A new study by researchers at the University of Liverpool has shown that the effects of pollutants can be passed down through generations in water fleas and can persist long enough to influence the evolutionary process.
Posted in Evolution Letters, the research adds new evidence to the debate about whether environmental influences can cause heritable changes in an animal’s biology.
Genes passed from parents to offspring are coated with a complex set of proteins and chemicals that determine how they are expressed – collectively known as the “epigenome”.
The epigenome is sensitive to environmental stresses, such as pollution, which can alter gene expression. Importantly, there is growing evidence that these stress-induced changes can be passed on from one generation to the next.
Dr Stewart Plaistow, Lecturer in Evolutionary Biology at the University of Liverpool, explains: “Epigenetic inheritance mechanisms are currently controversial in evolutionary biology as they provide a possible mechanism for the inheritance of environmental effects alongside the traditional Darwinian heritage.
“Although they are regularly demonstrated in plants, they are much more controversial in animals because epigenetic marks are often thought to be erased during embryo development.”
In this study, researchers examined an important epigenetic mark, cytosine methylation in DNA, in the water flea. Daphnia pulex.
They demonstrated that exposure of water fleas to low doses of pollutants had effects on the epigenome that persisted for more than 15 generations.
They exposed replicate populations of water fleas to three different freshwater pollutants for 7 months (~15 generations), then transitioned half of the populations to clean water for 8 months (>15 generations) .
They found that all three pollutants caused changes in DNA methylation. Importantly, some of these changes were detectable not only in continuously treated Daphnids, but also in those that had been returned to clean water, implying that these persistent changes were stably transmitted through the generations, even in the absence of the pollutant.
A follow-up experiment confirmed that three generations after exposure to the pollutants, the phenotypic effects were still detectable.
Dr Ewan Harney, Marie Curie Fellow at the Institute of Evolutionary Biology in Barcelona, said: “If these persistent, environmentally-induced changes in the epigenome are able to influence traits in the organism like growth and development, as appears to be the case, epigenetic processes like DNA methylation may play an important role in rapid adaptation.”
Laboratory work is underway to test whether these effects are independent of genetic makeup and whether they influence fitness.
The work was funded by the Natural Environment Research Council and supported by the University’s Center for Genomic Research.
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