varden of Canada's western Arctic provide an excellent opportunity to assess the influences of these factors on population genetic variation and structure. While work in southern areas has implicated the effects of population history (e.g., impacts of glaciation; Taylor et al 2001;Redenbach and Taylor 2002), contemporary landscape features (Koizumi et al 2006a), demography, (Koizumi et al 2006b, and natural selection (Bond et al 2014) on population genetic variation and structure in Dolly Varden, comparatively less work has been conducted in Canada's western Arctic populations. Northern Dolly Varden in Canada has been assessed as "Special Concern" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (COSEWIC 2010;Cook et al 2013).…”