ECR Spotlight – Luella Allen-Waller

Luella Allen-Waller

How did you become interested in biology?

I've had a particular fascination with ocean animals for as long as I can remember, despite growing up far from either coast in Wisconsin. I credit my parents with making sure I had a lot of access to local forests and lakes, and I loved nature. But I wasn't sure I wanted to major in biology until I got obsessed with symbiosis in an introductory lab course at Swarthmore College. My mind was blown when I learned that invertebrates like corals and sea anemones harbor photosynthetic algae (symbionts) inside their cells. We did an experiment with the symbiotic model anemone Exaiptasia diaphana where we set up lamps next to anemones that had symbionts versus anemones without symbionts. Without symbionts, nothing happened when we turned on the light. But symbiotic anemones would start turning toward the lamp every time. Microbes could change animal behavior! How wild is that? I wanted to tell everyone I knew. Now I've come full circle: 10 years later, I'm back writing about that same anemone species.

Describe your scientific journey and your current research focus

In undergrad I was lucky enough to study abroad in Madagascar and survey coral disease in the wild. Reef research was an enchanting experience for me, but also sobering, as I also learned from my advisor Gisele Bakary how coral health had declined in recent years. This motivated me to pursue research in marine pathology. After I got back to the USA, I joined Dr Liz Vallen's lab at Swarthmore to do an independent study of anemone cell biology, then had the chance to work in a couple great bacteriology labs. I worked more on coral diseases with Dr Kim Ritchie at Mote Marine Laboratory and then nematode–bacterial pathogenic symbiosis with Dr Heidi Goodrich-Blair at the University of Tennessee. For my PhD, I returned to the world of cnidarian–algal symbiosis by joining Dr Katie Barott's lab. My research investigates how climate change will affect corals, focusing on the nutritional interactions between cnidarian animals (i.e. corals and anemones) and different populations of symbionts. These symbionts are critical because they photosynthesize and provide energy to the animals that host them, but high temperatures cause cnidarians to lose their symbionts. I take cnidarians with naturally different symbiont species or population densities, expose them to heat stress and measure how the symbionts respond. Then I assess how these changes affect host health. How much sugar are these animals getting from their symbionts? Are the animals growing? Can they keep their cellular conditions stable? The goal is to figure out which symbiotic partnerships might be most resilient to climate change.

How would you explain the main findings/message of your paper to a member of the public?

The first few experiments I did for my PhD showed that heat stress makes coral cells more acidic. This is a problem for several reasons. First, like carefully tuned instruments, most enzymes only work in a narrow range of environmental conditions, so a change in pH harms cell functioning. Second, corals must tightly regulate pH throughout their bodies to create the right conditions to build their massive, complex skeletons, which create most of the habitat of a reef where other animals live. But despite this being a fundamental problem for corals, nobody could say whether this cellular acidification effect that we observed came from heat-stressed symbionts, or the coral host, or the loss of the symbionts that happens at high temperatures (called ‘coral bleaching’, because the animals turn white without their colorful algae). It's difficult to control the symbiont variable because corals can't survive without them. So, I turned to a more flexible species of sea anemone, E. diaphana, which can live with or without symbionts. To our surprise, our team found that turning up the temperature acidified the animals' cells regardless of how many symbionts were there to begin with. Heat treatment even acidified anemones that started out with no symbionts at all. This means that heat-driven acidification can't be a result of bleaching. If heat interferes directly with pH homeostasis, heatwaves are probably harming cell functioning before we see corals bleach. It also means that even though some corals manage to hold onto their symbionts during heatwaves, these bleaching-resistant animals are probably suffering severe consequences from ocean warming that were invisible to us before. We must transition away from fossil fuels if we want to keep any semblance of our reefs, and the 25% of ocean species (including many sharks, turtles, rays and commercially important fish) that depend on them.

What do you enjoy most about research, and why?

The best part is that feeling of awe when I get a new perspective. Whether it's turning on the confocal microscope and seeing that small universe inside of an anemone or a coral, or reading a great study from a researcher who approaches questions from a completely different angle that I hadn't considered, every little discovery can spawn more curiosity. In a similar vein, I love discussing new and surprising science with other people, because it lets everyone share that wonder and spread it.

What is the most important lesson that you have learned from your career so far?

Finding good mentors (including peers!) is key. My awesome coauthors on this project brought ideas and skills to the table that made it a much stronger study. Together, we built and troubleshot the experimental system, cheered each other on during early morning timepoints, and spent hours interpreting the story the data were telling us. All that work was much more feasible and rewarding with a team. Every success really is sweeter when shared (even when the success in question is overcoming seemingly basic but frustrating problems, like keeping our high-temperature water baths in the target range in a drafty basement lab in the middle of winter).

What do you like to do in your free time?

When I'm not in the lab I spend a lot of time walking my dog, writing poems, running and cooking. My friends say I make a lot of soups. They're a nice way to decompress from lab work, because you don't need to be precise at all: you can kind of make whatever you want with the ingredients you have. I also spend a lot of time meeting with other graduate workers to strategize about how to work together to make academia more just and equitable.

What's next for you?

I'm getting ready to defend my dissertation this summer. I'm also hunting for postdoctoral opportunities where I can build new skills to keep studying how symbioses respond to stress. In organisms like sea anemones and corals, the chemical exchanges between invertebrate animals and single-celled microalgae power the ecological functioning of entire seas. If we want to predict ecosystem responses to worsening climate change, it's not enough to measure how each individual organism will handle warming – we need to understand how the connections between species themselves can survive. That's one of the most urgent questions we face, and it's the one that motivates me.