Contrasting phenotypic variation among river and lake caught cisco from Great Slave Lake: Evidence for dwarf and large morphs

Coregonids are among a wide array of northern freshwater fishes that have received attention in evolutionary studies as they show phenotypic and life history variation. This intraspecific divergence is commonly manifested as dwarf and large morphs. We assessed and contrasted cisco (Coregonus artedi) in the Great Slave Lake (Northwest Territories, Canada) basin from adfluvial versus lacustrine life histories. Using conventional geometric and linear morphometric methods in conjunction with other phenotypic and life history attributes, we tested the hypothesis that the cisco in the two different environments constituted a dwarf and large species pair. River populations were sampled and compared to lacustrine from Great Slave Lake. Cluster analysis provided the strongest evidence for two phenotypic groups and these two clusters generally characterized lake and river caught cisco based on assignment success from multivariate analyses. The river form was smaller, had a more fusiform body shape, anteriorly positioned paired fins. Larger cisco showed smaller gill rakers spacing indicating that this morph may be feeding at a lower trophic level. Comparisons within river spawning groups showed that the same life history type was present in multiple rivers suggesting that human exploitation was not driving the observed life history. This study provides preliminary evidence that C. artedi exists as a species pair in Great Slave Lake. Moreover, this study adds to a growing wealth of research suggesting that the level of coregonine diversity in Great Slave Lake may rival that of the Laurentian Great Lakes prior to stock collapses. Crown Copyright (C) 2012 Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. All rights reserved.