Cells into Organs: could it evolve?

Dear Q, This doesn't make it a symbiont, colonies are made up of individuals. 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. 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? 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 Which has this to say on the Siphonophora... How can there be a cladistic analysis incorporating what is, according to you, a polyphyletic individual/colony?TTFN,WKP.S. there is a chance that the link to the paper abstract and online version might not work.

The Bluebottle or Portuguese Man-of-War describes it thusly:

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The Bluebottle or Portuguese Man-of-War is not a single animal but a colony of four kinds of highly modified individuals (polyps). The polyps are dependent on one another for survival.

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The float (pneumatophore) is a single individual and supports the rest of the colony. The tentacles (dactylozooids) are polyps concerned with the detection and capture of food and convey their prey to the digestive polyps (gastrozooids). Reproduction is carried out by the gonozooids, another type of polyp.

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Waikiki Aquarium information page describes the organism like this:

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Within the man-of-war colony, one individual is modified into a gas sac (pneumatophore) which supports the colony and keeps it floating at the ocean surface. A ridge along the top of the sac acts like a sail, and the movement of the colony depends upon the wind and ocean currents. It is the sail that gives the man-of-war its name, early explorers thought its shape resembled the helmets worn by Portuguese soldiers. Other members of the colony perform the tasks of food capture and feeding. The long, trailing tentacles (dactylozooids) are armed with stinging cells that contain nematocysts. Nematocysts inject a barbed thread and paralyzing toxin to capture and subdue prey like small fish. The tentacle transfers prey to the mouths of vase-shaped individuals (gastrozooids) that perform digestion. Nutrients from the meal are shared through a common gut system that connects all members of the colony. Communication between individuals is maintained through a network of nerve fibers. (MARINE LIFE PROFILE: INDO-PACIFIC PORTUGUESE MAN-OF-WAR)

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On life-cycle:

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Physalia- spend their entire life as a colony attached to a gas filled (mostly nitrogen) float-Pneumatophore; the
pneumatophore is not the same as a medusa, which is one individual
* have all three types of individuals: gastrozoids, gonozoids, and dactlyozoids
* the individuals are attached to tentacles trailing from pneumatophore; tentacles may be 9 meters long
* reproduces sexually and forms a modified planula larva- this develops into a medusa the comes to the surface and eventually develops into a colony through asexual reproduction (from zoology course outline: CNIDARIA: THE JELLYFISH, ANEMONES AND CORALS)

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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:

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Siphonophores challenge us to think about what we mean when we call something an individual, a concept that we usually think of as being quite straightforward. Is a single zooid or an entire colony the siphonophore individual? The answer is that you have to specify what features you are interested in before you can expect a meaningful answer. Do you mean ecologically? The entire colony functions as a single organism whether it is predator or prey. So the colony is an ecological individual. The same can be said for behavior. How about evolutionarily? There are two different components to this question. If we ask how evolution acts on siphonophores now, they are individuals. All the parts of the colony are genetically identical and the colony lives or dies as a whole (except for the eudoxids described later). So siphonophores are evolutionary individuals with respect to how natural selection shapes them today. The other way to look at evolutionary individuals is by descent. We can do this by taking a look at two animals and asking which structures descend from the same feature of a common ancestor. Just as this leads us to recognize that bat wings are modified arms, it shows that siphonophore zooids are polyps and medusae, structures that can be free living animals in other species. So this argument leads to the conclusion that the zooids of siphonophores are individuals. This is not contradictory to our previous conclusions, we are just looking at a different feature of individuality.

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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 lichen
family Pannariaceae (Lecanorales, Ascomycota)", Can. J. Bot. 80:625—634.

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The phylogeny of the family Pannariaceae (Lecanorales, lichenized Ascomycota) was investigated using ITS1—5.8S—ITS2 nuclear ribosomal DNA sequences representing 21 species. Phylogenetic estimations were performed using parsimony and a Bayesian Markov chain Monte Carlo (MCMC) tree sampling procedure. Several phylogenetic null hypotheses were tested, also using MCMC. The results indicate that Pannariaceae, as currently treated, is polyphyletic and that Degelia sect. Amphiloma, Fuscopannaria subg. Micropannaria, and Moelleropsis s.str. do not belong in the family. The inclusion of Parmeliella in the Pannariaceae could not be rejected, although it falls outside the family in the optimal trees. Psoroma, Santessoniella, Protopannaria, Fuscopannaria subg. Fuscopannaria, Moelleropsis s.str., and Pannaria unequivocally belong to the family. The Pannaria sphinctrina group belongs in Pannaria despite its green-algal photobiont. Protopannaria pezizoides is not, as sometimes treated, a Pannaria, although a relationship with Psoroma could not be ruled out. In the optimal trees, Moelleropsis s.str. is nested inside Fuscopannaria subg. Fuscopannaria and Santessoniella inside Psoroma, but null hypotheses of their independence from these genera could not be rejected. Pannaria cannot be divided into two monophyletic subgenera, Pannaria and Chryopannaria. The photobiont has changed twice or three times and the ascus apex and hymenial amyloidity twice within the Pannariaceae.

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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: 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.

I've always thought you were a pretty clear headed thinker Quetzal but you seem to be stuck on one track with this one. 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. 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. 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... 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. 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

You must have missed this bit from one of the quotes I provided. Here, let me repost it for you:

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(on the question of individuality) There are two different components to this question. If we ask how evolution acts on siphonophores now, they are individuals. All the parts of the colony are genetically identical and the colony lives or dies as a whole (except for the eudoxids described later). So siphonophores are evolutionary individuals with respect to how natural selection shapes them today. The other way to look at evolutionary individuals is by descent. We can do this by taking a look at two animals and asking which structures descend from the same feature of a common ancestor. Just as this leads us to recognize that bat wings are modified arms, it shows that siphonophore zooids are polyps and medusae, structures that can be free living animals in other species. So this argument leads to the conclusion that the zooids of siphonophores are individuals. This is not contradictory to our previous conclusions, we are just looking at a different feature of individuality.

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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.

I agree with you here more than Quetzal post
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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 initially
it 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

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.

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.

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

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