Model Systems for Experimental Evolution

gotothelight(Sinead)

Depending on whether a project is meant to develop evolutionary theory, test it, or tell us something about marine phytoplankton, different model systems are used in the lab.

Most of our general evolution “R&D” is done in Chlamydomonas, a unicellular freshwater alga that is a well-characterised model system for photosynthesis and experimental evolution. We can grow it easily, and have access to an arsenal of microbiological, molecular, and genetic tools. We use Chlamy for experiments where we need a lot of statistical power, or where the question we’re asking is so general that there’s no reason to futz over the pickier Ostreococcus. Making the leap from freshwater to marine systems may seem a bit much, but all of life plays by the same evolutionary “rules”, and the general insights gained in experimental evolution have held across systems spanning kingdoms, from viruses to bacteria to unicellular and multicellular eukaryotes. Plus, there are presently no marine microbial model systems that can be used to develop rather than use evolutionary theory, though we hope to change that with Ostreococcus.

Ostreococcus is a marine picoplankton, and as far as we know, it’s the smallest free-living eukaryote on the planet. We use it not only because it’s ridiculously small and cool, but because we’re interested in understanding how populations of marine microbes are likely to change as the oceans acidify. To know how a group of organisms is going to change between now and some point in the future, you need to know two things about the current and future communities: who’s there, and what are they doing. This means that we need to know how, on average, a genus responds to ocean acidification, but we also need to know how much variation in response is present within that genus. Since Ostreococcus comes in several ecotypes, we can use it to address the question of how the function and composition of groups of phytotplankton with similar biology (sometimes called functional groups) should change over the coming years. 

While algae are beautiful, evolution experiments can get long and involved, so we often use computer simulations to do thought experiments first. Models tell us what can happen, if our logic is right. They give us a range of possibilities. We can then set up experiments to look at what does happen.