A fortuitous discovery and some modern techniques of genetic decoding have together helped shed light on what was once the polar bear's mysterious evolutionary history.
Charlotte Lindqvist, assistant research professor of biology at UB, helped contribute to the sequencing of the entire mitochondrial genome of the oldest polar bear fossil ever to be unearthed – a jawbone and a tooth estimated to be 130,000 years old.
The results of the sequencing have revealed that the polar bear is an unexpectedly young species, forming its own branch of the evolutionary tree only 150,000 years ago. In the scheme of evolution, the polar bear is a species still in its infancy.
According to Lindqvist, the problem of the polar bear's phylogeny, or evolutionary identity, has been a long-unanswered question for the field of paleontology. Though biologists have previously been able to establish that polar bears evolved from the brown bear through genetic comparison of the two species as they exist today, when this split occurred and exactly how long it took could only be approximated.
"There have been a lot of estimates out there," Lindqvist said. "But since there have been really no fossils analyzed to support these estimates, they have ranged anywhere from 50,000 to up to more than 1,000,000 years, so it's been a pretty wide range."
The fossil, discovered in 2004 by a group of geologists in Norway, was from a fortuitously ideal period in the polar bear's evolution, providing the most illumination on its history that could have been expected.
"From the phylogenetic analysis of the fossil, we discovered that it was positioned almost exactly at the split point from when the polar bears split off from brown bears," Lindqvist said. "That really gave us a very good opportunity to date that splitting point much more precisely."
Apart from its location at a crucial point in the animal's history, the fossil was also uncommonly revealing due to its preservation in the arctic environment. Because all DNA is susceptible to the damages of decay and eventual destruction over time, the genetic codes of the majority of ancient fossils are unable to be analyzed upon discovery.
The process of degradation can, however, under certain conditions, be considerably slowed. This was precisely the case with this fossil.
"This particular fossil was extremely well preserved," Lindqvist said. "It was well imbedded inside layers of sediments and has been lying there for thousands of years in a very, very cold environment. So that's why the DNA and the whole fossil were so well preserved, allowing us to extract and analyze it to determine [the polar bear's] phylogeny."
Being able to analyze the fossil's mitochondrial genome, Lindqvist and her colleagues were able to directly compare its DNA to those of the modern species of polar bears and brown bears. Inspection of the comparison allowed them to determine many of the physical characteristics of the actual organism.
"We know a few things," Lindqvist said. "The size of it was comparable to modern polar bears, it was probably feeding off seals or something similar like polar bears are today, and it lived in an environment similar to what polar bears do today. But that's pretty much all you can say from just a jawbone and a tooth."
Although it is evident from the discovery that the polar bear evolved rapidly to adapt to its harsh environment, Lindqvist warns that it is questionable whether it will be capable of the adaptation that the effects of climate change are currently forcing upon it.
"It seems that they are so specialized that they might not be adaptable to drastic changes," Lindqvist said. "What I think will probably happen is that they will just react and move to places that are suitable for them."
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Photo: Courtesy of Laron Fomby
