Scientists solve major piece in the origin of biological complexity

Nov 06, 2013

Scientists have puzzled for centuries over how and why multicellular organisms evolved the almost universal trait of using single cells, such as eggs and sperm, to reproduce. Now researchers led by University of Minnesota College of Biological Sciences postdoctoral fellow William Ratcliff and associate professor Michael Travisano have set a big piece of that puzzle into place by applying experimental evolution to transform a single-celled algae into a multicellular one that reproduces by dispersing single cells.

"Until now, biologists have assumed that this single-cell bottleneck evolved well after multicellularity, as a mechanism to reduce conflicts of interest among the making up the organism," says Ratcliff. "Instead, we found that it arose at the same time as multicellularity. This has big implications for how multicellular complexity might arise in nature, because it shows that this key trait, which opens the door to evolving greater multicellular complexity, can evolve rapidly."

In an article published today in the journal Nature Communications, the researchers described how they produced the multi-celled strain by repeatedly selecting and culturing algae that settled quickly to the bottom of a liquid-filled test tube. After 73 rounds, they discovered that the algae in one of the tubes had gone multicellular.

Observing the new form, Ratcliff and Travisano discovered that it reproduced by actively breaking up, shedding motile single cells that go on to grow into new multicellular clusters. They developed a mathematical model that explained the reproductive benefit of this single-celled strategy over hypothetical alternatives in which the cluster would produce larger propagules. The model predicted that reproduction from single cells would be more successful in the long run. Even though single cells are less likely to survive than larger propagules, this disadvantage is more than made up for by their sheer number.

In collaboration with Matthew Herron and Frank Rosenzweig at the University of Montana, the researchers are now working to find the genetic basis for multicellularity and experimentally evolve even greater multicellular complexity.

"Understanding the origins of biological complexity is one of the biggest challenges in science," Travisano said. "In this experiment we've reordered one of the first steps in the origin of multicellularity, showing that two key evolutionary steps can occur far faster than previously anticipated. Looking forward, we hope to directly investigate the origins of developmental complexity, or how juveniles become adults, using the that we evolved in the lab."

Several years ago, Travisano and Ratcliff made international news when they evolved multicellularity in yeast. This work takes those findings further by initiating in an organism that has never had a multicellular ancestor and provides a new hypothesis for the evolutionary origins of the single-cell bottleneck in multicellular life cycles.

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dogbert
1.3 / 5 (13) Nov 06, 2013
Several years ago, Travisano and Ratcliff made international news when they evolved multicellularity in yeast.


They selected for that characteristic. It did not evolve in their lab.

This work takes those findings further by initiating multicellularity in an organism that has never had a multicellular ancestor ...


How did they determine that the algae never had a multicellular ancestor?

They simply selected for a characteristic they wanted. They did not evolve a new algae by selecting precipitates from 73 test tubes.
tadchem
1.4 / 5 (10) Nov 06, 2013
From a slightly different perspective, they artificially selected algae for low buoyancy. When a mutation arose for algae that had reduced ability to separate after mitosis, the attached cells 'naturally' joined the low-buoyancy cut.
This reminds me of Volvox, which can be considered a multicellular organism OR a colony of single-celled organisms, depending on the investigator's interest.
beleg
1.4 / 5 (10) Nov 06, 2013
Interesting that nature has at least two avenues to carry or pass on fore-bearers' information via reproduction.
The seed. The single cell.
The avenue taken is the path that offers the greatest 'protection' against the organism's acquired 'amour' to withstand the 'environment'.

There is no antonym for 'in utero'. If there were an antonym for 'in utero' that is the condition
for multicellularity reproduction.

The title (not the research reported) asserts a major piece of the origin of (biological) complexity has been provided.
I disagree with the title's assertion.
Lurker2358
1.3 / 5 (13) Nov 06, 2013
Observing the new form, Ratcliff and Travisano discovered that it reproduced by actively breaking up, shedding motile single cells that go on to grow into new multicellular clusters.


You have undifferentiated multi-cellular, but that doesn't at all explain the arrival of sexual reproduction in evolutionary terms originating from a non-sexual organism, which is what I think these authors are really after.

Cooperation among cells is a dubious definition for "multi-cellular", because "skin" is multi-cellular, but it's not an organism in and of itself.

in the case of a hydra, you can distinguish between individual cells and the whole organism.

In the case of these algae you cannot. Which means they are not fundamentally multi-cellular.

In essence, you have a colony of single-celled algae which are cooperating. Nothing more.
beleg
1 / 5 (3) Nov 06, 2013
For non-cooperating cells no amount of protection is sufficient. What concept of a 'host' can allow noncooperation as an evolutionary means to reproduce, let alone thrive?
Torbjorn_Larsson_OM
4 / 5 (4) Nov 07, 2013
Creationists commenting on science is hilarious. And it makes deconverts from religion, see Dawkins's Convert's Corner.

Especially here as everyone can see these nuts don't know what evolution is, they deny its very mechanisms when those mechanisms are observed to happen. =D

@beleg: "asserts a major piece of the origin of (biological) complexity has been provided.
I disagree with the title's assertion."

I dunno if you are one of the hilariously incompetent creationist anti-science parade here? If not: sexuality is considered a complex trait, and they do provide an observed constraint (single-cell sexuality preferred).

It would help if you quantify or qualify your disagreement. Because what is asserted without evidence can be rejected without evidence.
malapropism
5 / 5 (1) Nov 07, 2013
There is no antonym for 'in utero'. If there were an antonym for 'in utero' that is the condition for multicellularity reproduction.

Of course there is an antonym for "in utero": it is "ex utero". From the Latin to English - literally "in the womb" vs "out of the womb".

Reproduction ex utero is not a pre-condition for, nor has any necessary biological relationship to any process of, multicellular reproduction, that I'm aware of. By way of an example, in vitro production of a (human or other animal) embryo (aka "test tube babies") is by definition ex utero but the sperm and egg cells are nevertheless still separately single cells (and in fact, the fertilised egg remains a single cell for quite a long time post-fertilisation).
malapropism
3 / 5 (2) Nov 07, 2013
You have undifferentiated multi-cellular, ...

After several careful readings of this article nowhere can I find any reference to the multicellular algae being comprised of undifferentiated cells. It is possible they are but I think you are misrepresenting this as a stated fact when it is not.
Cooperation among cells is a dubious definition for "multi-cellular", because "skin" is multi-cellular, but it's not an organism in and of itself.

in the case of a hydra, you can distinguish between individual cells and the whole organism.

In the case of these algae you cannot. Which means they are not fundamentally multi-cellular.

In essence, you have a colony of single-celled algae which are cooperating. Nothing more.

This is not the definition of "multicellular", which means simply more than 1-celled. There is no requirement for individual cells to be distinguishable from each other in the way you are implying, for an organism to be deemed multicellular.
beleg
1 / 5 (2) Nov 11, 2013
"Reproduction ex utero is not a pre-condition for, nor has any necessary biological relationship to any process of, multicellular reproduction, that I'm aware of."

No one here suggested a "pre-condition" to reproduction.
The research focuses on what nature does to make a preference between single cell and multi-celled reproduction.
NikFromNYC
1.5 / 5 (15) Nov 13, 2013
So they clump? So what? That's not "complexity," more like just a regrettable mess. What if cats clumped together? Not a good thing.
malapropism
5 / 5 (1) Nov 14, 2013
"Reproduction ex utero is not a pre-condition for, nor has any necessary biological relationship to any process of, multicellular reproduction, that I'm aware of."

No one here suggested a "pre-condition" to reproduction.
The research focuses on what nature does to make a preference between single cell and multi-celled reproduction.

Hmmm. And yet your comment was that, "If [ex utero existed as a term] that is the condition
for multicellularity reproduction."

I regret I fail to see your argument. Perhaps you could explain?

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