ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Rune Sørås is an author on ‘ High latitude northern bats (Eptesicus nilssonii) reveal adaptations to high and low ambient temperatures’, published in JEB. Rune conducted the research described in this article while a PhD student in Clare Stawski's lab at the Department of Biology, Norwegian University of Science and Technology, Norway. Rune is primarily interested in understanding the physiological traits of birds and mammals as a tool to better understand how we can aid in the conservation of these animals.
Describe your scientific journey and your current research focus
My scientific journey started back in 2013 when I studied habitat use of boreal owls Aegolius funereus for my MSc thesis at the Norwegian University of Life Sciences (NMBU). The experiences and knowledge I acquired through this fieldwork paved the way for me later studying habitat use of other nocturnal flyers: bats. This eventually led to me starting my PhD in animal physiology at the Norwegian University of Science and Technology (NTNU). In my PhD, I aimed to study energy consumption in bats (particularly that of brown long-eared bats Plecotus auritus and northern bats Eptesicus nilssonii) close to the northern edge of their distributional range.
How would you explain the main finding of your paper to a member of the public?
Bats that rely on insects are particularly small mammals that need to consume lots of insects each night if they are to maintain a stable body temperature. If you look at bats living in the far north, this can be particularly challenging as temperatures can be quite low even in summer, which limits the activity of insects. Additionally, nights are short close to the Arctic, which gives the bats a shorter amount of time to hunt each night. We wanted to study the energy consumption of northern bats Eptesicus nilssonii to see how much energy they need to stay warm close to the northern limits of their distribution, and to what extent they reduce their energy consumption to lower their body temperature and enter the energy-saving state of torpor. By exposing the bats to different temperatures, we could measure how much energy (indirectly through oxygen) the bats needed to stay warm, and how little energy they used if they entered torpor. Interestingly, we could see that most bats entered torpor during the experiments. Despite being exposed to near-freezing temperatures, the bats in torpor did not increase their energy consumption to defend their body temperature from decreasing past a critical point. This may explain how they manage to hibernate for such long periods during winter in Scandinavia, and reduce energy consumption on a day-to-day basis in summer if they are unable to acquire enough food during the short nights.
What are the potential implications of this finding for your field of research?
To date, the energy consumption of vespertilionid bats worldwide has received very little attention, and the metabolic rate of only a few species has been estimated. As more and more research is revealing the important role bats play in pest control, and the current distribution of bats in the northern hemisphere is predicted to expand northwards, we think it is particularly important to better understand how bats cope with a wide variety of thermal conditions. Most importantly, as northern bats are the northernmost occurring species of bat worldwide, increasing our knowledge on the energy consumption of both torpid and normothermic northern bats can aid in future work to predict and conserve the presence of this elusive species.
Which part of this research project was the most rewarding/challenging?
It has been very rewarding to see how well the northern bats cope with the thermal challenges we gave them. By exposing them to temperatures that are both above and below what we would expect them to normally be exposed to during summer, we were expecting to see increased energy consumption at the different ends of the temperature range, both to dissipate heat at higher temperatures and to defend body temperature from decreasing past a critical level. Interestingly, the northern bats did neither of these. Hence, the species seems to cope particularly well with lower temperatures, as they did not need to increase resource use at the lowest temperatures. Similarly, future studies will need to expose northern bats to even higher ambient temperatures if they are to unveil how well this species copes with higher temperatures in their daytime roosts.
Are there any modern-day JEB papers that you think will be the classic papers of 2123?
The recent paper by Conradie et al. (2023; ‘An evaluation of a biophysical model for predicting avian thermoregulation in the heat’; doi:10.1242/jeb.245066) highlights our current need to predict species-specific sensitivity to climate change. The authors compared the predicted results from a biophysical model (NicheMapR) with empirical data on evaporative water loss, resting metabolic rate and body temperature collected under standard laboratory conditions. The study provides strengthening advice of the predictive power of such a model, yet also highlights the need for further empirical data on multiple taxa to increase the predictive power for future modelling.
If you had unlimited funding, what question in your research field would you most like to address?
One of the great challenges with funding opportunities today is that they are, especially on a scientific time scale, very short! Designing and performing studies on elusive wild animals, that need to be conducted within a few years, can be particularly demanding and challenging. Hence, unlimited funding would provide a great opportunity to study energy consumption in bats on a wider geographical scale, over multiple years, in different seasons and with different experimental protocols. For instance, in parts of our study system, we have a high recapture rate of individual bats (particularly of brown long-eared bats Plecotus auritus). This could provide us with the opportunity to expose the same individuals to similar treatments at different parts of the year. Given the longevity of bats, it would be particularly interesting to see to what extent energy consumption changes with age within the same individuals. Unlimited funding would also mean that we could increase data collection per trial by also measuring evaporative water loss and body temperature using a thermal camera.
As many species of bats also have particularly wide geographical ranges, understanding how the physiological traits within species may or may not differ is particularly interesting. With unlimited funding, it would be beneficial to support collection of empirical data on a wider geographical scale. To date, most studies on the physiology of bats are performed by separate research groups on a relatively small geographical scale. To further understand the geographic variation of physiological traits, physiologists studying energy consumption need to widen their horizon and collaborate across research groups to collect metabolic rate data across a species’ distributional range.
Rune Sørås's contact details: Department of Biology, Norwegian University of Science and Technology, Trondheim NO-7491, Norway.