Real-time natural selection on crops and their pests

May 4, 2010 • 8:23 am

Perhaps the most persistent criticism of evolutionary biology is that natural selection isn’t sufficient to explain life’s complexity.  This of course is the mantra of intelligent design, which claims that in principle natural selection can’t explain “irreducibly complex” traits (for a refutation of this see the discussion at TalkOrigins).

But there’s also criticism that there is not much evidence for natural selection.  I’ve discussed this in WEIT and in my recent review of two books (and of natural selection) in The Nation.  The refutations of this claim are easy: we have lots of evidence for selection occurring in nature, including the many studies cited by John Endler in his book Natural Selection in the Wild, and more recent studies including the famous work by Peter Grant and his colleagues on selection for break size in a Darwin’s finch (for a summary of recent studies go here).

Evidence for natural selection also comes from the many observations of animals and plants responding to human-induced changes in the environment.  These include the famous studies of wing color in the peppered moth, heavy-metal tolerance in plants, insecticide resistance in insects, size changes in animals due to overharvesting, and of course antibiotic resistance in bacteria.

Some creationists object to using these cases as evidence for selection, since the selection pressures come from humans, making these (so they say) analogous to artificial selection.  This objection is misguided.  Yes, the selection pressures result from human activity, but far from trying to produce a given response, humans do not want a response.  Who wants bacteria to become resistant to penicillin?

Further, unlike animal and plant breeding, these responses to anthropogenic changes in the environment are not directed to a particular end by human desire.  When a plant evolves resistance to lead or copper on mine tailings, it’s drawing on a naturally-occurring pool of genetic variation—exactly as if the plant were responding to high concentrations of metals that occur naturally on serpentine soils.  I see all genetic responses to human meddling with the environment as evidence for natural selection, and we’re going to see more as the climate gets hotter.  Evolution is going on around us all the time, but it’s often invisible.

In the past week there have been two new reports of natural selection causing evolutionary change as a response to human activity.  The first is in today’s New York Times: a discussion of how weeds in the U.S. are becoming resistant to the herbicide Roundup.  The Roundup story is complex, but the basics are that the herbicide’s active ingredient is glyphosate, an amino acid analog that kills plants by interfering with the synthesis of some amino acids in the growing points.  It’s really effective at wiping out weeds, but can also kill growing crop plants if it’s sprayed onto fields after planting.  In the 90s Monsanto also developed “Roundup Ready” varieties of transgenic crops (which now include corn, soybeans, cotton, and alfalfa), in which they introduced into plants a gene from bacteria that allowed amino-acid synthesis to proceed normally in the presence of Roundup.  The combination of Roundup and Roundup Ready crops made millions for Monsanto, and farmers liked the convenience of not having to till the soil before planting to get rid of weeds.  But there were lots of objections to the use of transgenic crops and to the dependence of farmers on corporations who made both herbicides and herbicide-resistant crops.

But now, as reported in the Times, weeds are evolving resistance to Roundup throughout the world. As one soybean farmer observed, “We’re back to where we were 20 years ago.”  So far only about 5% of crops are infested with resistant weeds, but I can confidently predict that natural selection will make things worse.

I haven’t followed the Roundup controversy closely, but the Times reports that Monsanto “once argued that resistance would not become a major problem”.  That’s insane. Any evolutionist will tell you that you can’t predict stuff like that.  More often than not, natural selection finds a way around these things, just as bacteria have devised insidious ways to combat antibiotics, and the antibiotics that replaced those antibiotics, and so on to the point where in some cases (like TB), we have bacteria that resist all known antibiotics.

The problem will get worse, and companies will have to develop new herbicides, putting farmers into the same spiral that doctors have been in with antibiotics for decades.

Crop plants are afflicted with insects as well as weeds, and those too can adapt to human-induced selection. A new report in The Proceedings of the Royal Society of London by Vincent Calcagno et al. shows that one crop pest, the European corn borer (Ostrinia nubilalis), seems to have responded to corn harvesting by changing its behavior, making the larvae less likely to be killed during the harvest.

The corn borer appears to have evolved from the sister species Ostrinia scapulalis about 500 years ago when corn was introduced to Europe.  O. scapulalis lives on the non-crop plant mugwort (Artemisia vulgaris). Both species undergo a winter “diapause”—a period of arrested development—in the stems of their plants. (We are talking about the caterpillars here, though both develop into moths.)

Calcagno found that, unlike the mugwort-infesting species, larvae of the corn borer move down from the tops of the plant before they diapause.  This was shown both in the wild, by putting both species on either corn or mugwort, and in the lab by making artificial “stems” out of food-filled plastic tubes.  The down-movement (“negative geotaxis”) of the corn pest did not depend on living in corn, but was also seen when the corn borer was forced to live in mugwort.  In contrast, O. scapulalis did not move down at all before diapause, but tended to overwinter right where it was in the plant.

Calcago et al. speculate that this difference was due to selection associated with the harvesting of corn.  That harvesting now involves lopping off the top 15-40 cm (about 6″-16″) of the plant to get the ears.  The truncated stalks are then left standing in the field over winter.  This would impose strong selection on corn borers to diapause further down in the stalk so they wouldn’t get lopped and killed.  Calcagno estimate that this selection is pretty strong, eliminating roughly half of the corn borers.  One would certainly expect a response to that selection, and it seems to have appeared in the last few centuries. This of course makes things worse for corn farmers, because many of the pests who would be killed during the harvest now survive.

Now their case isn’t airtight, for they haven’t actually nailed down the evolutionary cause of the species difference in movement. All we see is a difference between species and a pretty plausible story that is supported by experiments.  One way to test their idea would be to see what happens in populations of corn borers that aren’t harvested—presumably they would revert to the ancestral behavior.  (Farmers wouldn’t want to do this test, of course, but it could be done in an agricultural station.)  Calcagno et al. also mention another species of corn borer, O. furnacalis, that might have evolved independently in Asia. If that species showed the same down-moving behavior it would strengthen Calcagno et al.’s case for the evolution of a corn-harvesting-associated behavior.

What all this shows is that our control over nature isn’t as strong as we think.  As the volcano in Iceland abruptly reminded us, we can’t fool Mother Nature.  And we can’t fool natural selection, either.

Fig. 1.  The European corn borer doing its job.  It’s a pest because these infestations can stunt the plant or make the ears drop prematurely. (Photo from Iowa State University.)

UPDATE: Carl Zimmer goes into more detail about Roundup at The Loom.

h/t: Greg Mayer


Calcagno, V., V. Bonhomme, Y. Thomas, M. C. Singer and D. Bourguet. 2010. Divergence in behavior between the European corn borer, Ostrinia nubilalis, and its sibling species Ostrinia scapulalis: adaptation to human harvesting?  Proc. Roy. Soc. Lond. B:doi: 10.1098/rspb.2010.0433 (online).

23 thoughts on “Real-time natural selection on crops and their pests

  1. As the volcano in Iceland abruptly reminded us, we can’t fool Mother Nature.

    Er, what does the volcano in Iceland have to do with attempting to fool Mother Nature?

  2. “I haven’t followed the Roundup controversy closely, but the Times reports that Monsanto ‘once argued that resistance would not become a major problem’. That’s insane.”

    No, that’s business. And business people have neither morals nor shame, and will say or do just about anything, no matter how vile and evil, just to put another dime in their pockets.

    1. My, what a broad brush you paint with Grandma.

      Should we commence rounding up (no pun intended) these business people, along with anyone who has ever worked for them, then?

      Until we get a more reliable source and context for this Monsanto quote, I’ll hold back judgment.

      1. Hey, the brush isn’t broad enough. Our whole food production model is, if not evil, seriously misguided. There is plenty of skill, knowledge, observation and innovation involved in being a competent food producer, none of which requires a single application of roundup or any other chemical concoction. If you work with nature you end up doing less work; let her work for you: e.g. Voisin management-intensive grazing vs. confinement; Polyface farms; Eliot Coleman.
        As Joel Salatin points out, modern conventional farms are not a pleasant place to be; thus, succeeding generations, the smart ones, have moved to the city. Agriculture has been severely dumbed down in its reliance on Monsanto et. al. Hopefully there may be a countervailing trend from city back to the farm using knowledge-based rather than chemical-based methods; it’s hard for those who are struggling with the debt and the disappointment of conventional ag to change or to admit that the 40-odd years of subservience to the model they were sold led to a dead end.

        1. There has never been an alternative to more productive agriculture as soon as we started to run out of land surface. Besides more starvation, which indeed is “evil” or, correct and more appropriate on an atheist blog, immoral.

          The fact that despite an exponential growth in population absolute numbers of starvation has been constant is one of the literary greatest achievements of the human race.

          Similarly it is hard to see an alternative to the more productive use of land, energy and raw material that urbanization gives.

          In fact there is a corresponding trend of similar growth of urbanization vs absolute number of slum population as for agriculture, so one could probably make a case that that too is another great achievement.

          Again people would be hard up without this, but also all of nature as species would be unnecessarily pushed out of existence. Not necessarily more immoral as such, as morality chiefly concerns “own” species, give and take some live stocks and pets in our case. But disturbing anyway.

          knowledge-based rather than chemical-based methods

          That is both a false dualism and plain false. As you can see from the article it goes a whole lot of development and testing into biologically based methods. You can’t just sprinkle chemicals like water on pests and think they will necessarily be harmed. Homeopathic farming?!

          1. “We can’t feed the world without Monsanto et. al.” is a red herring. For one thing, there’s plenty of land. In my own area, the Fraser Valley, many hectares of prime ag land are devoted to hobby horses and huge front lawns. For another, unsustainable ag is one not very desirable way to correct for overpopulation.
            Cities have their charm, yes, but suburbs are passe. Urban developments in rural areas is the new paradigm.
            Sure a lot of science goes into developing new and better quick fixes for monoculture pest and weed problems. However, the power of natural selection makes it a Sisyphean endeavour, as the WEIT post points out. It does, however, fill pockets and keeps beaurocrats busy.
            Hmm, which works better: create a vast unnatural monoculture and dose it’s unwanted flora and fauna with poison, or promote a diverse farm ecosystem? Note that the latter doesn’t require any middlemen selling inputs, homeopathic(!) or otherwise.

        2. I’m afraid it is too broad when Woody says “…business people have neither morals nor shame, and will say or do just about anything, no matter how vile and evil…”

          Some people in business might be, but all are not. It’s just that simple.

          “modern conventional farms are not a pleasant place to be”

          Sorry, but I disagree. You are correct that world-wide there is an Exodus from the farm to the city, but it has more to do with economics and opportunity than how pleasant the farm might or might not be. Economic disadvantage in the US is, in part, due to debt incurred from high tech farming, but that is not the case in a large part of the developing world. People, mostly younger, leave for the perceived opportunities, excitement, and jobs in the city. Stewart Brand in the “Whole Earth Discipline” demonstrates this very well. He also explains why this isn’t necessarily a problem.

          Your implication that everyone should just go back to the farm and do things “the old way”, what ever the hell that is, is impractical, insufficient, and unsustainable for a growing population.

          1. 1) “Tommy/Tammy, come ride the tractor with daddy. Wear your respirator, we’re spraying today. Then we’ll pump out the manure tank and cull the crippled cows who have never walked a grassy field, and dose the rest with the usual pharmacopoeia.”

            2)Who said anything about “the old way”? Although certain essentials never change, for instance the long-term necessity of feeding the soil micro-herd. Not doing so is unsustainable. What “sustainable” means in farming is: a closed system. No need for external inputs – fertilizer, chemicals, the transport thereof, all dependent on petroleum.
            3)Farming is devalued. Responsibly stewarding the land is (quietly) exciting and deeply gratifying, and gives a sense of place that no money can buy, which brings us to:
            4)Do you think we are going to be able to rely on fossil fuels forever? Less than 50 years left. People will of necessity become more involved in their own food production/supply, it’s starting to happen now. And they will concomitantly have less appetite for idle travel.
            5)Big ag and all the supporting gov’t departments and agencies are in denial. Real, sustainable farming is more productive and efficient than big ag, and studies, even by said gov’t, have shown this to be true. Coleman cites some; if I have time I will look them up.

            1. 1) Jackie, I don’t know where you get this impression of “The farm”, but it is grossly wrong. The vast majority of farmers across the globe, let alone those in North America, experience nothing like this. No wonder farming is devalued with attitudes like that.

              2) “What ‘sustainable’ means in farming is: a closed system. No need for external inputs – fertilizer, chemicals, the transport thereof, all dependent on petroleum.”

              Please reference this definition because I can find nothing close to it! If you truly believe this, then you’re living in a dream world. Such a system has never been in existence (and never will be, as it is physically impossible). Please note: I am not suggesting we can’t make large improvements, but the idea we can live some magical, no external input, lives is BS and characteristic of old school environmental dogma.

              3) Ha! This is such a common attitude of people who want to tell others how to live. Yes, I think farming is great, actually, but who am I to tell another to stay on the farm, stay out of the city, don’t move beyond the rural existence? Your ideals aren’t shared by everyone else.

              4) Obviously not. That’s why we are looking at several strategies to reduce fuel consumption on the farm. Yes, people in “Big Ag” and Government jobs are actually trying to find ways to do this.

              And here you are making judgment on others again. Are you the “decider” telling people what is “idle travel”. I’m not even sure where that point came from!

              5) Ok, here we go. I knew it wouldn’t take long before the “Big Ag”, and “Government” conspiracy ideas started coming out. Re: Coleman, I assume you are talking about Eliot Coleman, a respected authority on organic methods. The picture comparing conventional and organic methods isn’t quite as rosey as you make it out to be. Read Eliot’s own report (Google: Report and Recommendations on Organic Farming), written for the USDA, where the conclusions include such phrases as “A total shift to organic farming would have a major impact (negative) on the U. S. economy” and “potential export needs would not be met”. The analyses also assume items like enough manure would be available (on site) to meet needs, unlikely IMO, and, labor costs would be reduced (not even close to realistic). Not to mention that the analyses in the report are based on 30-40 year old data at this point. Much has changed in that time, and no, it hasn’t all become worse.

              There are many aspects of both conventional and organic methods which will be useful (necessary) in the future and we need access to all of them. Simply chanting the out of date mantra “Green or Die” (yes, my words) is not a solution and is rapidly become part of the problem.

    1. I don’t know, but that seems to be the sort of thing that wouldn’t be too difficult to determine; we know how we made roundup-ready plants, so if it looks like the weeds stole the same bacteria genes, then it was probably some sort of lateral transfer (either from the bacteria directly, or from the roundup-ready plants). If we can’t find any evidence of those bacteria genes, it’s probably an independent development.

    2. Weed resistance to herbicides is well known to exist in wild populations and was observed well before GM crops hit the scene. Some cases of transfer of existing resistance across species has been demonstrated as well. By far, however, the current forms of resistance being observed are coming from selection of pre-existing genotypes. Wild populations have sifficient variation to encompass resistance.

      See : Stephen B. Powles and Qin Yu, “Evolution in Action: Plants
      Resistant to Herbicides”, Annu. Rev. Plant Biol. 2010. 61:8.1–8.31

      for more info on resistance prevalence.

  3. I’m an agronomis, and in the whole evolution-creationism controversy I missed this examples from my area. In my area we fight against new pests and diseases that cripple our crops a lot of time, and they’re perfect examples of evolution and against the designer… unless somebody say that this is the result of world fallen in sin, and we return to the beginning.

  4. Also, wouldn’t genetics test selection in spades, predicting such things as up to 10 % of gene-cultural selective sweeps in humans for example? I thought those measures were pretty exclusive of selection.

    What all this shows is that our control over nature isn’t as strong as we think. As the volcano in Iceland abruptly reminded us, we can’t fool Mother Nature.

    This is confusing two separate issues, likely aided and abetted by using anthropomorphism.

    Yes, some were surprised by the effects on airfare. But it was a known problem and a rare occurrence airplanes (and unfortunately national communications) aren’t constructed for.

    The failure of set technological means against an adaptive system is something else entirely. Again, you could say that some means aren’t constructed for this. But the point you make is that even if they were, it wouldn’t last indefinitely.

    To fight adaptive systems traits you need to take it to their own turf and develop adaptive technologies. Antibiotic development is one such area where it will (always) be needed and likely affordable. Agriculture another.

  5. “the Times reports that Monsanto “once argued that resistance would not become a major problem”. That’s insane. Any evolutionist will tell you that you can’t predict stuff like that.”

    And yet apparently for a decade or two nobody, or at least nobody who could have made a difference, understood that about antibiotics, or antibiotics would have been used much more cautiously. And presumably Monsanto employs one or two scientists?

    I suppose I’m just pointing out short-term thinking versus long-term thinking, rather than a communication gap. But the result is the same.

    And we’re all going to die of MRSA or TB or famine as a result! We’re doomed!

  6. Do I really have to parse my meanings that closely? Obviously the sun still “inputs” into the “closed system” farm. Also, why would you think I would presume to tell everyone to be a farmer? Are you perhaps feeling guilty for leaving the family farm? The travel comment was apropos petrol. How is it a conspiracy theory to allude to the fact that business and government work together? A conspiracy of conspiracies? E. Coleman has abandoned the term “organic” because it has become a game of obeying rules to obtain the certification for marketing reasons and has nothing to do with nurturing the soil and growing the best plants possible. He uses the term “deep organic” to connote what he does.
    I see there are accommodationiists in the Green department; that’s ok, it’s a free country. Meanwhile, I have two acres on which to practice my green religion.

    1. He! He! No, Jackie! For the record, I have absolutely no guilt regarding farming. On the contrary, I have invested the last 30+ years in it and other environmental concerns.

      When you say “What ‘sustainable’ means in farming is: a closed system. No need for external inputs – fertilizer, chemicals, the transport thereof, all dependent on petroleum.”, then you need to stand by what you said. Every definition I’ve found for sustainable ag has included external inputs, especially regarding transport, which, in the real world, will involve some petroleum. Do you really exist on your green farm without any petroleum or do you instead use it as efficiently as possible?

      Just because government and business work together does not imply something bad. When you use the term “Big Ag”, you are doing so with such intentions (broad brush again). You are implying negative collusion between government agencies and business interests. You are also disparaging all those individuals who work in those agencies and companies. You are ignoring any good intentions, ideas, and influence they may (and do) have. (No, I work for neither).

      E.Coleman may have abandoned the term, but it was his report that called for and spurred the move for registration. It is hard to understand why you can, on one hand, call for government recognition, and then when you get it, cry foul that its not what you want. If he’s walked away from it, then the blame lies with him as he is one of the few who could effectively work to correct it.

      If it is accommodationist to not dogmatically follow what has not been proven or totally abandon ideas simply because you don’t like where they come from, then so be it. Green Accommodationist I am! You might want to check out Philip Tetlock, however. One of his more interesting findings is that those who adamantly advocate what they Know to be true are almost always wrong in the end. Those who hedge their opinions and keep their options open have a much better track record of being right.

      I wish you well on your two acres. I’m glad that you can practice that religion there (interesting choice of words). Just consider carefully what you preach.

      1. I actually do everything manually, but 2 acres is a mini-micro farm. A healthy person can scythe that much in a day.
        My “closed system” is simply plants capturing solar energy, harvested by ruminants and people, converted into manure and compost to feed the soil. Voila! No need for Monsanto. Big Ag – a shorthand for huge monied R&D – develops new and better quick fixes for monoculture pest and weed problems. The power of natural selection makes this a Sisyphean endeavour, as the WEIT post points out. You think otherwise; fine. Let’s agree to disagree.
        I must note, however, that it’s bizarre that you would hold Coleman responsible for the takeover of “organic” by big business, or for the evolution of “organic” as a market force. Of course Nestle, General Mills etc. want a piece of the action.
        The people I admire in ag just do their thing, really well and creatively, always working with nature. IMHO they are the real leaders.

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