A recent study related to climate change illustrates inducible epigenetic marking and its inheritance1. This study examined the responses of wild guinea pigs (Cavia aperea) to heat. The same males were twice mated to the same females; once before and once after a two month period in which the males were kept at an unusually high temperature (30°C as opposed to normal temperature of about 20°C). Examination of DNA in liver biopsies taken before and after the heat treatment (the liver is important in temperature control in mammals) showed widespread differences of parts of the DNA molecules that had attached methyl groups. Not only that, but such differences (called differentially methylated regions, or DMRs) were also found between male progeny generated from the matings that took place before and after parental heat exposure. This indicates first that the fathers’ liver function changed in response to their heat experience, and that those changes involved altered patterns of DNA methylation and consequently patterns of gene function. Second, it shows that the sons inherited their DNA methylation patterns from their fathers (whether they were fathered before parental heat treatment or after it). In fact, it appeared that heat treated fathers passed on some DMRs that were identical to their own and some that weren’t, suggesting that these fathers passed on biological changes additional to those they themselves had in their livers. DMRs associated with the parental heat treatment were present in both liver and testes of the progeny, the latter indicating the possibility that they could be passed to subsequent generations, though that was not tested. The genes encountering changes to their methylation included some known to be involved in stress responses and temperature regulation, as well as regulatory genes that take part in wider cellular and developmental processes.
The environmentally induced responses to demanding conditions by zebrafish and guinea pigs demonstrate heritable phenotypic alteration that is not caused by genetic variation (i.e. variation in the genetic code) but by epigenetic change to the DNA’s chemical structure. In these epigenetic processes we therefore see two levels at which phenotypic plasticity provides adaptation to environmental change that differs from the conventional model in which random mutation generates phenotypic variation that is acted upon by natural selection. At phenotypic level, inducible plasticity is a source of variation, one that provides variation directly related to the nature of the inducing environmental stress. At the molecular level, rather than inducing random changes to gene structure, plasticity’s mechanism involves chemical marking of DNA that occurs directly and specifically in response to environmental change and that can be heritable. This is a process that enables immediate responses to environmental change and threat, responses that match the changes, and that can be passed on transgenerationally to adapt progeny against a continuing threat.
These laboratory studies strongly suggest that epigenetics can enable adaptation to problematic environments, in these cases pollution and an aspect of climate change. There is also good evidence, described in the next section, that it does so in real situations in the wild.
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References
- Weyrich, Alexandra, Dorina Lenz, Marie Jeschek, Tzu Hung Chung, Kathrin Rübensam, Frank Göritz, Katarina Jewgenow, and Jörns Fickel. ‘Paternal Intergenerational Epigenetic Response to Heat Exposure in Male Wild Guinea Pigs’. Molecular Ecology 25, no. 8 (2016): 1729–40. https://doi.org/10.1111/mec.13494 [↩]