Southeastern's Grizzled Pioneers
The mail held an oversized envelope with a return address showing it was from Dr. Gerald F. Shields, Institute of Arctic Biology, University of Alaska Fairbanks. From my viewpoint, the envelope held good news: the results of Shields' studies in genetic analysis are once again upsetting the standard views of how the world works.
In this case, much of the work has been done by Shields' graduate student Sandra Talbot. For four years, Talbot has been studying populations of brown bears by means of laboratory research in molecular biology.
Biologists in the Alaska Department of Fish and Game formed a network of collectors for the project, gathering samples of blood, skin, or other tissue from hunter-killed bears and bears captured for radio collaring. Talbot needed only tiny bits of the bears, because she was using a new technique that replicates genes of interest so that sufficient quantities of DNA have been produced for her to study.
Once Talbot had enough material from the gene of a given bear, she would determine the sequence of that gene, hunting for the same sort of unique molecular pattern that is now so often cited for identifying the villain in criminal cases. By comparing the sequences of the same gene from different bears, she was able to determine the degree of relationship between the bears.
After comparing the DNA sequences of five different genes from nearly 200 brown bears living in 19 different regions of the state, Talbot believes the evidence shows that genetically the brown bears of Alaska belong to three different populations. One population spans the Bering Strait from Interior Alaska to eastern Siberia; a second includes bears from ANWR to southeast coastal regions of Alaska. The third and most unique is found only on the ABC islands--Admiralty, Baranof, Chichagof--of Southeast.
Gene sequencing also permits scientists to see the ticks of a biological clock. The more similar two gene sequences are, the more recently have the possessors of those genes shared an ancestor. The opposite also applies: the more dissimilar the gene sequences, the more distantly related are the organisms from which the genetic material was obtained.
Talbot and Shields found the DNA from the island-dwelling brown bears of southeast to be different from that of the mainland brown bears; the two bear populations must have diverged many thousands of years ago. In fact, the bears of the ABC islands have a type of DNA that is more similar to that of polar bears than of other brown bears. Just possibly, the island bears may be descendants of an ancestral type of bear that also gave rise to the polar bear.
To explain this unexpected finding, the scientists postulate a scenario in which brown bears of the ABC ancestral type once populated larger areas of the north. As the last great ice age froze most of their home range, they were driven by the glaciers to small refuges on the big islands of Southeast. There a few survivors raised generations of cubs, finally outlasting the ice but never moving back to a mainland now occupied by their more recently arriving distant cousins.
If Talbot and Shields are right, then the island bears are descendants of the earliest lineage of brown bears to enter the Americas. The two mainland bears of Alaska and the other brown bear population so far identified in the Western Hemisphere, Montana grizzlies, are more recent immigrants from Asia.
The researchers hope to continue piecing out the relationships among brown bears throughout their existing range from Wyoming to Scandinavia, but they may encounter some politically generated rough spots in the path of their studies. The ABC islands are being considered (and vehemently debated) for their timber resources. Though Shields writes that he and Talbot intend "to leave the bear/timber dilemma in Southeast to wildlife managers and politicians," those people surely will demand that the scientists explain the evidence for, and the meaning of, the unique genetic status of Southeast's grizzled pioneers.
