Science Gazette

In water fleas, pollution has epigenetic consequences that last numerous generations

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According to a recent study headed by University of Liverpool researchers, the impacts of pollution can be passed down through generations in water fleas and may even alter the evolutionary process.

The study, which was published in Evolution Letters, adds to the debate over whether environmental factors may produce heritable alterations in an animal’s biology.

The ‘epigenome’ is a complex array of proteins and chemicals that are superimposed on genes handed down from parents to children and control how they are expressed.

Environmental factors, like as pollution, may affect gene expression, making the epigenome vulnerable. Furthermore, there is mounting evidence that these stress-related alterations may be passed down through generations.

“Epigenetic inheritance mechanisms are controversial in evolutionary biology at the moment because they provide a possible mechanism for the inheritance of environmental effects alongside traditional Darwinian inheritance,” explains Dr. Stewart Plaistow, a Senior lecturer in Evolutionary Biology at the University of Liverpool.

“Epigenetic markings are commonly considered to be wiped clean during embryo development in animals, despite the fact that they are consistently proven in plants.”

The researchers focused at one significant epigenetic signature in the water flea Daphnia pulex, methylation of cytosine in DNA.

They showed that modest dosages of contaminants produced long-lasting impacts on the epigenome of water fleas, lasting 15 generations or more.

For 7 months (about 15 generations), they exposed duplicated populations of water fleas to three distinct freshwater contaminants, then switched half of the populations to clean water for 8 months (>15 generations).

All three contaminants caused alterations in DNA methylation, according to the researchers. Importantly, some of these alterations were seen not only in continuously treated Daphnia, but also in those that had been switched back to clean water, showing that these long-term changes were handed down through generations even after the contaminant was removed.

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A follow-up experiment revealed that phenotypic effects were still visible three generations after pollution exposure.

“If these environmentally-induced persistent changes to the epigenome are able to influence organismal traits like growth and development, as appears to be the case, epigenetic processes like DNA methylation may play an important role in rapid adaptation,” said Dr Ewan Harney, a Marie-Curie fellow at The Institute of Evolutionary Biology in Barcelona.

In the lab, researchers are examining whether these effects are genetically independent and if they affect fitness.

The study was sponsored by the University’s Centre for Genomic Research and financed by the Natural Environment Research Council.

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