Some copepods, diminutive crustaceans with an outsized place in the aquatic food web, can evolve fast enough to survive in the face of rapid climate change according to new research.
The copepods are small and paddle their way through the coastal waters of oceans and estuaries around the world in large numbers.
Carol Eunmi Lee is a professor at the University of Wisconsin–Madison and senior author of a new study on the copepods. They'reVulnerable to Climate Change.
As ice melt and precipitation patterns change, the copepods need to adapt to much fresher water in their environment.
In salty water, many copepods evolved. They will have to adjust to keep their body chemistry.
The lead author of the study is a graduate student at the National Biodefense Analysis and Countermeasures Center.
The researchers studied how some copepods responded to the pressure. They kept a population of the small crustaceans from the Baltic Sea in their lab and they were able to reproduce through many generations.
There were 14 groups of a few thousand each. The experiment took place in the environment of the Baltic. The other 10 groups were exposed to declining salt levels. Each generation had their water reduced for a period of three weeks.
After six generations and 10 generations, the researchers will sequence the genomes of each line of copepods. The strongest signals of natural selection were found at parts of the genome believed to be important in regulating ion levels.
There are a lot of ion in the water. These ion are precious when you get to freshwater. "So, the copepods need to suck them up from the environment and hang on to them, and the ability to do that depends on these ion transporters that we found undergoing natural selection."
The researchers found at the end of the experiment that copepods with certain genetic combinations of the ion transporter were more likely to live through successive generations.
"With the number of genes we have in our copepods, there's no way we'd see the amount of parallelism we did unless something was driving it."
Positive Epistasis is a genetic mechanism in which the positive effect of a variant of a gene is amplified when working with other key genes. The idea that the effect of each single gene has the same weight and that the effects of many genes add up in a linear fashion was championed by Sewall Wright and others.
Computer simulations of evolution show that it would have given us more variation among our 10 lines. We didn't see it.
It was possible to show positive epistasis at work in parallel evolution and to describe the power of genetics for studying climate change thanks to the large amounts ofgenomic data from modern sequencing and computing simulations. The new study shows that positive epistasis can drive the parallel evolution of groups of animals by favoring sets of all genes.
"This copepods gives us an idea of what it takes, an idea of what the conditions are needed, that enable a population to evolve rapidly in response to climate change." It shows how important evolution is for understanding our changing planet.
More information: David B. Stern et al, Genome-wide signatures of synergistic epistasis during parallel adaptation in a Baltic Sea copepod, Nature Communications (2022). DOI: 10.1038/s41467-022-31622-8 Journal information: Nature Communications
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