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Biodiversity of Arctic char (Salvelinus alpinus) : sympatric morphs and hybridization with Dolly Varden (S. malma) in southwestern Alaska

University of British Columbia

Resource polymorphism and natural hybridization are evolutionary phenomena that play an important role in the development of reproductive isolation during speciation. The Arctic char (Salmonidae: Salvelinus alpinus) exhibits substantial phenotypic and genetic diversity across its Holarctic range, making it an ideal species to examine the role of intraspecific trophic polymorphism in driving reproductive isolation and the interactions between hybridizing species in sympatry. In one southwestern post-glacial lake previously analyzed for resource polymorphism (Lower Tazimina Lake), I found evidence for two genetic groups of char and for significant differences in the distribution of microsatellite variability among at least two of the three previously described body-size morphotypes (‘large’, ‘medium’, and ‘small’–bodied char; maximum FST = 0.09). I also found significant associations between genetic type and gill raker counts among body-size morphs (r = -0.73, P < 0.001). These data represent the first record of genetically distinct sympatric Arctic char morphs in Alaska and provides further evidence that morphological differences associated with feeding and growth trajectories reflect niche diversification and may promote genetic divergence. Furthermore, I evaluated the level of natural hybridization and ecological segregation between two sympatric sister species of char, Arctic char and Dolly Varden (Salvelinus malma), from two southwestern Alaskan lakes. A total of N = 725 char were collected from 44 microhabitats across two lakes (Lake Aleknagik and Lake Nerka) and genotyped at 13 microsatellite loci. Using genetic admixture (Q)-values generated through Bayesian-based clustering, hybridization levels between Arctic char and Dolly Varden were found to be minimal; less than 0.5% of samples were classified as hybrids. Concurrent analyses with NEWHYBRIDS, however, supported the presence of late-generation hybrids in Lake Aleknagik with up to 7% of all samples representing F₂ hybrids or backcrossed Dolly Varden. The existence of two discrete gene pools in sympatry (FST= 0.172–0.187 across the two lakes) which were generally spatially separate and low levels of contemporary hybridization between Arctic char and Dolly Varden helps to solidify their taxonomic status as distinct biological species. Moreover, high levels of reproductive isolation between these sympatric species may be driven largely by strong pre-mating spatial segregation.

Text

2014-10-23

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50852

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/