EVOLUTIONARY BIOLOGY OF ANADROMOUS, RESIDENT, AND LANDLOCKED ARCTIC CHARR (SALVELINUS ALPINUS) IN LABRADOR, CANADA

Abstract

The breadth of biological forms observed in nature is found in miniature within Arctic Charr (Salvelinus alpinus). This species’ incredible phenotypic variation and distinct morphs makes it highly useful for investigating the genetic sources of morphological differentiation and reproductive isolation. In this thesis I used microsatellite, mtDNA, and SNP data to assess the neutral and adaptive genetic characteristics of Arctic Charr morphs within Labrador, Canada (a region only recently deglaciated ~9000 years ago and subsequently colonized by charr). In addition to populations of anadromous and landlocked morphs, this work found evidence for small resident charr that occur in sympatry with, but are genetically distinguishable from, anadromous charr. Multiple landlocked lakes were also found to harbour genetically distinguishable, size-differentiated, sympatric morphs. Investigation of the charr colonization history of this region using mtDNA revealed the secondary contact and introgression of three charr glacial lineages (Arctic, Atlantic, and Acadian). However, mtDNA did not consistently differ by morph type and the sympatric morphs detected in this region likely evolved following the introgression of these three glacial lineages. While there was generally little evidence of genetic parallelism, a few key SNPs, genes, paralogs, and genomic regions consistently differed between sympatric size-differentiated morphs and between allopatric landlocked and anadromous morphs. Furthermore, some of the loci that differentiated sympatric resident and anadromous morphs also differentiated allopatric landlocked and anadromous populations, suggesting that the loss of anadromy may be genetically predictable. However, a population’s genetic characteristics were not solely a function of morph type but were uniquely dictated by the interactive effects of morph life history, geography, glacial history, and environment. A review of the genetic differences between sympatric morphs in Salmonidae confirmed the interactive influence of glacial history as well as contemporary neutral and adaptive processes on incipient speciation within salmonids. This work reveals that salmonids, and particularly Arctic Charr, are excellent models to uncover speciation mechanisms that are potentially relevant across the tree of life. This work therefore has applications for the conservation of morph diversity and implications for our mechanistic understanding of evolution.