Isle Royale DNA analysis shows more females than expected, suggesting that population decline there may reflect kin relationships, not gender imbalance.
Updated: March 5, 2013 - 12:10 PM
The wolves of Isle Royale may not be on the edge of extinction after all.
Of nine wolves left on the island in Lake Superior, about half are female, according to new DNA analysis of their scat. That’s considerably more than the one or two that researchers had believed — a gender imbalance that they theorized could be driving a decline in the population of the famous wolves.
For the moment, National Park Service officials say, the unexpected findings will give them some breathing room to decide whether to embark on a precedent-setting “genetic rescue” of the wolves. That would involve artificially introducing one or more new wolves to the island. That decision to interfere with nature would have far-reaching implications for wildlife management at other national parks as well.While one leading wolf researcher hailed the DNA results as great news, they also raise questions about the family relationships and behavior of wolves — especially these, the longest and most intensely studied of any in the country.
In effect, their problem may be the equivalent of an incest taboo. The wolves, which migrated to the island in the 1950s when an unknown number crossed the frozen lake, are now largely descended from just two animals.
“We are not seeing the courtship behavior that we would expect,” said Rolf Peterson, a biologist at Michigan Technilogical University who has tracked the wolf and moose dynamics on the island for decades. “That indicates they are avoiding breeding with close relatives.”As far as the researchers could tell, last year there were no pups born on the island — the first time that’s happened since 1971, Peterson said. Last year they counted just nine wolves left, the lowest number ever recorded. In the summer, they discovered the carcasses of three that had fallen into an abandoned mine pit and drowned.
However, several of the female wolves are young, born after 2011, and wolves usually don’t start mating until they are at least 2 years old. It’s possible that as early as this spring they could start reproducing, said Dave Mech, a wolf biologist with the U.S. Geological Survey.
“I’ve been telling people not to panic,” Mech said.
The Isle Royale wolves have always been closely related, he added, and that has not stopped their reproduction before.
But genetic similarity may not be the dynamic that’s driving their mating behavior, said Phil Hedrick, a wolf geneticist at the University of Arizona. Wolves raised as littermates may be just as inhibited by their sibling relationships. Hedrick described a famous case of a wolf pack discovered in the early 1980s in Sweden — the last 10 left after they were extirpated from the country. They lived together for years without mating, he said. But then a lone male wolf arrived from the north, and the pack split into two. Only after that did the two groups begin to crossbreed.
“There are more than 200 now,” he said.
Still, a lot depends on how closely related they are, Hedrick said. It is unlikely that wolves that are siblings or father and daughter would mate or do so successfully. The wolves’ genetics are only one issue that will drive the park’s decision about their future, said Superintendent Phyllis Green. Another factor is the long-term viability of the island’s moose, the wolves’ primary source of food. For the moment, the moose population is high in large part because the number of wolves is so small. This year, there has been a near record number of twin moose calf births, a surprise to the researchers who have been vividly describing this winter’s study on their website.
But if the moose start to decline as a result of climate change — as some suspect is happening in northeastern Minnesota — then giving the wolf population a boost might not be a good idea, she said.
“At this point, I have more questions than answers,” Green said.
Meanwhile, the wolves on Isle Royale, which are largely oblivious to the people who control their fate, have been engaged in a drama all their own.
Last spring Peterson and his co-researcher, Michigan Technological University Prof. John Vucetich, succeeded in putting a radio collar on a single female they call Isabelle, allowing them to track her movements and spot her during their near-daily winter observation flights.
On Feb. 2 they saw Isabelle running for her life, with three other wolves in pursuit. When the pursuers caught her on the edge of the icy water, two attacked her while a third, her brother and littermate, watched.
“This was no scrappy dogfight,” Vucetich wrote on the researchers’ website. “These wolves lunged and sank their teeth into Isabelle with the same fury and power they use to bring down a 900-pound moose. I think they are going to kill her.”
They didn’t. That day, at least, they backed off, leaving her bleeding on the ice.
“Mercy or torture?” Vucetich wondered.
But they appear to have it in for her, the researchers said, because days later they had her trapped on an icy ridge above the lake. Again, they backed off.Isabelle may have left her pack in order to find a mate and start her own pack, generating deadly competition for the right to reproduce.
“The motivation that drove Isabelle’s assailant is simple — to eliminate a female who might steal a mate or raise pups,” he wrote. What they don’t know, he said, “is that Isabelle’s reproductive future was very much in doubt before this attack.”
Josephine Marcotty • 612-673-7394
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