| Summary: | Knowledge of genetic diversity and population structure is of fundamental
importance in the development of gene conservation sampling strategies to capture
and preserve allelic diversity. Such knowledge is critical if we are to understand how
to manage and maintain diversity in species and populations. To assess the effects
of sampling strategy on capture of allelic diversity in widespread species, I studied
Sitka spruce (Picea sitchensis (Bong.) Carr) populations as a model. Sitka spruce is
a conifer that occupies wide geographic and ecological niches from 33° N to 60° N
latitude along the Pacific coast of North America. A total of 1600 individual trees
were sampled in eight populations classified as core or peripheral based on
ecological niche, and continuous or disjunct based on distribution. In each
population, 200 trees were spatially mapped and genotyped for eight cDNA-based
sequence-tagged-site (STS) co-dominant markers. One important finding of this
study is the similarity in genetic diversity as measured by expected heterozygosity
between core populations (mean HE = 0.58) and peripheral populations (mean HE =
0.56). Another remarkable result found by this study is strong spatial structure as
evidenced by coancestry in peripheral populations, both continuous and disjunct, but
not in core populations. For example, trees located within 50 metres of each other in
peripheral, disjunct populations had coancestry values greater than 0.20 while in
core populations, trees within the same distance class had coancestry values below
0.06. Differences in population structure were attributed to an aggregation of similar
multi-locus genotypes, in a structured, isolation by distance manner in peripheral
populations, both continuous and peripheral but not in core, continuous populations.
Irrespective of population classification, over 75% of the alleles were common and
widespread. Only one allele, representing two percent of all alleles was classified as
rare and localized on average, and this allele was limited to one core, disjunct and
two peripheral, disjunct populations. To capture localized alleles (both common and
rare), sampling should cover more populations over the geographic and ecological
range of species at a cost of fewer individuals per population. The conservation of
peripheral populations may present the best opportunity for preserving rare alleles. === Forestry, Faculty of === Graduate
|
|---|
