September 12, 2011 | David F. Coppedge

Venus Flytrap De-Darwinized

Darwin had a fascination for the Venus flytrap, but is it appropriate to conjure up his ghost when talking about it?  The carnivorous plant still defies evolutionary explanations, especially now, when a recent paper drew attention to more amazing design features from macro to micro.  For some reason, writers still feel a compulsion to mention Darwin’s name when talking about a plant that defies his evolutionary ideas.

Even though the Venus flytrap (Dionaea muscipula) grows only in America (particularly, in the Carolinas), it has long fascinated botanists from around the world.  Recently, a team of plant biophysicists from Germany and Saudi Arabia went hunting for the clever plant’s secrets.  Publishing in PNAS,1 they concentrated on plant hormones involved in the stimulation of the traps, the fast closure followed by slow constricting closure, and the formation of an “external stomach” on the trap surfaces that digests the prey.  They found that signals for trap closure follow different signaling pathways than those for digestion.  In sum, “These findings demonstrate that prey-catching Dionaea combines plant-specific signaling pathways… with a rapidly acting trigger, which uses ion channels, action potentials, and Ca2+ [calcium ion] signals.”  That’s a lot of cooperation between multiple parts, each exquisitely adapted to their role in the goal of catching bugs.

Students who have played with Venus flytraps in school know that it takes two strokes of the trigger hairs separated by a short pause, or two strokes of separate hairs, to make the trap shut.  This prevents needless trap resets from falling leaves or other non-prey objects.  But they probably didn’t realize they have just tripped an electrical switch leading to a series of mechanical events: “Insects touching these mechanosenory organs protruding from the upper leaf epidermis of the Venus flytrap activate mechanosensitive ion channels and generate receptor potentials, which induce an action potential.”  Prior to closure, the trap has been set by storing elastic energy, allowing it to close within 100 milliseconds (1/10 second).  But even when sprung, that’s not all.  A whole sequence of coordinated events is set into action:

However, the trap is not completely closed at this moment. To hermetically seal the trap, it requires ongoing activation of the mechanosensitive hairs by the trapped prey. Unless the prey is able to escape, it will further stimulate the inner surface of the lobes, thereby triggering further APs [action potentials]. This forces the edges of the lobes together, sealing the trap hermetically (prey-dependent slow closure) to form an external “stomach” in which prey digestion occurs. The second phase of trap closure is accompanied by secretion of lytic enzymes from the glands covering the inner surface of the bilobed leaf trap. Thus, digestive glands do not secrete until stimulated by natural or artificial prey. Additionally, prey-derived compounds stimulate digestive glands leading to acidification of the external stomach and production of lytic enzymes.

The authors seem fascinated by this process, as any observer would be.  How can a plant act like a meat-eating animal?  “Many similarities between fast processes involved in carnivory and signals of the nervous system suggest similarity in mechanisms,” they said.  And sure enough, “ion channels and chemical factors are at the basis of triggering mechanisms in both systems.”  Both tigers and Venus flytraps employ calcium signals, ion channels, exocytosis, and secreted substances.  In particular, the researchers discovered an interplay between two plant hormones, jasmonic acid and abscisic acid: “Whereas the former systematically alerts neighboring traps to the presence of prey and elicits secretion, the latter regulates trap sensitivity, protecting the carnivore from untimely prey catching during periods of drought.”  This little plant thought of everything (so to speak).

The analogy between carnivory in two completely different kingdoms of life is so uncanny, the authors elaborated on it in their concluding discussion:

Our results imply that phosphorylation/dephosphorylation reactions are important modulators of plant carnivore excitability.  This reveals another analogy to the nervous system, where both electrical excitability and synaptic transmission is strongly modulated by such posttranslational modifications.  Dionaea assembles an extensive signaling network that relies partly on plant-specific components (which it uses for its own specific purposes) and partly on mechanisms resembling those of higher animals. However, in contrast to nerve cells in animals, terrestrial plants lack fast voltage-dependent Na+ [sodium] channels, possibly due to the fact that Na+ gradients in such plants are minor. Thus, Na+ currents would not be very efficient to transiently depolarize the membrane potential.  Instead, plants possess a rapid (R-type) anion channel current component in addition to the slow (S-type) anion channels (SLAC1). This anion channel exhibits voltage-dependent features of neuronal calcium and sodium channels. Upon depolarization, this channel type activates with fast kinetics, whereas hyperpolarization causes deactivation. Hence, this type of plant anion channel has all of the properties to substitute for Na+ channels and to drive the Dionaea AP [action potential].

Of all the nerve – a plant that is vastly unrelated to the animal kingdom has analogous components for hunting prey found in mammals with central nervous systems.  Why, then, did these authors call it the “Darwin plant”?  No common ancestor of plants and animals would have had all these components, and no sequence of transitional forms shows carnivory from the most primitive plants to this exotic angiosperm – a flowering plant, by the way, that does not need bug meat to survive, since it has all the photosynthetic gear to get by. What’s Darwin got to do with it?

Nevertheless, the ghost of Darwin lurked in the shadows from beginning to end:

  • Venus flytrap’s leaves can catch an insect in a fraction of a second.  Since the time of Charles Darwin, scientists have struggled to understand the sensory biology and biomechanics of this plant, Dionaea muscipula.

  • Although this type of plant carnivory has been known since Darwin’s time, insights about the hapto-electrochemical coupling associated with the trapping behavior of Dionaea remain rather limited.

  • Urea had already been shown by Darwin to induce secretion in Dionaea.2

  • Sequencing the genome of the Venus flytrap and identifying the genes encoding key elements in mechanoelectric trap contraction will allow us to further understand the action of the Darwin plant and to characterize both similarities and differences between analogous processes in the two kingdoms. Furthermore, with the ion channel genes identified and functionally expressed, it will be possible to reconstitute the Dionaea AP and secretion process known since Darwin’s time.

This repetition of Darwin’s name is especially puzzling since the authors made no attempt to explain how this amazing plant evolved (they didn’t even invoke the phrase convergent evolution).  Darwin wrote a book on insectivorous plants in 1875, in which he described experiments he performed on the Venus flytrap, but he did not provide a theory for how the plant might have evolved, nor did he mention it in his best-known work, On the Origin of Species by Natural Selection. To the contrary, the quotations above almost emphasize that Darwin did not understand how this wonder of nature originated.

Nor was Darwin the first to study the plant.  It had been discovered in 1763, almost a century before the Origin.  A description and illustration of it was sent by British naturalist John Ellis to Linnaeus in 1769, with the comment, “My dear Friend, I know that every discovery in nature is a treat to you; but in this you will have a feast” (source: Hunt Institute).  William Paley gave it a short description in his 1804 book Natural Theology, or, Evidences of the Existence and Attributes of the Deity Collected from the Appearances of Nature.3  So by all rights, he could have been honored instead of Darwin in the current paper, having it called “the Paley plant.”

1. Escalante-Perez et al., “A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap,” PNAS, published online before print September 6, 2011, doi: 10.1073/pnas.1112535108.

2. Footnote in paper refers to Charles Darwin, Insectivorous Plants (John Murray, 1875), available at Darwin-Online.UK.

3. Paley, Natural Theology, p. 367, published at Darwin-Online.UK.

If you stand for fairness and historical accuracy, snatch that well-designed plant out of Charlie’s gnarly hands and let’s set the record straight.  This plant is more irreducibly complex than Behe’s man-made mousetrap.  (The scientific name, by the way, means “Dione’s daughter’s mousetrap”).  It’s even more exquisite than Ellis, Linnaeus or Paley could have imagined.  Darwin would have croaked if he had been told what these scientists found.  Since the Venus flytrap clearly bears the hallmarks of intelligent design, let’s call it “the Paley plant, known since the time of the famous Biblical creationist, Linnaeus.”

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Comments

  • Joe G says:

    Haven’t you heard? If someone can imagine a way it “evolved” then it is a sure thing that nature could do it.

    See, that was easy.

    “Evolution, bringing imagination to life.”

  • graceout says:

    The “Babel-fish” from “Hitchhikers Guide to the Galaxy” comes to mind. (Yes, I’m strange that way.)  The premise in HGG was the assumption that, since God would NEVER create something that so blatantly demonstrated His existence, then God must NOT exist.

    I’m expecting similar logic to start to “emerge” as more and more ID continues to surge over Darwin.  Love the “Paley Plant”!

  • graceout says:

    By the way, Darwin never did get around to explaining the origin of species in his best-known work, “On the Origin of Species by Natural Selection, or the Preservation of Favored Races in the Struggle for Life.”

  • GuyM says:

    “Darwin wrote a book on insectivorous plants in 1875, in which he described experiments he performed on the Venus flytrap, but he did not provide a theory for how the plant might have evolved, nor did he mention it in his best-known work, On the Origin of Species by Natural Selection.”

    I believe this is not correct. Darwin gave a theory of how all things evolved, its called natural selection. I think you meant to say that he did not give a specific pathway (i.e. intermediate forms) that would have led to the Venus fly trap. I would point out that he also did not give specific intermediate forms for the Platypus or the Penguin and probably one or two other plants and animals. He also did not mention several species in “On the Origin of Species by Natural Selection” but this does not mean that either A) he could not or B) he should have attempted to. Darwin gave possible pathways for several organs and/or animals, to try to conclude that because he did not specifically give such a pathway for one individual plant means that he could not and said plant is therefore proof of ID is somewhat simplistic.

    From a personal perspective I see absolutely nothing in your article to suggest that the Venus fly trap did not evolve, just like everything else. I dare say that the biologists who wrote the paper are also of the opinion that the trap evolved from other flora. This leads me to this…

    “This repetition of Darwin’s name is especially puzzling since the authors made no attempt to explain how this amazing plant evolved (they didn’t even invoke the phrase convergent evolution).”

    I suspect the reason they did not attempt to give explanations of how the plant evolved is because the paper was not about evolution but about the Venus fly trap and how it “functioned”. The authors of the paper would have assumed evolution, as they are entitled to do since they are biologists, and assumed that their general audience would assume it as well, since they would also be biologists (mainly). If I was writing a paper on the latest piece of software I had developed I would NOT give a history of how the computer and computer languages developed. It is another rather long bow you draw to say that because the authors of this paper did not give an evolutionary explanation, which is not the purpose of the paper, that this implies they couldn’t and hence shows ID.

  • Editor says:

    GuyM:
    OK, where is it?  Charlie and his disciples have had 150 years to explain the Venus flytrap.  If not in his Charlie’s books, then where?  The burden of proof is on the evolutionists. You can’t just assume it evolved.  That’s like assuming your team will win the game, so no need to play.  Sorry; ID is on the field, and challenges the Darwin team to match their might to their boast.

    Impressive as your faith in natural selection is (“From a personal perspective I see absolutely nothing in your article to suggest that the Venus fly trap did not evolve, just like everything else. I dare say that the biologists who wrote the paper are also of the opinion that the trap evolved from other flora.”), that’s the problem!  Evolutionists assume it evolved.  Evolutionists state their OPINION.  “The authors of this paper would have assumed evolution, as they are entitled to do since they are biologists”—what?  Nobody is entitled to assume a myth in science.  Please cite the Absolute Authority that granted biologists this entitlement that no other human being can claim.

    Proposition: The Venus flytrap is irreducibly complex and defies evolution.  Please cite empirical evidence (not assumptions) to defeat the proposition.  Don’t play this game:
    1. Assume evolution.
    2. Observe a fact.
    3. Make up a story to force the fact into the assumption of evolution.
    No, no, no.  The referee will call foul.  We (and the PNAS scientists) have just reported on elaborate signaling pathways, genes, structures, hormones, proteins, and all kinds of machinery working together to catch bugs, analogous to systems in animal carnivores, with NO transitional forms between green algae and this angiosperm.  This is evidence for ID and a defeater for Darwinism.  What say you?  Assume evolution and I will have to slap your hand again.

  • Buho says:

    GuyM wrote, “to try to conclude that because he did not specifically give such a pathway for one individual plant means that he could not and said plant is therefore proof of ID is somewhat simplistic.”

    That’s not just simplistic.  That’s a strawman.  Nobody said that.

    GuyM wrote, “I suspect the reason they did not attempt to give explanations of how the plant evolved is because the paper was not about evolution but about the Venus fly trap and how it “functioned”.”

    The old adage applies:  “Evolutionary speculation is inversely proportional to the facts available for study.”  The editor’s challenge above is apropos.

  • John S says:

    ‘look these guys were not attempting to find a pathway, so to use the fact that they didn’t find one to say ID is real is misdirection at best.  Biologists know that it evolved, just like everything else.  Even though we have no idea how, why, when or where – the flytrap evidence is missing.  But because we know we will find it someday we are allowed to use a rather long bow because…because we are smarter than you and your mom wears army boots, you sons of a window dresser.’

    You are entitiled to assume since you are ‘biologists’.  I drop my bow and bow to your prodigious hubris.

    Wait, where do you think you’re going?  Oh no, cmon kids we won’t let Rudolph join in ANY reindeer games will we?

  • huttarl says:

    GuyM, if Darwin’s general theory of how organisms evolved justifies calling the Venus flytrap “the Darwin plant,” would we also be justified in calling an elephant and a fly each “the Darwin animal,” and a coconut palm and A. thaliana also “the Darwin plant”?

  • GuyM says:

    @Editor
    “OK, where is it?  Charlie and his disciples have had 150 years to explain the Venus flytrap.  If not in his Charlie’s books, then where?”
    I believe the current theory is that the plant started out as a sticky trap. Then adapted to mave its tenticles and leaves in a specific direction giving the plant a better chance of sticking to and engulfing a passing insect. Next it sped up its response time to detecting prey. From there it is believed that it would have become more selective and tried to only catch live prey and ignore the debris that lands on it. Finally, it would have developed its sensory hairs and digestive glands to help digest its prey.

    “Evolutionists assume it evolved.  Evolutionists state their OPINION.  “The authors of this paper would have assumed evolution, as they are entitled to do since they are biologists”—what?  Nobody is entitled to assume a myth in science.  Please cite the Absolute Authority that granted biologists this entitlement that no other human being can claim.”

    Not quite correct. The people you are refering to are biologists not “evolutionists”. Biology is founded on evolution, it is not just evolution, and as such they use it to explain observed data and to predict outcomes. The problem with “God did it” is that it explains nothing and predicts nothing, so as a scientist it would be a fairly useless hypothesis. Your use of the word “myth” is also totally incorrect, evolution is a fact that has been observed many times. It is the driving force of evolution, i.e. natural selection, that forms the theory that Darwin devised. Unitl a better theory comes along that explains the data and makes acurate predictions and falsifies evolution due to random mutations guided by natural selection (i.e. Darwinian evolution) biologists are not just “entitled” to use it but are forced to, since it is the only useful theory going around. The last sentence is a bit strange, anyone can use evolution as a “given” since it is the accepted biological process of our origins. Also, the people who make up the biologists are PHD’s who have spent their entire lives studying these matters, they are some of the most brilliant people of our time. I personally believe that entitles them to some things, like their “opinion”.

    “Proposition: The Venus flytrap is irreducibly complex and defies evolution.  Please cite empirical evidence (not assumptions) to defeat the proposition.  Don’t play this game:
    1. Assume evolution.
    2. Observe a fact.
    3. Make up a story to force the fact into the assumption of evolution.”

    Proposition: The Venus flytrap is not irreducibly complex and is a fine example of evolution due to natural selection, using the proccess stated above. Please cite empirical evidence (not assumptions) to defeat the proposition. Don’t play this game:
    1. Assume irreducible complexity and ID.
    2. Observe something that you believe is irreducibly complex.
    3. Make up a story to force the something into the assumption of ID.

    “No, no, no.  The referee will call foul.  We (and the PNAS scientists) have just reported on elaborate signaling pathways, genes, structures, hormones, proteins, and all kinds of machinery working together to catch bugs, analogous to systems in animal carnivores, with NO transitional forms between green algae and this angiosperm.  This is evidence for ID and a defeater for Darwinism.  What say you?  Assume evolution and I will have to slap your hand again.”

    No, no, no. The referee will call foul.  We (and the vast majority of PHD scientists alive today and that have lived over the last 150 years) have just reported on elaborate signaling pathways, genes, structures, hormones, proteins, and all kinds of machinery working together to catch bugs, analogous to systems in animal carnivores, with transitional forms between green algae and this angiosperm.  This is evidence for Darwinian evolution and a defeater for ID.  What say you?  Assume ID and I will have to slap your hand again.

    I have a question for you.
    How did God do it? None of this “it is not for us to know” rubbish either. A clear explanation of how it created everything is required otherwise what is the use of the theory? A theory that states “God did it” is useless, it predicts everything and explains every possible observation, and every other non possible observation, even before you observe it.

  • GuyM says:

    @Buho
    “That’s not just simplistic.  That’s a strawman.  Nobody said that.”
    It was a clear implication of the paragraph, or was I reading a different story? Since it was a clear implication my argument was not a strawman but a valid point.

    “The old adage applies:  “Evolutionary speculation is inversely proportional to the facts available for study.”  The editor’s challenge above is apropos.”

    Pointless, and silly, statement? Not sure how this comes from the sentence of mine that you quoted. The paper in question is clearly about the funcitioning of the plant and has nothing to do with evolution. Darwinian evolution is not the only thing that biologists are studying.

    @John S
    “‘look these guys were not attempting to find a pathway, so to use the fact that they didn’t find one to say ID is real is misdirection at best.  Biologists know that it evolved, just like everything else.  Even though we have no idea how, why, when or where – the flytrap evidence is missing.  But because we know we will find it someday we are allowed to use a rather long bow because…because we are smarter than you and your mom wears army boots, you sons of a window dresser.’”

    I don’t generally like to be rude so I’ll refrain from saying EXTACTLY what I think of this rubbish. John, where did you get this mess from? It doesn’t even come within a bull’s roar of anything I wrote or what was intended from the paper in question. Try again.

    @huttarl
    “GuyM, if Darwin’s general theory of how organisms evolved justifies calling the Venus flytrap “the Darwin plant,” would we also be justified in calling an elephant and a fly each “the Darwin animal,” and a coconut palm and A. thaliana also “the Darwin plant”?”

    I believe that it was named “the Darwin plant” because Darwin was particularly fascinated by carnivous plants and in particular the Venus flytrap. He performed many experiments on them and was the first to show that the plant destinguished between live prey and general debris. It has nothing to do with his theory of evolution due to natural selection. Since he was not particularly interested in Elephants or flys or, more importantly, is not specifically known for said interest, I see no reason why such an honourific would be forthcoming. Truely another pointless comment. Try again.

  • Editor says:

    Well, readers, GuyM fell into the trap.  When confronted with the challenge to provide evidence for evolution of the Venus flytrap, all he could do was tell stories and make bald assertions and appeals to authority.  That’s because evolution is a belief system, not a science.  It is assumed from the get-go, and all evidence is forced into it.  You will also notice that HE was the one who brought up God in this discussion.  That’s because evolution is a religion, supported by religious arguments (i.e., God wouldn’t have done it that way, God is a non-explanation).  When challenged with falsifying evidence for Darwinism, he gave the playground defense of tossing back the charge instead of facing it.

    Now that you see how a Darwinist responds to actual evidence, becoming petty and vindictive, saying “I believe” over and over, I don’t see the point of giving him further opportunities to display his ignorance of history and philosophy of science or to advertise his religion.  We gave him a lot of space.  Let someone better informed try, provided they follow the rules.

  • ranapaige says:

    I am not a biologist, but I am a thinking human being.  GuyM started that diatribe by assuming the impossible right off the bat.  “I believe that the current theory is that this plant started out as a sticky trap”,  Really?  How did that happen, and why?  Did it just pop into evolutionary existaece?  Why different than all the other plants?  Where did the sticky come from and why?

    Remembering that plants don’t think, why and how did it develop all the things that make it do what it does?  And even if it could think, how did it just change itself?  How did it know that it needed to change? How did it survive before it developed “sticky”?  How and why did it develop all the tools that make it work and survive today, and until it did…How did it make it through all those transitions?

    I think that even a biologist would agree that just because you have a theory, doesn’t mean it is always correct as we have seen many, many theories proved wrong over the years by the same people who stood on the proverbial soap box and ranted about how correct they were the first time. 

    One other thing that you assumed and passed on as gospel, implying that those who believe in ID are not smart enough to catch it and don’t deserve to be heard….You imply that all biologists are evolutionists….I hate to pop your bubble Guy, but all biologists and NOT evolutionists!!!! 

    The odds of all those things happening by chance are staggering.  And this is just one plant.  Tell me again how and why you believe that I evolved from swamp goo!  I love fairy tales….. 

  • ironclad says:

    GuyM: “Biology is founded on evolution”

    um, ah, not really.  Biology existed well before Darwin or ever the concept of evolution that you are generously striving for.  Besides, even decades after Darwin, with the advancement of science and the introduction of new fields like Microbiology, not one example of natural selection could be detected, except mere mention of the term ‘evolution’ in passing.

    “I believe the current theory is that the plant started out as a sticky trap.”
    It is good that you believe.  But evidence would have been better.

    “Then adapted to move its tentacles”
    How did the adaptation take place?

    “Next it sped up its response time to detecting prey.”
    How fast the speed?  And how do you know this?

    “From there it is believed that it would have become more selective”
    It is “believed”? Again?  Where does belief stop and the evidence begin?  How did it become selective?  Please describe the scenario in more scientific terms.

    “and tried to only catch live prey”
    How do you know the plant “tried”?  How many attempts before the plant was successful?  Did you quantify this?  And how are you sure that it “only” tried to catch the live prey?

    “and ignore the debris that lands on it”
    All of this you found out through your “belief”?

    “Finally, it would have developed its sensory hairs”
    How did it develop the hairs?

    “and digestive glands”
    How did it develop the glands?

    “to help digest its prey”
    So how did it manage to do all these things (and survive) before these traits came along?

  • Editor says:

    Readers: Further argument with GuyM is now closed.  We gave him more than the usual space to present his opinions.  Then he wrote a very demeaning rant that broke the rules for comments (not posted).  Rather than give him any more opportunity to display his passionate ignorance, let’s all focus on the Venus flytrap itself and the evidence presented in the article.  If you wish to comment on that, fine.  Please keep your comments short and on point.  Remember that this is a news service, not a forum.

  • mescalante says:

    The lead author of the PNAS paper writes:

    Dear all (especially the Editor),

    First of all thank you very much for the time you took in reading the paper and for all the comments related to it (the good and the critical too). Second of all this paper never tried to explain any evolution on the Venus flytrap, only to get a better understanding on how this amazing piece of nature works, because is unbelievable that a plant can do what the Venus flytrap can do, at least I find it fascinating. I’m not an evolutionary biologist, even when I found evolution a really interesting matter I will never try to explain the evolution of anything because I don’t have enough knowledge to try it. If anyone has any questions, about (molecular biology) the findings I’m more than willing to answer. Thank again for the critics I’ll take it into account for the next one.

  • Editor says:

    Dear Dr. Escalante-Perez,
    Thank you very much for your comments.  Your humble attitude is refreshing.  Actually, the molecular biology portions of the paper were the most interesting and insightful, moving the science forward on this wonder of nature.

  • TruthSeeker says:

    Excellent article and also well-thought out response to some rather negative comments by a poster. I found it all helpful and illuminating.

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