| Summary: | Across Arctic charr’s Holearctic distribution we see repeated patterns where multiple ecotypes diverge along ecological resource gradients. Arctic charr occur in both anadromous and lacustrine forms. Furthermore, lacustrine ecotypes are seen repeatedly specializing their morphology, trophic ecology, and life history along a benthic pelagic axis and along the depth gradient. Typically, a pelagic ecotype cooccurs with a profundal benthivorous ecotype. With increasing intraspecific diversity, a third piscivorous ecotype may also occur. These patterns of ecotype divergence occur in multiple lakes, therefore I studied if ecotypes occur in a random manner or if there is evidence for repeatability in their phenotypes. Life history was studied among five lakes to assess the repeatability of life history traits finding that variation in traits may be related to the number of ecotypes. The next study examined the repeatability and correlations among habitat use, diet, morphology, and life history. As these traits were found to be correlated differently in the ecotypes and at differing levels of intraspecific diversity, I propose the presence of an adaptive trait syndrome in Arctic charr ecotypes. Finally, in the anadromous Arctic charr I developed a method to quantify the number of marine migrations performed by an individual. These estimates of marine experience were discussed in relation to their influence on trophic ecology where there is increasing specialization with successive migrations. We also report an estimate of the number of marine migrations required for maturity in Arctic charr. This work demonstrates the importance of developing new methods and of studying diversity at a multi-trait level to improve our understanding of biodiversity and ability to manage and conserve species in accelerating climate change.
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