Evolutionary Relationship and hybridization of brown bears and polar bears

Topics: Bear, Polar bear, Ursus Pages: 4 (1163 words) Published: December 3, 2013


The distinct evolutionary relationship and hybridization of brown bears (Ursus arctos) and polar bears (Ursus maritimus).

Fast morphological evolution has been seen over the years throughout mammals of the earth, as it is an important driver of specialization and speciation. Ursus, is the genus in the family of Ursidae (bears) that includes polar bears (Ursus arctos), black bears (Ursus americanus), and brown bears (Ursus maritimus). The polar bear and brown bear specifically are closely related. In fact, there are estimates that polar bears branched off from brown bears during the mid to late Pleistocene, becoming isolated on Siberian costal enclaves, an Arctic sea ice environment. (C. Lindqvist et al. 2010) For this reason it is ironic that the two species have successfully been able to produce hybrids not only with human influences, but also within the wild. This paper will describe proof of the distinct evolutionary lineage and recent hybridizations of polar bears and brown bears.

The polar bear is the only ursid that seems to be a uniquely adapted high-arctic specialist. (Hailer et al. 2012) They roam the Arctic ice sheets, swim in coastal regions and have a fully carnivorous diet of seal flesh and blubber. Molecular and paleontological data indicate that the polar bear evolved less than a million years ago from a distinct other ursid, the brown bear. A brown bear has a complete omnivorous diet. (Slater et al. 2010) This is because they live in a completely different geographical region than polar bears. Brown bears can be found throughout mountains and forests of the Holarctic and in the Tundra. (PreuB et al. 2009) G. Slater et al. (2010) looked at dietary specializations using phylogenetic tests to estimate the rate that morphological specialization occurred in polar bears. It was observed that very fast evolution of semi-aquatic adaptations and dietary specialization produced cranial morphology that is...

Bibliography: C. Lindvist et al. (2010). Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear. PNAS. Vol. 107. 11
F. Hailer et al. (2012). Nuclear Genomic Sequences Reveal that Polar Bears are an Old and Distinct Bear Lineage. Science. Vol 336. 344-347
A. PreuB, U. GansloBer, G. Purschke, U. Magiera. (2009). Bear-hybrids: behaviour and phenotype. Zool. Garten N.F 78. 204-220.
G. Slater et al. (2010). Biomechanical Consequences of Rapid Evolution in the Polar Bear Lineage. PLoS ONE. Vol. 5. 11. 1-6
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