New genetic clock reveals oldest known marine plant: Baltic seagrass clone is more than 1,400 years old

Using a new genetic clock, a team of researchers from Kiel, London, Oldenburg, and Davis, California, has determined the age of a large marine plant clone for the first time. This seaweed clone from the Baltic Sea dates back to the migration period 1400 years ago. The newly developed clock can be applied to many other species, from corals and algae to plants such as reeds or raspberries. The scientists have published their work today in the journal Nature Ecology and Evolution.

“Vegetative reproduction as an alternative mode of reproduction is widespread in the animal, fungal and plant kingdoms,” explains research leader Dr. Thorsten Reusch, Professor of Marine Ecology at the GEOMAR Helmholtz Center for Ocean Research in Kiel. These so-called “clonal species” produce genetically similar offspring by branching or flowering and often reach the size of a football field or more. However, these offspring are not genetically identical.

Previous work by a team led by GEOMAR researchers had already shown that somatic mutations accumulate in vegetative offspring, a process similar to cancer. Now, a team led by Prof. The process of accumulating mutations to develop a new molecular clock that can determine the age of each clone with high precision.

Researchers at the University of Kiel, led by Professor Reusch, applied this new clock to a worldwide dataset of the seagrass Zostera marina (eelgrass), ranging from the Pacific to the Atlantic and Mediterranean.

In Northern Europe in particular, the team found clones several hundred years old, comparable to the age of large oak trees. The oldest identified clone was 1402 years old and came from the Baltic Sea. This clone reached this advanced age despite a harsh and changing environment. This makes the grass eel clone older than the Greenland shark or the Ocean Quahog, which only live a few hundred years.

These new age and lifespan estimates for clonal species fill an important knowledge gap. Especially in marine habitats, many fundamental species that form the habitat, such as corals and sea grasses, can reproduce vegetatively and their clones can become very large. The continuous production of small shoots or fragments, genetically identical but physically separated from the parent clone, means that age and size are disconnected in these species.

The new study now provides a tool to date these clones with high precision. “Such data are, in turn, a prerequisite for solving one of the old puzzles in conservation genetics, namely why such large clones can persist despite variable and dynamic environments,” says Reusch.

Once a high-quality grass eel genome was available, work could begin. Another key factor in the study was that colleagues at the University of California, Davis (UC Davis) had kept a seaweed clone in their culture tanks for 17 years, which served as a calibration point.

“This paper shows how interdisciplinary interactions between cancer evolutionary biologists and marine ecologists can lead to new insights,” says Dr. Werner, Lecturer in Mathematics and Cancer Evolution at QMUL, who focuses on the somatic evolution of tumors that also develop clonally.

Prof. Dr. Baums, molecular ecologist at HIFMB, adds: “We can now apply these tools to endangered corals to develop more effective conservation measures, which we urgently need as unprecedented heat waves threaten coral reefs.”

“We expect that other seagrass species and their clones of the genus Posidonia, which extend for more than ten kilometers, will show even higher ages and thus be the oldest organisms on Earth,” says Reusch. These will be the future objects of study.