Population fragmentation and subsequent isolation in different refugia during
the glacial advances of the Pleistocene are believed to have had a significant impact
on current levels of genetic and morphological diversity. Despite the importance of
these glacial refugia for biodiversity, our understanding of their distribution on the
northwestern coast of North America and their relative impact on populations
remains limited.
As the most isolated group of islands in the Pacific Northwest, Haida Gwaii
has been the subject of intense study both from the perspective of its complex
glacial history and endemic flora and fauna. The ubiquitous presence of glacial
features on this archipelago points to extensive ice cover during the late Wisconsin
(Fraser glaciation) and populations which could only have become established
postglacially. However, the large assemblage of unique mammalian and avian fauna
found on Haida Gwaii has led to suggestions that these divergent vertebrates
actually evolved through long isolation by continuously inhabiting these islands or
nearby regions throughout the last glacial maximum.
To assess Haida Gwaii’s role as a glacial refugium and the relictual status of
its endemic black bear (Ursus americanus), marten (Martes americana), short-tailed
weasel (Mustela erminea), caribou (Rangifer tarandus) and Saw-whet Owl
(Aegolius acadicus), a broad phylogeographic study using sequence comparisons of
the mitochondrial gene cytochrome b was undertaken. Phylogeographic structure
was observed in the black bear (n= 33), marten (n= 18) and short-tailed weasel (n=
32).
Based on parsimony, maximum likelihood, and neighbour-joining analyses of
719 bp of cytochrome b, two geographically structured black bear lineages were unambiguously identified: 1) a continental lineage found in the Yukon, Alberta,
Alaska, Montana and Pennsylvania (americanus) and mainland BC (americanus
and cinnamomum) and 2) a coastal lineage found on Haida Gwaii (carlottae),
Vancouver Island (vancouveri) and the Olympic Peninsula (altifrontalis). The two
lineages were defined by 24 synapomorphies and an average sequence divergence of
3.6%. Average intralineage divergence was 0.1%. Similarly, two geographically
structured lineages, continental and coastal, were also identified in marten using the
same types of analyses on 3II bp of cytochrome b. The continental lineage
included marten from mainland BC (caurina and abietinoides) and Newfoundland
(atrata) whereas the coastal lineage included marten from Haida Gwaii (nesophila)
and Vancouver Island (vancouverensis). The two lineages were defined by three
synapomorphies and an average sequence divergence of 1.2%. Average intralineage
divergence was 1%. Phylogeographic structure was also observed in the short-tailed
weasel using 148 to 673 bp of cytochrome b. Three major lineages were
identified and named according to their putative refugial source areas: Beringia,
which included weasels from Japan (orientalis) and the Yukon (arctica), a
continental or southern source, which encompassed weasels from mainland BC
(richardsonii, invicta,fallenda), Manitoba (bangsi), and Ontario (cicognanii), and Haida Gwaii which included only those weasels from Haida Gwaii (haidarum).
Short-tailed weasels from Vancouver Island (anguinae) and some areas along the
coast demonstrated an affinity to both southern and Haida Gwaii weasels. Relative
to the continental lineage, the coastal lineage was defined by 13 synapomorphies;
the Beringian lineage was defined by 10 synapomorphies. Average sequence
divergence was 2.5 % and 2.2% respectively. Divergence between the coastal
weasels and Beringian weasels was 2.4%. There was little mtDNA diversity within
the coastal lineage as the average intralineage divergence was 0.8%.
Little or no phylogeographic structure was observed in the caribou and Saw-whet
Owl. Of the 313 bp examined in two barren ground caribou (granti) and seven woodland caribou (four tarandus and three dawsoni), three tarandus and two
dawsoni formed a lineage defined by one synapomorphy. The two barren ground,
one tarandus, and one dawsoni were excluded from this lineage by one to three
substitutions. Similarly, little phylogeographic structure was observed in the Saw-whet
Owl. Analyses of a 241 bp of cytochrome b sequenced from this species
indicated no genetic divergence between individuals as far apart as Haida Gwaii
(brooksi) and Manitoba (acadicus). The maximum divergence observed between
individuals was 0.4%.
The phylogeographic patterns from these five species have two major
implications with regard to the issue of glacial refugia and the relictual status of the
Haida Gwaii endemics: 1) With the possible exception of haidarum, the suite of
morphological features characterizing the endemics carlottae, nesophila, dawsoni
and brooksi appear to have been derived postglacially. In fact close genetic affinity
of these endemic subspecies with adjacent conspecifics suggest that population
fragmentation caused by glaciers has had little effect on morphological
differentiation and that adaptation to local ecological environments has played a
more influential role in their evolution. 2) Emerging data of a mid-Pleistocene split
of many vertebrate taxa and the geographic distribution of these various generic
lineages, including the black bear, marten and short-tailed weasel in this region
cumulatively suggests that a refugium existed on the continental shelf off the central
coast of British Columbia and was possibly part of a larger (or series of refugia)
refugium which extended further north and south along this coast. Given the broad
assemblage of taxa which might have persisted here during the last glaciation, this
refugium was probably ecologically productive and as such, was likely to have been
an important alternate source area for the postglacial recolonizarion of northwestern
North America. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/8707 |
| Date | 23 October 2017 |
| Creators | Byun, Soyong Ashley |
| Contributors | Reimchen, T. E., Koop, Benjamin F. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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