ECR Spotlight – Ellie Laetz Free

Ellie Laetz

How did you become interested in biology?

I grew up in southern California and the beach was a large part of my childhood. In high school, my biology teacher (Mr Bob Perry) developed his curriculum to include a large project where students conducted a long-term monitoring study of a beach near our school. We studied the environmental conditions, animals and algae that washed up on the beach, as well as the marine mammals and birds that visited the beach. Once I started learning about the marine environment, I was hooked and I've been learning about the oceans ever since.

Describe your scientific journey and your current research focus

After high school, I attended San Francisco State University, where I completed a BSc in Biology with an emphasis in Ecology. As a student, I had the opportunity to conduct research projects in various labs on campus, studying topics like growth rates in sharks and Paleozoic sea urchins. The most interesting project I participated in took place at the Estuary & Ocean Science Center under the direction of Prof. Stillman (UC Berkeley, SFSU), Dr Levebre and Dr Benner on the effects of temperature and ocean acidification on calcifying algae. This project introduced me to (eco)physiology and the ability to explain how biological processes work across levels of biological organization.

Wanting an international adventure, I joined the Organismal, Evolutionary and Paleobiology MSc program at the University of Bonn, Germany for the next step in my education. In Bonn, I worked closely with Prof. Wägele, who introduced me to the fascinating world of sea slugs and symbiosis. After conducting two projects in her lab and finishing my MSc degree, I began my PhD with Prof. Wägele as my main supervisor. I was also supervised by Prof. Bartolomaeus, whose lab excels in advanced imaging techniques like fluorescence and electron microscopy. My doctoral work focused on how and why solar-powered sea slugs steal chloroplasts form their algal food using a variety of advanced imaging techniques and live-animal experiments. I completed my PhD three years later (2017) on the enigmatic solar-powered sea slugs that I still research today.

After my PhD, I conducted short postdoc projects with the Leibnitz Center for Tropical Research (ZMT) in Bremen, Germany and Scripps Institute for Oceanography in La Jolla, California, before settling into a longer-term postdoctoral position at the University of Groningen, in The Netherlands. With the help and support of Dr Sancia van der Meij, I started my own group working on the ecophysiology of animal–algae symbioses. In 2022, I was offered an Assistant Professorship, which has allowed me to grow my group from a few MSc students to a large lab with students of all experience levels. For more information about my current projects, please see https://emjlaetz.wixsite.com/evolution-and-ecophy.

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

Some sacoglossan slugs can hijack the ability to photosynthesize by stealing chloroplasts from the algae they eat, earning them the nickname ‘solar-powered sea slugs’. They store these chloroplasts in their bodies and profit from the energy produced by photosynthesis. The emerald sea slug, Elysia viridis, feeds on multiple algal species, which determine the amount of time it is solar powered. For example, chloroplasts stolen from Bryopsis species are retained for months, but those stolen from Chaetomorpha species are only retained for a few weeks.

In this study, my colleagues and I examined E. viridis to see if kleptoplasty provides advantages in the warmer ocean waters that are coming due to climate change. We suspected that extra energy from chloroplasts would help, but we were also curious to know if the oxygen produced by photosynthesis would also benefit starving slugs. This is because warmer water holds less oxygen and oxygen is a crucial factor in determining an organism's thermal tolerance. Therefore, these slugs could have multiple benefits from feeding on Bryopsis species, that we wouldn't expect from animals that fed on Chaetomorpha species. We acclimated specimens fed each alga to their current maximum temperature (17°C) and the increase predicted due to climate change (22°C), before measuring their thermal tolerance. We also measured their metabolic rates before and after their thermal tolerance, to see how heat stress changes their metabolic rates.

Slugs acclimated to 22°C had higher thermal stress limits, surviving ∼35°C before physiological shutdown. After thermal stress, slugs decreased their metabolic rates, probably to conserve energy. We also examined the effect of light. Under higher light, slugs exhibited improved thermal tolerance, possibly because increased photosynthetic oxygen production alleviated the oxygen limitation from warmer water. As these slugs starved, they slowly digested their chloroplasts, so their ability to withstand heat and light stress disappeared accordingly. We therefore conclude that E. viridis can cope with heat waves by suppressing metabolism and adjusting heat tolerance; however, starvation influences a slug's thermal tolerance and oxygen uptake such that continuous access to algal food for its potential nutritive and oxygenic benefits is critical when facing thermal stress.

Why did you choose JEB to publish your paper?

We chose JEB for this paper because it was by far the most appropriate journal to showcase a large, manipulative experimental study like the one my colleagues and I conducted here. This study included multiple treatments, experiments and measurements because my colleagues and I wanted to get a broad understanding of how photosynthesis impacts thermal tolerance, metabolism and survival in a solar-powered animal. Studying all of these factors at once paid off because we were able to unravel the complex dynamics governing how this slug currently interacts with its environment and how it will likely interact with the warmer future oceans it inhabits. The best part is, we can now predict that this species will survive climate change, as long as its algal food is able to survive too!

What do you enjoy most about research, and why?

My favorite part of research is getting to work with an international team of researchers with different levels of experience, to discover things that no one has ever seen before. This year, my lab proudly speaks 12 languages, represents 3 continents and comprises researchers from three generations. Every year, I enjoy learning from the experience of my senior colleagues and re-discovering the wonders of sea slugs and advanced imaging with younger colleagues.

What is your favourite animal, and why?

Blue Dragon nudibranchs (Glaucus spp.) are probably my favorite animals, although, when you study sea slugs, there's a lot of competition! I am particularly drawn to these animals because they display a striking shade of blue, which is a rare color in nature. Even more impressively, this sea slug feeds on venomous cnidarian species like the Portuguese man-o’-war. Its immunity to the venom is impressive enough, but this sneaky slug is also able to steal the stinging cells from its cnidarian prey and use them for its own defense!

Do you have a top tip for others just starting out at your career stage?

I just started a role as an Assistant Professor and it is definitely the largest step up I've ever taken. When I was a BSc student, I took some courses on didactics, especially for biology and this has been incredibly valuable now that I am responsible for developing my own courses. Since beginning my PhD, I have supervised a few students every year and this supervision experience has proven invaluable now that I am leading a lab of ten people. Therefore, I recommend starting to teach alongside your research if you are interested in staying in academia and signing up for a didactics course or two if possible.