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Anti Vasemägi, Professor
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Unsung climate hero in our lakes – scientist unlock the genome of perch that keeps the methane emissions in check
Published: 10 March 2022
Life from microbes to vertebrates has evolved countless solutions to colonize practically every imaginable part of Earth. Among the less familiar evolutionary innovators is a sturdy fish, Eurasian perch, which thrives also in acidic and dark freshwater lakes, where other fish species die.
Life from microbes to vertebrates has evolved countless solutions to colonize practically every imaginable part of Earth. Among the less familiar evolutionary innovators is a sturdy fish, Eurasian perch, which thrives also in acidic and dark freshwater lakes, where other fish species die.
Earlier work has shown that this keystone species can substantially reduce emissions of the powerful greenhouse gas, methane (CH4), from lakes to the atmosphere. Researchers from the Swedish University of Agricultural Sciences (SLU) in collaboration with Estonian and Finnish scientists sequenced whole genomes of perch collected from thirty-two lakes to better understand the molecular mechanisms of adaptation to dark and acidic aquatic environments.
“This work sheds light on how evolution has generated solutions to the challenges posed by dark and acidic environment”, says Anti Vasemägi, professor at the Department of Aquatic Resources (SLU Aqua). “By analysing almost one million single nucleotide polymorphisms, we identified thousands of genetic variants that help us understand what makes perch a dominant species in darkwater lakes.”
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Perch from a humus-rich lake . Photo: Anti Vasemägi
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Perch - an unheralded climate hero
Wetlands and lakes are the largest natural methane sources to the atmosphere. Darkwater lakes across the boreal zone, in particular, are active emitters of methane. Compared to other greenhouse gases, CH4 is a very powerful greenhouse gas, about 25 times more potent than carbon dioxide.
“However, the amount of methane emission from lakes is strongly reduced by perch, which exerts high grazing pressure on zooplankton,” Vasemägi said.
“The reduction in zooplankton density increases the abundance of methane consuming bacteria, which, in turn, reduce methane emission rates up to ten times. Given that perch is a very abundant and widespread species from Scandinavia to Eastern Siberia and there are millions of lakes emitting CH4, this small fish should be considered as an unheralded climate hero, who helps to reduce the amount of methane released to the atmosphere. Therefore it is important to understand what adaptations make perch thrive in these types of lakes.”
Important role in evolution
The researchers found that footprints of selection associated with darkwater environment were most common in the regulatory regions of the genome, confirming their important role in evolution.
“Thus, adaptation in perch can be compared to the evolutionary history of our own species, since it is the regulatory , that make us humans different from great apes,” says Mikhail Ozerov from the University of Turku, first author of the study.
“Remarkably, we did not detect strong signals of selection in the genes involved in the processes of absorbing and processing light signals, which we had expected given the dark environment,” he added. “We found no evidence to suggest that opsins, which act as photosensitive elements in the eye, play a special role in adapting to altered light conditions.”
In addition to the extreme visual environment, darkwater lakes are acidic, with low availability of minerals.
"Thus, it was not unexpected that strong selection patterns were present in a number of genes that play important roles in the regulation of osmotic balance and transport of calcium, potassium, sodium and other ions," Ozerov said. "Our study demonstrates that adaptation to seemingly simple environments can be multifaceted and complex."
"One of the reasons why I am excited about this work, supported by the Swedish and Estonian Research Council and the Swedish University of Agricultural Sciences, is that it links together small variations of the genome, ecology and global biogeochemical processes,” concluded Vasemägi. “We do not expect that the small fish will stop the warming of the planet, but it may help us to understand how it works.”
The study "Whole-genome sequencing illuminates multifaceted targets of selection to humic substances in Eurasian perch", has been published in Molecular Ecology.