Grizzly Bear Family Tree
Scientists unravel genetic linkages of 1115 grizzly bears in the NCDE.
Science Center Objects
Building a family tree of grizzly bears can both satisfy our natural curiosity about bear society and answer many ecologically important questions about the ways bears interact with each other and the landscape.
The grizzly family tree will allow us to answer questions about dispersal, effective population size, similarity of diet and habitat between offspring and mothers, inbreeding, and the relationship between habitat and fitness (the number of offspring a bear has). Once we address each of these basic questions, we can also evaluate the implications of our results as it relates to climate change to understand what actions are needed to conserve grizzly bears in the future. Our team is using genotypes collected across the 8 million acre Northern Continental Divide Ecosystem between 1998 and 2012 to build the family tree.
Collaborators: Kate Kendall (USGS Ecologist Emeritus), Amy MacLeod (University of Alberta), Dave Paetkau (Wildlife Genetics International).
Funding: Glacier National Park Conservancy, NSF, David H. Smith Conservation Fellowship
Summary:
Scientists at the USGS used genotypes from 6160 hair samples collected from 1115 grizzly bears between 1998 and 2012 to assess changes in genetic diversity over time in the Northern Continental Divide Ecosystem (NCDE) in northwest Montana. They found:
- Genetic diversity was lower in 3 southern regions in 2004
- Genetic diversity increased in those regions by 2012
- Initial low diversity resulted from a few animals with very high reproductive success (i.e. a small number of dominant male bears)
- The increase in diversity was due to movement into those areas from throughout the ecosystem
Introduction
Genetic diversity is one index of population health that reflects population size and also a population’s potential to adapt to changes. Generally speaking, breeding between close relatives, a small population size, and difficulty moving throughout an ecosystem can all lead to lower genetic diversity. On the other hand, increasing genetic diversity can be a sign that bears are able to easily move between regions, bringing new genes to places where they have previously been missing or rare. USGS biologists teamed up with other federal and tribal scientists to collect grizzly bear hair samples from baited hair traps and naturally-occurring rub trees affixed with barbed wire. 6,160 grizzly bear samples were collected, leading to the identification of 1115 unique bears (figure 1).
Genetic diversity in 2004
First, researchers calculated genetic diversity from samples collected in 2004 for each bear and its neighbors and found that three regions that had lower genetic diversity than the rest of the ecosystem (EC, SE, SW in figure 2).
Genetic diversity in 2012
Between 2004 and 2012, the SE and EC regions showed rapid increases in genetic diversity, with levels approaching those in the northern core of the ecosystem near Glacier National Park (figure 2).
Reproductive success
USGS researchers then built a massive family tree with the 1115 bears and were able to show that each southern region was almost entirely dominated by single extended grizzly bear families in 2004 (figure 3). Individuals within a family often share similar genes, suggesting that this, along with relatively low numbers, was likely to be the cause of the relatively low genetic diversity in 2004.
Movement into low genetic diversity regions
Researchers next used the family tree to look at the role of movement, by using the locations of a bear’s parents to determine where that bear came from. In striking out on their own to areas far from where they were born (figure 4), these bears improved the genetic health of the population. Genetic diversity is usually a very slowly changing measure of the health of the population and the movement we observed was responsible for the rapid increases in diversity.
Conclusion
This USGS study highlights the importance in maintaining movement corridors for wildlife to ensure that the genetic health of populations is maintained or improved. The large protected areas in the NCDE allowed movement of bears bringing new genes into areas that had historically been dominated by few bear families, increasing the flexibility of the population to adapt to future changes.
Future research
USGS researchers are now working with scientists and managers from the state of Montana and the Canadian provinces of Alberta and British Columbia to include additional bears and analyze international and cross-jurisdictional movements. Analyzing the new data will allow researchers to identify the best way to use family tree data to assess the quality of grizzly bear habitat and barriers to their movement.