The contribution of plasticity to adaptive divergence: domestication as a model

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The appearance of every plant and animal is affected by a combination of nature (inherited genes) and nurture (life experiences in a given environment). Plants growing in poor soils will usually grow slower than genetically identical plants in good quality soils, for example. In the same way, different environments will provide different cues to individuals, turning certain genes on or off depending on the processed signal. These environmentally-induced differences in morphology and gene expression are called phenotypic plasticity. The traditional nature vs nurture conflict is far too simplistic - the two interact. Identifying the precise ways in which this interplay plays out is a new frontier for evolutionary biology.A modified trait, such as leaf size or antenna length, might help a plant or animal survive, colonise and thrive in a new environment. This potentially could give rise to a new population or even a new species. However, in some cases a population in a novel environment might develop a worse phenotype and either not survive, or have to evolve to persist. While we can construct hypotheses for how plasticity aids in the exploitation of new environments and the exploration of new morphology, both of which can provoke the emergence of new species, we lack good data on how common these different pathways are when populations diverge and new species form.To do this we will compare turnips, cabbages and other domesticated Brassica crops with their closest wild relatives. In our pilot study, wild turnips look different when grown in crowded and uncrowded conditions (to mimic a wild and cultivated environment, respectively). In particular, the wild turnip develops larger roots in the uncrowded environment, i.e. the wild plant grows more like the cultivated plant when grown in a cultivated environment. Similarly, wild plant gene expression, when grown in cultivated conditions, resembles the cultivated plant more closely than when grown in wild conditions. This suggests that plasticity of the wild relative may have been important in the origin of the domesticated species, "pushing it" in the right direction for humans to select. By analysing several Brassica crops and their wild relatives we can see if the same changes happen in the different species too. This replication forms a model example for understanding how evolution works, and how important the different types of plasticity are in driving evolutionary divergence.We will further test whether plasticity played an important role in the early stages of domestication by growing multiple species that are closely related to the wild progenitor, but have never been domesticated. If we find that the never-domesticated species do not exhibit the same degree of plasticity in the traits we identify as involved in domestication, then the progenitor is unique in its plasticity, predisposing it to domestication.In addition, this will also let us know which genes are important for making a cultivated plant, significant information which can be used by crop breeders to improve the food we eat, as indicated through our discussions with Brassica breeders. Our data will also reveal whether changes in gene sequence or gene expression are involved in the differences between wild and cultivated plants. It will also reveal whether a third way in which genes can be turned on and off (specific chemical modifications called methylation) is important in the evolution of plasticity. Methylation might be especially important because these modifications can occur much faster (within minutes or hours) than DNA sequence changes.Not only will we be answering fundamental questions about how new species form, but the findings could help to develop crops that can withstand different environmental stresses. In a future facing climate change and an increasing human population we need this sort of information to plan better strategies to feed more people.