No “designer genes” for this momma bear! Mara Weisenberger/USFWS

Judy Gust (USGS) preparing samples Melanie Wike/NPS

The Kodiak Archipelago is home to nearly 3,500 of the most magnificent brown bears in the world. It is here that the Kodiak National Wildlife Refuge was established in 1941, its foremost purpose being the protection of these national treasures. Kodiak brown bears have long been classified as a distinct subspecies, Ursus arctos middendorffi, one of two currently recognized brown bear subspecies in North America. However studies on Kodiak’s bears show that genetically they should not be classified as their own subspecies.

Recent breakthroughs in genetic analyses have allowed biologists to pursue investigations into the genetic health of Kodiak’s bears.  Biologists hoped to discover if concerns about genetic diversity in the bears is warranted and if their isolation from other populations leaves them more vulnerable to environmental disruptions. They also hoped to discover if Kodiak’s bears are really different from other brown bears.  To address these questions, staff at the Kodiak National Wildlife Refuge initiated a study in cooperation with the U.S. Geological Survey’s Alaska Science Center (ACS) and the Alaska Department of Fish & Game. The ACS Conservation Genetics Laboratory examined samples from nearly 300 bears, analyzing genetic material to determine a variety of results.

The study confirmed that brown bears of the Kodiak Archipelago have extremely low levels of nuclear genetic diversity. Indeed, their nuclear genetic diversity is the lowest of any documented brown bear population in North America. By comparison, it is less than half the level of the nearest brown bear population on the Alaska mainland. This low diversity suggests that the population was probably founded by a small number of bears, and that it has been isolated from populations on the Alaska mainland for a long time, probably since the end of the last ice age (10,000-12,000 years ago.) Genetic data also suggest that movement of bears between Kodiak and Afognak, the two main islands in the Archipelago, is so limited that Afognak’s bruins comprise a distinct population from those on Kodiak Island.  

Interestingly, patterns of mitochondrial DNA diversity (genetic material that is passed on only from mother to offspring; sorry daddies don’t count here!) are different between Afognak and Kodiak. Afognak’s diversity level is extremely low, with only two female lineages. This indicates close evolutionary relations among Afognak brown bears. On the other hand, seven lineages were found within the Kodiak Island population – a level comparable to that found at Katmai National Park on the Alaska mainland. The Kodiak Island population tends to be divided into distinct “neighborhoods” composed of female relatives; ursine versions of the Hatfields and McCoys.  Although, all bears are quite capable of traveling great distances, daughters tend to set up house close to their mothers. Males, on the other hand, tend to disperse widely and breed with females from other lineages.

Examination of a gene thought to govern immune response showed extremely low levels of variation of the Kodiak brown bear. This finding is of concern, because it could indicate that Kodiak bears have a limited capacity to respond to new diseases introduced to the island. Presently, however, the risks appear to be low. The Archipelago’s populations are considered healthy and show no physical or genetic signs of inbreeding or decreased fitness.

One of the main motivations for this study was to see if genetic variation was sufficient to estimate the size of the bear population on Afognak (where heavy forest cover makes accurate aerial surveys virtually impossible) through genetic analysis. Unfortunately, given the low genetic variation we observed, population estimation using genetic tagging is not considered possible.  

Increasingly genetic data has been used, in conjunction with other data sources, to support the classification of species and subspecies of animals. Genetic evidence collected in this study provides virtually no support for the Kodiak bear’s subspecies designation. Nevertheless, Kodiak bears possess unique physical characteristics and, like other isolated populations, will likely diverge from mainland populations over time. Regardless of questions concerning their status as a subspecies, biologists continue to consider the Kodiak brown bear as a population of special value. 

A more detailed accounting of this study can be found in the report “Genetic Characterization of Brown Bears of the Kodiak Archipelago”*.