Beneath the Waves: The Remarkable Evolution of Seagrasses 

A story for International Darwin Day 

In 1859, ‘On the Origins of Species’ by Charles Darwin was published. This world famous book is perceived as the foundation of evolutionary biology. The concept of evolutionary adaptation through natural selection did not only spark scientific debate in the 19th century, it still inspires researchers to this day. Yves Van de Peer, director of the VIB-UGent Center for Plant Systems Biology and group leader of the lab for Bioinformatics and Evolutionary Genomics, does research on the evolution of plants. In his latest publication, he and a team of scientists studied the evolution of seagrasses to understand how these plants adapted to an extremely challenging environment. To celebrate Darwin Day, we want to dive deep into this research and explain why evolutionary research remains important to this day.  

The strange journey of seagrasses 

You might be wondering why the evolution of seagrasses is so interesting. Let us go back in time. Life on planet Earth started in the sea, billions of years ago. From then on, organisms slowly evolved and migrated to freshwater and land. Land plants evolved from freshwater algae around 450 million years ago, which led to the enormous diversity we see today: mosses, ferns, conifers, flowering plants, and grasses. ​ 

Surprisingly, some 100 million years ago, from (only) three independent lineages, some plants were able to migrate ‘back to the sea’, eventually leading to the 80 or so different species of seagrasses we know today. In contrast, re-adaptation to freshwater happened more than 200 times, and we now recognize thousands of freshwater plant species. This means that seagrasses must have undergone an extremely rare set of adaptations to be able to survive fully submerged in a highly saline environment with chronic light limitations, while rooting in soil with constantly reducing sediment under considerable hydrodynamic forces. 

Seagrasses Cymodocea nodosa. Copyright Thorsten Reusch (GEOMAR)
Seagrasses Cymodocea nodosa. Copyright Thorsten Reusch (GEOMAR)

How did they do it? 

Despite this challenging new marine environment, seagrasses did not only survive, they thrived! Today, we estimate that seagrasses cover an area between 600.000 km² and 1.6 million km², making them among the most widely distributed flowering plants. This raises the question: what adaptations did these plants go through? And what can we learn from this? 

A team of 38 scientists from Belgium, the Netherlands, Germany, the USA, and Italy tried to find an answer to these questions. Professor Yves Van de Peer, director of the VIB-UGent Center for Plant Systems Biology, coordinated the genome sequencing and analysis of three of the most important seagrass species: the Mediterranean Neptune Grass (Posidonia oceanica), the widely distributed Little Neptune Grass (Cymodocea nodosa), and the Caribbean Turtlegrass (Thalassia testudinum). They studied the whole genome and determined which gene families and pathways play a role in seagrasses' structural and physiological adaptations to marine environments. They compared these findings to the genome and pathways of their freshwater relatives. ​ 

Divers above a Posidonia seagrass meadow. Copyright Gabriele Procaccini (SZN)
Divers above a Posidonia seagrass meadow. Copyright Gabriele Procaccini (SZN)

The study revealed that the seagrass and freshwater sister lineages all share an ancient whole genome triplication at around 86 million years ago. This is interesting because genome multiplications are considered macromutations that increase biological complexity, facilitate adaptation, and reduce the risk of extinction. It also became clear that, rather than (extra) genes evolving completely novel functions, there was the fine-tuning of many genes and pathways. For example, a higher efficiency of the genes regulating salt tolerance occurred, necessary to survive the high salinity of the sea. Other gene functions became useless and disappeared. The stomata, the tiny holes in the leaf surface that enable gas exchange with the atmosphere, are no longer necessary in seagrasses and were lost. ​ 

“In evolutionary biology, we often speak of “use it or lose it.” The evolution of these seagrasses is quite a compelling example of this. Functions that are no longer necessary were lost during evolution, while new ecologically important functions emerged or improved” – Professor Yves Van de Peer. 

Insights for conservation ​ 

The importance of seagrasses cannot be underestimated. They fulfill critical ecosystem functions, such as coastal erosion protection and carbon sequestration. While occupying only 0.1% of the ocean surface, seagrasses have been estimated to bury 27 to 44 teragrams of organic carbon per year globally, accounting for 10 to 18% of the total carbon burial in the oceans and being up to 40 times more efficient at capturing organic carbon than land-forest soils. Along with mangroves and coral reefs, seagrass meadows are among the most biologically productive ecosystems on earth. Because they act as breeding grounds for a huge variety of organisms, including fish, mollusks, crabs, and shrimp, but also for marine megafauna, such as sea turtles and manatees, the importance of seagrasses is unrivaled. ​ 

Due to global warming, seagrass meadows are disappearing on a worldwide scale, leading to a marine biodiversity crisis, and a loss of carbon burial. Understanding how seagrasses adapt to changing environments is crucial for the restoration and survival of seagrass meadows and, therefore, the survival of entire marine ecosystems. ​ 

“How seagrasses adapted to new ecologically important functions involves the interaction of many genes that play roles in many different pathways. By understanding their evolution, and the genes that are important for survival, we can now begin to test and manipulate them experimentally. This way, we can help plant survival under changing conditions, improve nature management, and restore entire ecosystems” – Professor Yves Van de Peer. 

In conclusion, Darwin’s legacy is still of huge importance today. Evolutionary biology focuses on adaptation and survival. This knowledge teaches us more about our living planet and can be implemented to preserve and protect fragile ecosystems. In the light of a changing climate, Darwin’s publication remains now, 165 years later, as poignant as ever. ​ 

Inspired by this blog? Want to read more about this research? You can find the original publication here. Nature plant, doi:

Steve Bers

Steve Bers

Science Communications Expert, VIB

About the VIB-UGent Center for Plant Systems Biology

The VIB-UGent Center for Plant Systems Biology wants to gain insight into how plants grow and respond to the environment. Scientists study how leaves and roots are formed, which micro-organisms live on and around the plant and which substances the plant makes. They map out the genetic diversity of the plant kingdom. This knowledge can lead to sustainable innovations in agriculture and food.

About VIB

VIB’s core mission is to generate disruptive insights in the molecular underpinning of life and to translate these actively into impactful innovations for patients and society. VIB is an independent research institute where some 1,800 top scientists from Belgium and abroad conduct pioneering basic research. As such, they are pushing the boundaries of what we know about molecular mechanisms and how they rule living organisms such as human beings, animals, plants, and microorganisms. Based on a close partnership with five Flemish universities – Ghent University, KU Leuven, University of Antwerp, Vrije Universiteit Brussel, and Hasselt University – and supported by a solid funding program, VIB unites the expertise of all its collaborators and research groups in a single institute. VIB’s technology transfer activities translate research results into concrete benefits for society such as new diagnostics and therapies and agricultural innovations. These applications are often developed by young start-ups from VIB or through collaborations with other companies. This also leads to additional employment and bridges the gap between scientific research and entrepreneurship. VIB also engages actively in the public debate on biotechnology by developing and disseminating a wide range of science-based information. 

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