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With our experiment we showed that the transition to multicellularity can
occur
more quickly and more easily than previously thought.
And by watching the steps that our snowflake yeast
take to evolve multicellularity, it gives us an idea of the steps that are required for other
multicellular organisms in nature
to evolve. We started our experiment with single-celled yeast
and we evolved them in an environment which favored large-size.
The yeast responded to this by evolving to grow as these
snowflake clusters of several hundred cells.
Um, snowflake yeast have a cool emergent
multicellular way of growing in that they grow to a certain size
and then they don't get any larger and once they hit that size,
they begin reproducing by spinning off smaller multicellular propagules.
It turns out that these propagules are effectively juveniles
because they can't reproduce until they get back to their parents size.
The size of the cluster is a multicellular trait
and it's also one that evolves in response to the environment. If we put
them in an environment
which favors large size, they evolve to delay reproduction till they get bigger.
And if we put them in an environment which favors small size they shrink.
We also see the evolution of division of labor among the cells in the cluster.
Some of the cells altruistically sacrificed their life and this actually
benefits the cluster
because the cells that die allow the large cluster to regulate
the number and size of the offspring that they produce. What it, what it shows in
this case
is that, um, a trait that is
a characteristic of the group of cells as a whole.
No one individual cell, ya know, is responsible for the size of the cluster.
So an emergent multicellular level trait
is both variable among our different genotypes
of our snowflake yeast and it is
heritable. So for evolution
to occur, right, you need to have heritable variation in a trait.
And then, um, you need to have a selection acting on that trait
and in response to that selection, a change in that trait value through time. So in this case,
we have some clusters which are genetically they only make small clusters,
and some snowflake yeast which genetically grow to be a larger size
and if we select for bigger size then
through time these clusters evolve to be larger and larger
which shows that, um, there's been a sort of
a change in the way in which these yeast are evolving. Now selection instead of
acting, um, discriminating between different single cells
is discriminating between different clusters. And that's a key step in the evolution
of multicellularity
You need a shift in this in this level of selection from single cells
to clusters and in addition to selection
itself shifting to the cluster level, we see adaptation occurring at cluster level traits
which shows us that they're evolving as simple multicellular
groups or simple multicellular organisms as opposed to
single-celled yeast. The reason I got going on
experiment I actually stem from a conversation I had with my try to sign
it was my postdoctoral bison now
I was so aggressive the time and we're sitting over coffee just sorta
talking about the coolest thing we can do in the lab now will be
the best experiment and we've had evolving
some simple multi-state organisms would be fantastic
didn't really know how to do it we got it would just be that the most exciting
thing to do
with a month we had a sex chat an approach and I was in the lab doing
experiments you that he was actually
the one wit dat unit using with that sledding on
on rapid settling really good media and think that are bigger are going to
settle patenting they're small
nothing wat if you throw a handful sand and water if federal that in the water
very quickly if you better handle a mud into the water
and slurry to Bozeman particle sell very slowly that just because the mud
particles
are much smaller and finer in the same particles even though I really do think
entity
and so I think we sell them one particle its small
felt very slowly but evolved to you to be really large
store at the mall to stick together into clusters
then they can sell fast and I'll have to fly to allege
so that was that was Mike since I it worked really well so we know that bit
what he say larry is a vaulted repeated be put the history black
right over the last roughly billion years it's evolved independent me
in about twenty five different groups but not that many times given that
length of time
but a billion years 2500 it's just a handful and so
there's been a lot of debate over whether evolving what he say their uses
is actually a pretty easy thing to do
or whether it's if they're very challenging and only evolves under very
specific circumstances
and in our experiment here we show that within two months
in the lab we can take single cell use and evolve new movie sailor
organisms from which means that it's much less constrained than previously
thought
I'm
and I mean if you could extend that out too thinking about life in general
if you have a plan it's occupied by save a life would you expect to see more pics
/a organisms on are not
perhaps he would given that we can do in the lab
with just you know a few billion you cells
in two months if you're planning to contains trillions and trillions a
single cell organisms
and you have that going on for millions of years you might expect motivating
to be a tool been interested in
arm the evolution cooperation and conflict for a long time
I did my PhD here to you with for Denison
working without liking plants and they're right sobil
bacterial symbionts it from the school me to them where the bacteria pride for
lies in plain
I give them a home in and resources but have a lot of
conflict and and conflict mediation ago than the system
and so make you feel organisms are basically
extremely cooperative group a single cells their next
there mister examples above the most
well integrated well have been cooperating it to you that exist in
nature
by in my body is trillions of cells and only a tiny fraction
ever get to reproduce arrested in just are are supporting crew
for my reproductive cells actually go on did to family next
your generation and so that's basically extreme altruism
you know 99.999 carried on
percent of sales my body are reported actress
and that's really cool and and and if not get easy to evolve right
giving up individual reproduction is is pretty costly
and thought it only law under some conditions and so
arm so I came to this with through
theoretical and experimental background in in in thinking about
problems up operation conflict so for 6 from television is a description
approach right and fed him say doing a comparative study we take
um something which is you say there that that
that has a i'm ok if the relative in a maybe diverged from a common ancestor in
in
in nature about 20 million years ago and then and then trying to figure out
what's different about them and what made might actually
have been required for the transition to market a lady by comparing them
um were involving something in the lab met
sort of that approach evolving from the lattice is usually called experiment
election
doesn't have to mean a lab you can appeal to you especially with the
accessibility of next-generation sequencing next-generation sequencing an
excellent addition this can go hand in hand
because you have you have your own you have your poor
fossil record in your freezer right like me we have frozen down our our youth
populations
every 50 generations a parks famine which me the weekend poll out
living living fossils from from our multi hundred generation experiment
and then we can be compared to my growing into doing competition at day's
end
and looking at them physiologically but we can also seek with them
I think I genetically with different everyone to figure out how those genes
into transcribed we can do
lots of syrup quĂmica said he's and
so sort next-generation microbiology annex from television really are
I very well said to each other opened I think
until recently people having trying to use experimental Ishant actually
making things it big music from tuition
very very successfully detest evolutionary and ecological questions
about basic you know prophecies I S B C a share
adaptive radiation sex long-term maintenance engine experts City
I mean they're they're Armada really wonderful trout evolution
I studies in which basic evolutionary and ecological prophecies are explored
but nobody's ever tried to use it actually create something new as far as
I know
um and so this
probably a bit a a limitation that
fighters have impose on themselves but you know you would never try to evolve
look at the menu cuz it's hard to do
and is unlikely to work in the lab so know we
up until now is actually tried um and also this does not that many
about 100 people doing is from devolution at and
so you know if if more people were someone else probably overdone
one of the things that has sorta from kept Greece just back from from from
working with working on this question more right working on
the on the first steps and the transition to market a lady that
they don't have a model system where you actually have
the entire series have steps from single-celled ancestor
all the way through team supermarket chain organism we have
passionate than that
but but we have arm are organisms that have
basically diverged from a common ancestor so for example one that best
systems for working on questions about what is a very audible within
algae babies really fantastic how GI
which in the last two hundred million years up
have evolved looking for unity and is there sort of nice intermediate forms
there as well
things that are not quite as complex as as a sailboat box
but were forced to compare
single cell organisms that have been evolving $400 million generations
democracy organisms that have been evolving for 102 million generations
and last time they share a common ancestor is way back when when dinosaurs
were and
and as a result is a lot of stuff that happened in intervening time that makes
direct comparisons challenging and as a result is
check is difficult to disentangle housing consequence for example
if you think that the genome complexity is an important precursor
to evolving on what he say organism and you look
at at a wall box and acclaimed among us want more Taylor 13
you tailor any been separated by 102 million to generations
it's hard to tell if if the bigger genome size and the whole box
is a cause I'll be at least in what is a very involved likes
orkut the consequence how the pac-10 the ball like has been evolving as a more
detailed organism
for 102 million generation so
with our system we actually have the entire transition and we have
frozen living representatives up the entire series
going from a single cell organism all the way up to a small snowflake
up to a bigger Southlake and the beer Southlake has cool division labor
at this most complete doesn't so we can ask lot interesting questions about this
transition in a very fine scale
because we have the entire series making our freezer so we can look at
how body paint change the time anything the key questions about
the Orjan a mock you save their development
from scratch we can look at the genetic changes and and molecular I change that
underlie
these these these poke sort of you to change things but changes in body paint
we're actually looking at the interaction between revolution what he
say lady
and evolution aging here really interesting results
a met that that were actually reading up right now
and yet as a whole actually other sweeter things that admitted a more
tactical
but in 20