A study led by the Institute of Marine Sciences in Barcelona (Spain) shows that these increasingly frequent phenomena can cause changes in the genetics of fish.
The Barcelona Institute of Marine Sciences (ICM-CSIC) has prepared, in collaboration with the Fisheries Research Institute of Qingdao, in China, an investigation that reveals that the marine heat waves, increasingly intense, frequent and lasting due to global warming, cause permanent changes in the gene expression of fish. This fact affects both his immune response as well as its way of reacting to external stimuli and its metabolism.
The changes in gene expression due to the increase in water temperature they originate from alterations in DNA methylation levels and can persist over time.
For the elaboration of the work, published in the magazine Molecular Ecology, the scientists simulated a wave in the laboratory of heat by increasing the temperature of the water by 3.6 °C in a series of tanks in which several sea bass were kept (Dicentrarchus labrax) just born.
Experiment with sea bass
These conditions were maintained only during the first two months of life of the fish, after which they normalized. As a result, the researchers found a series of molecular scale changes in sea bass that were kept three years later despite the fact that their external appearance was normal.
These changes were detected in tissues with different embryonic origin, including the brain, which comes from the ectoderm; the muscle and the testicles, which come from the mesoderm; and the liver, which is formed from the endoderm.
As explained Francesc Piferrer, ICM-CSIC researcher and head of the work, “this indicates that the affectation took place in a generalized way during the early development of the fish, which implies that changes can be permanent.
“Everything depends on at what time during the life of a fish heat wave occurs; if it occurs during the early stages of development, it can leave permanent marks as we observed in sea bass and that could be transmitted to offspring”, the first author of the study details in this regard, Dafni Anastasiadi, who currently works at The New Zealand Institute for Plant and Food Research.
These marks induced by an environmental change and common in tissues of different embryonic origin are epigenetic because overlap the DNA sequence of sea bass, that is, they are found above their genetic information in certain places in the genome and, if they are common in all tissues, they are called metastable epialleles.
It is the first time that metastable epialleles have been described in fish, information that, according to the researchers, could be used in programs to monitor the impacts of global warming on marine life, since they allow the life history of individuals to be reconstructed. And it is that, knowing these metastable epialleles, it is enough to take a DNA sample from a fish to find out whether or not you were exposed to a heat wave or to abnormal environmental conditions during their early life stages.
All this highlights the importance of knowing the sublethal effects of marine heat waves on fish, something that was not known until now.
“Since the epigenetic mechanisms are present in all animals, this could serve to monitor not only one species such as sea bass, but also others, whether fish or not, that respond to disturbances in the environment”, concludes Piferrer, who ensures that the identification of this type of epigenetic marks conserved in groups of species could be a key tool for evaluating the effects of global warming on a large scale.