In hot water in the land of ice – Using geothermal sticklebacks to investigate the future effects of climate change

Written by: Bethany Smith, PhD student at the Institute of Biodiversity, Animal Health & Comparative Medicine, University of Glasgow

Climate change is one of the greatest threats to global biodiversity in the history of mankind. While its effects are complex, one key prediction is an increasing global mean surface temperature. The Intergovernmental Panel on Climate Change (IPCC) projects an increase of between 0.3°C and 4.8°C by 2100, dependent on the actions we take. To facilitate conservation efforts, we need to understand how animal populations will respond. We can do this by investigating animal species that have adapted to different thermal contexts to identify which traits have allowed them to do so. Widely distributed animal species tend to experience temperature gradients naturally, such as with latitude and altitude. However, these types of temperature gradients are spread over large distances, so there are also other concurrent factors that make up the differences between the “warm” and “cold” populations such as photoperiod, vegetation characteristics and other interacting animal species. Therefore, in order to investigate how a species adapts to thermal climate specifically, you would ideally want a somewhat large temperature difference contained within a short distance, thus controlling for these other factors as much as possible. Warm geothermal water welling up from underground can create dramatic temperature gradients over short distances, providing an invaluable context for addressing questions about adaptation to temperature specifically. In fact, these study systems have been referred to as “natural warming experiments”¹ that effectively allow us to see into the future of climate change.

In June of this year I left my usual haunt at the Graham Kerr building in Glasgow to travel with my supervisor, Dr Kevin Parsons, to Hólar University’s Department of Aquaculture and Fish Biology in Sauðárkrókur, Iceland. There, I spent a month and a half running an experiment for my PhD project funded by the Fisheries Society of the British Isles. In Iceland there are numerous hot springs and outlets from geothermally heated residences that have created warm-cold habitat pairs within very short distances. Many of these habitat pairs are home to threespine sticklebacks (Gasterosteus aculeatus), a fish well known in ecology and evolution for its ability to adapt quickly to new environments. My experiment aimed to take advantage of a nearby cold-warm habitat pair by transplanting fish into the opposite habitat and observing the gene expression responses.

The first task was to prepare the fish needed for my experiment by catching, tagging, weighing and photographing them. Catching them was simple – we set minnow traps in each habitat overnight. Tagging was trickier, as I needed to inject small amounts of a brightly-coloured non-toxic silicone substance called a visual implant elastomer tag underneath their skin in specific locations, thus giving each fish a unique identifier. The weighing and photographing were done to see how their condition would change over the month and if their starting state would affect how well they coped with transplantation. While the sticklebacks recovered from the tagging, we set about putting six 1m³ fish cages in each habitat. We then let the mud settle for a few days before releasing 25 fish into each cage. Three cages in each habitat received fish taken from the warm habitat and the other three cages received fish taken from the cold habitat. The sticklebacks were then left for 30 days to allow ample time for gene expression changes to occur.

While I waited, I had plenty of time (in between lab work) to take in my surroundings. Iceland’s landscape feels very similar to Scotland – brown moorland, heather and mountains. I grew up in the Scottish countryside, but I’ve lived in Glasgow for the past seven years, so the rural surroundings felt like coming home. A major difference is the daylight hours – in June the sun hardly sets, so at first I had trouble sleeping, but after a while I grew to like the longer days. Additionally, my research crept into my life a little, as the hot springs that produce such interesting environments for study are also used for the hot water in the houses there. This resourceful system unfortunately has the side effect of the hot water smelling like sulphur, making showers a little strange!

But, eventually, it was time to bring the fish back in. With the help of University of Glasgow postdoc Ana Costa, I set traps in the cages to re-collect the fish. We checked every hour and brought caught sticklebacks back to the lab for processing. We repeated the measurements taken at the start and collected brain, liver and muscle tissue samples. With a lot of hard work, and several petrol-station burgers to fuel us, we managed to get all the fish processed, take down the cages, pack the samples and ship them to Glasgow. Hopefully we will be able to gain insights into how the warm-adapted sticklebacks have been able to cope with the higher temperatures. I thoroughly enjoyed my time in Iceland, and I’m very happy with how my experiment turned out.

Bethany is a Fisheries Society of the British Isles (FSBI) funded PhD student in evolution at the University of Glasgow since 2018. She studies evolution and plasticity in gene expression in Icelandic sticklebacks across geothermal and ambient habitats. Her work will hopefully provide some insight into how temperate freshwater fish may cope with the increases in temperature that have been projected for many regions under climate change. She grew up in the countryside near Stranraer in southwestern Scotland, and in her free time she enjoys baking, making art and nature photography.

Feature image courtesy of Bethany Smith.

¹ Woodward, G. et al. (2010) ‘Sentinel systems on the razor’s edge: Effects of warming on Arctic geothermal stream ecosystems’, Global Change Biology, 16(7), pp. 1979–1991. doi: 10.1111/j.1365-2486.2009.02052.x.

Edited by Ana Costa, Lucy Gilbert and Taya Forde