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EPIGENETICS AND EVOLUTION

The Modern Evolutionary Synthesis is based on the assumption that only heritable genetic variation and its random mutational origin explain evolution by natural selection. However, the line between genetic and environmental interactions is blurred by processes such as phenotypic plasticity and epigenetic variation and not well understood. To date no research has been directed towards understanding the importance of epigenetic variation (biochemical modification of DNA building blocks without changes in the actual DNA sequence) in the evolution of natural populations. This may in part be because of the difficulty to disentangle the relative contributions of epigenetic- vs. genetic variation in local adaptation. In many cases epigenetic variation is also under genetic control, making its quantification of little use to address questions related to ecologically relevant processes such as local adaptation, individual fitness and speciation. Dr Jaco Le Roux from the C·I·B recently received funding from the National Research Foundationís Blue Skies Research Programme to investigate epigenetic variation within and among natural and invasive populations of the grass Pennisetum setaceum, commonly known as fountain grass. The proposed research will be the first attempt to quantify epigenetic variation and its inheritance in natural populations of a plant species.

You may want to ask “Why specifically choose fountain grass to study epigenetic variation?” Fountain grass represents, in many ways, an ideal study system. Firstly, previous research [http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000590] has illustrated that globally distributed populations of fountain grass represent a single genotype (clone) and therefore eliminates the effects of actual genetic (DNA) variation on individual and population fitness. Secondly, fountain grass exhibits extensive levels of phenotypic plasticity (differential phenotypic responses to environmental variation within the same genotype) and this may likely be linked to differential gene expression as a result of epigenetic mechanisms. Thirdly, autopolyploidy (doubling of chromosomes) has been documented in fountain grass and this research may shed light on the importance of such genome duplication events in facilitating epigenetic change over time.

By studying differences in levels of DNA methylation (a well-understood epigenetic mechanism in plants) this research will aim to: 1) quantify natural epigenetic structure and 2) determine the degree of heritability of environmentally-induced epigenetic variation.

Environmentally-induced epigenetic variation that is heritable over multiple generations would have far-reaching consequences for our current understanding of how evolution operates in natural populations. Even if epigenetic diversity is not heritable, it would still play a critical role in better understanding the so-called “genetic paradox” in invasion biology; introduced species that are often inbred but nevertheless thrive under novel selection pressures in their new environments. For example, is it possible that environmentally-induced epigenetic changes allow rapid adaptation in new and novel environments? Does epigenetic variation facilitate or enhance phenotypic plasticity and subsequently contribute to successful invasions? Can the time over which epigenetic variation is accrued explain the lag phases often associated with newly introduced species?