Plant adaptation to climate change learning from model Betula species

Overview

The current global rate of plant extinction far outstrips background extinction rates linked to increasing pressure from drivers such as invasive species, habitat loss and human induced climate change. The impact of these pressures on tree species and forest ecosystems is of particular significance given their intrinsic biodiversity value and the associated services they provide, such as climate change mitigation through carbon capture, habitat refuge for endangered species, and vital role in management of water catchments. Resilient forests are at the heart of the battle against human mediated habitat loss, to prevent extinction, and to achieve sustainable livelihoods. For forests to be sustainable in the long term and survive the multiple stressors they face, the adaptive potential of key tree species must be realised, a process that forest managers can facilitate. However, for such strategies to be grounded in science, the molecular, morphological, physiological and ecological diversity between and within populations needs to be quantified. With these data in hand, the following key questions can be addressed:

• How much adaptive diversity do species and populations exhibit?
• What is the strength of climate in determining adaptive potential?
• What role does hybridisation play in adaptive potential?
• What is the role of environmental and ecological drivers in determining adaptive potential?

Model species are an essential tool to answer such questions. Birches (Betula spp.) are an core component of Scottish forests, often seen as pioneer species and a key component of tree planting mixes. Understanding the extent of adaptation and by extension, what constitutes ‘good quality’ seed, is essential to inform planting programmes and ensure the sustainability of populations. Anecdotal evidence suggests that some ‘certified’ birch seed orchards are a mix of two native Birch species – B. pendula and B. pubescens yet the implications of this for the success of plantings and the preservation of adaptive potential remain unknown. Evidence exists for local adaptation in B. pendula but the extent of adaptation in B. pubescens has not been studied. In addition, the two species hybridise, which may provide an extra, as-yet unstudied mechanism for adaptive change and as B. pendula is diploid (2n=28) and B. pubescens tetraploid (2n=56), cytological studies are particularly informative for the detection of hybridisation.

This project would centre around the following research objectives, whilst providing sufficient flexibility to allow the successful candidate to incorporate their own interests and expertise.

• Resolve the B. pendula and B. pubescens genetic-ecological boundary using flow cytometry, morphometrics, molecular biology in wild populations and common garden studies.
• Test the impact of seed orchard approaches on fitness in different environments, i.e. does genetic mixing between provenances from different latitudes reduce the mean fitness of progeny in the field, and common garden experiments using controlled crosses.
• Detail barriers to breeding: what determines the success or failure of interspecific crosses?
• Assess the role of hybridisation in maintaining or eroding adaptive potential.
• Quantify the degree of ecological separation among Betula species and their hybrids.

Click on an image to expand

Image Captions

Birch Forest (Gustav Klimt 1903) image from Christies https://www.christies.com/lotfinder/Lot/gustav-klimt-1862-1918-birch-forest-4807502-details.aspx

Methodology

The project will conduct detailed analysis of Betula populations in the field at various sites to determine the fine-scale local distribution of different Betula species and hybrids, including detailed evaluations of the local environment. Individual plants will be mapped and sampled for subsequent genotyping and cytotype determination via flow cytometry. Local patterns of spatial genetic organisation will be compared to environmental variables to identify primary drivers of spatial partitioning. Parallel experimental work will use individuals sampled from populations in which species occur in sympatry/isolation to undertake controlled crosses and subsequent progeny testing. Crosses will be undertaken in a range of controlled environmental conditions representative of the primary environmental drivers at the home sites, to evaluate the extent to which mutational change is mediated by specific environmental factors. Competition experiments will be carried out to evaluate the fitness of progeny from different environments / genetic backgrounds. The candidate will have the opportunity to learn a range of methods to explore traits of the species likely to be of life history significance, such as growth, physiology and reproduction, and evaluate extent and patterns of variation through measurement in experimental trials. Full training in statistical techniques will be provided including, use of mixed models to evaluate components of variation, sequence data handling, population genetic analysis.

The candidate will also have the opportunity to take the project beyond the UK & Ireland distribution to study populations across its worldwide range.

Project Timeline

Year 1

Literature review, including survey of drivers for elevated mutation rates and polyploid advantage. Field season 1 – sample and data collection. Glasshouse experimental work.

Year 2

Lab and Data analysis. Field season 2: sample and data collection. Glasshouse experimental work.

Year 3

Molecular lab work, data collection and analysis.

Year 3.5

Finalise data analysis and write up.

Training
& Skills

The project will provide the candidate with training in experimental design, quantitative trait analysis, evaluation of spatial variation, molecular lab techniques and data analysis. The project represents an opportunity for broad training in methods and approaches that will equip a successful student for a range of future careers. In addition, the student will receive training, advice and guidance on data handling and statistics, presentation, scientific writing and production of published work from a diverse and experienced team of supervisors.

References & further reading

Donnelly K, Cavers S, Cottrell JE, Ennos RA (2018) Cryptic genetic variation and adaptation to waterlogging in Caledonian Scots pine, Pinus sylvestris L.. Ecology and Evolution  8, 8665–8675.  https://doi.org/10.1002/ece3.4389

Jump AS, Marchant R, Peñuelas J (2009). Environmental change and the option value of genetic diversity. Trends in Plant Science, 14, 51-58.

Gray, A. (2019). The ecology of plant extinction: rates, traits and island comparisons. Oryx 53 (3): 424-428.

Gray A., Perry A, Cavers S, Eastwood A, Biermann M, Darlow A, Thomas, V, Lambdon P (2017). Hybrid plants preserve unique genetic variation in the St Helena endemic trees Commidendrum rotundifolium DC Roxb. and C. spurium (G. Forst.) DC. Conservation genetics 18(1): 241-246.

Stace, CA. (2019) New Flora of the British Isles (4th ed). Cambridge University Press.

Further Information

Alan Gray: alangray@ceh.ac.uk; 0131 445 8471
Alistair Jump: a.s.jump@stir.ac.uk; 01786 467848
Stephen Cavers: scave@ceh.ac.uk; 0131 445 8552
Joan Cottrell: joan.cottrell@forestresearch.gov.uk; 0300 067 5927

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