Tommy Norin

Project title

Unravelling why metabolic rate scales with body size

What is your project about?

The rate at which organisms expend energy and require food and oxygen – their metabolic rate – changes (scales) with body size, but usually out of proportion; for a given increase in size, metabolic rate increases less. Why this is so – and why there appears to be variation in how steep this scaling relationship is among species and taxonomic levels – are some of the biggest unanswered questions in biology. The overall aim of my research programme is to answer these fundamentally important questions, with a focus on metabolic scaling of animals. In this project, I will use comparative studies and multi-generational artificial selection experiments, in combination with genetic analyses, to unravel the mechanistic basis for why and how metabolic rate scales with body size.

How did you become interested in your particular field of research?

My interest in biology has been there as long as I can remember. I became specifically interested in animal physiology and metabolic rate during my studies at Aarhus University, where I took courses in animal physiology during my Master’s. The courses were taught by very passionate zoophysiologists, and they ignited my interest in experimental biology. That was also when I decided to pursue a career in research, and I got a PhD scholarship from Aarhus University to explore my newfound interest in animal physiology at the Section for Zoophysiology, a stronghold for comparative physiology. My PhD supervisor’s interest in respiratory physiology inspired me and led me down the path I am on now.

What are the scientific challenges and perspectives in your project?

Metabolic rate has long been thought to scale out of proportion to body mass in a fixed way for all organisms – driven by physical properties of how oxygen and nutrients to fuel metabolism are delivered throughout the body – meaning that metabolic rate should always increase the same amount for a given increase in body mass, regardless of the organism or species. My project and new ideas challenge this traditional view – I believe that metabolic scaling is shaped by ecological rather than physical factors, and that there is profound but systematic variation in metabolic scaling among individuals, species, and taxonomic levels. It will be a challenge to prove this definitively, and to convince the broader scientific community of my new view on metabolic scaling. However, successfully doing so could put an end to the century-long debate about why and how metabolic rate scales with body size, and improve our ability to understand and predict how much energy and oxygen animals use and need. This is of not only high fundamental interest but also especially important now, as ongoing climate warming is changing the metabolic rates and body sizes of life on earth. To understand and predict the consequences of this, we need to know why and how metabolic rate scales with body size. Metabolic scaling also has applications beyond animals, for example for understanding age- and size-dependent energy expenditure in humans, in both health and disease – something that, surprisingly, is still poorly understood.

What is your estimate of the impact, which your project may have to society in the long term?

To understand how much food and oxygen organisms of different sizes need, and whether they can persist in an environment with limited resources or not, we need to know how their metabolic rate scales with body size, and why there is variation in this scaling relationship among species. My project will investigate this both within and across generations, which, among other things, can improve our ability to predict the impacts of climate change, as metabolic scaling is used to model how changing temperature and oxygen levels affect the energetic demands and distributions of organisms in a warmer future. If such predictive models are inaccurately parameterised, it has implications for global biodiversity forecasts and food security. For example, the ongoing reduction of fish body sizes in warmer waters decreases their biomass and jeopardizes global food security by reducing the amount of fish for food. A better understanding of why and how metabolic rate scales with body size can help us predict the extent and consequences of this more accurately.

Which impact do you expect the Sapere Aude programme will have on your career as a researcher?

It is absolutely fantastic to be awarded a Sapere Aude grant, and to be recognised as a leading researcher in my field. The grant enables me to expand my research group with more team members, and strengthen my international network through new collaborations with leading scientists around the world. The Sapere Aude programme is Denmark’s premier early-career researcher excellence scheme, and the recognition that comes with this prestigious grant will boost my chances of securing additional competitive funding, both within Denmark and internationally. The recognition as a Sapere Aude research leader will also help attract the most talented young researchers to my group in Denmark, which will strengthen both my own research programme and Danish research in general.

Background and personal life

I am originally from Aalborg, where I lived until I moved to Aarhus to study biology. During my PhD and subsequent postdocs, I have lived in Australia, Canada, and Scotland for about 5 years total, before returning to Denmark in 2018. I love to travel for both work and leisure. When I travel for leisure, I often go on hiking or fishing trips. I also play squash.