Family tree study finds one male griz had 101 descendants

By CHRIS PETERSON

Hungry Horse News

Using genetic analysis U.S. Geological Survey Scientist Tabitha Graves and Nate Mikle recently completed a first look at the “family tree” of grizzly bears in the Northern Continental Divide Ecosystem.

The 8-million plus acre area stretches from Glacier National Park south to Ovando. The pair looked at genetic data gathered from 1,115 bears in a 2004 study done by researcher Kate Kendall and again in 2009-2012 through hair follicle samples of bears.

The family tree, printed out on one sheet of paper, stretches 20 feet, Graves noted in a recent interview.

The thrust of this initial study was to determine the genetic diversity of bears on the fringes of the ecosystem, namely in the southeast and southwest corners.

There was initial concern that bears in those regions, where population density is relatively low, would lack genetic diversity.

One male grizzly living in the Scapegoat Wilderness area had 101 descendants, Graves noted.

That one individual explained the relatively low genetic diversity in the southeast region in 2004. That same male had a son that had eight offspring and two daughters that had 10 and eight offspring of their own.

In other words, the study found, it was one big bear family.

But over time, genetic diversity increased in the region, as “immigrant” bears came into that portion of the ecosystem and mated with other bears.

In the southwest, a similar story. One male dominated reproduction, siring 17 offpsring, most of which dispersed only short distances. Of those 17 offspring, 14 came from just four females, three of which were three generations of a single family — grandma, daughter and granddaughter. All told, that male had 61 descendants.

The study also found that a fairly large number of females — 50 percent — didn’t have any detection of offspring. That doesn’t mean that the bears didn’t necessarily have cubs, just that they weren’t detected. Even so, “a fairly large number don’t successfully reproduce,” Graves noted.

The takeaway from this initial study, Graves noted, is that fringe populations are showing greater genetic diversity over time.

“Which is good news for the population,” she said.

Future studies will look to tie in this genetic data with data from collared bears from Montana Fish, Wildlife and Parks population trend studies to see how bear dispersal affects genetic diversity.

They’d also like to determine if females will adopt another female’s cubs and the fitness of bears in relationship to habitat and offspring.