Fatty acid signatures and stomach contents of four sympatricLakeTrout: assessment of trophic patterns among morphotypes inGreatBearLake

Abstract

Sympatric diversification in Lake Trout is generally linked to differences in habitat use (especially depth) as a result of foraging on different prey items. However, extensive sympatric divergence has taken place in the shallow waters (≤30 m) of Great Bear Lake, with multiple Lake Trout morphs varying in head and fin characteristics. To investigate diet partitioning as a potential explanatory mechanism for this diversification, we assessed trophic characteristics and relationships among four sympatric shallow‐water morphs of Lake Trout via analyses of fatty acids and stomach contents. Fatty acids and stomach contents both identified Lake Trout, Cisco and Mysis as key prey items in Lake Trout diets. Interestingly, terrestrial invertebrates were also seasonally important among morphs, reflecting temporal variability of available prey in this arctic lake. Some diet partitioning was observed among morphs; Morph 1 was characterised as a generalist, Morph 3 was more benthic‐oriented, and Morphs 2 and 4 were mainly pelagic feeders. Of the latter, Morph 4 was the most specialised, whereas Morph 2 exhibited alternative feeding tactics of benthic cannibalistic and pelagic piscivorous feeding. Our findings demonstrate that complementary dietary methods can elucidate habits of opportunistic feeders, a task that can often be problematic, given their complex and variable diets. Our results add new information and perspectives on the current model of Lake Trout differentiation, demonstrating niche partitioning based on benthic versus pelagic habitat use and generalist versus specialist feeding tactics.

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

“…The lake is located in Canada's Northwest Territories, on the Arctic Circle, between 65 and 67°N latitude and 118 and 123°W longitude. The lake's limnological and biological characteristics are typical of Arctic freshwater systems, with low productivity and interspecific diversity (Johnson, ), but considerable intraspecific diversity within Lake Trout (Chavarie et al., ; Chavarie, Howland, Harris et al., ; Chavarie, Howland, Venturelli et al., ; Chavarie et al., ) and Cisco ( Coregonus artedi ) (Howland et al., ).…”

“…Morph 1 was characterized by a smaller head and intermediate fins, Morph 2 had the largest head and jaws but smallest fins, Morph 3 had the longest fins and a robust body shape, and Morph 4 had a thick curved lower jaw and the smallest caudal peduncle of the morphs. Based on analyses of fatty acids and stomach contents, Morph 1 was defined as a generalist, Morph 2 had higher proportions of fish in its diet than the other morphs, Morph 3 was a benthic‐oriented generalist, and Morph 4 was regarded as a pelagic specialist (Chavarie et al., ). Adult growth rates, age and size at maturity, and survival rates differed among morphs, consistent with predictions from foraging theory.…”

“…(), Chavarie et al. () : the generalist, the piscivore, the benthic‐oriented, and the pelagic specialist, morphs 1–4, respectively.…”

“…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, , ).…”

Life history differences between fat and lean morphs of lake charr (Salvelinus namaycush) in Great Slave Lake, Northwest Territories, Canada

“…In Great Bear Lake, several morphologically distinct morphs of shallow-water lean lake charr have been described (Blackie et al, 2003;Alfonso, 2004;Chavarie et al, 2013Chavarie et al, , 2014Chavarie et al, , 2015a. In Great Slave Lake, a fat morph occupied mostly deep waters, ate mostly invertebrates, especially opossum shrimp, had a narrow caudal peduncle, light body color, greater buoyancy, and deep anterior body, whereas a sympatric lean morph occupied mostly shallow waters, ate mostly fish, were streamlined in shape, darker in color, and less buoyant (Zimmerman et al, 2006(Zimmerman et al, , 2009.…”