| Summary: | dissertation An empirical molecular approach was used to: (1) determine the phylogenetic relationships and dates of divergence for the eight members of the bear family, Ursidae; (2) determine if the phylogenetic relationships within the brown bear correlate with geographic location and/or morphological differentiation; and (3) determine if endangered brown bear populations in the lower 48 states have lower levels of genetic diversity than nonendangered brown bear populations in Alaska and Canada. Paleontological and molecular data have been used to reconstruct the phylogenetic relationships within the Ursidae, but these analyses have produced conflicting results. To resolve these controversies, DNA sequence data were collected from six mitochondrial DNA (mtDNA) regions for all eight bear species, and weighted phylogenetic analyses were performed using the combined data set of 1,916 nucleotides. Our results support the hypothesis that the giant panda was the first species to diverge from the ancestral bear lineage followed by the spectacled bear. The six remaining species diverged sequentially over four and half million years with the polar bear species emerging from within a group of brown bear lineages during the mid-Pleistocene. To more thoroughly examine the evolutionary relationships of brown bears and polar bears, mtDNA sequence data were generated for 438 brown bears and four polar bears collected from across their geographic ranges. Phylogenetic analysis of this comprehensive data set: (a) revealed five major genetic groups of brown bears; (b) confirmed the divergence of the polar bear lineage from within the brown bear clade; (c) suggested no direct correlation between mtDNA differentiation and morphological differentiation, and (d) identified genetic groups with and without phylogeographic structuring. MtDNA sequence analysis and nuclear microsatellite analysis were used to measure genetic diversity in two endangered and three nonendangered North American brown bear populations. The two endangered populations had lower levels of genetic diversity than the most diverse population, but the differences were not statistically significant. However, the nonendangered Kodiak Island population had significantly lower levels of diversity than the most diverse population. Results from these studies were used to make recommendations for the conservation and management of bear populations.
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