In this Insight, Dr. Kielland of the Norwegian University for Science and Technology (NTNU) discusses his paper “Warm and out of breath: thermal phenotypical plasticity in oxygen supply,” the challenges associated with developing the methods used in the paper, and how his research can be interpreted in the context of increasing temperatures.

What’s your paper about?

Basically, we have developed models that can estimate how much oxygen animals absorb from the ambient medium. We use this to estimate how much animals can acclimatise to changes in oxygen content in the environment, especially in water changes with temperature.

What is the background behind your paper?

Animals need oxygen to support life, as most of the chemical reactions in the cells of the body require oxygen to function properly (referred to as aerobic metabolism). In water, oxygen is increasingly less soluble with increasing temperatures. At the same time, diffusion of oxygen occurs faster due to thermodynamics, making more of it available for water-breathing individuals. The question then is: is this increased availability of oxygen enough to sustain the (increased) metabolism of the freshwater water flea (Daphnia magna)at higher temperatures? This is because, being ectothermic, their body temperature and thus metabolism also increases in parallel to oxygen availability.

How did you come up with the idea for it?

The work is part of a larger study that aims to quantify variation in both life history traits and population dynamics caused by exogenous (i.e. environment) and endogenous variables (i.e. acclimation, epigenetic effects, genetic variation).

What are the key messages of your article?

We found that our study animal (Daphnia)does increase its ability to absorb oxygen from their environment as temperatures increase. We know this, as we exposed different individuals of the same genotype (clone) to different temperatures. This response is strongest within the highest temperature range (22-28 °C), where the “oxygen challenge” is expected to be most pronounced for this specific arctic genotype. However, the observed ability to increase oxygen supply failed to compensate for the increased oxygen demand. Thus, the ability to acclimatize oxygen uptake and demand is not sufficient to cope with the increasing deficiency of oxygen, which is expected with warmer waters.

How is your paper new or different from other work in this area?

As far as we know, this is the first study that readily quantifies oxygen uptake on a whole-organism level.

Who should read your paper (people that work in a particular field, policy makers, etc.)?

Every other scientist working with oxygen use by animals should read our paper! If anyone seeks to model where oxygen becomes critical for an individual, this will be a defining paper as we accurately describe a method to measure critical oxygen levels for very small organisms. Furthermore, as this is fundamental science, our works helps establish a solid base of knowledge needed by the more applied scientists. With our future work, we are contributing to a field where policy makers may use other models, built on our models, to estimate changes in (e.g.) body sizes of fish as temperatures increase. (see point 8 in next section)

About the research

What is the broader impact of your paper (outside of your specific species and study system)

The models and methods are applicable to every animal that use oxygen for their metabolism! Only a few easily measured variables are needed.

Why is it important?

Here we wanted ask, in relation to future increasing temperatures, do animals risk having a deficit of oxygen to sustain their metabolism? Can we expect that animals can acclimatize to these changes without evolving (referred to as plasticity)?

Did you have any problems setting up the experiment/gathering your data?

The animals we use can handle sincerely low oxygen levels, which means that we need a very long time frame to allow the animals to reach these levels (up to 24h). At this point, traditional methods struggle to measure oxygen use at such low oxygen levels (1-2mg oxygen pr L water). As it is close to zero oxygen, diffusion of oxygen into the measuring chamber can be quite dramatic if not sealed properly.

Where you surprised by anything when working on it?

I was surprised to see how critical oxygen levels (how low oxygen content can become, before aerobic metabolism is “shut off”) is quite independent of temperature. Critical oxygen levels hardly changes from low to high temperatures, even though oxygen demand increases by a wide margin!

What does your work contribute to the field?

We managed to fix the diffusion problem in the equipment, which made us ahead of the equipment producer (the current method they recommend was developed by our last papers, where there is significant diffusion at low oxygen levels). Our models can be applied to any study organism in water (and probably also those that breathe in air, but not so relevant for these) to investigate various research questions.

What are the big questions still to answer?

Is performance in animals really constrained by the availability of oxygen, or is there sufficient genetic variation to cope with the decreases we experience across temperatures? The present multitude of variation among populations seem to suggest that, given time, animals may adapt to a wide array of oxygen content.

What is the next step in this field going to be?

Perhaps, understand if temperature and oxygen content affect performance in animals separately or whether the effect of the variables are always linked.

What would you like to do next?

We are currently using this model to investigate if it can be applied to describe how animals’ size are constrained by oxygen and if this can explain the “temperature-size rule”. This latter rule shows a negative correlation between animal size and temperature (even within genotypes), and many believe it is due to less oxygen. This is because larger animals require more oxygen and thus developing a smaller size enables them to persist across a wider span of temperatures.

About The Author

How did you get involved in ecology?

I headed into ecology because it would allow me to spend a lot of time in nature, studying animals in their native environment and enjoying the time outside.

What are you currently working on?

I’m currently working with evaluating how wildlife is affected by hydropower production and evaluating fish cultivation management. I have also been involved in how we monitor the status of the national freshwater ecosystems and how we can use historical datasets to study this. 

What’s your current position?

Researcher in freshwater biology

What project/article are you most proud of?

My first article on transgenerational plasticity will always be reflected upon as an article where we succeeded to publish negative results at a high level, even though it meant moderating the current evidence and methods of that research field.

What is the best thing about being an ecologist?

Being outside in a “pristine” environment, observing healthy populations of animals!

What is the worst thing about being an ecologist?

It tends to rain a lot in Norway…!

What do you do in your spare time?

I enjoy downhill mountain biking, as well as road biking and the occasional scuba diving. We also have a weekly quiz team.

Read the paper in full here or the plain language summary here.