When did single-celled organisms first become multi-celled organisms?

[Soul Invictus]

I am trying to understand the adaptive process for SSOs.

I am trying to find out the earliest known time according to the geologic time table that SSO's would have become MSOs. Would these have been sponges or prokaryotes?

I also am trying to understand what the catalyst was that triggered the environmental change in order for this process to take place.

I'm trying to follow the evolutionary trail in reverse.

Thanks in advance.

[dancer_rnb]

What do you mean by multicell? Would chained bacilli count?

[Berthold]

This site (http://en.wikipedia.org/wiki/Doushantuo_Formation) may be close to it.

[Worldtraveller]

I don't kinow if it will point you towards what you're lookng for exactly, and I've long since lost the link I had. There was a good discussion of this on IIDB a few years ago, and my (rather faulty) memory recalls a long bit about sponges being where the research was going.

Google scholar shows up lots of potentially interesting looking titles if you search "transition multicellular sponges"....hope that helps.

[Soul Invictus]

What do you mean by multicell? Would chained bacilli count?

I've since learned that it appears that I'm referring to the evolution of multicellularity. I only want to rely on Wiki for a basic introduction, rather than a scientific opinion.

[JAD]

About November 6th 4004 B.C. plus or minus two days.

:D

[nygreenguy]

Would these have been sponges or prokaryotes? Def not sponges.

I also am trying to understand what the catalyst was that triggered the environmental change in order for this process to take place. I dont think there needed to be one. Multicellularity was simply more effective!

[Faid]

Guess it's time to post this:


The green alga, Chlorella vulgaris, is a well-studied eukaryote, which has retained its normal unicellular form in cultures in our laboratories for thousands of generations. For the experiments reported here, steady-state unicellular C. vulgaris continuous cultures were inoculated with the predator Ochromonas vallescia, a phagotrophic fl̄agellated protist (` flagellate'). Within less than 100 generations of the prey, a multicellular Chlorella growth form became dominant in the culture (subsequently repeated in other cultures). The prey Chlorella first formed globose clusters of tens to hundreds of cells. After about 10±20 generations in the presence of the phagotroph, eight-celled colonies predominated. These colonies retained the eight-celled form indefinitely in continuous culture and when plated onto agar. These self-replicating, stable colonies were virtually immune to predation by the fl̄agellate, but small enough that each Chlorella cell was exposed directly to the nutrient medium.


And a blog review:

http://pleion.blogspot.com/2008/11/watching-multicellularity-evolve-before.html

[David B]

I'm far - very far - from being an expert.

But there are things around today that sometimes are single cells, sometimes multicellular, and my best guess is that they are phenomena that adapted to the change from single cellular to multicellular by finding their own particular evolutionary niche, which has been pretty constant over deep time.

http://en.wikipedia.org/wiki/Slime_moulds

My best guess is that slime moulds were involved in the transition from single cellular to multicellular organisms.

But I'm a layman, who gets his views from reading, and thinking about, pop science books and tv documentaries,

If anyone comes in on the thread who is better informed than me, I'll be fascinated by what they have to say.

David

[nygreenguy]

I would say ANYTHING today was even close to being involved in the transition.

[Worldtraveller]

See this new paper (http://secularcafe.org/showthread.php?t=991) posted by Oolon.

[Berthold]

But there are things around today that sometimes are single cells, sometimes multicellular,...

David
You mean, such as animals and plants? :D

[nygreenguy]

I would say ANYTHING today was even close to being involved in the transition.


Meant to say wasn't

[Soul Invictus]

I've been gone for a while...I was out sick. I think the period I'd also like to know more about is the period of 'rapid' growth which is commonly referred to as the Cambrian explosion.

What explains complex life just happened to start appearing and how it was apparently rapid?

[premjan]

Hox genes. Also I think oxygen may have increased making it easier to generate connective tissues.

[Faid]

Also, we have found that there was already a significant amount of diversity before the Cambrian, and many ancestors of modern phyla can be traced there. See Ediacaran Biota. (http://en.wikipedia.org/wiki/Ediacaran_biota)

[Steviepinhead]

This paper (http://www.pnas.org/content/97/9/4457.full) -- and other similar research -- suggests that early animal embryonic fossils have been found in the precambrian Duoshantuo formation of southwest China, which "must fall within the range 570 ± 20 Ma" range," according to the authors.

Obviously, if you've got various stages of multicellular animal embryos, you've got multicellularity already firmly established.

Though there are arguments which question the legitimacy of the fossilzed embryos, the authors also sum up other lines of evidence for a deeper history of multicellularity which pre-exists the Cambrian:
The prediction that stem-group and perhaps even crown-group bilaterians existed in Neoproterozoic times, well before the Precambrian boundary, is supported by many kinds of argument. The most general and important of these arguments is that almost all major bilaterian clades already are represented in the Lower Cambrian, in remarkably preserved deposits such as the Chengjiang fossil lagerstätte (1). Fossil remains of diverse bilaterian forms from the Lower Cambrian have been obtained from many other regions of the globe as well (2–4). The latest Precambrian also has yielded trace fossils of unmistakable bilaterian origin (5–7). These remains indicate that major evolutionary diversification of animals already had occurred by the onset of the Cambrian, and, therefore, more remote ancestral forms must have been alive earlier.

Cladistic analyses, both morphological and molecular, clearly indicate that the bilaterians are monophyletic, i.e., they derive from a latest common ancestor that gave rise only to bilaterians (see ref. 8). How deep in time were this common ancestor and its offshoots, the common ancestors of the three great bilaterian clades (ecdysozoans, lophotrochozoans, deuterostomes; refs. 8–10) is unknown. Molecular phylogenies based on sequence comparisons of protein domains shared by all bilaterians suggest that the time of divergence of these proteins may extend back to 600–1,200 million years (megaannuum; Ma) ago (11–16).

In addition, arguments based on regulatory evolution lead to the proposition that microfaunal bilaterian stem groups must have evolved through several stages of regulatory complexity during Precambrian time (17, 18). But thus far, unequivocal paleontological evidence of bilaterian forms has extended only to the final period of the Neoproterozoic, a few million years before the Cambrian “explosion” (5–7, 19, 20).

(My parapgraph breaks, just to ease the eyestrain.)

Of course, early animals were probably not the first multicellular critters, since there are various other branches of the eukaryote clade that "precede" animals or plants (fungi, yeast, and the like...).

So we're probably looking at something on the order of 800-1,000 million years ago. And that may well be an underestimate.

[David M]

I've been gone for a while...I was out sick. I think the period I'd also like to know more about is the period of 'rapid' growth which is commonly referred to as the Cambrian explosion.

What explains complex life just happened to start appearing and how it was apparently rapid?

Remember that "rapid" is being used in the context of geology, taking into account how much has now been found of the pre-cambrian ancestors of what was first found in the cambrian it looks as though this period of 'rapid' diversification took at least 50-70 million years.

As to why it happened it does seem to match the timeframe of the development of Hox genes which help control body plans as well as the rise of hard body parts which leave much better fossil remains.

[lpetrich]

I've tried to research the evolution of multicellularity, but it had been hard for me to find any list of presumed origins of multicellularity.

The favorite theory is the colonial theory, that multicellular organisms evolved from colonies of one-celled organsims; the others are the syncytial theory and the symbiosis theory.

The syncytial theory states that a one-celled organism's nucleus divided repeatedly, with the organism's cytoplasm getting divided into partitions surrounding the nuclei. Some multicellular organisms do go through syncytial phases, like early fly embryos. The fertilized egg cell's nucleus divides several times before the cell's cytoplasm gets partitioned to make a cell around each nucleus. However, this syncytial phase likely evolved as a way of speeding up embryonic development, as did all-at-once segmentation layout, and is not an ancestral animal-kingdom feature.

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Returning to the question of which groups it evolved in, it can be hard to say, because it can be difficult to draw the line between colonial organization and true multicellularity with cell differentiation.

Many one-celled organisms make colonies called biofilms, which can sometimes contain several species.

Going beyond biofilms, some prokaryotes differentiate and have well-defined colony shapes. Cyanobacteria make "heterocysts", which do nitrogen fixation for their neighbors. Some actinobacteria produce fungus-like branching filaments, which accounts for their earlier name, actinomycetes.

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Among the eukaryotes, the Opisthokonta, Amoebozoa, Archaeplastida, and Chromalveolata all have multicellular members, while multicellularity is rare or absent from the Rhizaria and the Excavata.

Amoebozoa is the simplest case. Many amoebas are solitary, though there is a possibly-monophyletic group of social amoebas called the Mycetozoa. Of them, Dictyostelium discoideum is the best studied. Its life cycle alternates between solitary and social, with solitary amoebas joining together to make a sluglike mass that makes spores that hatch into more solitary amoebas.

Phylogeny of lobose amoebae based on actin and small-subunit ribosomal RNA genes. (http://www.ncbi.nlm.nih.gov/pubmed/12949141)
Phylogenetic position of Multicilia marina and the evolution of Amoebozoa. (http://www.ncbi.nlm.nih.gov/pubmed/16738126)
Ultrastructure, SSU rRNA gene sequences and phylogenetic relationships of Flamella Schaeffer, 1926 (Amoebozoa), with description of three new species. (http://www.ncbi.nlm.nih.gov/pubmed/19036635)

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The Amoebozoa are likely closest to the Opisthokonta, which contains animals and fungi, both with multicellular members.

Turning to the animal kingdom, the ancestral bilaterian was rather elaborately multicelled, and the ancestral metazoan was likely multicelled, though much less elaborate than the ancestral bilaterian. Their closest relatives are the choanoflagellates (collar flagellates), which are solitary or colonial. The ancestral metazoan is likely a descendant of some colonial choanoflagellate.

Though there are many multicellular fungi, it has been hard for me to find anything on the evolution of fungus multicellularity.

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Turning to the Archaeplastida, they contain the glaucophytes, the viridiplantae (green algae and land plants), and the rhodophytes (red algae). All three groups have one-celled members, though only the latter two have multicelled ones. Rhodophyta is mostly multicellular, though Viridiplantae has both one-celled and multicellular members.

Multicellularity has evolved several times in Viridiplantae, though I have not been able to find estimates of how many times. For instance, the ancestors of Volvox and related multicellular green algae had become multicellular in the Triassic, while the ancestors of land plants had become multicellular long before.

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And finally the Chromalveolata. Several of its branches are one-celled only, like haptophytes and cryptophytes, but the Alveolata and Stramenopiles / Heterokontophyta do have multicellular members.

Most alveolates (ciliates, apicomplexans, and dinoflagellates) are one-celled, but there are some colonial dinoflagellates.

The stramenopiles includes diatoms and golden algae, which are mostly one-celled, and brown algae (kelp, etc.) and oomycetes (water molds), which are mostly multicellular. I've been unable to find much on the evolution of their multicellularity.

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Summary of how many times eukaryote multicellularity has evolved:

Metazoa: almost certainly once
Fungi: ?
Amoebozoa: once?
Green algae: ?
Red algae: ?
Stramenopiles: ?

[dancer_rnb]

Aren't muscle cells multi-nucleated?

[lpetrich]

Yes they are. They are formed from muscle precursor cells (myoblasts) that merge; this merging helps in coordinating its contraction.

[Peez]

Soul Invictus:
When did single-celled organisms first become multi-celled organisms? I've since learned that it appears that I'm referring to the evolution of multicellularity. I think the period I'd also like to know more about is the period of 'rapid' growth which is commonly referred to as the Cambrian explosion.Just to clarify: multicellularity seem to have evolved several times independently, and the ancestors of animals seem to have been multicellular for as much as 100 million years before the "Cambrian explosion".What explains complex life just happened to start appearing and how it was apparently rapid?Note that the "Cambrian explosion" refers to animals, and animals are not the only "complex life" on our planet. That being said, a number of hypotheses have been put forward to explain why different animal phyla evolved relatively rapidly at that time, but the short answer is that we simply don't know. I should add that a very great deal of evolution occured before and since the "Cambrian explosion", and, as has been pointed out by others, "rapid" here means over many millions of years (it is a relative term).

Peez

[Peez]

dancer_rnb:
Aren't muscle cells multi-nucleated?If I may nit-pick (sorry, I just cannot help myself): the cells that make up your "voluntary" or "skeletal" muscle (your muscular system) are indeed multi-nucleated (each "muscle fiber" is a single cell), as are the muscle cells of your heart, but the "smooth" muscle of your esophagus, stomach, intestines, blood vessels, etc. are not. As far as I know this is generally true for chordates, but I don't know about other groups of animals.

Peez

[nygreenguy]

Aren't muscle cells multi-nucleated?
So are pollen. Also, the polar nuclei in the female gametophyte of angiosperm is multi-nucleate AND it gets fertilized to become the triploid endosperm.

But why do you ask about multi nuclei?

[dancer_rnb]

Ipetrich mentioned syncytial theory. I remembered muscle cells were multi-nucleated, but couldn't remember the details.