Cells into Organs: could it evolve?

It is important to appreciate that these systems are not required for multicellular life, just our own particular brand of it. There are many multicellular species which are capable of absorbing nutrients simply by diffusion from the environment. As soon as any colonial form has developed a trade off with only a few cells reproducing the other cells are freed up to develop other specialised functions.Look at sponges and you will see many specialised cell types not organised into true 'organs'.TTFN,WKThis message has been edited by Wounded King, 02-15-2005 05:02 AM

Are you suggesting that Physalia is actually some sort of cross species symbiosis? As I understand it it is an obligate colonial certainly but I don't remember ever coming across the idea that the seperate zooids originated with distinct species.I also don't recall off hand a species of Volvox with a free living individual stage of the life cycle. I know that Chlamydomonas is often given as the 'unicell' ancestor of the colonial Volvocaceae and that some are classed as colonial and some as multicellular. What particular species of volvox were you thinking of? The seasonality in your example makes me think of the seasonal sexual reproduction of V. carteri which produces a spore like zygote which can survive a ponds drying up. Can you be a bit more specific about the source of your examples? References always appreciated.TTFN,WK

What you recall corresponds to what I remember learning about Volvox. I've had a brief scan on pubmed and google and I haven't found what Q was talking about yet, I'm wondering if it is a Volvocine but not actually a species of Volvox, but the problem is that there is just so much stuff out there.If you have access to journals you might be interested in a new paper. There is no need to actually own Gilbert as Pubmed has the entire text online in a searchable format.TTFN,WKThis message has been edited by Wounded King, 02-17-2005 16:15 AM

It's a seasonal switch from asexual to sexual reproduction. It may not strictly be 'The' life cycle, in as much as colonies can simply cycle asexually during the spring period, but it is fairly significant in terms of the continued existence of the population over the year.It is particularly relevant as it is reminiscent of the seasonality you were suggesting is shown by free living Volvox individuals clustering together to form colonies. All I was suggesting is that you might have got mixed up between seperate individuals clustering to form colonies and overwintering zygotes being reactivated and forming colonies. I thought it was more usual for the daughters to form inside the colony.I'm not sure why you think I should have chosen a paper on phylogeny, that seems entirely peripheral to the question of the Volvox lifecycle, unless you were actually thinking of another member of the Volvocales.Your abstract from Desnitski(2000) actually seems to suggest that V. tertius, rather than V. aureus, produces
the 'male' individuals. A free swimming (haploid?)'sperm' also hardly constitutes the sort of free living individuals you suggested in your original post. Why don't they appear to be based on cellular differentiation? What do the gonozooids do? Does each seperate zooid type have its own reproductive subpopulation allowing a 'budding' of the colony by growing seperate zooids in situ. Have the gonozooids accumulated all of the genetic information neccessary to form the individual zooid systems and if so how does this differ from the sort of specialisation seen in volvox? As far as i can find out the gonophores release gametes into the water where they meet up and form planula larvae, do the various different zooids just then meet up in some sort of post-breeding assortment? As I understand it the larva produces the individuals for the colony by asexual reproduction. Relax, I'm just asking for more details, I am totally unaware of the situations you are describing, is it so unreasonable to ask for some clarification and sources? Does being on the evolutionary side somehow absolve you of having to support things with evidence?I don't know anything about Mixotricha, but I suspect that Lynn Margulis loves it.TTFN,WK

In terms of the Dicty 'slug' or Grex, I notice that they also have an aggregated sexual pathway and I wondered if the asexual fruiting system was actually a derived characteristic, i.e. it arose subsequently to the sexual reproductive pathway. A quick literature search showed that this is not an original idea (what a surprise). Not as irreducibly complex as you might imagine.TTFN,WK

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.

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

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