leeb
Urceolatae
Posts: 24
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Post by leeb on Sept 2, 2009 10:57:39 GMT -10
Sam,
N. albomarginata does not catch only termites so in that sense its traps are not termite specific.
But as long as its catching termites benefits the plant there would be selection for it to do so.
As you noted earlier evolution continues, today its food supply is over 50 percent termites, perhaps in future a descendent species might evolve that catches 100 percent termites.
Its pitchers may decay after filling with termites, but as long as this does not occur until after the plant has been able to extract nutrients from the termites this does not matter, as the full pitchers would be unable to catch other prey anyway. There only needs to be selection to evolve traps that delay decaying until after the termites have been at least partially digested, and the fact that not all traps that catch large numbers of termites decay suggests this is occurring.
The observation that other Nepenthes produce trichomes is interesting, but the N. albomarginata ones are more obvious to humans, so perhaps they are also more obvious and/or palatable to the termites.
It would be interesting to know if the N. bicalcarata plants that had their trichomes removed had caught any termites; or if they had been visited by termites that removed the trichomes but avoided being caught. More observations are called for.
N. albomarginata provides a food supply, the trichomes, near its traps, which results in the social termites being caught only occasionally, but in large numbers when they are caught. Over the life of a plant which potentially spans many years or decades this can give a considerable benefit and be selected for even if the chance of any individual pitcher catching termites is not 100 percent. Thus the selection can be for taking advantage of the occasional bonanza catch of termites. After all the studies done have shown that the plants are managing to get more than half their prey as termites.
The continual background catch of other prey such as ants would help the nutrient status of the plant as well of course.
If the plant could attract termites from a distance this would seem to be even better for the plant; however firstly the termites may not have sense organs capable of detecting food at a distance, and secondly if they could attract termites from a distance this would just result in the traps filling up as soon as they opened, the plant would then have to digest the termites and grow new pitchers before it could start again, which might not speed up the process much depending on how long it took to grow new pitchers; or it could have so much prey in all its pitchers that it was overwhelmed in nutrients and got the plant equivalent of indigestion; or perhaps worse still if the trichomes were very attractive to termites they would find the developing pitchers and remove the trichomes before the pitcher opened and thus the plant would not catch any termites at all.
The Hospitalitermes termites and their near relatives forage for fungi, lichens and algae on surfaces in large colums, this presumably results in some climbing onto the trunks of trees in forest environments. I do not know how high they climb, it would indeed be interesting to know how many are caught in N. albomarginata upper pitchers as opposed to lower ones.
And N. albomarginata may not need a specialised termite trapping strategy, merely inducing them to gather near its pitcher openings seems to be enough to take advantage of their column swarming behaviour.
I also wonder, given the size of the columns of these termites involving hundreds or thousands of termites, if when they find one of the pitchers of N. albomarginata the column necessarily spreads out in the vicinity and as a result finds any other available pitchers on the plant.
LeeB.
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Dave Evans
Nobiles
dpevans_at_rci.rutgers.edu
Posts: 490
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Post by Dave Evans on Sept 3, 2009 10:56:00 GMT -10
How does this study support the suggestion that N. albomarginata “specializes” in the capture of termites. As far as I can tell, it does not. It merely quantifies one data set. It does suggest the white band is a termite lure. But only after the termites literally walk into it while foraging. Are you saying because it is not a visual lure, which I doubt would work on termites as they doesn't see very well, it is not a lure? You're saying N. albomarginata makes food for termites for no particular reason, but does make nectar/food like all other species of Nepenthes for generalized insects to eat as a lure? Is that your theory? Sam, I think maybe you've got the evolutionary process backward. It would be the action of termites in feeding themselves to the Nepenthes which would encourage the development of the normal level of hairs under the peristome to change into this solid band we see on N. albomarginata. I don't see this evolutionary process being much different from the mutations, species interactions and reinforcing behaviors in both N. albomarginata and N. lowii. Both are examples of how animals interacting with plants caused them to speciate and they did so by finding new, and possibly unique, uses for the same structure all the other species have. Most Nepenthes imitate flowers, but termites don't really visit flowers... (And tree shrews don't crap in flowers either) Now if the plant isn't imitating a flower and is producing food which is only eaten by specific termites, I would have to think it is those termites which acted as the driving force in the evolution of the species and now continue to reinforce the specific trait as they are still feeding themselves to the plant whenever they can. Considering how dominant albo is in hybrids, I think this selection process has been acting on N. albomarginata for a long time. Throughly scrubbing away (or not letting them develop) all alleles which lead to flower imitation; keeping it in the past so-to-speak. I'm under the impression ants are dominant now, but in the past, ants were fewer and termites more dominant. I'm thinking Nepenthes probably lost adaptations for termite capture due to ants being more numerous and now mostly capture ants. However, N. albomarginata is still catching termites so it is clear the termites are selecting this species at a higher rate than other Nepenthes species. Could some other past species of termite had a preference for other past species of Nepenthes? I don't see why not... Nepenthes in general make highly specialized traps; refining the trap further to a specific prey type seems like a continuation of the same process to me.
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Post by leilani on Sept 3, 2009 21:50:29 GMT -10
Dave,
The fact that N. albomarginata produce and termites eat the tricomes does not necessitate the conclusion that they act as “lures”. This is the suggestion (one of the premises) of those advocating this hypothesis. In lieu of the identification of some termite-specific method of attraction this remains simply an assumption, a suggestion, the “once upon a time” of this story. It has clearly been established that termites treat these tricomes as a food source when found but this fact alone does little toward offering evidence that they are specifically produced to take advantage of a gullible band of termites. As far as I know, to date, no attractant has been identifies or isolated. (If, I was to assume that these tricomes act as “lures” then, I would think that a chemical process would be the most likely method of sensory signaling.)
No I’m not! I’m questioning this very assumption. To say “N. albomarginata makes food for termites” assumes the conclusion I'm questioning.
Look, its a good story. I don’t think that it is quite ready to be codified into knowledge, as it seems to have become in Stewart's book. (In Clarke's Nepenthes of Borneo this hypothesis was still treated with a dash of healthy skepticism and a call for more study.)
Personally, I think the hypothesis fails for flawed assumptions and that the evidence produced so far fails to the point. One fundamental assumption is made explicit by yourself and seems to have been accepted without question from the start: that the tricomes found in the banded area (and elsewhere) serve a function parallel to nectar production. However, I think this assumption breaks down quickly when scrutinized. I think the whole “bait and trap analogy” may be getting overplayed in the analysis of the data. This assumption of parallel functions lies at the heart of the whole hypothesis and seems, to me, to have biased the process of study itself.
It seems perfectly plausible to me that the whole scenario of the “bonanza catch” may well have little to do with N. albomarginata at all .... other than it's good fortune at being there when it rains candy. And, that the “bonanza catch” is more likely an epi-phenomenon of termite behavior rather that the result of any scheme by N. albomarginata to win the environmental lottery. After all, other species, if we accept Moran’s testimony, have also won the termite lottery without obvious bands or tricomes.
There are better ways to right a good story than to just copy a best seller.
The argument for N. lowii collecting bird and mammal scat would seem less problematic as it it is merely an extension of the existing trapping mechanisms and processes and does not require we assume any new modalities of attraction.
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Dave Evans
Nobiles
dpevans_at_rci.rutgers.edu
Posts: 490
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Post by Dave Evans on Sept 4, 2009 7:10:39 GMT -10
No I’m not! I’m questioning this very assumption. To say “N. albomarginata makes food for termites” assumes the conclusion I'm questioning. Look, its a good story. I don’t think that it is quite ready to be codified into knowledge, as it seems to have become in Stewart's book. (In Clarke's Nepenthes of Borneo this hypothesis was still treated with a dash of healthy skepticism and a call for more study.) Personally, I think the hypothesis fails for flawed assumptions and that the evidence produced so far fails to the point. One fundamental assumption is made explicit by yourself and seems to have been accepted without question from the start: that the tricomes found in the banded area (and elsewhere) serve a function parallel to nectar production. However, I think this assumption breaks down quickly when scrutinized. It seems perfectly plausible to me that the whole scenario of the “bonanza catch” may well have little to do with N. albomarginata at all .... other than it's good fortune at being there when it rains candy. And, that the “bonanza catch” is more likely an epi-phenomenon of termite behavior rather that the result of any scheme by N. albomarginata to win the environmental lottery. After all, other species, if we accept Moran’s testimony, have also won the termite lottery without obvious bands or tricomes. Well, I still think it is more of the termites targeting the plant, than the plant targeting the termites. Would another method of attractant really be needed? If the band of hairs under the peristome is enough to reliably cause these termites to stampede and thereby push each other into the pitcher opening--would the plant really even need to produce a chemical lure that acts on termites? Sure, other Nepenthes plants catch the same termites, but near the same rate? My empty water buckets also catch random insects, but they are not producing any attractant... Sometimes herding animals will stampede off of a cliff. Was the cliff "designed" to catch them per-sey? Is occasionally falling off a cliff enough of an ecological push to end the stampede behavior in the herding animals? Apparently not, it still provides the whole species with an overall protective behavior even if it sometimes kills a fairly large number of individuals. Now when human hunters take advantage of this behavior; it is a well designed trap...
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leeb
Urceolatae
Posts: 24
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Post by leeb on Sept 4, 2009 10:19:45 GMT -10
Sam,
I agree that there is currently no evidence that the trichomes act as lures. However as noted above, it may not be possible to lure the termites if they have no means to detect food at a distance, and even if it was possible it may be counterproductive to do so. However if the termites are common enough that during the lifespan of a pitcher the probability of termites investigating it approaches unity then luring termites is not necessary; merely providing a food source to induce them to stay on the pitcher long enough for large numbers of them to be trapped is sufficient. Then the selection pressure is to catch the occasional termite bonanzas, there must be enough tasty trichomes supplied to keep the termites occupied long enough to fill up the pitchers. Other Nepenthes species pitchers may occasionally catch the same termites as they crawl over the pitchers but not in the same numbers because they do not keep the termites occupied long enough removing tasty trichomes.
LeeB.
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Post by leilani on Nov 9, 2009 23:38:41 GMT -10
Since I have about played out all I have on N. albomarginata and termites lets back up a bit to N. lowii and N. ephippiata.
I did a little research on this and found almost nothing but conjecture. As far as I can tell the suggestion that bird excrement may play a significant role in Nepenthes feeding activities originates, as noted by Clarke, with Juniper et al. in their study of N. pervillei. Clarke extends this suggestion to N.lowii in his book "Nepenthes of Borneo". Clarke states that "some observations I made suggest that the upper pitcher of this plant may have evolved to catch something very different from insects." He is cautious and uses words like "suggest" and "may have".
Clarke's suggestion is that N. lowii "may" have evolved ( .. or be evolving) to capture bird excrement is interesting but, except for his observations that bird dropping comprise a fair portion of the "catch" in N. lowii upper pitchers, is unsupported.
Stewart's new books continue this line of speculation but also offers no evidence whatsoever.
I like when scientists allow themselves to speculate beyond the data and both Clarke and Stewart wisely frame these suggestions as hypothesis rather than scientific fact.
Dave, on the other hand, states this story as if it were fact.
and repeats Clarke's "story fillers" ...
This seems to be another story gaining acceptance simply by its repetition. The only reference to tree shrews I can find at all is in Clarke's book where he reports that "Corner (1996) noted that tupaias often scrambled among N. lowii pitchers."
As for the supposed unique characteristics of N. lowii and N. ephippiata: extra strong pitchers and tendrils, modified peristome with ridges "for the shrews paws to grip" and comfortable toilet design ...... come on! This is just filling in the blanks to facilitate the story ..... not evidence.
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Dave Evans
Nobiles
dpevans_at_rci.rutgers.edu
Posts: 490
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Post by Dave Evans on Nov 10, 2009 12:49:05 GMT -10
Clarke's suggestion is that N. lowii "may" have evolved ( .. or be evolving) to capture bird excrement is interesting but, except for his observations that bird dropping comprise a fair portion of the "catch" in N. lowii upper pitchers, is unsupported. Unsupported by a lack of what? People continue to find N. albomarginata pitchers full of termites and people continue to find scat; even watch and tape tree shrews using the pitchers of N. lowii as toilets. Feces are also found in pitchers of N. macrophylla. Could you explain what you mean by unsupported? Other species of Nepenthes have not been observed to have animals interact with them in the same manner and neither has N. ephipeata as it has rarely even been observed in habitat... These interactions are species specific, only one species of termites reacts of N. albomarginata in this manner and so far, only one species of tree shrew has been observed using N. lowii-service stations. Only one species of ant has been found living on N. bicalcarata... Seems to fit the pattern. Only one or two crab spider(s) commonly found on wide spread N. gracilis, the association doesn't seem quite as strong in this pairing though.
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Post by thezyo on Nov 10, 2009 16:22:19 GMT -10
This brings up a question I've had for a couple months - I want to know what to feed my neps for their optimum growth, which I'm taking to mean in the wilds in Sumatra/Borneo/etc. where they have been living for at least a few hundreds of years. I think it would be good to start a list somewhere of the sorts of prey that are naturally found in pitchers in the wild, be it termites or what have you. I know termites have been found in albomarginata, snails in jacquelineae, leaf litter for ampullaria - I'd like there to be more emphasis on taking pictures of the *insides* of pitchers when people on the hunt for them in the wild, because I'm certain bical wasn't made for consuming cichlid fish pellets in the fields of the tropics.
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Post by leilani on Nov 10, 2009 18:00:51 GMT -10
Dave Evans .... Uhh ........... evidence. By unsupported I mean in the scientific sense of empirical observation and quantification. Where are the citations, where are the pictures, the video, the studies. As I said, the citations above were all I could find. There may be much more evidence than I am aware of and if, you know of any, please point it out to me. How about a picture of a lemur sitting on a N. lowii or N. ephippiata pitcher? How about an observational study that counts the number of times these visitations happen. How about a quantitative analysis of the feeding patterns of these plants. The whole lemur conjecture seems, to be, to be a fun but too easy and misleading extension of the bird hypothesis. Again, to me, Clarke's conjecture seems a good story based upon reasonable assumptions and I like it. What I am saying is that these conjectures remain just that and that until more evidence is presented they should be treated with a good deal of skepticism. Just the other day a friend observing N. ephippiata asked about the "fluffy white stuff". I found myself repeating the lemur story and they loved it. I did, however, end the converstation with "at least that is what they say". thezyo ..... Welcome to the forum! Growing your plants to optimum potentials means supplying them with the nutrients and conditions they require. It makes no difference where these nutrients come from.
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Dave Evans
Nobiles
dpevans_at_rci.rutgers.edu
Posts: 490
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Post by Dave Evans on Nov 10, 2009 18:42:17 GMT -10
www.msnbc.msn.com/id/31507593What lemur story about N. ephippiata? Personally, I suspect N. e. might have an association with a bat or bats... That puffy structure formed by the downward pointing elements (transposed peristome ribs, hanging from the lid just like in N. lowii) and the huge, concave lid looks like it would reflect a very recognizable pattern via sonar. I also have a couple of friends who've visited Borneo and personally observed twenty and fifteen years ago that N. lowii pitchers, "are full of crap. You really don't want to be bumping into them and they can be really difficult to avoid as they occur in giant clusters hanging down from the canopy." LOL. I think even lay people can recognize a pile of turds without taking its temperature, or performing some other "scientific ritual", first! You're saying everyone making these observations are merely repeating the same stories. If they continue to see the same things, I suppose their reports might sound repetitious... There is some disconnect here, but I'm not sure what... That's what is called good science, when the same suspect facts can be observed over and over again by different people. It is when they are only seen once or twice that you really have to question the suspect "facts". Nobody finds much insect prey in N. lowii upper pitchers, whether they are named Clarke, Moran or Scholl. They do find pitcher after pitcher filled with excrement. I swear, Sam, you just like to see me put this in writing N. ephippiata is completely data deficient and its range is not even clearly known. There hasn't been any animal/plant interactions scientifically recorded or casually observed for N. ephippiata to date. Considering how similar N. lowii and N. ephippiata are, it would not surprise to me if we were to find out ephippiata also has a very similar animal association. But there isn't any data at this point. (which is what you seem to be indicating is the story of N. lowii, I think...) For Clarity:N. lowii, well known and moderately studied species. Lots of data. N. ephippiata, poorly known and rarely seen species. A couple of voucher specimens from a couple of mountains. No other data. And only clone in cultivation--I hope this has changed or will change soon.
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kain
Insignes
Posts: 144
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Post by kain on Nov 14, 2009 11:17:49 GMT -10
It seems to me that, whether we are talking about N. lowii or N. albomarginata or any species adaptations, we are discussing chicken and egg questions. As in: which came first, the termites or the trichomes? Species evolve both independently, through mechanisms such as genetic drift, and co-dependently through selection pressures due to changing environmental factors, prey composition, etc. While we're at it, we might discuss whether N. albomarginata and the specific termites it preys upon simply like to live in the same type of soil and so are usually sympatric and that both are adapting to the environment and prey composition in which they find themselves. It seems to me that, if there are usually a lot of termites in the areas in which N. albomarginata grows, the plant would evolve in a manner that takes advantage of an ubiquitous food source. While I agree that one cannot lend an anthropomorphic slant to the discussion (i.e. N. albomarginata lures hapless termites to their inevitable doom through devices of sugary cleverness) it is true that advantageous mutation leads to selection. Too, one must always remember that natural selection only acts upon the individual and never upon the species as a whole. Individuals that survive and are more fertile contribute more to the general population than those that (perhaps) do not possess the same advantageous mutation(s). Time yields a species more fully at home within the environment (read that: "prey composition", in this case) in which it lives. It is not a matter of intent, more a matter of survival. In terms of scientific proof, Sam is right that experiments done in controlled conditions with equal numbers of different prey types might lend some clarity to the "termites and trichomes" question, but such experiments would likely be impossible in situ and so would have other problems stemming from their artificial circumstances. Too, isolating some form of chemical lure from N. albomarginata trichomes would go a long way toward justifying an as yet unclear mechanism for prey attraction (if one indeed exists). This also applies to the N. lowii question - if tree shrews (or whatever) like the same kinds of trees as N. lowii (or the same environments in some way, in any case), there is no reason that N. lowii would not evolve to take advantage of a large food source. In response to a "Why would it?" question, I would simply say, "Why not?" Chance plays a large part in the evolution and co-evolution of all species. As a last point, I would say that evolution toward increasing specialization in sympatric, closely related species is almost inevitable as each evolves to exploit specific environmental conditions (like prey resources) differently from its sister species in order to decrease the competition it has to deal with. By which I mean that those who experience less competition will tend to do better and eventually dominate the species' gene pool. Duly noted that not all Nepenthes are sympatric, but most of them are sympatric with at least one other Nepenthes species. Too, there is nothing like an isolated environment with limited resources (islands, high mountains, etc.) for increasing species diversity.
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Post by leilani on Nov 14, 2009 15:07:36 GMT -10
Dave ... It’s a great way of getting other people to do your research for you. Thanks for the article. It is exactly what I requested and pretty clearly supports the conclusion. kain ..... Clarity and common sense ..... I agree. Unfortunately, “devices of doom” and “sugary cleverness” make for a more entertaining story. yes .... The conclusion would not seem to pay proper respect to the role of environmental ‘stress’ in evolution. An organism without significant stress my well reproduce to great numbers but be so fragile as to collapse to extinction with even a moderate change of conditions occur. One might reasonably argue that those species experiencing more competition will be stressed to a greater level of environmental fitness, survive friendly and unfriendly times and “eventually dominate the species’ gene pool”.
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kain
Insignes
Posts: 144
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Post by kain on Nov 14, 2009 15:32:33 GMT -10
You point out the exact difficulty with increasing specialization in any species. Yes, they are better adapted to the specific environment in which they find themselves, but they are more vulnerable to environmental changes. Generalists are better at adaptation to changing conditions, but specialists persist in every environment despite this fact. I see no reason why there wouldn't be both generalist and specialist Nepenthes. In the case of N. albomarginata (and N. lowii, etc.) we may be dealing with plants tending towards specialization. As to whether they are becoming more or less specialized, that requires more time than any of us have.
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kain
Insignes
Posts: 144
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Post by kain on Nov 14, 2009 15:46:42 GMT -10
To get back to the original point of this discussion, the "causal element" is mutation or genetic drift. Features don't evolve "to do" anything. They happen randomly and then are selected for or against by environmental conditions that impact the viability of the individual(s) with the mutation. The environment is what determines whether a mutational feature is of benefit or is detrimental and any assumption we make about the whys and "purposes" of it is philosophical noodling and impacts the organism itself not at all.
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Post by leilani on Nov 14, 2009 16:16:49 GMT -10
.... very nicely stated.
.... these alone?
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