Plasticity and microevolution of diatoms

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Martina Doblin discusses that Marine microbes like diatoms play a crucial role in global nutrient cycles and ecology.

Image courtesy of interviewee. March 25, 2024

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This video video discusses the significance of diatoms, which are single-celled, photosynthetic organisms found in the ocean. Diatoms play a crucial role in the planet’s ecology by producing about 20% of Earth's organic matter, which forms the basis of the oceanic food web and influences climate regulation through carbon dioxide absorption during photosynthesis. They possess unique glass-like cell walls that contribute to their role in organic matter production and carbon storage.

The research focuses on understanding how diatoms respond to unprecedented changes in ocean conditions due to climate change. There are approximately 200,000 diatom species, each with diverse genomes that may lead to varying responses to environmental changes. The study emphasizes diatoms' plasticity – their ability to adapt physically and functionally to different environments.

Using trait-based approaches, researchers aim to simplify the complex genetic diversity of diatoms into manageable traits that can help predict their future behavior in changing ocean conditions. These traits include growth rate, cell size, and pigment content. The research findings suggest that the relationship between phenotypes and genetic relatedness is not straightforward, indicating that phenotype cannot always be predicted from genotype alone.

The study also identifies constraints within the trait landscape, suggesting that while diatoms can adapt, their responses may be limited. The findings have implications for modeling oceanic primary production and understanding diatoms' future role within the changing marine ecosystem. Moving forward, the research will explore diatom responses in the context of environmental stressors and their potential for adaptive evolution in response to climate change.

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As we say it, are single celled,

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microscopic photosynthetic organisms that,

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I guess have two halves to them.

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They come from the Greek word diams, meaning split in Hal.

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And these two gulls are, are forming a,

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a complete cell.

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Uh, the diatoms, the cells in the ocean can, exist

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as solitary cells

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or, in joined up chains of cells

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and sometimes have these spine on.

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They are incredibly important in terms

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of our planetary function.

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They produce, 20% of the organic matter on the earth

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to feed the rest of the food web.

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So they are the most important

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primary producers in the ocean.

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And their combined photosynthesis is equivalent to about

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the photosynthesis that takes place in tropical rainforest.

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So they're fundamentally important the way

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that the earth climate system functions,

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because in the process of photosynthesis,

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they take up carbon dioxide

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and they regulate the amount

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of carbon dioxide in the atmosphere that,

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dissolves into the ocean.

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And through this process, they create organic matter.

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And the organic matter in the open ocean, doesn't,

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exist, or stay buoyant in the ocean.

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It thinks slowly

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because the diatoms have glass like walls,

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and this makes them heavy.

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Uh, diatoms are food

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or zooplankton and other organisms.

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And so the organic matter they produce

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is transferred into the food web.

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And if it isn't eaten in the surface ocean, it starts

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to think, and it can, it can feed a lower tr

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it can feed, organisms in the lower part of the ocean.

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But some of this material even makes it down into the deep

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ocean where it is sequestered in a long-term

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carbon store.

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So diatoms through their very, process of photosynthesis

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actually then are fundamentally important in the way

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that the earth climate system works.

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So without diatoms,

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our planet would look very, very different.

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So a fundamental question we're asking in our research is

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how will diatoms respond

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to contemporary changes in the ocean

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that are happening at an unprecedented rate?

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Diatoms are known to be incredibly diverse.

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There are some 200,000 species of diatoms

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that live in the ocean,

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and each of them has a very, diverse genome.

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And this is the result of their evolutionary history.

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So the genomic differences between some diatoms can be

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as great as the genomic difference between mammals

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and fish, for example.

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So they have enormous capacity to have very diverse

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responses potentially to changes in their

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growth environment.

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And, and so this is, what makes this,

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I guess question that seems simple enough.

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How will diatoms to respond

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to changes in the contemporary ocean?

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Um, it makes it actually quite a challenge

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because we have, potentially very divergent responses

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or a very broad range of response.

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And so I guess one of our first questions is to ask

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what is their ability in terms of their physiology

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to respond to these changes?

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And, we call this plasticity,

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and it's kind of nice that I'm holding up

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a plastic petri dish.

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It sort of further underlines

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what we're exploring here in our research.

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What is the limit of this plasticity?

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And can we represent it

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in attractable way in simulation models that predict

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the future of marine primary production in the ocean.

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This fundamentally important parameter that changes

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the amount of carbon dioxide in our atmosphere changes the

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amount of carbon that reaches the sea floor and is in

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and is a long term carbon store

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and changes the way that the whole food web operates.

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By plasticity, I mean the interaction of a genotype

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with its growth environment.

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And this is the manifest phenotype that,

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I'm referring to.

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So, the phenotype is the

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manifestation of the,

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of the genotype interacting with the environment.

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And we know, for example,

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that diatoms can grow in a very broad range of temperatures.

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And so this makes them thermally plastic.

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Uh, so they're able to maintain a reasonable amount

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of growth across, say, 20 degrees, which means

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that theoretically they could be transported from the

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tropical war motions, all the way,

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to almost the southern ocean and survive.

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So organisms, that are plastic have large capacity to

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survive and function under very broad

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environmental condition.

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We have been using trait based approaches in our querying

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of how diatoms will respond,

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because this approach already starts to simplify

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or deal with some of the complexity.

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So instead of asking the question, what will all

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of the diversity, the genomic diversity

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of these diatoms yield, in terms of responses, we're,

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we're representing diatoms by their trait.

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And traits are the many things that describe the phenotype.

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So in humans, we think of eye color, height,

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pigmentation of skin.

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These are traits in humans.

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For diatoms, they can be growth rate, cell size,

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pigmentation, content

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that facilitates the process of photos.

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So these traits then in combination,

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describe the phenotype.

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And so the trait based approach is becoming very, a,

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a well adopted approach

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because it starts to make these questions tractable

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in the way one might describe

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diatoms in earth simulation models where we are trying

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to understand what will they look like in the future ocean,

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how many, how many types will exist, in a warmer

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or acidic ocean, for example.

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So our, approach is not only trait based.

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We were interested in growing organisms

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and exploring their traits in ways

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that allow our observations

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to take place over reasonably short timeframes

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with some degree of efficiency.

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And so my lab has been involved in, I guess undertaking

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miniaturization of assays to try

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and, grow diatoms in smaller volumes

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and to be able to assay them for different traits.

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And these traits vary from cell size

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and pigment content to things like, physiologically how,

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how much reactive oxygen species they contain

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and potentially even into their metabolomic

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transcriptomic response.

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And so what this enables is a, I guess a speeding up

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and a more, I guess reasonable, feasible way

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that we can explore the responses of many different types

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of, or many strains, many species of diatom at the same time

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and in a reasonable timeframe, start to explore patterns of,

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phenotypic plasticity.

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Our findings of this research really, really interesting.

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First of all, we were able to describe phenotypes

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across a two dimensional trait gape.

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And what I mean by that is that we analyzed many,

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many traits and we were able to reduce the number

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of traits into two axes where we described most

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of the variation of the taxa that we examined.

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And so all of a sudden we've gone from

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a very complex data set into a much more simplified data set

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where it becomes clearer to see patterns

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and differences across phenotype.

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What we also saw was that across the traits scape,

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and you might imagine it's a big right angle to axi

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and all the phenotypes are plotted.

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Uh, we noticed that the phenotype trait space was not

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evenly occupied.

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There were some areas that seemed to be inaccessible

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and other areas where we saw a clustering of phenotype.

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And so this raised eyebrows to say, well, perhaps,

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not all trade combinations are.

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The other thing we noticed was that the, the phenotypes,

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they bore no relationship with the genetic relatedness

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of the organisms that we were examining.

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So it meant that you couldn't predict the phenotype

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from the genotype.

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And so this is very interesting.

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We use a lot of, genomic approaches

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to quantify diversity in the ocean.

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Uh, but that doesn't necessarily mean that we're easily able

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to describe the phenotype.

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And so this raises the interest in, kind

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of quandary is that how do we represent

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this diversity perhaps?

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Actually this phenotype approach not only simplifies the

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measurement, it actually perhaps is more revealing about the

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sort of, patterns that may exist in nature.

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Uh, the other finding that we had was that

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when we changed the number of traits

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to describe the trait space,

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we could actually reproduce this pattern, which suggested

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that we didn't need all the traits that we needed,

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only a subset of them.

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And this shows that there may be strong

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correlations between trait.

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And so we're we're, able to potentially

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simplify our complex problem even further.

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So these represented some exciting breakthroughs

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because it, it meant that,

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we could then basically describe, start

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to see these potential constraints on the way

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that phenotypes, I guess, are manifest in nature.

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Though plasticity is not

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possible across this entire trait scape,

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there were certain patterns so

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that if organisms were put into new growth environments,

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we saw them shift,

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but in a constrained way across this trait scape.

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So, all of a sudden now we are starting to understand

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that there may be limits to plasticity or constraints

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or pathways of plasticity.

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And this is an exciting, I guess frontier

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because it means that all of a sudden we potentially have,

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a narrow asset of possibilities

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for diatoms in the future ocean.

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So the implications of this work suggest

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that our complex problem

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of representing diatoms in simulation models of the ocean

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and, and what primary production will look like in the

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future, suggests that we can actually

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represent this complexity in a way that uses traits,

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their correlations,

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and phenotypic constraints, if you like,

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that could describe, both plastic

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and possibly evolutionary

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or adaptive responses to changes in the ocean.

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And, and so this is, I guess a, a real frontier

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that we want to keep exploring.

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So what trait combinations are effective strategies

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for particular types of change in the ocean?

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So we know that broadly the ocean is becoming warmer.

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There are very few places that are actually cooling,

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but it's also becoming more acidified, more deoxygenated,

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potentially more structured in its vertical layering.

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So we are reducing potentially the amount of nutrients

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that can be brought up from the bottom ocean,

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deep ocean into the surface to fuel productivity,

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to fuel photos, and create a growth environment for diatoms

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where they can grow very quickly and produce a lot of cell.

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And so these dimensions of, of, trait plastic

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exciting ones that we think are tractably able

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to be represented in models through the trade gape approach

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and that short-term changes

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and potentially even long-term changes

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are possible to be represented.

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Our experimental approaches here in these multi-well plates

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as sort high throughput method mean

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that we can actually create experiments

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that may last one year in a laboratory setting,

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but help us, create an adaptive, a selection environment

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for the diatoms to say

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that if we consistently apply heating, acidification,

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deoxy oxygenation, what will be the pathway that may go

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beyond plasticity and I guess lead into adaptive evolution?

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So genetic changes in these populations,

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we can actually follow that in time.

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Diatoms are these very, useful organisms

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because they have short generation times rapid growth rates,

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and we can see many generations within one year,

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that basically simulates how they might be responding

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to directional changes in, in the ocean.

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So in all this, this is a very exciting place to be.

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In terms of our next steps, we have the possibility of in,

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incorporating plasticity

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and evolution into biochemical

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simulation models of the ocean.

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We have the possibility to do some really cool experiments

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to explore the dimension of biological change in diatoms.

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And, I guess we have the possibility to work

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with other organisms in this way.

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So diatoms are only one group of phytoplankton.

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There are other types like cyanobacteria

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that we can ask the same questions on

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and see if we see consistent patterns

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or similar kind of strategies if you like,

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within other groups

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of photosynthetic organisms that grow in the ocean.

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So it's been a really interesting study.

The Vital Role of Diatoms in Our Ecosystem

00:00:01 - As we say it, are single celled, microscopic photosynthetic organisms that, I guess have two halves to them. They come from the Greek word diams, meaning split in Hal. And these two gulls are, are forming a, a complete cell. the diatoms, the cells in the ocean can, exist as solitary cells or, in joined up chains of cells
00:00:35 - They are incredibly important in terms of our planetary function. They produce, 20% of the organic matter on the earth to feed the rest of the food web. So they are the most important primary producers in the ocean. And their combined photosynthesis is equivalent to about the photosynthesis that takes place in tropical rainforest.
00:01:07 - that the earth climate system functions, because in the process of photosynthesis, they take up carbon dioxide and they regulate the amount of carbon dioxide in the atmosphere that, dissolves into the ocean. And through this process, they create organic matter. And the organic matter in the open ocean, doesn't, exist, or stay buoyant in the ocean.
00:01:36 - because the diatoms have glass like walls, and this makes them heavy. diatoms are food or zooplankton and other organisms. And so the organic matter they produce is transferred into the food web. And if it isn't eaten in the surface ocean, it starts to think, and it can, it can feed a lower tr it can feed, organisms in the lower part of the ocean.
00:02:10 - ocean where it is sequestered in a long-term carbon store. So diatoms through their very, process of photosynthesis actually then are fundamentally important in the way that the earth climate system works. So without diatoms, our planet would look very, very different. So a fundamental question we're asking in our research is
00:02:41 - to contemporary changes in the ocean that are happening at an unprecedented rate? Diatoms are known to be incredibly diverse. There are some 200,000 species of diatoms that live in the ocean, and each of them has a very, diverse genome. And this is the result of their evolutionary history. So the genomic differences between some diatoms can be

Exploring Diatoms' Plasticity in Changing Oceans

00:03:12 - and fish, for example. So they have enormous capacity to have very diverse responses potentially to changes in their growth environment. And, and so this is, what makes this, I guess question that seems simple enough. How will diatoms to respond to changes in the contemporary ocean? it makes it actually quite a challenge because we have, potentially very divergent responses
00:03:43 - And so I guess one of our first questions is to ask what is their ability in terms of their physiology to respond to these changes? And, we call this plasticity, and it's kind of nice that I'm holding up a plastic petri dish. It sort of further underlines what we're exploring here in our research. What is the limit of this plasticity? And can we represent it in attractable way in simulation models that predict
00:04:17 - This fundamentally important parameter that changes the amount of carbon dioxide in our atmosphere changes the amount of carbon that reaches the sea floor and is in and is a long term carbon store and changes the way that the whole food web operates. By plasticity, I mean the interaction of a genotype with its growth environment. And this is the manifest phenotype that, I'm referring to.
00:04:49 - manifestation of the, of the genotype interacting with the environment. And we know, for example, that diatoms can grow in a very broad range of temperatures. And so this makes them thermally plastic. so they're able to maintain a reasonable amount of growth across, say, 20 degrees, which means that theoretically they could be transported from the tropical war motions, all the way,
00:05:19 - So organisms, that are plastic have large capacity to survive and function under very broad environmental condition. We have been using trait based approaches in our querying of how diatoms will respond, because this approach already starts to simplify or deal with some of the complexity. So instead of asking the question, what will all
00:05:49 - of these diatoms yield, in terms of responses, we're, we're representing diatoms by their trait. And traits are the many things that describe the phenotype. So in humans, we think of eye color, height, pigmentation of skin. These are traits in humans. For diatoms, they can be growth rate, cell size, pigmentation, content that facilitates the process of photos.

Exploring Diatom Traits for Future Ocean Modeling

00:06:20 - describe the phenotype. And so the trait based approach is becoming very, a, a well adopted approach because it starts to make these questions tractable in the way one might describe diatoms in earth simulation models where we are trying to understand what will they look like in the future ocean, how many, how many types will exist, in a warmer or acidic ocean, for example.
00:06:53 - We were interested in growing organisms and exploring their traits in ways that allow our observations to take place over reasonably short timeframes with some degree of efficiency. And so my lab has been involved in, I guess undertaking miniaturization of assays to try and, grow diatoms in smaller volumes
00:07:22 - And these traits vary from cell size and pigment content to things like, physiologically how, how much reactive oxygen species they contain and potentially even into their metabolomic transcriptomic response. And so what this enables is a, I guess a speeding up and a more, I guess reasonable, feasible way that we can explore the responses of many different types
00:07:57 - and in a reasonable timeframe, start to explore patterns of, phenotypic plasticity. Our findings of this research really, really interesting. First of all, we were able to describe phenotypes across a two dimensional trait gape. And what I mean by that is that we analyzed many, many traits and we were able to reduce the number
00:08:29 - of the variation of the taxa that we examined. And so all of a sudden we've gone from a very complex data set into a much more simplified data set where it becomes clearer to see patterns and differences across phenotype. What we also saw was that across the traits scape, and you might imagine it's a big right angle to axi
00:08:57 - we noticed that the phenotype trait space was not evenly occupied. There were some areas that seemed to be inaccessible and other areas where we saw a clustering of phenotype. And so this raised eyebrows to say, well, perhaps, not all trade combinations are. The other thing we noticed was that the, the phenotypes, they bore no relationship with the genetic relatedness

Understanding Phenotype and Genotype in Diatoms

00:09:30 - So it meant that you couldn't predict the phenotype from the genotype. And so this is very interesting. We use a lot of, genomic approaches to quantify diversity in the ocean. but that doesn't necessarily mean that we're easily able to describe the phenotype. And so this raises the interest in, kind of quandary is that how do we represent this diversity perhaps? Actually this phenotype approach not only simplifies the
00:10:03 - sort of, patterns that may exist in nature. the other finding that we had was that when we changed the number of traits to describe the trait space, we could actually reproduce this pattern, which suggested that we didn't need all the traits that we needed, only a subset of them. And this shows that there may be strong correlations between trait. And so we're we're, able to potentially
00:10:33 - So these represented some exciting breakthroughs because it, it meant that, we could then basically describe, start to see these potential constraints on the way that phenotypes, I guess, are manifest in nature. Though plasticity is not possible across this entire trait scape, there were certain patterns so that if organisms were put into new growth environments, we saw them shift,
00:11:04 - So, all of a sudden now we are starting to understand that there may be limits to plasticity or constraints or pathways of plasticity. And this is an exciting, I guess frontier because it means that all of a sudden we potentially have, a narrow asset of possibilities for diatoms in the future ocean. So the implications of this work suggest that our complex problem
00:11:35 - and, and what primary production will look like in the future, suggests that we can actually represent this complexity in a way that uses traits, their correlations, and phenotypic constraints, if you like, that could describe, both plastic and possibly evolutionary or adaptive responses to changes in the ocean. And, and so this is, I guess a, a real frontier
00:12:05 - So what trait combinations are effective strategies for particular types of change in the ocean? So we know that broadly the ocean is becoming warmer. There are very few places that are actually cooling, but it's also becoming more acidified, more deoxygenated, potentially more structured in its vertical layering. So we are reducing potentially the amount of nutrients that can be brought up from the bottom ocean, deep ocean into the surface to fuel productivity,

Exploring Diatom Adaptation in Ocean Changes

00:12:37 - where they can grow very quickly and produce a lot of cell. And so these dimensions of, of, trait plastic exciting ones that we think are tractably able to be represented in models through the trade gape approach and that short-term changes and potentially even long-term changes are possible to be represented. Our experimental approaches here in these multi-well plates
00:13:06 - that we can actually create experiments that may last one year in a laboratory setting, but help us, create an adaptive, a selection environment for the diatoms to say that if we consistently apply heating, acidification, deoxy oxygenation, what will be the pathway that may go beyond plasticity and I guess lead into adaptive evolution? So genetic changes in these populations,
00:13:38 - Diatoms are these very, useful organisms because they have short generation times rapid growth rates, and we can see many generations within one year, that basically simulates how they might be responding to directional changes in, in the ocean. So in all this, this is a very exciting place to be. In terms of our next steps, we have the possibility of in, incorporating plasticity
00:14:10 - simulation models of the ocean. We have the possibility to do some really cool experiments to explore the dimension of biological change in diatoms. And, I guess we have the possibility to work with other organisms in this way. So diatoms are only one group of phytoplankton. There are other types like cyanobacteria that we can ask the same questions on and see if we see consistent patterns or similar kind of strategies if you like,
00:14:44 - of photosynthetic organisms that grow in the ocean. So it's been a really interesting study.

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Plasticity and microevolution of diatoms

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