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Post by lordpyro on Jan 9, 2012 23:15:41 GMT
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Post by bobtheglob on Jan 9, 2012 23:24:17 GMT
Thats pretty cool! I just wish I could see a pic of it.
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Post by lordpyro on Jan 9, 2012 23:39:17 GMT
i agree i tried to find one and wasnt able too im sure there will be some soon enough
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Post by ICPS-bob on Jan 10, 2012 5:52:14 GMT
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Post by Randy Zerr on Jan 13, 2012 2:54:52 GMT
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Post by Apoplast on Jan 23, 2012 16:01:01 GMT
Okay, so I anticipate this comment will open a can of worms (given the article, enjoy the pun). I would therefore like to make two disclaimers before I begin:
1. This was a well done study and for a single does a great job of demonstrating that this species is likely obtaining a good amount of animal derived N in natural settings.
2. I fully recognize that plant carnivory occurs along a gradient and is not a dichotomous measure.
Now for the comment. This paper got me thinking about how carnivory in plants is defined. The current operating metric for classifying a plant as carnivorous seems to be trapping animals and efficiently obtaining nutrients from said animals. At first glance that all seems well and good. However, I feel as though it misses something important which was highlighted by the recent study of teasel (Dipsacus).
Let's use that example and that of bromeliads to examine the first criterion for plant carnivory. Both teasel and many broms collect water. Any plant that collects water is likely to trap and drown insects. I can show this with a can partly filled with water placed just about anywhere outside. The real question becomes whether these water holding structures are modified to increase trapping efficiency. I've seen no studies that compare insect capture rates between suggested carnivorous plants and dummy pitchers with no modifications (although they may be out there).
The second criterion is digestion. All plants are capable of digesting proteins. All. This is because all plants synthesize proteins and then break them down to translocate them across their tissues. You may be saying "But this is internal, isn't it unusual for plants to express this trait externally?" No. When first discovered the uptake of amino acids through roots was considered uncommon. Upon further examination it was discovered that amino acid uptake is typical. Beyond this, root tips of a variety of plants have been shown to exude protease enzymes, increasing the availability of amino acids for uptake. Though it has not become widely recognized, this process is likely important and typical in most plants as well. Thus, it is probable most plants digest proteins external to themselves. The real questions then becomes do they have modifications to do so for animals they have trapped?
What is the point? In both cases, the difference between plants that are probable carnivores and those which are clearly not can be viewed as a question of degree or a question of trait modification. I would like to argue for the latter. The latter implies that the species is under selection for obtaining animal nutrients. It is free from the particulars of the trap or digestion, but restrictive in the sense that it only allows for plants which either have or are likely evolving structures for the efficient acquisition of animal nutrients.
This brings us back to the study on Philcoxia. While I believe this to be a very well done study, I think that it, and all studies aiming to quantify nutrient movement using isotopic tracers are missing the critical evolutionary component. The leaves of Philcoxia are indeed highly modified, but given that it is not only nematodes which are adhered to the surface but also sand grains as the authors note, this modification could be under selection primarily to attach the sand grains. This adaptation would create diffused light (the sand looks quite white) or would increase the boundary layer thus reducing transpiration losses. Given the prevalence of nematodes in the soil, it seems likely that any sticky surface in the soil has the potential to trap and kill nematodes; the uptake of the animal nutrients is then a secondary benefit.
The definitive study on carnivory, for Philcoxia or any species, is one that focuses less on element transfer and enzyme presence, but rather demonstrates that the probable carnivorous trait is primarily under selection for the efficient acquisition of nutrients from animal sources.
I could go on about how this related to a number of known and probable carnivores, but if you've gotten this far you have had enough patience with me for the moment. I would very much like to hear the thoughts of people actively researching carnivory in plants. I know a few of these scientists read this forum, and it would be informative to get your thoughts on the matter. Thank you anyone who has read this far!
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Post by Dave Evans on Jan 24, 2012 3:47:01 GMT
"The Philcoxia minensis plant has flowering leaves above the ground too, but it's what's beneath the soil that has fascinated scientists. The subterranean leaves, each about the size of a pinhead, are able to absorb some light through the white soil of the Cerrado, a tropical savannah region in Brazil. Prof. Oliveira was fascinated by the Philcoxia plant because its underground leaves were seemingly lacking in function, unable to absorb much light because they lacked direct exposure to the sun. But the team supposed that if the leaves didn't perform a regular function, they must have a more unusual one. Read more: www.dailymail.co.uk/sciencetech/article-2085079/Worm-eating-plant-Philcoxia-minensis-discovered-Brazil-traps-prey-sticky-underground-leaves.html#ixzz1kLFI9iJQ" I cannot understand that quote. Of course the leaves are used for absorbing light. The plants are all native to white sands in exposed habitats. The sand conducts the light to the leaves no problem. All I see are rosettes of leaves and flower stems; does this author imply the flowers are absorbing and doing the photosynthesis for the plant? Really, I think it is the leaves, the sand and worm covered leaves, just like in most other carnivorous plants. Is this how those CP Legends get started? Did Gavin Allen just make this stuff up for his article? "Flowering leaves" indeed. The leaves above ground look the same as those from below. The only two kinds of CP's I can think of the do not use the leaves for photosynthesis are Utricularia and maybe Genlisea. And the original article by Caio G. Pereira, et al. doesn't mention this at all. Rather they mention, 'the leaves are placed near ground level; with most just under the surface.' They also discuss how the environment the four species are native appear conductive to the development of carnivory which is a completely different subject. |
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Post by John Brittnacher on Jan 24, 2012 3:50:24 GMT
The definitive study on carnivory, for Philcoxia or any species, is one that focuses less on element transfer and enzyme presence, but rather demonstrates that the probable carnivorous trait is primarily under selection for the efficient acquisition of nutrients from animal sources. How are you going to show a trait is under selection for carnivory? You end up with arguments like VFTs have traps because if the traps didn't work they wouldn't have them. That is why most scientific approaches look at nutrients and other things you can actually measure. You many notice that in spite of all the media sites promoting Philcoxia there has been nothing on the ICPS web site per se. It has been mentioned a few times in CPN. Personally I don't think we know enough about the plant to admit it to the club as a full member yet. |
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Post by Apoplast on Jan 25, 2012 0:44:42 GMT
Hi Dave - I agree some of the wording was a little strange especially given that the publication made it into PNAS. Regardless, it was not this article alone that made me consider the limitations of the current paradigm for classifying a plant as carnivorous.
Hi John - My concern is not whether Philcoxia or teasel are popularly considered to be carnivorous. Indeed there still seem to be people who do not consider Roridula carnivorous but paradoxically are happy to include Darlingtonia. I'm more interested in how these adaptations are quantified.
Selection strength can and is quantitatively measured on populations of various species. I don't claim that there won't be difficulties in this case given that any uptake of limiting resources, even under accidental circumstances, are likely to increase fitness measures. But I suspect it will eventually be necessary to incorporate an evolutionary understanding to defining carnivory as is the case with other traits. As we find more and more ways in which plants are taking up nutrients, isotopic tracer studies will be considered inconclusive as a method to declare carnivory in plants.
I believe that finding a conclusive assay of the strength selection for the efficient acquisition of animal proteins is going to be necessary in both defining the role of plant carnivory in the spectrum of plant nutrient uptake and in understanding how the unusual adaptation arises. It is fertile ground for future research, and the person or persons who can detail how a conclusive study of that nature looks will revolutionize how carnivory in plants is studied.
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