| Summary: | Biodiversity within species is influenced by both adaptation and acclimatization in order to exploit a range of environments. Taxa within the genus Salvelinus are considered some of the most diverse vertebrate species on earth particularly Arctic char, Salvelinus alpinus, and lake trout, Salvelinus namaycush, due to various morphotypes, ecotypes, and life history strategies documented. The goal of this thesis was to describe factors influencing the formation and maintenance of biodiversity within species, using lake trout within the brackish waters of Husky Lakes, NT. To accomplish the goal I 1) determined life history types present within the Husky Lakes drainage basin (HLDB); 2) assessed how differences in rearing environment influenced physiology; 3) assessed differences in growth rates and longevity among life history types; and 4) assessed genetic structure among life history types and sampling locations. My data indicate that three life history types are present within the HLDB, freshwater resident, semi-anadromous, and brackish-water resident, suggesting two discrete early rearing environments are used (fresh and brackish water). Assessment of rearing in fresh (0 psu) or brackish water (5 psu) indicates that lake trout reared in brackish water out performed those raised in fresh water when transferred to 20 psu salt water. Additionally, brackish-water residents grew faster and lived longer than did semi-anadromous and freshwater resident lake trout in the HLDB. Also, brackish-water residents were genetically differentiated from sympatric semi-anadromous life history types suggesting segregation in spawning habitat. These findings are the first documentation of a brackish-water resident life history type within lake trout and one of only a few within salmonids. This novel life history type appears to be influenced by both phenotypic plasticity and local adaptation to brackish-water environments allowing for faster growth rates, increased longevity, and a larger abundance in Husky Lakes. Within this thesis ...
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