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Author | Topic: Cells into Organs: could it evolve? | |||||||||||||||||||||||||||
Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Dear Q,
In point of fact, most of the articles I checked continue to call the various polyps that make up Physalia individuals, making the organism not just a colony, but a symbiont This doesn't make it a symbiont, colonies are made up of individuals.
(see, for example, the UMich Animal Diversity entry on Physalia physalis and the UCMP Berkely Hydrozoan page are pretty typical. I have actually visited both of these sites previously and neither of them suggests that the different Zooid lineages were once distinct, nor do they agree with your description of the Siphonophores budding.
UMich Animal Diversity writes: An "individual" is actually a colony of unisexual organisms. Every individual has specific gonozooids (sex organs or reproductive parts of the animals, either male or female). Each gonozooid is comprised of gonophores, which are little more than sacs containing either ovaries or testes. Physalia are dioecious. Their larvae probably develop very rapidly to small floating forms. Fertilization of P. physalis is assumed to occur in the open water, because gametes from the gonozooids are shed into the water. This may happen as gonozooids themselves are broken off and released from the colony. So Physalia are dioecious? that hardly seems consistent with your budding description, but then your whole budding concept for individual zooid lineages seems bizzarre when you are claiming that there is a specific reproductive lineage of gonozooids, unless they are for a distinct sexual phase of the Physalia life cycle? But then how would that work?
However, I think you'll be hard-pressed to find any article that doesn't describe these organisms as symbiotic colonies of different polyps/medusae. But most hydrozoa have both Polyp and Medusa stages, why shouldn't the different Zooids simply be specialised developmental sub-programs, with the gonozooids entering directly into the medusoid reproductive phase. What you are suggesting now is considerably different from your original claim unless you are using 'symbiotic' in a strictly cross species sense, in which case I suspect you are wrong. You don't really seem to have provided any substantial support for your claims yet, and indeed the online references you have given belie them. I'm afraid I don't have access to the 25th aniversary edition of 'Sociobiology' but I might go to the library to get out the 1980 edition. I have to say that 1980 isn't really a very current reference, although that isn't neccessarily a point against it. If there truly were distinct evolutionary origins of the Zooids I'm surprised there are no molecular papers discussing their differing genomes. One article that does touch on the phylogeny of the Siphonophora is
Phylogeny of Medusozoa and the evolution of cnidarian life cycles Collins AG Journal of Evolutionary Biology, Volume 15 Issue 3 Page 418 - May 2002 To investigate the evolution of cnidarian life cycles, data from the small subunit of the ribosome are used to derive a phylogenetic hypothesis for Medusozoa. These data indicate that Cnidaria is monophyletic and composed of Anthozoa and Medusozoa. While Cubozoa and Hydrozoa are well supported clades, Scyphozoa appears to be paraphyletic. Stauromedusae is possibly the sister group of either Cubozoa or all other medusozoans. The phylogenetic results suggest that: the polyp probably preceded the medusa in the evolution of Cnidaria; within Hydrozoa, medusa development involving the entocodon is ancestral; within Trachylina, the polyp was lost and subsequently regained in the parasitic narcomedusans; within Siphonophorae, the float originated prior to swimming bells; stauromedusans are not likely to be descended from ancestors that produced medusae by strobilation; and cubozoan polyps are simplified from those of their ancestors, which possessed polyps with gastric septa and four mesogleal muscle bands and peristomial pits. Which has this to say on the Siphonophora...
The present analysis is consistent with the idea that siphonophores are derived from an ancestor with a typical hydrozoan life cycle. Nevertheless, siphonophore colonies have key differences from benthic hydrozoan colonies, including relatively determinant growth and composition by zooids that cannot replicate the colony form (Mackie et al., 1987). Selection has clearly acted on the whole form of the colony in siphonophore species, but their descent is likely from a colony of less highly integrated zooids. Any debate about whether the siphonophore is an individual or a colony amounts more to a semantic discussion rather than a biological question. How can there be a cladistic analysis incorporating what is, according to you, a polyphyletic individual/colony? TTFN, WK P.S. there is a chance that the link to the paper abstract and online version might not work.
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Quetzal Member (Idle past 5902 days) Posts: 3228 Joined: |
The Bluebottle or Portuguese Man-of-War describes it thusly:
quote: Waikiki Aquarium information page describes the organism like this:
quote: On life-cycle:
quote: I will say that I misspoke slightly: there are only one or two spots that appear to be "zooid producers", and produce all the different types by budding based on some trigger. This goes against what I said about the zooids each budding their own type. For a bit more on siphonophore organization and lifecycle, see Siphonophores. The article as this to say about your "individuality" question: quote: As to how we can develop a phylogeny from a colony/symbiont: how do we develop a phylogeny from any other symbiotic organism? For example, the phylogeny of lichens (which even you'll have to admit are symbionts, yes?), is quite doable. See, for instance: Ekman and Jrgensen PM, 2002, "Towards a molecular phylogeny for the lichenfamily Pannariaceae (Lecanorales, Ascomycota)", Can. J. Bot. 80:625—634. quote: Developing a phylogeny is apparently a bit more complicated that a straight molecular phylogeny of more complex metazoans. This doesn't surprise me unduly. In the lichen case, they investigated one of the two organisms making up the symbiont, apparently, and derived their phylogeny from that. In the case of Physalia, or any of the other hydroids, it would probably be easier - the zooids are genetically identical except (apparently) developmentally. However, this does not indicate that they were differentiated from a single organism - rather the concensus appears to be as I stated. PS: I'm afraid I don't have access to the 25th aniversary edition of 'Sociobiology' but I might go to the library to get out the 1980 edition. I have to say that 1980 isn't really a very current reference, although that isn't neccessarily a point against it. If there truly were distinct evolutionary origins of the Zooids I'm surprised there are no molecular papers discussing their differing genomes. The page numbering may be different in another edition. It is, however, Chapter 19: The Colonial Organisms and Invertebrates. Is there some point to your argument, or are you simply interested in a parallel to your discussion of the Chlorella evidence? I mean, dueling references is all fun and everything, but it would seem to obscure the basic point I'm trying to get across: there are examples in nature that contradict/answer LDS's question. You know, it might be an interesting exercise for you to find your own examples for a change rather than simply nit-picking everyone elses. I'm happy to continue this discussion with you, however. I stand by what I have posted, and nothing you've presented thus far substantively contradicts what I've written.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
I've always thought you were a pretty clear headed thinker Quetzal but you seem to be stuck on one track with this one.
In the case of Physalia, or any of the other hydroids, it would probably be easier - the zooids are genetically identical except (apparently) developmentally. However, this does not indicate that they were differentiated from a single organism - rather the concensus appears to be as I stated. So the colony develops from a single zygote into a planula which becomes a medusa which then goes on to reproduce asexually to produce the individuals for the colony, and they are all genetically identical, but you still contend that the different Zooids are from distinct evolutionary lineages? Based on what evidence? Where is this consensus of yours? Certainly not in the quotes you provided, none of them suggest distinct evolutionary lineages for the Zooids and they clearly show differentiation from a single zygote.
In the lichen case, they investigated one of the two organisms making up the symbiont, apparently, and derived their phylogeny from that. Which is fine as far as it goes but certainly wouldn't address many different species forming a colonial organism and fitting such a polyphyletic organism into a phylogeny of the hydrozoa, unless you constructed a seperate phylogeny for each zooid. This is all rather beside the point anyway since they are all genetically identical.
Is there some point to your argument, or are you simply interested in a parallel to your discussion of the Chlorella evidence? I mean, dueling references is all fun and everything, but it would seem to obscure the basic point I'm trying to get across: there are examples in nature that contradict/answer LDS's question The point is that while Physalia is a great example of a colonial organism arguably well on its way to developing what could legitimately be called organs, it is not the product of many different evolutionary lineages. Or perhaps it is but I have found no evidence for it as yet. This was a pretty staggering claim and all I asked you to do was back it up, and so far all you have provided is a 25 year old reference from 'Sociobiology'. In terms of reference dueling I fear that none of your references have supported the portions of your examples that I was actually raising objections to. In fact the only clear statement about evolutionary origins is from the paper I previously cited which says...
The present analysis is consistent with the idea that siphonophores are derived from an ancestor with a typical hydrozoan life cycle. It is a parrallel to my discussions of the colonial Chlorella, and also the Nylon bug, in as much as I feel that we on the evolutionary side of the EvC debate have an obligation to police ourselves in terms of the rigour and accuracy of our science because, lets face it, the creationist really aren't up to the job for the most part. If we go around exaggerating the evidence, and I'm certainly not suggesting it is intentional, then all we are doing is reinforcing creationists' impressions that we are liars who twist and misinterpret the facts to fit our theory. When I get my science wrong I am always glad that there are people like you Mammuthus and SFS around to correct me.
You know, it might be an interesting exercise for you to find your own examples for a change rather than simply nit-picking everyone elses. I'm happy to continue this discussion with you, however. I stand by what I have posted, and nothing you've presented thus far substantively contradicts what I've written. But you also haven't provided any evidence substantiating what you wrote either for the Physalia or the Volvox examples. I personally feel that the fact that Physalia is composed of genetically identical individuals who all develop from a single zygote is pretty clear evidence against your multi-species symbiotic origin of Zooids. Obviously what counts as substantive is in the eye of the beholder. I did actually raise an example, that of the sponges, admittedly it was only 1 sentence. If you are under the impression that I never provide my own examples for any topic then there are obviously many of my posts you haven't come across, understandably enough given the volume of posts on the board. TTFN, WK
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Quetzal Member (Idle past 5902 days) Posts: 3228 Joined: |
You must have missed this bit from one of the quotes I provided. Here, let me repost it for you:
quote: I'm not making this shit up, as you seem to think. There is a gradation in hydroids from single medusae/polyp to sessile colonies composed of different polyps to free-floating colonies like Physalia. All the references I have posted have referred to the component zooids as individuals. And most of them have referred to the various different zooids as different kinds of organism. This is where I get my idea. I never claimed I couldn't be wrong. Although admittedly I'd be surprised - this is the way I've been considering this organism from the first time I was introduced to it. IF, in fact, as you state the different zooids are simply different developmental forms of a single organism that are somehow differentiated in form in the colonial version, then don't we have a much more complicated affair to explain? How did this differentiation occur? Why do these forms resemble other, free-floating/swimming versions of the hydrozoa? Why do some hydrozoa have different zooids (for example, the absence of the float)? If we're not dealing with a symbiont, then we have some very weird developmental/organizational issues to address.
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Brad McFall Member (Idle past 5063 days) Posts: 3428 From: Ithaca,NY, USA Joined: |
I agree with you here more than Quetzal post
message33 but seeing as how I am being asked to write things in plainer speech elsewhere (I will), that said, I am tempted in this discussion to pull together all the biophilosophy on classes and individuals, so as to speak to the phrase for instance "how natural selection shapes them today" etc, as the point of individuality is that of existence in a bound space and time and mere assertion of individuality is a sign of Darwinian thinking prima facie. If one is to be clear NOT to overstate/overgeneralize/oversocialize evolutionary biology initiallyit seems to me NECESSARY to operate in the thread with the word "individual" lightly (and this would be less or not a problem if the question was on the lowest initial level of discussion that this thread started out on) because the relation of homology and analogy get difficult to keep univocal when ANY kind of organ vs tissue is being received by the individual as constituitive. Let me see first if I am at the point under discussion. We are talking NOT about genetic differences in lineages (sufficiently) but about the individuality of organ formation IN INDIVIDUALS over geological time? If one had already vested interests in Organacism(as to concepts of emergence etc) as opposed to more narrow molecular approaches then one can use the word "individual" as if it was scientific without realizing the "appearence from the outside"(opps I started to get opaque). That is included because I might understand what Quetzal is saying too but I just am not as sure. Ok,so Wilson said it. I saw Q mention that before. Big Deal. There are ecologists who worked with my grandfather who are still alive and dont believe any of Sociobiology and even wrote a textbook"Field Biology" in which that was said. The original poster said that the thread raised MORE questions and I dont see any change in this state since my last post on this thread. This message has been edited by Brad McFall, 02-19-2005 07:57 AM
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Quetzal Member (Idle past 5902 days) Posts: 3228 Joined: |
Let me back up a minute. I had something of a rude shock last night. Your comment about evolutionary lineages triggered it. For over 30 years I have been thinking of, and referring to, this organism as a symbiont. The shock came when I realized that I had never considered the implications of this categorization. OF COURSE it would have to have different evolutionary lineages if it was a symbiont. All the other symbionts I know do. However, for a bit, there I stuck: I couldn't think of any other organism which showed such extreme morphological and functional differentiation that WASN'T a symbiont, not to mention the free-living polyps, etc. So I rolled over and said "okay, no problem. Obviously there's another explanation." Then, of course, my (treasonous) brain obligingly pulled up an example. Now don't laugh: the example bears no relation to the siphonphores. However, it does have a functional analog: it is a non-symbiotic colonial organism with functional and morphological differentiation: the Hymenoptera. The order even has solitary individuals. With drones, queens and workers, the organization was similar enough to make things click: obviously these are not distinct organisms (although individual agents), and they show a degree of differentiation that in the siphonophores is taken to the extreme. I've been filtering all the data through the "symbiont" lens (hence all my confusion about "individual" vice "distinct organism"). Don't bother looking up the Wilson reference: he never said symbiont. I "translated" that chapter just like all the other references.
So you were right, and I've been wrong for 30+ years. I suppose I should thank you for correcting my long-standing misapprehension. However, I'm absolutely not feeling remotely gracious about this. So, credibility shattered, I'll simply retire leaving you in sole posession of the field.
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Brad McFall Member (Idle past 5063 days) Posts: 3428 From: Ithaca,NY, USA Joined: |
Sounds good to me. I would hate to be the behavorist translating the waggle dances into derived categories of morph differnces on the bugs'shaped differences. I know that is slightly fictional. I have been impressed with how mud wasps niche construct as well. I guess I am done here too.
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Sylas Member (Idle past 5290 days) Posts: 766 From: Newcastle, Australia Joined: |
So you were right, and I've been wrong for 30+ years. I suppose I should thank you for correcting my long-standing misapprehension. However, I'm absolutely not feeling remotely gracious about this. So, credibility shattered, I'll simply retire leaving you in sole posession of the field. Ouch! What a fascinating insight into the nature of substantive debate, and how real progress is made when all sides take seriously the input of others and attempt to make progress in discussion. And also the harsh uncompromising brick wall of the external shared reality we attempt to describe, and for which some descriptions must fail. Yet sometimes, as a vanquished sportsman sadly retires from the field at the close of play, the fans in the stadium rise to their feet and give spontaneous applause to a battle fought well and fairly, and for the contribution of the loser to the whole edifying event, and in recognition and hope that we shall see them again on the field another day. The raising and resolution of a problem helps give real insight into the examples, much beyond what would have been obtained in a bare recitation of most accurate perspective. The chagrin will be fleeting; you've made a real contribution to this matter. Thanks. Cheers -- Sylas
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Now don't laugh: the example bears no relation to the siphonphores. However, it does have a functional analog: it is a non-symbiotic colonial organism with functional and morphological differentiation: the Hymenoptera. I won't laugh, in fact the same analogy occurred to me previously, but I thought it might seem a bit outre as a comparison. TTFN, WK
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