| Summary: | Hybrid zones have been studied extensively over the last two decades, but
relatively little attention has focused on the historical processes generating hybrid zones.
Phylogeography, a subdiscipline of biogeography, evaluates patterns of genetic variation
to infer the processes that have shaped the geographic and demographic histories of
species and can provide insight into the historical contingencies that facilitated
hybridization. Phylogenetic relationships of char (Pisces: Salvelinus) have suggested that
hybridization has been a recurring theme throughout their evolutionary history. In this
thesis, I used sequence variation in the mitochondrial DNA (mtDNA) control region to
perform a hierarchical phylogeographic study that examined intraspecific, interspecific,
and trans-species polymorphisms in Salvelinus. I developed a diagnostic assay that
identifies bull trout (S. confluentus) mtDNA clades and revealed the presence of both
lineages in two coastal watersheds in British Columbia. Headwater stream capture
following the last glaciation is suspected to have facilitated this "double invasion". A
nested clade analysis (NCA) was performed to evaluate if a widespread hybrid zone
between Dolly Varden (S. malma) and bull trout in northwestern North America resulted
from two processes: secondary contact of previously isolated lineages and continuous
contact resulting from historical introgression in a shared refuge. Despite ambiguity in
the statistical parsimony network, NCA provided evidence of secondary contact between
Beringian Dolly Varden and bull trout and introgressed (with bull trout mtDNA) Dolly
Varden. In addition, I found a degree of phylogeographic substructure amongst bull
trout and introgressed Dolly Varden in the Chehalis Refuge, which suggests that
introgression has been geographically localized. In a species-level phylogenetic analysis,
the "approximately-unbiased test" was used to compare alternate tree topologies and I
found that Arctic char lineages were not monophyletic in relation to Beringian Dolly
Varden and bull trout. The consensus parsimony tree and the phylogeographic
distribution of lineages suggested that both bull trout and Dolly Varden may have
experienced historical contact with different Arctic char lineages. I suggest that
hybridization has played a significant evolutionary role in the diversification of char.
This work presents the most extensive phylogeographic analysis of Salvelinus to date and
provides a comparative framework for both small scale and regional studies in
northwestern North America.
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