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The Arctic char ( Salvelinus alpinus) species 'complex' has fascinated biologists for decades particularly with respect to how many species there are and their geographic distributions. I review recent research on the species complex, focussing on biodiversity within northwestern North America, which indicates (i) what was once considered a single taxon consists of three taxa: S. alpinus (Arctic char), S. malma (Dolly Varden), and S. confluentus (bull trout), (ii) morphological and genetic data indicate that S. alpinus and S. malma, and S. malma and S. confluentus exist as distinct biological species in sympatry, (iii) sympatric forms of S. alpinus exist in Alaska as in other areas of the Holarctic, (iv) Dolly Varden comprises two well-differentiated subspecies, S. m. malma and S. m. lordi, in the eastern Pacific and the northwestern Canadian Arctic that meet at a contact zone on the southern edge of the Alaska Peninsula, and (v) Dolly Varden and bull trout consist of several population assemblages that have legal status as distinct conservation units under US and Canadian law. This research has significantly revised what constitutes the S. alpinus species 'complex', provided insights into the ecology and genetics of co-existence, and promoted conservation assessment that better represents biodiversity within Salvelinus. A geographically and genetically comprehensive analysis of relationships among putative taxa of Pan-Pacific Salvelinus is still required to better quantify the number of taxa and their origins. [ABSTRACT FROM AUTHOR]

Biological data from 66 populations of Arctic charr, Salvelinus alpinus, from eastern North America were analysed to test the applicability of the countergradient hypothesis as an explanation of differences in seasonally adjusted growth rates. Samples were obtained along a 37° latitudinal gradient and partitioned among anadromous, normal lacustrine, and dwarf lacustrine Arctic charr morphotypes. Models relating length-at-age or age-specific growth rates to latitude were estimated for each morphotype. Length-at-age declined with latitude for anadromous and lacustrine charr. Age-specific growth rates also varied with latitude, particularly for normal lacustrine charr. Results of analyses provide support for the countergradient hypothesis in growth performance of normal lacustrine morphotypes, where northern populations compensate for the shorter growth season with a greater rate of growth than southern populations. Anadromous charr exhibited equivocal evidence of countergradient variation, while results for dwarf lacustrine Arctic charr populations were inconclusive owing to the limited range of ages, and latitudes for which data were available. [ABSTRACT FROM AUTHOR]