Icelandic fish offer clues to how aquatic life adapts to warming waters
Fish that have adapted to naturally warm geothermal waters in Iceland display distinct physical, behavioural and genetic differences from members of the same species living in cooler environments, according to research led by the University of Glasgow.
Published in Nature Communications, the study provides new insights into how aquatic species may respond to rising global temperatures, identifying genetic pathways linked to adaptation alongside changes in metabolism, appetite and fat storage.
The researchers used Iceland's geothermal waters as a natural model for climate change, studying populations of threespine sticklebacks living in both ambient-temperature lakes and much warmer geothermal habitats, where water temperatures can reach 27.8°C.
By comparing the fish, the team identified consistent biological differences in populations that had adapted to warmer conditions.
Fish living in geothermal waters showed hyperphagia, a condition characterised by excessive hunger and food intake. They also accumulated larger fat reserves during the summer and retained those energy stores more effectively during periods when food was scarce.
Alongside these physiological changes, the researchers identified a range of genetic adaptations associated with life in warmer waters.
Although the precise DNA changes differed between geothermal fish populations, suggesting that adaptation can follow multiple genetic routes, all warm-adapted fish shared changes affecting the MAPK cell communication system, signalling pathway involved in growth and responses to stress. The team also identified a genomic inversion present only in the geothermal populations, which they say works alongside the MAPK pathway to support adaptation to higher temperatures.
Dr Kevin Parsons, co-lead author of the study at the University of Glasgow, said: "Our study is the first to show the specific genetic changes caused by adapting to warmer waters, offering key insights into the impact that climate change could have on aquatic ecosystems.
"We discovered that while the detailed DNA adaptations to warmer waters vary between fish populations, the overall impact of these changes was similar in all warm water-adapted fish, with changes to their body size, appetite and metabolism."
The findings have implications for understanding how cold-blooded animals respond to climate change. While some marine species may be able to migrate to cooler waters, freshwater populations isolated in lakes and rivers may have little choice but to adapt to rising temperatures.
Dr Matthew Brachmann, co-lead author of the study, said using Iceland's naturally heated waters allowed researchers to observe long-term adaptation under real-world conditions.
"Climate change is already causing rapid temperature increases in our waters, forcing some aquatic life to adapt to survive," he said.
"By focusing on indigenous fish living in different natural water temperatures in Iceland we have been able to show the real-world impact of adapting to warmer waters, with adapted populations showing clear physical, behaviour and genetic changes."
The study, Parallel adaptation to geothermally-warmed habitats due to common structural variation and functional developmental pathways, was funded by the Biotechnology and Biological Sciences Research Council and the Natural Environment Research Council. Pic: Tobias Bjørkli
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