Wild things may be changing at a genetic level to survive in modern cities

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Plants and animals have a long history of acclimatizing to city living – think of raccoons and their expert pillaging of compost bins. But now biologists are beginning to see signs that something more fundamental is happening. They say wild things may be changing at a genetic level to survive cities and their polluting, habitat-fragmenting ways.

Fish in New York's chemically-laden Hudson River have evolved a genetic variation that gives them resistance to PCBs, for example. Birds nesting under highway overpasses in Nebraska have developed shorter, more agile wings, allowing them to quickly swerve from oncoming traffic.

And weeds occupying patches of earth surrounding sidewalk trees in France have evolved to produce fewer dispersing seeds, which travel on the breeze and fall uselessly onto concrete. Instead, they produce compact seeds that drop close to the plant where they can germinate.

On one hand, urban evolution is not new. Peppered moths in Britain changed colour from white to black in heavily polluted areas during the Industrial Revolution. White moths were picked off by predators while the black ones, camouflaged in a newly sooty environment, survived to breed more black moths.

What may be different this time is the number of city-dwelling creatures evolving to live in inhospitable habitats.

As cities grow in population and size, so too does their influence on the environment. One hundred years ago, two out of every 10 people were city-dwellers. Today, more than half of us live in cities that are spreading across more and more of the planet.

A small but growing number of scientists say urban evolution may be accelerating in tandem with that growth. And there could be tradeoffs that we are only beginning to glimpse.

It pays to downsize

University of Tulsa ecologist Charles Brown says he was surprised it took just 30 years for the cliff swallows in his study to evolve shorter wings that help them avoid traffic.

Since 1982, he and Mary Bomberger Brown, an ornithologist at the University of Nebraska–Lincoln, have been studying a group of birds that make their gourd-shaped mud nests under highway overpasses in southwestern Nebraska.

Over the years, they recorded a steady drop in the number of road-killed birds.  This came as a surprise, because the colonies were growing and traffic had not declined. But as they compared the wing length of road-killed birds with those caught in nearby mist nets, they were in for another surprise – those caught in mist nets had noticeably shorter wings.

The researchers, who published their results last year in the journal Current Biology, believe net-caught birds avoided road deaths thanks to shorter wings that let them dodge traffic. Unlike their road-killed cousins, they survived long enough to pass down genes for shorter wings.

But is such urban evolution a necessary and positive development, or an evil to combat?

"It often results in an organism becoming better adapted to its environment," says Brown. "I suppose it's good if we are hoping that the organism persists."

Isaac Wirgin has a different view. He is a specialist in environmental medicine at New York University Medical Center and a lead author of a 2011 study in the journal Science on pollution-resistant tomcod fish in the Hudson River.

"In my mind, it's not a good thing," he says. "Usually evolution theory says if you adapt to something – like this resistance phenotype in tomcod – you're less good at reproduction or life expectancy, or you're more sensitive to other stressors."

Written By: Sharon Oosthoek
continue to source article at cbc.ca

11 COMMENTS

  1. It’s called remainder. This language has intent all over it. I would guess the reason you don’t see dispersing seed weeds on French sidewalks is because they are dead. They didn’t choose to drop their seeds nearby, weeds that drop their seeds nearby (a trait that at one time had no benefit and so was never acknowledged as perfectly normal behaviour) are still dropping their seeds nearby. An evolutionary changes did occur but not because of the sidewalks, we just see it happening because of the sidewalks.

    I’m wondering if maybe each individual DNA sequence of each individual plant, insect, fish, mammal and so on shouldn’t be considered absolutely distinct from all other DNA sequences. Species becomes more of a suggestion than a hard fact. Every individual organism is therefore distinct from every other organism. We are all transitional. Anyone of us can harbour the next great gene.

    • In your second paragraph, you hit the nail on the head.

      I always urge folks to step back from individuals when studying or discussing evolution. While you are correct about an individual harboring the next great gene…. It isn;t about individuals when you are talking about evolution, it is about populations. It is a little weird to think about, but, if one thing has this break through gene and the gene dies with one thing, the gene pool has not been altered but transiently. If the gene establishes and spreads into the population….. then we are talking evolution.

      In reply to #1 by aquilacane:

      It’s called remainder. This language has intent all over it. I would guess the reason you don’t see dispersing seed weeds on French sidewalks is because they are dead. They didn’t choose to drop their seeds nearby, weeds that drop their seeds nearby (a trait that at one time had no benefit and so wa…

      • In reply to #2 by crookedshoes:

        In your second paragraph, you hit the nail on the head.

        I always urge folks to step back from individuals when studying or discussing evolution. While you are correct about an individual harboring the next great gene…. It isn;t about individuals when you are talking about evolution, it is about populations. It is a little weird to think about, but, if one thing has this break through gene and the gene dies with one thing, the gene pool has not been altered but transiently. If the gene establishes and spreads into the population….. then we are talking evolution.

        I understand for evolution to occur the population has to adopt the trait. I see the evolutionary trigger as something that has already occurred prior to the die off, perhaps thousands of years prior, it’s just a matter of time to see if the trigger will survive and result in an evolved species. The mutation (trigger) has to preexist the environmental pressure. The article makes it sound as if the sidewalk made the plant change its DNA but that had most likely already occurred.

        Maybe trigger is the wrong word, bullet?

        • I think you are correct. You choose different language to express the concepts than I; however, I think you have it dead right.

          In reply to #3 by aquilacane:

          In reply to #2 by crookedshoes:

          In your second paragraph, you hit the nail on the head.

          I always urge folks to step back from individuals when studying or discussing evolution. While you are correct about an individual harboring the next great gene…. It isn;t about individuals when you are talki…

  2. Life has always evolved and adapted to all conditions affecting it….. but the most alarming jump to the process of evolution has got to be the large amounts of nuclear radiated waste products that humans have poured out into the ocean as bi product for the last half a decade – toxic sludge that ends up in the food chain and yes this nasty stuff has the potential to alter DNA codes at the genetic level….so we may have all sorts of strangely mutated creatures evolving as we speak….they will be some of the only creatures likely to be highly tolerant to nuclear radiated outflow water like the strange bacteria that lives in the liquid around the spent fuel rod cells of nuclear power plants.

  3. In reply to #5 by Light Wave:

    …strangely mutated creatures

    “Go ahead, eat it“, challenges Lisa Simpson.


    BBC reported a recent study in which a certain u.k. bird (songbird size, I think) is adapting to city noises; specifically, their song / whistle is changing so as to be heard above urban cacophonies. Singularly, I find this encouraging – yet, as the researcher mentioned in closing, the trade-off of adaptation is loss in biodiversity. Poor mother nature can go only so far, it seems :/

    • In reply to #8 by crookedshoes:

      BTW,
      of course this is occurring. I’d be alarmed if it weren’t.

      Too true. If there were not some adaptation occurring on account of human behaviour, I would be a little surprised. Let’s see if it can keep up with the devastation.

  4. In reply to #1 by aquilacane:

    It’s called remainder. This language has intent all over it. I would guess the reason you don’t see dispersing seed weeds on French sidewalks is because they are dead. They didn’t choose to drop their seeds nearby, weeds that drop their seeds nearby (a trait that at one time had no benefit and so wa…

    I’m currently reading this as a direct result of this article and your comment, it makes for fascinating reading.

    Evolutionary Ecology of Weeds from Iowa State University: Jack Dekker.

  5. In reply to #7 by veggiemanuk:

    In reply to #1 by aquilacane:

    It’s called remainder. This language has intent all over it. I would guess the reason you don’t see dispersing seed weeds on French sidewalks is because they are dead. They didn’t choose to drop their seeds nearby, weeds that drop their seeds nearby (a trait that at on…

    Ooh, I would strongly advise not listening to me. But it’s cool you found this article interesting. You don’t have to know how evolution works to see that it is occurring. Like a car, I may not know all of the functions of the internal combustion engine but don’t try telling me it’s ferries.

  6. In reply to #5 by Light Wave:

    Life has always evolved and adapted to all conditions affecting it….. but the most alarming jump to the process of evolution has got to be the large amounts of nuclear radiated waste products that humans have poured out into the ocean as bi product for the last half a decade – toxic sludge that en…

    I accidentally said Decade – I meant to say Half a Century….actually its about 65 years of Nuclear waste bi products leaking into the eco system…of course wild things are changing that’s evolution……Duh all Living things are changing both long term and also forced to change on a quicker short term level simultanoeusly

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