Multiple generalist morphs of Lake Trout: Avoiding constraints on the evolution of intraspecific divergence?. Issue 21 (5th October 2016)

• Record Type: Journal Article
• Authors: Chavarie, Louise; Harford, William J.; Howland, Kimberly L.; Fitzsimons, John; Muir, Andrew M.; Krueger, Charles C.; Tonn, William M.
• Is Part Of: Ecology and evolution. Volume 6:Issue 21(2016:Nov.)
• Page Start: 7727
• Page End: 7741
• Publication Date: 2016-10-05
• Subjects: arctic -- mixSIAR -- niche partitioning -- polymorphism; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.2506
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: A generalist strategy, as an adaptation to environmental heterogeneity, is common in Arctic freshwater systems, often accompanied, however, by intraspecific divergence that promotes specialization in niche use. To better understand how resources may be partitioned in a northern system that supports intraspecific diversity of Lake Trout, trophic niches were compared among four shallow‐water morphotypes in Great Bear Lake (N65 ° 56′ 39″, W120 ° 50′ 59″). Bayesian mixing model analyses of stable isotopes of carbon and nitrogen were conducted on adult Lake Trout. Major niche overlap in resource use among four Lake Trout morphotypes was found within littoral and pelagic zones, which raises the question of how such polymorphism can be sustained among opportunistic generalist morphotypes. Covariances of our morphological datasets were tested against δ 13 C and δ 15 N values. Patterns among morphotypes were mainly observed for δ 15 N. This link between ecological and morphological differentiation suggested that selection pressure(s) operate at the trophic level (δ 15 N), independent of habitat, rather than along the habitat‐foraging opportunity axis (δ 13 C). The spatial and temporal variability of resources in Arctic lakes, such as Great Bear Lake, may have favored the presence of multiple generalists showing different degrees of omnivory along a weak benthic–pelagic gradient. Morphs 1–3 had more generalist feeding habits using both benthic and pelagic habitats than Morph 4, which was a top‐predator specialist in the pelagic habitat. Evidence for frequent cannibalism in Great Bear Lake was found across all four morphotypes and may also contribute to polymorphism. We suggest that the multiple generalist morphs described here from Great Bear Lake are a unique expression of diversity due to the presumed constraints on the evolution of generalists and contrast with the development of multiple specialists, the standard response to intraspecific divergence. Abstract : Major overlap in dietary niches among Lake Trout morphotypes were found within littoral and pelagic zones, which raises the question how such polymorphism can be sustained in this opportunistic generalist feeder. The spatial and temporal variability of resources of Arctic lakes, such as Great Bear Lake, may have favored the presence of multiple generalists showing different degrees of omnivory polymorphism along a weak benthic‐pelagic gradient. We suggest that the multifaceted generality detected in Great Bear Lake should be considered as a unique expression of diversity due to the presumed constraints on the evolution of generalists, as multiple specialists is the standard response to intraspecific divergence.