Epigenetic variation in seagrass clones: key to success without genetic variation?

Seagrass meadows form the foundational basis of some of the most productive and highly diverse coastal marine ecosystems on the planet. Their global decline has a negative impact on economically important species and results in the loss of ecosystem services worth more than ? 16,000 ha-1 year-1. Thus, it is crucial to understand drivers of resilience in seagrass. Genetic variation is considered key to evolutionary adaptation and long-term survival of populations. However, clonal seagrass meadows that are expected to show low genetic variation, are among the oldest living organisms on our planet. The key to this paradox may be epigenetic variation (molecular changes altering gene expression, but not the DNA sequence) that compensates for lack of genetic variation. Our project uses state of the art genomics techniques in combination with field surveys and common garden experiments to address the importance of epigenetic variation for the resilience of the seagrass Zostera marina (eelgrass), the most widely distributed seagrass in the northern hemisphere. Based on samples from a millenium-old clonal eelgrass meadow in the Baltic Sea, we show for the first time that variation in DNA methylation, the most stable epigenetic mechanism, promotes variation in fitness-related traits of ecological relevance: photosynthetic performance and heat stress resilience. While genotypic diversity has been shown to enhance stress resilience and invertebrate diversity in seagrass meadows composed of several genotypes, we suggest that epigenetic variation plays a similar role in clonal meadows with the potential to secure function and resilience not only of Z. marina plants, but of the entire associated ecosystem. Consequently, conservation management of clonal plants must include epigenetic variation as indicator of resilience and stability. This study can be a first step towards more sustainable seagrass restoration that largely depends on the success of replanted shoots to overcome natural variability. Given that 40% of all plants reproduce clonally, our findings are important to other fields such as invasion biology and crop breeding of clonal plants.

Outcomes Achieved: - Increased international research collaboration with colleagues from 7 universities in Europe and the US - Invitation of AJ to present at the prestigious Gordon Research Conference in 2019 Expected: - publications:1 published, 1 submitted, 2 in progress - Project proposals with partners of this project Impacts The functional role of methylation variation in clonal plants is of applied interest for management programs of clonal organisms designed to assess evolutionary potential and population stability, and to minimize the loss of biodiversity. Our results can be directly relevant for restoration of coastal biodiversity associated with seagrass ecosystems that largely depends on the success of replanted shoots to overcome natural variability. Given that 40% of all plant species can reproduce clonally, our findings are further important to other fields, such as invasion biology and crop breeding strategies of clonal plants.

Seagrass meadows are at the structural basis of highly diverse and productive ecosystems, providing a great number of goods and services. Their decline worldwide is thus a source of concern and it is crucial to understand the drivers of resilience in such foundation species. Genetic variation is considered a key to evolutionary adaptation and survival in the long term. However, the ecological and evolutionary success of clonal lineages, challenges the direct relationship between genetic diversity and adaptation. For example, in the seagrass Zostera marina large, old clones show high phenotypic plasticity in the absence of genetic variation. The key to this paradox may be the epigenetic variation (molecular-level changes altering gene expression, but not the DNA sequence). Even in the absence of genetic variation, epigenetic variation can cause heritable variation in phenotypic traits and thus can play a crucial role for an organism s immediate and evolutionary response to its environment. Nonetheless, we know very little about the importance of epigenetic processes in natural populations and many questions remain to be answered to fully appraise the role of epigenetics in plasticity and adaptation. Our proposal will use state of the art genomics techniques in combination with field survey and common garden experiments to address the importance of epigenetic variation for the resilience of Zostera marina. The objectives of the project are 1) to investigate the presence and drivers of epigenetic diversity within Zostera marina clones; 2) to assess the functional consequences of epigenetic variation in Zostera marina clones; and 3) to investigate the heritability of epigenetic variation within Zostera marina meadows. The project will fill fundamental knowledge gaps in the role of epigenetic versus genetic diversity as drivers of ecosystem resilience.