
De novo origins of multicellularity in response to predation - mazsa
https://www.nature.com/articles/s41598-019-39558-8
======
pkrein
This has big implications for the Fermi Paradox:
[https://en.wikipedia.org/wiki/Fermi_paradox](https://en.wikipedia.org/wiki/Fermi_paradox)

In particular, the jump from unicellular to multicellular life is (was) one of
the top leading candidates for the Great Filter.
[https://en.wikipedia.org/wiki/Great_Filter](https://en.wikipedia.org/wiki/Great_Filter)

Importantly, it was one of the filter candidates "behind" us. It will be
exciting to see if other potential filter steps can be so conclusively
eliminated over time.

~~~
azernik
One of the interesting ones I've heard talk about lately is the "interstellar
travel" step - Earth is on the lower end of the size range for rocky planets
that can support an atmosphere and magnetic field to shield surface life from
radiation. And because of the tyranny of the rocket equation, life developing
on larger rocky planets may have a much harder time reaching orbit.

A good demo video:
[https://www.youtube.com/watch?v=amjuJJwI3iM](https://www.youtube.com/watch?v=amjuJJwI3iM)

On a planet with twice the Earth's mass, it would take a larger-than-Saturn-
sized rocket to put a Mercury-sized payload into orbit.

EDIT: And said Mercury-sized payload would have to spend more of its mass on
heat shielding than the human Mercury capsule if it's intended to come back
down.

~~~
travisoneill1
This wouldn't stop von neumann probes [https://en.wikipedia.org/wiki/Self-
replicating_spacecraft](https://en.wikipedia.org/wiki/Self-
replicating_spacecraft)

~~~
azernik
The upmass requirement for bootstrapping that kind of system would be quite
large.

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ZeroFries
Do these cells already have the blueprints for multicellular organization,
latent until selection exerts pressure for its manifestation? Is it much
easier to reproduce the phenomenona since it's already happened before? Do
cells ever go back to the single life?

~~~
hetman
The authors indicate the blueprints were already present but the multicellular
expression stopped being optional in their evolved population:

 _The ability of wild-type C. reinhardtii to form palmelloids suggests that
the founding population in our experiment already possessed a toolkit for
producing multicellular structures. However, while the palmelloid condition is
expressed facultatively in wild-type C. reinhardtii, the strains that evolved
in our experiment are obligately multicellular._

Maybe I'm not familiar with how this term is used in biology but given the
above it seems the "de novo" claim in the paper title is a little
sensationalist.

~~~
mrfusion
That makes it way less interesting. The first time multicellular life happened
it took billions of years and simple single cell organisms had to figure it
out from scratch.

~~~
rossdavidh
...or, it's not that different from dividing completely into two, and they
just didn't do it for a long time because there weren't enough predation-based
species to make it worth doing?

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lettergram
I actually wrote a program which showed behavior that appeared to be "social"
after predictors were added to the simulation.

The postulation being organisms have a pressure (from predators) to form
groups and eventually societies. Essentially, they'd either survive by
evolving to be social, evolve defense mechanisms or die out. Social evolution
may actually be the shortest path for non-aggressive species because they
simply have to bare one another, as opposed to evolve long claws or something.

Very hard to prove, but our model showed given the options social interactions
appeared more likely with basic reward circuitry.

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est31
So the paper says that filter-feeding predators might have been the reason, if
you are bigger than a certain size you become irrelevant to them. But how does
the filter predator become so big without multicellularity? I mean: filter
predators always have to be bigger than their food, no? So isn't it rather
coevolution?

~~~
flukus
Cells can become quite large, the nerve cells in your back run the length of
your spine for example, so it's certainly possible for a single cell to trawl
through the ocean like a filter feeder and pick on smaller targets. Maybe
tendril feeder would be a better description for a single cell though.

There's also caulerpa
([https://en.wikipedia.org/wiki/Caulerpa](https://en.wikipedia.org/wiki/Caulerpa))
can be large but only have a single cell, googling turns up several other
surprisingly large single cells.

~~~
est31
Cells can become large, but can't a single big cell also escape a filter
predator that's also a single big cell? There needs to be some reason for why
in most cases, both are multicellular.

~~~
kd5bjo
From a mechanics of materials perspective, having a larger size also means
being easier to break. Multicellularity seems to be a way to have preferred
breaking points that are cheaper and easier for the organism to repair.

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lurquer
Perhaps I'm missing something, but it seems they artificially selected for
single-celled organisms that are sticky and clump together (thus making them
-- as a group -- too large to be eaten.)

As the 'stickiness' doesn't really pose a disadvantage to the single-celled
organism, the trait persists even after the predator is removed.

In short, can a collection of 'stickier-than-normal' single-celled organisms
truly be referred to as a multicellular organism? Aren't they stretching the
definition of multicellular? Each of the units, after all, reproduces on its
own and there is no differentiation.

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SubiculumCode
Not biologist, but I wonder whether these model organisms are valid. One might
expect that today's single cell organisms may have had multicellular
ancestors, but have kept the--I struggle for the word--the required genetic
machinery for multicellular form in dormant/unexpressed fashion, but otherwise
relatively intact and ready for expression given certain evolutiinary
presures. This would be in contrast to the original evolution of multicellular
life. Edit: I see others here have expressed this idea already, and more
elegantly.

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jamiek88
Great that I could just read all that info without jumping through hoops or
just getting the abstract.

Interesting that the changes were then stable over many generations once the
predator was removed.

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Halluxfboy009
As far as I understand this paper, the experiment did not generate a
multicellular species. Perhaps the experiment actually generated an algae
colony?

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aaaaaaaaaaab
I guess this means that thousands of new multicellular “species” are born in
the wild each day. Fascinating!

