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

Abstract

Range expansion in north-temperate fishes subsequent to the retreat of the Wisconsinan glaciers has resulted in the rapid colonization of previously unexploited, heterogeneous habitats and, in many situations, secondary contact among conspecific lineages that were once previously isolated. Such ecological opportunity coupled with reduced competition likely promoted morphological and genetic differentiation within and among post-glacial fish populations. Discrete morphological forms existing in sympatry, for example, have now been described in many species, yet few studies have directly assessed the association between morphological and genetic variation. Morphotypes of Lake Trout, Salvelinus namaycush, are found in several large-lake systems including Great Bear Lake (GBL), Northwest Territories, Canada, where several shallow-water forms are known. Here, we assess microsatellite and mitochondrial DNA variation among four morphotypes of Lake Trout from the five distinct arms of GBL, and also from locations outside of this system to evaluate several hypotheses concerning the evolution of morphological variation in this species. Our data indicate that morphotypes of Lake Trout from GBL are genetically differentiated from one another, yet the morphotypes are still genetically more similar to one another compared with populations from outside of this system. Furthermore, our data suggest that Lake Trout colonized GBL following dispersal from a single glacial refugium (the Mississippian) and support an intra-lake model of divergence. Overall, our study provides insights into the origins of morphological and genetic variation in post-glacial populations of fishes and provides benchmarks important for monitoring Lake Trout biodiversity in a region thought to be disproportionately susceptible to impacts from climate change.

Multiple generalist morphs of Lake Trout: Avoiding constraints on the evolution of intraspecific divergence?

“…Reduced somatic growth and higher reproductive investment were found in the generalist morph (Morph 1), high growth rates throughout life characterized the piscivorous morph (Morph 2), and intermediate life histories defined the more benthic‐ and pelagic‐oriented morphs (Morph 3 and Morph 4) (Chavarie, Howland, Venturelli et al., ). Finally, the four morphotypes showed some genetic differentiation from one another, especially Morph 2 when compared to the three other morphs (Harris et al., ). However, morphotypes were genetically more similar to one another when compared with populations from outside Great Bear Lake, supporting an intralake model of divergence (Harris et al., ) (Table ).…”

“…Finally, the four morphotypes showed some genetic differentiation from one another, especially Morph 2 when compared to the three other morphs (Harris et al., ). However, morphotypes were genetically more similar to one another when compared with populations from outside Great Bear Lake, supporting an intralake model of divergence (Harris et al., ) (Table ).…”

“…Overlap and seasonality of diets, and similarity in habitat use among the four morphs led us to question the degree to which trophic and habitat partitioning has driven this divergence (Chavarie et al., ). Although these Lake Trout are at a young stage of differentiation (i.e., <2,000 years; Harris et al., ), the lack of major differences in habitat and diet was unexpected because sympatric differentiation is typically linked to easily identifiable resource‐based segregation (Skúlason, Snorrason, & Jonsson, ; West‐Eberhard, , ).…”

Genomic tools for new insights to variation, adaptation, and evolution in the salmonid fishes: a perspective for charr

“…Wilson et al, 2004;Adams et al, 2007a;Gomez-Uchida et al, 2008;Corrigan et al, 2011;Kapralova et al, 2011;Garduño-Paz et al, 2012;May-McNally et al, 2014;Gordeeva et al, 2015) and in lake charr (e.g. Guinand et al, 2012;Harris et al, 2015). Morphs of Arctic charr also differ significantly in functional loci such as immunological genes (Kapralova et al, 2013;Conejeros et al, 2014).…”

Habitat overlap of juvenile and adult lake trout of Great Bear Lake: Evidence for lack of a predation gradient?

“…Variation at 23 microsatellite loci was assessed as previously described by Harris et al (2015). Variation at 23 microsatellite loci was assessed as previously described by Harris et al (2015).…”