Phylogeny is the study of animals that seeks to reconstruct evolutionary relationships among organisms using morphologic traits, molecular data, DNA gene sequencing (20).To visually represent these relationships, phylogeneticists have developed cladograms or phylogenetic trees like the one below that represent what we think has happened evolutionarily.
Adapted from a lecture at Texas A&M University –Kingsville
This phylogenetic tree shows the relationship between the Families of the Order Carnivora. The Family Ursidae is highlighted in purple to indicate the Family in which polar bears belong.
Genetic information taken form dead bears can give insight into the phylogenic relationship between members of the Ursus genes. Upon her euthanization, Ida’s body was donated to science before being cremated. In 1991, a study by Shields and Kocher analyzed the genetic sequence of an extant polar bear and found that similarities in mtDNA sequences in brown bears and polar bears (18). This discovery sparked the studies of Cronin and his colleagues as they began to use mtDNA sequences to explore the phylogenic relationship between polar bears, black bears, and grizzly bears.
Here is a summation of results by Cronin et al. (19).
1. mtDNA in brown bears of the Archipelago in southeast Alaska is more closely related to the mtDNA of polar bears than it is to other brown bears
2. mtDNA sequences of Archipelago brown bears and polar bears differ by 1%
3. mtDNA sequences of polar bears and other brown bears differ by 2.6%
In his review on polar bears Dr. Amstrup, a leading polar bear researcher, discusses the results of these studies and several others. Reading these unfamiliar terms and gene sequences, it is easy to become overwhelmed by this data; however, in concluding his dissertation he gives these thoughts on the evolution of polar bears:
All DNA evidence, regardless of some areas of uncertainty corroborate conclusions from the fossil record that the polar bear is a recently derived species and is undergoing rapid evolution. The extreme arctic marine environment is undoubtedly exerting strong selection pressures for rapid adaptation (8).
This website was created as a part of a class project in the Animal Physiology Class at Davidson College.
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