Tigger pods

by woceht

This is a post for the people who ask me what I do.  Let’s see if I can explain this intelligibly…

Meet Tigriopus californicus.  He is a kind of copepod.   Affectionately christened tigger pod by ex lab postdoc Brad Foley.  Note similarity to evil plankton from Sponge Bob.  The picture should have a scale but he is about 1mm long, which is about the size of your average household ant, unless you have scary monster ants in your house.  We can tell he is male because of the claspers on his antennules (knobs at the ends of the two things sticking out of his head).  Females don’t have claspers.

We like tigger pods in our lab because they are very good as a model system (read easy to collect, breed in beakers, relatively short life cycle, genetic tools, etc…).  They don’t swim very well so they are stuck in tidepools in the high intertidal and don’t travel very far down the coast so populations are physically isolated from one another (allopatric).  Our species is from North America, and has been found from Alaska to Baja California (though the southern Baja ones might be slightly reproductively isolated).  Different populations are genetically very different (~20% mitochondrial divergence) but they can still reproduce with one another.  [Slight sidetrack: Actually Ron Burton the granddad of Tigriopus and his postdoc Felipe have just published a very interesting review on mito-nuclear coevolution.  You should read it.  Very interesting perspective from the inside of a cell and how its components interact with one another.  I wonder what Jerry Coyne makes of it.  In Drosophila world mitos are very conserved and species seem to be able to exchange them at will. O.o]  Tigger pods are very good for testing questions like how do species form?  How do things stop being able to reproduce with one another?  Like how does that process start and what happens after?  My labmate Barret is working on this for her thesis.

I would like to point out at this point that much of the work that has been done has been from the viewpoint that the key incompatibilities arise neutrally, by chance, in a process that we evolutionary biologists call genetic drift.  This diverges from what most people think of when they think of evolution, where some environmental selective force causes things to be different.  How does this happen?  If you think about it life is kind of like a lottery.  If you think of tigger pods as many coloured pieces of paper in a hat, and at each drawing you draw out maybe 10% of those papers, add 9 pieces of paper of the same colour to each piece you draw out (representing those that survive and contribute to the next generation), then you are going to get a whole different set of coloured papers, just by chance.  Repeat this a few times, and you can start to imagine how genes fluctuate just by chance with nothing to do with the environment.  In the early part of the 20th century 3 very smart men called Bateson, Dobzhansky and Muller came up with a model about how these neutral changes occurring in isolation can lead to maladaptation of hybrids when populations are brought back together and mate with each other.

Ecologically we used to think tigger pods were much less interesting, but thankfully for this ecologist this is changing because I’m stubbornly an ecologist (that is how my brain seems to work; I think about the environment a lot; it is what drives me to become an ecologist) and yet I want to graduate.  For example.  They live in these tidepools that are isolated from the ocean for days at a time and dry up.  How do they do this?  And also they live at different latitudes.  How do different environments drive local adaptation in individual populations?  That is what I am working on currently.

As an ecologist why did I choose to go into a neutral evolution lab?  Haha.  Well I knew I wanted a more evolutionary perspective but I didn’t fully appreciate the difference between drift and selection when I started here.  Reproductive isolation seemed like an interesting problem.  It’s been a fun learning experience that has endowed this ecologist with a long term perspective.  I like being the thorn in my advisor’s side that reminds her that selection is important too… 😛

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