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

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.

By working with domesticated Brassica species we have immediate and relevant impact for crop breeders, farmers and policy makers. Further, our investigations are ideal for expanding current, and identifying new, outreach opportunities to local schools and the general public.

Crop breeders and farmers

We will work directly with the Agriculture and Horticulture Development Board and UK Brassica Growers Association to catalyse this translation of research into impact. We have already discussed potential impacts with Brassica breeders (see letter of support from Richardson) and it is clear that plasticity could be very important, but is often overlooked. Our research will detail how the environment modulates key agronomic traits (growth, yield, flowering time, photosynthesis) which could lead to agronomists and farmers making different choices when it comes to selecting varieties, especially if the environment is variable or unpredictable. Understanding the molecular basis of plasticity can inform breeding strategies. By the end of Work Package 3 we will have established the degree to which methylation, gene expression and genomic variation are interlinked. We will identify candidate genes underlying agronomically important traits, and this sets the stage for improved marker-assisted selection to expedite breeding. This in turn could lead to positive impacts for farmers and in turn for consumers.

Policy makers

Our project will have direct relevance for governmental policy because of the applied aspects of our investigations. The presence of plasticity in crops could buffer against climate change and our project will specifically investigate the extent to which crop domestication and recent breeding has impacted on plasticity. Our aim is to be in a position to inform the Departments for Environment, Food and Rural Affairs (Defra) and International Development (DfID). We have requested £2580 to work with Public Policy|Southampton to identify mechanisms of impact early in the project and to develop a Policy Brief and chair a face-to-face meeting with relevant parliamentary/NGO stakeholders in the final year of the project.

General Public

A deeper understanding of the role of phenotypic plasticity in domestication and evolution, which we will generate in our project, has the potential to impact on the general public. PI Chapman has recently been discussing the potential for a television series about domestication with the BBC, and the general interest, albeit in the early stages, has been very positive (the proposal is due to be discussed at a higher level later this year; see letter of support from Swain-Diaz).

From a climate change point-of-view, the general public often have an interest in how species will be impacted and our research will detail more about how wild plants might be affected by changing temperatures and weather patterns. That plasticity can be selected and give rise to new species is an exciting and important finding which we believe will be of interest to readers of popular science books and magazines. We will contact the New Scientist, for example, about our research because of this potential mechanism to impact on the public.

Through the UoS Science Day we will display our findings to the thousands of people who visit annually. This year PI Chapman will be handing out 'experiments in a bag' which will encourage children to grow plants in contrasting environments (sunny vs shaded, for example) and email their results back. These will then be collated and distributed.

Finally, we intend to use the research as the backbone for a University outreach scheme which gives Sixth form students hands-on lab experience. The students will use a range of approaches to understand the scientific process and to understand how funded research has real-world impact, for example for evidence-based policy-making.