Ghost pipe

I discussed symbiosis last week and mentioned the mutualistic relationship between a plant (Trout Lily) and an animal (an ant). There are, of course, other sorts of symbioses. Commensalism occurs when one participant benefits while the other is not harmed. And relationships are parasitic when one organism benefits, to the detriment of the other.

Ghost Pipe belongs to the genus Orobanche. This innocent looking woodland herb makes its living by parasitizing other plants. Individuals are entirely without chlorophyll and are not, therefore, capable of photosynthesis. They have modified roots, called haustoria, which attack, penetrate, and link to the plumbing (xylem (water supply) and phloem (nutrients)) of the host. Individuals are entirely dependent and are obligate, holoparasites.

If we assume that the progenitor of the genus was photosynthetic, I wonder how parasitism of this sort developed. It is difficult to imagine that a single mutation could have given rise to holoparasitic plants because all of the photosynthetic machinery would have had to have been be lost (mutationally) and, at the very same time, all of the machinery required for parasitism would have had to form. Although this seems unlikely, there are those who would argue that novel adaptive strategies can happen in this way, and all at once. Be that as it may, I imagine a slower, less hurried, move from one strategy to the other. I imagine that a fully photosynthetic ancestor gave rise to plants like Orobanche, but only through a hemiparasitic intermediate such as Mistletoe.  Although hemiparasitic plants are capable of providing nutrient via photosynthesis, they tap their hosts for water and mineral support. From there, the mutational jump to holoparasitism would seem more plausible.


19 thoughts on “Ghost pipe

      • No, I mean the great mystery of how a world in which nothing had ever been alive suddenly became a world in which one thing was alive. And not only that, but the thing that was suddenly alive also had the ability to reproduce itself. That’s two miracles in quick succession.

        • Ahh .. OK .. I get it. Yes. I’ve heard people say that Louis Pasteur certainly proved to all of us that Spontaneous Generation was nonsense. And, at the same time, however, the same people will agree that it had to happen once to account for life, as we know it. And, I’m OK with that. I think the two miraculous events you describe are actually one-and-the-same. One of the defining characteristics of things that are alive is that they reproduce. Given that definition, I’m OK with theoretical considerations of how those first replicators might have arisen. If you have genuine interest in the topic you might read Dawkins’ text, The Blind Watchmaker. The book and the topic, in a more general sense, are things that I have much interest in, but one which are not widely discussed.

        • Oh .. I forgot .. no argument I would make concerning the rise of that capacity of replication would suggest that any part of the process happened rapidly. The sorts of scenarios which get serious consideration required something more than a billion years to work through. And, that’s surely not sudden, by any measure.

  1. The big news here in NL these past months centers around our hapless provincial government. With that in mind i’m tempted to draw parallels from the ghost pipe to individuals who’ve been party to all the fun. I think I’ll refrain, though.

  2. Very interesting – I am uprooting creeping common bindweed often this season … and I was thinking how unfair they are, spineless parasites using other plants that manage to grow real stems 🙂

  3. I barely have enough brain cells to follow the science. What I can relate to is the perfect name for this specimen! Amazing that such a long stem can support the bloom!

  4. I’ve never seen this one before, but have seen Dodder frequently (is Dodder a hemiparasite? A strategy did didn’t know about!). Also speaking of evolutionary jumps, hasn’t more recent evidence (and this is totally from my memory of something I may (or may not) have read, so take that for what you will), shown punctuated equilibrium to really not be supported?

    • Good question about PE. I believe that answer is yes and, at the same time, no. It depends on what sorts of organisms you’re investigating. It seems that certain sorts of life histories may lend themselves more easily to a temporal pattern like PE while other life histories may lead to a more gradual pattern of divergence (r versus K selected species for example). It also depends upon the timescale studied. Dawkins has pointed out that, if you’re time scale is small enough, all divergence must be gradualistic. As time scale gets larger and larger, however, you may not be able to resolve gradualistic chance and conclude that divergence occurs in jumps or in rapid bursts. So, you see, your question is a very good one and I think any final answer is not clear. I think the best answer is … it depends. At this point we will proceed with tests of multiple working hypotheses. Thanks for checking in! It was great to see your name in my comments section. Oh … forgot … I believe Dodder is holoparasitic. I see no mention of it having the capacity to support itself photosynthetically. I believe that the formation of haustoria is ‘switchable’ such that they are only produced when a suitable host is recognized.

      • That is as far as I understand it to be applicable as well. Depending. But is this a question of simplest explanation, as we don’t know of transitional forms or enough time to “justify” gradual change so we just “assume” PE occurred. Or is more a lack of understanding?

        • I’m not sure I’ve presented this argument to you before Jen … but think about it … if your record is good enough, and your time scale fine enough, all change is gradual … unless, of course, you’re going to make the argument for saltationism. Although there is some chance that large, homeotic, mutations might result in a selectively advantageous genotype it is more likely to be nonviable. I think it is more reasonable to assume that change takes place in very small steps (cummulative step selection). And, you are correct in pointing out that our understanding of these changes is incomplete. This incompleteness can make what were, in real time, gradualistic changes (occurring over long periods of time) look to have been punctuated (and taking place in a geologic instant). Thanks for asking. D

  5. I photographed some of these for the first time a few weeks ago. My uneducated guess might be that they developed the twin strategies over time and then abandoned photosynthesis for a possibly easier way of obtaining what they need. Sort of the same as your theory but not as well-expressed.

    • Indeed. In the competitive world of plants, whatever advantages there were in growth and in reproduction would be selected for. Plant parasitism of this sort is an evolutionary no brainer … just another way of making a living (if not an unusual one for an organism which is typically photosynthetic). I wonder how many times, in the evolution of plant families, parasitism has evolved? I’ll wager … many, many times.

Respond to this post if you'd like.

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: