Abstracts (first author)
Investigating the contribution of epimutations to long-term adaptation using models and experiments
There is more to heredity than DNA sequence alone. Epigenetic changes are defined as changes in gene expression due to chromatin modifications without changes in DNA sequence. We know that some epigenetic changes can be transmitted between generations. Epimutations can be encoded by variety of mechanisms including histone modifications, changes in methylation patterns, or even small RNAs. However, investigations of how transgenerational epigenetic inheritance may affect adaptation are only just beginning. We use a combination of modeling and experimental microbial evolution to investigate how transgenerational epigenetic inheritance affects adaptive walks, where fitness increases in a population by the sequential fixation of novel beneficial genetic mutations (or novel beneficial epimutations as well).
In our model, we address how different assumptions about how the epigenetic system works affect its role in adaptation. In particular, we contrast the evolutionary effects of heritable epigenetic changes that are genetically-encoded responses to environmental change (adaptive plastic responses that can be transmitted) with epigenetic variation is sequence independent and random with respect to fitness (pure epigenetic variation). We find that epimutations can contribute to adaptation alongside genetic mutations if they are reasonably stable, and outline cases where epimutations can speed up adaptation relative to an equal mutational supply of genetic mutations, and cases where genetic assimilation is likely (or unlikely) to happen. We test the predictions of our model using experimental evolution with the unicellular algae Chlamydomonas reinhardtii. By using different selective environments and manipulating the epigenetic system both chemically and genetically, we show how differences in epimutation supply affect fitness gain over approximately 150 generations.