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Posted by on Mar 2, 2014 in Education, Evolution, featured, Science | 10 comments

Coevolution

In a recent discussion thread, one of my readers asked about cooperative evolution. After a brief discussion, what he was interested in was coevolution. So here you go Void.

Coevolution is a well known concept in the biological community. But, as I often do, I fired up my citation manager to see what was current on a topic. Typing “coevolution” into PubMed results in over  100 hits (for 2014 alone) dealing with coevolution.[1] That’s more than one paper per day (at a minimum) for something that creationists often say is impossible. So what do we mean when we say coevolution.

According to Kevin Yip and Prianka Patel (and others) at Yale University,

Coevolution (covariation/correlated mutation) is the change of a biological object triggered by the change of a related object.

What we mean is that an evolutionary change in one population is somehow caused by an evolutionary change in another population. There are thousands of examples of this. Indeed, if you think about evolution as survival of the fittest (or of the frequent) then almost all evolution is coevolution. Evolution, the change in allele frequency in a population is the result of some cause, whether it be another biological population or an environmental effect.

Gould and Mayr’s punctuated equilibria (original 1977 PDF) theory suggests that populations of organisms are generally stable unless acted upon by an outside force.  Even Darwin was well aware that humans often and relatively easily cause changes in populations based on needs or desires. The several hundred breeds of dog that exist today all descended, with modification, from wolves starting about 30,000 years ago. Indeed, modern dogs, while able to interbreed with wolves are so different as to be considered a different species. Humans have directly influenced the evolution of hundreds of plant and animal species for food and entertainment. Just to list a few: roses, cattle, chickens, pigeons, varieties of cabbage including broccoli and kale, maize/corn, wheat, and dozens of insects (indirectly). But this isn’t really coevolution, this is us changing something.

Nothing evolves without influence from something else. In a very real way, we are connected to everything on Earth. We exist because of the history of life, the influences of millions of other species, and the environments that our ancestors lived in. In turn, we have directly and indirectly influenced millions of populations to change as well.  Sorry for the digression.

In his book “The Greatest Show on Earth“, Richard Dawkins describes several examples of coevolution. It seems like he took all the good ones too.

Let’s take an easy example. Bacteria. Humans don’t like being sick. When bacteria infect modern humans, we gear up and go to war. We have developed a variety of chemicals that destroy bacteria. Chemical warfare is only illegal against other humans. Against bacteria, it’s plenty acceptable. So, we have created an environmental change in our bodies. When we get bacteria we don’t like. We attack. Bacteria mutate easily. The so-called SOS response. Bacteria that survive the barrage of chemicals designed to kill them make up much more of the gene pool than those that didn’t do so well against the antibiotics. Which, of course, is why your doctor always tells you to take all of your antibiotics. Even creationists who don’t accept evolution still take all their antibiotics.

So the bacterial population is evolving to be resistant to antibiotics. In the same way we can look at something like flowers and insect pollinators. Dawkins described it well, I’m going to shorten it considerably. It is spring here in Texas and it seems like every plant is purposefully pumping pollen into my nose in order to kill me. That’s not their purpose. Those plants (oak and cedar mainly) have a really stupid way of sexually reproducing. The males make tons of pollen, then eject it into the wind and hope for the best. The best being that one pollen grain lands on the female part of another tree of the same species. It takes a lot of energy to make all that pollen.  And that’s energy that might be more usefully spent somewhere else.

Some flowers have a different system. They get some help. Flowers and various insects have coevolved. One the one hand, the flower has evolved to be attractive to insects, usually a specific species or group (even the disgusting carrion flowers). The attractiveness to insects takes many forms. Some flowers give the insects a high energy treat (nectar). Some have become shaped like a female insect. Some give off a smell that attracts insects. Some have developed a complicated arrangement of colors that alert insects to the presence of nectar. And some do some or all of these. The goal is to attract insects that will then get pollen stuck to them. As the insects visit several flowers, the pollen gets rubbed up against the female parts of the flower.

Insects have evolved in tandem, with certain groups or species being attracted to one or more types of flowers. Some insects and plants have evolved rather elaborate structures for this process. Like the Hawk moths and orchids of Madagascar.

2008Image

The hawk moth (Xanthopan morganii Walk. ssp. praedicta R. & J.) visiting the Madagascar Star Orchid (Angraecum sesquipedale Thou.). (Illustration by Emily Damstra for the Smithsonian Institution)

NHM_Xanthopan_morgani

Xanthopan morgani
Natural History Museum of London

The nectar for the moth is contained in that long bit hanging down under the flower. So the moth has evolved a tongue that, in some cases, is well over 9 inches (22.9 cm) long. An extreme, but not uncommon example of coevolution.

This relationship, between plants and their insect pollinators, is mutualistic. Both species get a benefit. But that’s not always the case.  Most of the real world is actively trying to eat and/or avoid being eaten. The often called “arms race” between organisms fits here. Big cats that are bigger and stronger are capable of taking larger prey that is closer to the herd (herding being a defensive mechanism). Still, it’s easier to kill smaller animals farther from the herd. So the big cats are causing the prey species to evolve into larger, better herding animals. The weaker, smaller predator species has trouble getting enough animals to survive, so the predator population tends to be larger and stronger too.

I’ve used an example of this long before, but I’m not entirely sure of the accuracy of it now. I’ve attempted to update this description with information in parentheses.  Cheetahs are fast (with high acceleration and awesome maneuverability) . Still, it’s a lot easier to catch a slow (less maneuverable) gazelle. So the gazelles that survive tend to be faster (and more maneuverable). The cheetahs that are fast (and maneuverable) don’t have any problems, but the slower cheetahs (for whatever reason) tend to have more trouble catching appropriate prey. So the cheetahs are evolving to be faster (and more maneuverable).

Over time, you get both predator and prey populations that are insanely fast (and maneuverable).

So coevolution is a big workhorse process in the real world and has led to some… interesting species in our wold.

_____________________________

[1] This research has also led to me adding about two dozen papers to my personal collection.

  • Void L. Walker

    Awesome, Smilodon. This is exactly what I was hoping for. Concise and to the point. I really like the example of not so friendly coevolution that you gave. Some people assume that coevolution necessarily entails mutually beneficial outcomes, but that is clearly not always the case. Evolutionary arms races have always fascinated me. Thanks again for taking the time to do this :-)

  • http://www.facebook.com/people/John-Pieret/100000023960330 John Pieret

    I think there is another kind of “coevolution” to be considered. There are close relatives to wolves, including foxes, or cheetas, including lynx, that did not grow bigger and faster (though maybe grew more agile and quicker) that specialized in smaller prey that their larger, faster, stronger kin might occasionally take but could not sustain them. In short the foxes were coevolving with the wolves and the lynx with the cheetas.

    • Void L. Walker

      I like that example, John. Where did you learn of it?

      • http://www.facebook.com/people/John-Pieret/100000023960330 John Pieret

        I’m sorry to say that it was sort of my own idea … that is, it popped up in my mind in response to this discussion and I have no source to link to. I would be very much surprised if it was an original thought on my part as opposed to something that I read long ago and simply regurgitated without an ability to give a citation. But it seems to me to be obvious. Everything coevolves, one way or another, with everything else in its environment.

        • Void L. Walker

          Very true, and good thought. The example you gave is a nice one. In a certain way everything is coevolving.

    • SmilodonsRetreat

      Cheetahs/Caracals/Leopards, Lynxes wouldn’t have been in that same group. Although, there was a Eurasian cheetah about the size of a lion in the prehistoric times (the actual time frame escapes me right now).

      But yes.

      And cheetahs are sort of a special case anyway because of the bottleneck.

  • kraut2

    “Even creationists who don’t accept evolution still take all their antibiotics.”

    Not quite true – most of them accept the notion of micro evolution. After all – the bacteria is still a bacteria and did not evolve into a multicellular organism.

    • SmilodonsRetreat

      Most, but not all. I still know people who are “species immutabilists” meaning that they think species don’t change at all.

      And the point that I’ve been trying to make for a year now is that there is ONLY microevolution. In terms of the real world, there is no such thing as macroevolution. Species only change within themselves. Now it happens that occasionally one part of a population of species may change to the point where it can’t interbreed with another part of the population and we get to name it a new species.

      But that is all that happens. There never has been a time and there never will be a time when one animal is born and it is so different from it’s parents that it’s a new phylum. It never happened in the Cambrian and it won’t happen now.

      http://www.skepticink.com/smilodonsretreat/2013/09/16/where-higher-orders-of-life-come-from/

      • kraut2

        Of course – all evolution is micro evolution.

        As an example:
        http://www.cbc.ca/news/technology/cities-causing-genetic-changes-in-plants-animals-1.2533951
        I however find this comment quite confusing:

        “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.”

        Is evolution not about the pro creative success of a species in a given environment? If “adaption” does not secure the survival of a species in a challenging environment – than adaption does not work. Here it seems to work.
        What then does he mean by not a “good thing?”

        • SmilodonsRetreat

          Usually (always), there’s a “cost” to evolving. Bacteria that can pump our toxic chemicals out of their cells before damage occurs use a lot of energy that could be spent doing other things (like reproducing).

          In this case, Wirgin mentions that although the fish can survive previously toxic levels of PCBs, they are less able to survive the “natural” low oxygen conditions that happen (probably seasonally).

          In a way, it’s good. The fish can survive toxins. In a way, it’s bad, they can’t survive low oxygen conditions. Like antibiotic resistant bacteria, if the PCBs go away, then the fish will probably revert back to the non-PCB resistant variety that can survive low oxygen better.

          It’s always, always a trade off. Survive one thing, be stressed and maybe die by another. Survive that and reproduce less frequently. Reproduce more, but need much more food. Evolution is populations balancing on a knife edge, even without humans being involved. Look at the Galapagos finches.