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← Need to feed could have driven single cells to evolve into colonies

Need to feed could have driven single cells to evolve into colonies - Comments

Neodarwinian's Avatar Comment 1 by Neodarwinian

Or need to procreate.

Wed, 10 Aug 2011 03:10:13 UTC | #859560

Anonymous's Avatar Comment 2 by Anonymous

Comment Removed by Moderator

Wed, 10 Aug 2011 04:08:36 UTC | #859566

mordacious1's Avatar Comment 3 by mordacious1

If you don't have Ed Yong's blog bookmarked, DO IT! Do it now! You'll thank me later.

Wed, 10 Aug 2011 06:35:15 UTC | #859583

AtheistEgbert's Avatar Comment 4 by AtheistEgbert

The answer is fairly obvious--the more power you have the better chance of survival. This is a simple numbers game, reproduce more copies of yourself means more power and therefore a more likely chance of success.

Wed, 10 Aug 2011 09:41:56 UTC | #859614

DavidMcC's Avatar Comment 5 by DavidMcC

Quite so, Neodarwinian.

And clustering is but the first step to true multicellularity. Ratcliff says, “The tricky step is the shift in individuality from the single-cell to the cluster. The cluster must become the unit on which selection acts, and subsequent adaptations must occur in cluster-level traits. Until this shift has occurred, a cluster of cells is just a cluster of single celled organisms, not a simple multicellular organism.

I still wonder whether the first colonial choanoflagellates (sponges) arose due to a genome duplication in a free-swimming choanoflagellate, which then became a bit like a haploid cell to the diploid of the new form. Some of the extra genes in the "diploid" could be used to make the sponge, if it remains compatible with the "haploid" form "plugging in" to it to reproduce. The sponge would then play the female role, except that it would also produce "sperm"! A kind of "half-way house" to sex, isn't it?

Wed, 10 Aug 2011 11:55:21 UTC | #859648

DavidMcC's Avatar Comment 6 by DavidMcC

It looks like I'm wrong, at least for any known extant sponge: Porifera

... Choanocytes (also known as "collar cells"), which line the spongocoel and function as the sponge's digestive system, are remarkably similar to the protistan choanoflagellates.

...

Sexual reproduction in sponges is relatively simple. Sperm from one sponge swims to the egg of another, producing a motile larval stage.

Wed, 10 Aug 2011 14:13:17 UTC | #859701

Rawhard Dickins's Avatar Comment 7 by Rawhard Dickins

I imagine for some early cells the problem was trying to separate rather than trying to stay together. In much the same way trying not to fly would have been a problem for some of our small ancestors, rather than working out how to fly.

Solutions to some of the big jumps in evolutionary history will not have been such a big issue, otherwise they wouldn't have happened without magic wand waving (as some would have us believe).

Wed, 10 Aug 2011 15:11:11 UTC | #859725

Alan4discussion's Avatar Comment 8 by Alan4discussion

Sponges provide a very interesting example.

So what then exactly is a sponge? The sponges are perhaps best described as a group of single cells that all manage to work together. To understand a sponge by examining a single one of its cells, even though most are practically identical, would do you no more good than studying the single cell of any other multicellular creature. The organism must be studied as a whole. Yet experiments have shown that if a sponge is strained through a silk mesh the separated individual cells will regenerate and form themselves into several new sponges. That even beats the legendary powers of sea stars for regeneration.

http://www.northwestwildlifeonline.com/Porifera%20Homepage.htm

Wed, 10 Aug 2011 15:42:59 UTC | #859737

Zeuglodon's Avatar Comment 9 by Zeuglodon

This is interesting. Before now, I put more emphasis on the arms-race argument for multicellularity - that cells travelling as a pack could overpower rivals or beat them at getting the resource they needed. This article has opened up other possibilities for further experiments.

Comment 4 by AtheistEgbert. The answer is fairly obvious--the more power you have the better chance of survival. This is a simple numbers game, reproduce more copies of yourself means more power and therefore a more likely chance of success.

Yes, but it's not the only factor. You could reproduce yourself until you're blue in the face, but if you die ridiculously easily or have insufficient phenotypes for the job, you could still be outcompeted. Worse, a population explosion would lead to a population crash, effectively committing genetic suicide. And as Pratchett once wrote, "obvious" does not equal "true", hence the scientific investigation.

Comment 5 by DavidMcC. I still wonder whether the first colonial choanoflagellates (sponges) arose due to a genome duplication in a free-swimming choanoflagellate, which then became a bit like a haploid cell to the diploid of the new form. Some of the extra genes in the "diploid" could be used to make the sponge, if it remains compatible with the "haploid" form "plugging in" to it to reproduce. The sponge would then play the female role, except that it would also produce "sperm"! A kind of "half-way house" to sex, isn't it?

Hm. I think the idea of the haploid-diploid distinction coming early in the evolution of sex in this way has merit, but it seems a bit premature to assign 'male-female' distinctions this early. It could be more like a pair of haploid cells with no specialisations for 'egg' or 'sperm' features i.e. interchangeable gametes. The two main 'bodies' of chaonflagellates then release them into the water currents and they fuse with whatever in the mass spawning, similar to how coral reefs disperse their gametes today. This could then develop into the spore system seen in fungi, before it later acquired male-female specialisations. This is all speculation, though, I admit.

Comment 7 by Rawhard Dickins. I imagine for some early cells the problem was trying to separate rather than trying to stay together. In much the same way trying not to fly would have been a problem for some of our small ancestors, rather than working out how to fly.

No: the cells needed a special adhesive structure like collagen or silicate crystals to bind themselves to other cell bodies. These were additions that came later, not inherent properties of the cell. Remember, cell evolution occurred in water, not on land. The movements of water would quickly separate them.

Wed, 10 Aug 2011 19:09:42 UTC | #859822

Eosimias's Avatar Comment 10 by Eosimias

Weren't some single-celled algae enticed to evolve into multi-cellular life in a lab as a defense from being eaten?

I can't remember where I read that, though... It might have been in "Finding Darwin's God" or "Your Inner Fish."

Thu, 11 Aug 2011 08:03:57 UTC | #859983

DavidMcC's Avatar Comment 11 by DavidMcC

Comment 9 by Zeuglodon

Hm. I think the idea of the haploid-diploid distinction coming early in the evolution of sex in this way has merit, but it seems a bit premature to assign 'male-female' distinctions this early.

Like I said in my subsequent post, having found out more details about the sponges, I withdrew the hypothesis. It now looks like it was, after all, the "need to feed", not the need to breed that brought about sponge multicelluarity, if sponges really did evolve from choanoflagellates, and not the other way around.

Thu, 11 Aug 2011 11:23:31 UTC | #860032

DavidMcC's Avatar Comment 12 by DavidMcC

... However, I do not withdraw the suggestion that the sponges evolved from choanoflagellates as a consequence of a genome duplication in the latter.

Thu, 11 Aug 2011 13:20:19 UTC | #860059

Ornicar's Avatar Comment 13 by Ornicar

I was thinking about something I saw in a Richard Dawkins speech about darwinian medecine. 1 - Most mutations have negative effects 2 - When a mutation has a positive effect (on the gene reproduction), it has generally a negative effect as well. It's a trade off.

For example, some bacteria make the host cough, therefore spreading the disease. So if, in a colony of bacteria, one individual appears and makes the host cough, this will help the whole colony to spread, whether individuals make the host cough or not. But if "making cough" is a trade-of, the "non making cough" bacteria will be stronger, on other respects, than the "making cough" ones. But the "making cough" ones will help the whole colony to spread. So you could be infected by two famillies of the same root, strong ones that don't make you cough, and weak ones that make you cough. A rough case of self symbiosis, maybe a first step toward multi-cellular organisation.

Thu, 11 Aug 2011 15:36:38 UTC | #860099