Associate Professor of Biology and head of the Davies Marine Population Genomics Lab Sarah Davies studies ecological genomics, population genetics, molecular ecology, coral ecology, climate change, and symbiosis.
Your research looks at how reef-growing corals adapt to climate change. What drew you to this field of study?
My lab focuses on two aspects of coral biology. The first is thinking about how corals might respond under climate change, asking questions about how their algal and microbiome partnerships might predict these responses. It’s thinking about how this unique consortium of the coral host, their algal symbiont inside of them, and their microbiome interact to predict how they will perform under climate change. We wonder if they can change things like their algal symbiont or their microbiome to survive the future.
Corals are really cool. This is what drew me to work on them. They’re such a cool situation because you have an organism that is a rock, an animal and a plant all in one, and they are really basal metazoans. We tend to think of these organisms as not being very sophisticated, but they have tons of crazy things that they do. For example, they allow an algal symbiont to live inside of their cells. It’s an endosymbiosis, meaning that the algae is integrated inside of the host cell. It’s super fascinating from an immunity standpoint. When we, as humans, have a foreign object that comes into our bodies, we mount an immune response and get rid of it. The second part of our lab is really interested in that fundamental question of, ‘how do you allow something that’s not supposed to be there—that has a totally different genome—to live inside your cells? So this idea of immunity recognition and how that might trade off in the symbiosis is one part of our work.
Your research uses the term, “ecosystem engineers” when referring to coral. Can you explain what this means?
When people go snorkeling on a reef, they think of corals as rocks, right? They hit them accidentally, and they can totally ruin your snorkel. They really are building actual ecosystems. Just like trees are building forests, corals are building all of the homes to all of the other invertebrates and baby fish. They’re like sanctuaries for baby fish. They are like the buildings in a city. Corals themselves are alive and building more cities as we speak right now. When we take a sample from a coral in the field, you can’t even tell where we sample from it when we come back because they are constantly building reef. They are truly building an ecosystem. And the engineering part of it is so sophisticated when you think about it, right? You have this basal metazoan that we think of as being unsophisticated—like a jellyfish type of creature that doesn’t even have a brain. But it’s secreting these gorgeous calcium carbonate skeletons that are so diverse in what they look like.
It’s really quite crazy, when you think about it. Humans are so lame, we just build bones, and we all build the same bones. But corals are busy building brains or branches or lettuce-like structures. It’s so pretty.
Your lab looks at corals and their algal symbionts and how the two can potentially slow or accelerate evolution. What has your research found so far?
Partnerships can be quite rigid in some species. Some have very close knit relationships with a certain strain of algae, and they really don’t associate much with other algae, and other corals are more plastic and can have diverse consortiums of algae living inside them. There’s a species we work on in the Caribbean, for example, that can associate with a variety of algae from different genera.
How a coral does under climate change scenarios depends on who it’s associating with. And then it can also have a stressor, and change who it’s hosting with afterwards. That’s called symbiont shuffling. So it’s this idea that a coral can have mostly one symbiont, and then a little bit of another—because they have millions of cells within them. They could have mostly one algal symbiont, but then they could have little sneaky background amounts. Then under a bleaching event those sneaky ones can repopulate afterwards. So there’s a lot that happens in corals, and we’ve seen that a lot in the field. They can switch partnerships under extreme environmental conditions.
I think one of the coolest things that one of my graduate students—who is co-advised with Tom Gilmore—is working on is intentionally changing the algal symbiont in the lab. We can culture the algal symbionts and then infect them into different model sea anemones. They’re not the same as corals, but we use them as a model system to understand symbiosis. We infect them with different algae, see how that manifests from an immunity standpoint, and think about how that can restructure how cells talk to one another. We think that some of the symbionts are more mutualistic and easier to control for the host, and then some of the symbionts are sneaky and are able to kind of evade the host immune system and behave differently.
In the field component, we’re really interested in monitoring what happens in situ in these extreme environmental conditions. For example, we went to Panama in August last year during a heating event, and then monitored these corals that we’ve had tagged in the field for a few years. We returned after a bleaching event in 2023. Did they change their algal symbiont in response to this bleaching event? That’s the ecological side, and then on the more molecular side, we’re trying to get into the nitty gritty of what changes in the host when you host different algae.
One of the projects in the Davies lab includes research on long range coral dispersal in the Caribbean. What drew you to studying the Caribbean?
Most of my PhD work was in the Pacific. I will say there are certain aspects of working in the Pacific that I miss, because it’s a lot more resilient to climate change. There’s many more species in the Pacific. The Caribbean is in a much more dire state of ecological collapse than the Pacific, I think. It probably just has to do with redundancy. The Caribbean just has far less redundancy than the Pacific has.
But really, what’s kept me in the Caribbean is this fascinating challenge that we’ve encountered. We thought this one species that I worked on for my postdoc was all one species, and then we started noticing all of these weird patterns in the data that weren’t explained by anything. Then we sequenced the symbionts, and they were all different—but not in a way that was predictable. Then we were like, ‘well this is weird.’ So then we needed to sequence the host, and what we found was cryptic genetic variation. Everything that we thought was one species is actually three different species. We call them cryptic lineages. We just had a big paper out this year in Nature Ecology & Evolution, talking about this cryptic variation and how it matters, because it’s super functionally relevant. All of the main responses that we observed in a climate change experiment were explained by the cryptic variation of the host. It changes who you are and which algae you associate with. It changes where you’re able to live and how you respond to climate change. This cryptic genetic variation is what’s kept me in the Caribbean and kept me excited to do work here.
Interview by Kelly Broder (COM’27)