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University of Groningen: Legacy of Ancient Ice Ages Shapes How Seagrass Responds to Environmental Threats Today | India Education | Latest Education News | World Education News


Deep evolution casts a longer shadow than previously thought, scientists report in a new paper published the week of August 1 in the Proceedings of the National Academy of Sciences. Smithsonian scientists and colleagues, including Jeanine Olsen, professor emeritus at the University of Groningen, examined eelgrass communities – the foundation of many coastal marine food webs along the northern Atlantic and Pacific coasts – and discovered that their ancient genetic history may play a more important role than the present. daily environment to determine their size, structure and who lives there. And that could have implications for how seagrasses adapt to threats like climate change.

About half a million years ago, when the world was warmer, some eelgrass plants made the difficult journey from their homes in the Pacific to the Atlantic. Not all plants were hardy enough to cross the Arctic. For those who succeeded, a series of ice ages during the Pleistocene epoch further affected their extent. These millennial struggles have left lasting signatures in their DNA: Even today, populations of eelgrass in the Atlantic are much less genetically diverse than those in the Pacific.

Yet in the classic “nature versus nurture” debate, scientists have been amazed to discover that genetic inheritance sometimes does more to shape modern seagrass communities than the current environment. “We already knew there was a great genetic separation between the oceans, but I don’t think any of us ever dreamed that it would be more important than environmental conditions,” said marine biologist Emmett Duffy. at the Smithsonian Environmental Research Center and lead author of the report. “It was a big surprise for everyone.”

Seagrass in warm water
Seagrass is one of the most widespread shallow-water plants in the world. Its range extends from semi-tropical regions such as Baja California to Alaska and the Arctic. In addition to providing food and habitat for many underwater animals, eelgrass provides a plethora of services to humans. It protects coastlines from storms, absorbs carbon and can even reduce harmful bacteria in the water.

But in most places where it grows, eelgrass is the dominant – or only – seagrass species present. This makes its survival essential for the people and animals that live there. And the lower genetic diversity in the Atlantic could make it difficult for some populations to adapt to sudden changes. “Diversity is like having different tools in your tool belt,” said co-author and ecologist Jay Stachowicz from the University of California, Davis. “And if all you have is a hammer, you can put some nails in, but that’s about it.” But if you have a full range of tools, each tool can be used to perform different tasks more efficiently.

Conservationists have already seen eelgrass disappear from some areas as waters warm. In Portugal, its southernmost point in Europe, eelgrass has begun to recede and move further north into cooler waters. “I don’t think we’re going to lose eelgrass in the sense of extinction,” said co-author Jeanine Olsen, professor emeritus at the University of Groningen in the Netherlands. ‘It’s not going to be like that. He has a lot of tricks up his sleeve. But local extinctions, she pointed out, will occur in some places. This could leave regions that rely on their local eelgrass struggling.

Realizing the urgent need to understand and conserve seagrass around the world, Duffy and his colleagues came together to form a global network called ZEN. The name stands for Zostera Experimental Network, a nod to the scientific name for eelgrass, Zostera marina. The idea was to unite seagrass scientists from around the world, doing the same experiments and surveys, to get a coordinated global picture of seagrass health.

For the new study, the team surveyed seagrass communities at 50 sites in the Atlantic and Pacific. With 20 plots sampled per site, the team came away with data from 1,000 eelgrass plots. They first collected basic data on seagrass: size, shape, total biomass and the different animals and algae living on and around them. Next, they collected genetic data on all seagrass populations. They also measured several environmental variables at each site: temperature, water salinity, and nutrient availability, to name a few. Ultimately, they hoped to find out what shapes seagrass communities more: environment or genetics?

After running a series of models, they discovered a multitude of differences between Atlantic and Pacific seagrass ecosystems, differences closely aligned with the genetic divergence between the Pleistocene migration and subsequent ice ages. While Pacific seagrass often grew in “forests” that regularly exceeded 3 feet in height and sometimes reached more than twice that height, the Atlantic hosted smaller “meadows” that rarely approached this height. Genetic differences also aligned with total eelgrass biomass. In the Atlantic, evolutionary genetics and the current environment have played an equally important role in eelgrass biomass. In the Pacific, genetics had the upper hand.

Conserve the future
The fact that ancient genetics can play such a large role – sometimes stronger than the environment – worries some ecologists about the ability of eelgrass to adapt to more rapid changes. “Global warming, by itself, is probably not the main threat to eelgrass,” Olsen said. Pollution from cities and farms, which can cloud water and lead to harmful algal blooms, also endangers seagrass beds. That said, the wide range of environments in which eelgrass can survive speaks to its hardiness. “I’m hopeful because our results illustrate long-term resilience to repeated and major shifts in thermal tolerances and the wide range of eelgrass habitats over roughly half of the northern hemisphere,” Olsen said. “With the genomic resources now available for eelgrass, we are beginning to analyze gene functional changes and their regulation in real time. It’s very exciting.’

To protect existing eelgrass beds, maintaining current diversity is a good first step. In places that have already lost eelgrass beds, restoration is promising. Some successes already exist, such as on the east coast of Virginia. But many restoration efforts achieve only limited success. As Stachowicz pointed out, this raises additional questions. “Should you restore seagrasses using plants from local environments, or should you think ahead and try plants with genetics better suited to future environmental conditions?” He asked. “Where should you hedge your bets? Maintaining or enhancing genetic diversity may be the best way to provide seagrass populations with the diverse toolbox needed to survive in an uncertain future.

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