Abstract:
Evolutionary theory predicts that clonal organisms are more susceptible to extinction than
sexually reproducing organisms, due to low genetic variation and slow rates of evolution.
In agreement, conservation management considers genetic variation as the ultimate
measure of a population’s ability to survive over time. However, clonal plants are among
the oldest living organisms on our planet. Here, we test the hypothesis that clonal
seagrass meadows display epigenetic variation that complements genetic variation as a
source of phenotypic variation. In a clonal meadow of the seagrass Zostera marina, we
characterized DNA methylation among 42 shoots. We also sequenced the whole genome
of 10 shoots to correlate methylation patterns with photosynthetic performance under
exposure to and recovery from 27°C, while controlling for somatic mutations. Here, we
show for the first time that clonal seagrass shoots display DNA methylation variation that is
independent from underlying genetic variation, and associated with variation in
photosynthetic performance under experimental conditions. It remains unknown to
what degree this association could be influenced by epigenetic responses to
transplantation-related stress, given that the methylomes showed a strong shift under
acclimation to laboratory conditions. The lack of untreated control samples in the heat
stress experiment did not allow us to distinguish methylome shifts induced by acclimation
from such induced by heat stress. Notwithstanding, the co-variation in DNA methylation
and photosynthetic performance may be linked via gene expression because methylation
patterns varied in functionally relevant genes involved in photosynthesis, and in the repair
and prevention of heat-induced protein damage. While genotypic diversity has been
shown to enhance stress resilience in seagrass meadows, we suggest that epigenetic
variation plays a similar role in meadows dominated by a single genotype. Consequently, conservation management of clonal plants should consider epigenetic variation as
indicator of resilience and stability.
