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A Surprising Idea About the Risks of Extinction

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Isle Royale is 200 square miles of land in the watery expanse of Lake Superior. One cold winter 70 years ago, wolves came over an ice bridge and settled into a largely isolated island existence. Unfortunately, island life has not been good for them.

By 2016, the number of wolves on Isle Royale declined from a peak of 50 to just two, a male and a female. As a result of inbreeding, they were half-siblings as well as father and daughter. They had a pup together that lived less than a year. Even before that, scientists were finding wolves on Isle Royale with crooked spines and extra ribs.

The wolves of Isle Royale inspired Chris Kyriazis and his colleagues at UCLA to simulate animal populations over hundreds of generations. Their findings were counterintuitive: What doomed the wolves is not just the small number that have lived on the island in modern times, but perhaps also the large number of wolves that lived thousands of years ago. Kyriazis presented his study at the Evolution 2019 conference, and the team posted a preprint of the article, which has not been peer reviewed yet, on bioRxiv.

A large ancestral population can lead more quickly to extinction, the authors argue, because harmful but recessive mutations are not purged over thousands of years. The chances of any one individual getting two copies of the mutation is low, so natural selection doesn’t get a chance to act on it. But if the breeding population then dramatically shrinks—as when the wolves of Isle Royale isolated themselves from wolves on the mainland—those harmful mutations start to come into play.

Now, if the ancestral population were smaller, the purging of harmful mutations could have taken place beforehand. Of course, a population too small to get rid of harmful mutations might simply go extinct. What the simulations find, Kyriazis says, is a “sweet spot” for population size.

“People usually just think about how small is the population now—and how small it’s been over the last 100 years,” Kyriazis says. These simulations suggest the deep history of a species even thousands of years ago can be relevant for conservation today.

The team next simulated what this finding might mean for the practice of genetic rescue, when individuals are brought in to diversify an inbred population. The Isle Royale wolves actually went through a natural genetic rescue when a lone male wolf arrived on this island and had 34 pups. But this “rescue” ultimately failed, ending with the two wolves left in 2016. In 2018, the National Park Service actually moved the first of 15 wolves to Isle Royale as part of a planned genetic rescue. The simulations suggest that rather than aiming to introduce the most genetically diverse wolves from the biggest populations, one might go for wolves from more moderately sized populations.

In practice, though, actually applying these findings will be easier said than done. “It can be a useful guide to help us to think about those deleterious, recessive mutations, but at the end of the day you have to do what you have to do because there’s only wolves in so many places that can be moved,” says Kristin Brzeski, a conservation geneticist at Michigan Technological University who studies the Isle Royale wolves. Eight of the recently relocated wolves came from Michipicoten Island in Canada, where caribou, their usual prey, had disappeared. The wolves were starving and had to be moved if they were going to survive.

Philip Hedrick, a population geneticist at Arizona State University who has studied the wolves at Isle Royale, says the simulations oversimplify a few things. Greater genetic variation also helps a population adapt, for example, especially as climate changes in the future. And often, having just one copy of a deleterious, recessive mutation can slightly decrease an individual’s fitness, he says, so the mutation’s frequency could be low even in large populations.

In the meantime, the genetic rescue at Isle Royale has hit a few unrelated snags. Two relocated wolves died and another left the island when an ice bridge formed during the polar vortex this winter. But scientists have been studying the wolves there for 50 years and will likely continue to for much longer. Isle Royale has one of the most well-studied wolf populations in the world, and it may well reveal how genetic rescue actually works.

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3 Comments on "A Surprising Idea About the Risks of Extinction"

  1. Sissyfuss on Fri, 5th Jul 2019 3:33 pm 

    Isle Royale is in my home, the Upper Peninsula of Michigan. But if you look on the map by all rights it should be Canada’s.
    It is amazing the amount if complexity Gaia uses to make the entire system sustainable. Consider the relationship between lightening and atmosphere, coral reefs and sea life, humans and the 6th Mass Extinction. Whoops, don’t know if she’s to blame for that last one. That depends on free will rallying against biological imperatives. Something that is in desperate need like never before.

  2. Cloggie on Sun, 7th Jul 2019 5:17 am 

    The war on tourarism has only just began:

    https://edition.cnn.com/travel/article/how-to-stop-overtourism/index.html

    Amsterdam (700k) no longer advertises Amsterdam, with 18 million visitors now, 30 million expected in 2030.

    Won’t be long until you have to buy an entrance ticket to a beautiful city.

    #CO2TaxNow!

  3. Davy on Sun, 7th Jul 2019 6:20 am 

    This vital effort should be more than just a tax. It is obvious carbon taxes have not been very effective wherever they have been attempted. Late stage capitalism is not environmentally oriented. Corporations will make efforts but competitive pressures limit results. Government policy has a place but like corporate efforts is limited by an electorate not interested in sacrifice. This is not to say these efforts should be given up on but instead there should be stronger moral policy of promotion of good behavior and the penalizing of bad. Education must be pushed at all levels so the general public understand the challenges. This is not just in regards to climate but also general ecological issues.

    None of this is happening quick enough nor widespread enough. These efforts are not effective compared to economic growth impulses. It appears planetary problems have now entered a stage where negative feedback loops are converging. This leaves us with the acknowledgement that we are and will be in a generalized decline of both our civilization and the planet we live on. Acknowledgment should be a call to action of the awakened individual. The word awakened is not meant to indicate status but instead a mental state of an individual called to action.

    You can lower your foot print through localism. Individuals can do rehabilitation efforts locally. Individuals can do community building efforts that seek to strengthen local sustainability and resilience. Renewables are an important aspect of this effort but so is work on the natural environment. Plant things and grow food is a must. Conservation efforts found through consumption and waste management efforts are vital. This is more about meaning than hope. Hope that the problem will go away is denial. Hope that our collective condition can be made less bad should be the goal instead. It is only by admitting failure can we learn new ways to find meaning through the relevance of survival efforts.

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