Humans and bears - Wild encounters

[brotherbear]

http://wildpro.twycrosszoo.org/000ADOBES/Bears/Bears_IUCN_ActionPlan/bearsAP_chapter3.pdf 

When addressing the question of the hierarchial
relationships of all members within the bear family,
molecular analyses agree that the giant panda is the oldest
bear species followed by the spectacled bear (Nash and
O’Brien 1987; Wayne et al. 1989; Goldman et al. 1989;
Zhang and Ryder 1993, 1994; Talbot and Shields in press
b; Waits 1996). Thus far, the use of cytological (Nash and
O’Brien 1987), immunological, DNA hybridization, and
isozyme data (O’Brien et al. 1985; Goldman et al. 1987;
Wayne et al. 1989) to reconstruct the hierarchical
phylogenetic relationships of the six remaining bears (ursine
bears) has produced inconclusive results with the exception
of support for a close grouping of the brown bear and the
polar bear. MtDNA sequence analyses (Zhang and Ryder
1993, 1994; Shields and Talbot in press; Waits 1996) have
improved the resolution of the branching order of the
ursine bears, but ambiguities still remain. The mtDNA
gene trees have suggested that the sloth bear lineage was
the first ursine bear lineage to emerge (Zhang and Ryder
1994; Waits 1996; Shields and Talbot in press). The
branching order of the remaining species is unclear. The
first mtDNA study suggested that the American black
bear and the sun bear lineages diverged as sister taxa after
the sloth bear lineage and before the Asiatic black bear
lineage (Zhang and Ryder 1994). In a second study (Waits
1996), the branching order of the American black bear,
sun bear, and Asiatic black bear lineages could not be
statistically resolved (95% confidence interval) suggesting
that these three species underwent a rapid radiation event.
The third study (Talbot and Shields in press) suggested
that the American black bear and Asiatic black bear

diverged as sister taxa after the sloth bear lineage and
before the sun bear lineage.
At approximately the same time as the divergence of
the American black bear, Asiatic black bear, and sun bear
lineages, an ancestral lineage diverged that led to brown
bear and polar bear lineages. The polar bear lineage
emerged from within a cluster of brown bear lineages
(Cronin et al. 1991b; Zhang and Ryder 1994; Waits 1996;
Talbot and Shields in press a, b) as a sister group to brown
bears from the Alaska islands of Admiralty, Baranof, and
Chicagof (ABC islands). In contrast, results from a separate
mtDNA sequence analysis (Zhang and Ryder 1993)
suggested that the polar bear lineage was an ancient
lineage that grouped with the spectacled bear lineage. In a
more extensive analysis, Zhang and Ryder (1994) revealed
that three polar bear lineages grouped with the brown bear
and one polar bear lineage grouped with the spectacled
bear. The authors suggest that the polar bear/brown bear
grouping more accurately represents the true phylogeny
of the polar bear. However, they also propose a recent
hybridization event to account for the polar bear/spectacled
bear relationship and suggest that future studies include
additional polar bear samples.
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