Is it an amoeba or an elephant?
When I talk about my interest in understanding the web of life, I often tell the story of my first undergraduate class, where we were told: “At the moment that you look at an amoeba under the microscope, and you cannot distinguish it from an elephant, you’ll become a biologist.” I must admit, maybe I am not there yet. But the more I learn, the blurrier the lines separating species are. When I lean into that blur, into what connects living things rather than what divides them, that is where my passion for biology ignites. It is also, as it turns out, exactly where my PhD project lives.
There is a beautiful book series I am now reading called Kinship: Belonging in a World of Relations, edited by Robin Wall Kimmerer, Gavin Van Horn and John Hausdoerffer. In its premise, it moves away from kinship as we usually understand it, a word for family and human social bonds, towards seeing all relationships in the living world as deep connections between and beyond species. All living things, and what sustains us, exist in the same web of mutual interdependencies, shaping and being shaped by one another. Through more than 70 essays, we are invited to rethink kinship, and to remember how plants, bacteria, mountains, animals, rivers, fungi and others who share life with us are our kin.
Hologenomics studies an animal or plant together with all the tiny microbes that live on and inside it. Together, they form a single unit that we can call a holobiont. Recently, I started looking at hologenomics, which is the scientific framework of my project and doctoral network, as another branch of kinship studies. It is a deeper ecological attempt to understand living beings as communities, rather than in isolation. For too long, in order to understand our natural world, we tried to single things out, to break knowledge into smaller, independent units and study them one at a time. This made, and still makes, sense. However, it is now time to also observe and study life in its full complexity. We are not independent units, but homes within homes of vast communities of animals, plants, bacteria, fungi and more. Our human bodies, for instance, host in our guts alone trillions of microbes, roughly as numerous as our own cells. These microbes are not simply passengers, as they help us digest our food, support the development of our immune system, and might even influence our mood swings. We have co-evolved together to a point where you cannot fully understand one without the other.
The invisible world within the gut of wall lizards
This project focuses on a group of small lizards that can be found across the Mediterranean basin, known as wall lizards (Podarcis genus). If you have ever visited southern Europe, you have likely come across a quick and tiny lizard sunbathing on a stone wall. What makes them particularly fascinating for my research is their different diets. Wall lizards are omnivores, with most of their food intake comprising a mix of insects and plants. Some species, like the exceptionally beautiful Podarcis pityusensis from the Pityusic Islands, have been described as eating more plants than others. Eating plants, especially for a lizard, is not as trivial as one might think. Tough plant fibers are hard for most animals to break down on their own. The ones that manage it, like cows, horses, and perhaps our lizards, tend to also rely on their gut microbes to assist in this task. One might then ask if lizards’ gut microbiome changes when they shift their diets, or if perhaps it might even lead the way. These are the central questions of my next few years.
Following the clues inside the gut
To try to connect some of the pieces of this big puzzle, I am combining two approaches. First, I will rely on data collected in previous years of wall lizards with varying diets, from more insect-based to more plant-based. By looking at their gut microbes, I want to understand which lizards carry the best toolkit to degrade plant material, and hopefully, this will help us understand their different inclinations to eat plants. This type of research is called observational, as we simply observe the natural patterns and try to draw correlations between them.
The second part of my project will be what we call an experimental study, as it will include the manipulation of the natural patterns and will allow us to draw causational explanations. During this phase, I will test if the “toolkit” present in the gut of different lizards can be transferred between species. In a very controlled setting, inside a laboratory, we will do a transplantation of gut microbes from a more plant-consuming lizard into a lizard that is less adapted to a plant-rich diet. After the transplantation, we will expose them to a plant-enriched diet, and see how it may affect them. We are curious to see if, by giving them the “right” set of microbes, lizards that are less adapted to eat plants will be able to better digest them. We are also keen to understand how it changes their foraging behaviour towards plants. Will they suddenly want to go vegan?
Why It Matters: Life is not built in isolation
Wall lizards are under increasing pressure from habitat change, urbanisation, and climate shifts. On islands in particular, where lizards also play important ecosystem roles, including seed dispersal and contributions to pollination networks, populations are often small and isolated, and therefore more vulnerable to local disturbances. As environments change, so does the availability of food sources, which raises a fundamental question: how are these animals coping with such disturbances? Understanding the role of gut microbes in the dietary flexibility of wall lizards may help us better predict how resilient different populations are to environmental change, with important implications for conservation of both wall lizards and the ecosystems they live in.
Looking beyond lizards, this research may also help shape our understanding of the flexibility of other species in adapting to new conditions. Adaptation may occur at the holobiont level, involving not only the host itself, but also the community of microbes living within it. As Robin Wall Kimmerer would say, adaptation may belong in a world of relations. I believe this was what my first biology class was waving towards: the amoeba and the elephant might not be the same, but neither are they opposites. The boundaries between organisms are more porous than we once thought, and even the invisible creatures we all carry inside quietly shape our own fate. Fully understanding adaptation and how to become resilient to change requires looking deeper at the relationships that make it possible. This is the biology I want to study.
