Lichens are at risk because they adapt so slowly to climate change


Lichens are important for stabilizing soils and providing food for some animals, but the algae they contain are adapting to climate change at a rate of just 1°C every million years.


February 15, 2022

Lichen (Folmannia orthoclada) on rock in the Atacama Desert. This lichen contains Trebouxia algae

Matthew Nelsen

One of life’s most important symbiotic partnerships could be threatened by global warming.

Lichens – a composite organism made from cyanobacteria or algae entangled in the body of a fungus – can be overtaken by changing climatic conditions thanks to a slow rate of evolution of the algal component of the old collaboration.

Matthew Nelsen of the Field Museum in Chicago and his colleagues studied how the climate preferences of lichen algae – which Nelsen describes as the lichen’s “understudied” partner – have changed over the course of evolution, and how this relates to what what are algae. in the face of ongoing climate change.

The team focused on a single genus of algae, Trebouxia, which is found in about 7000 species of lichens. For comparison, there are only about 6,400 described species of mammals on Earth today.

“It really puts into perspective that it’s a huge diversity that these algae are responsible for maintaining,” Nelsen says.

The team collected data on where Trebouxia occurs across the globe and noted climatic conditions at each location. The group also used a database of Trebouxia genes to create a global family tree for algae, which revealed which forms of algae were ancestral to others. Using all of this information, Nelsen’s team was able to estimate how fast Trebouxia – and the lichens it lives in – have adapted to changing climatic conditions in the past.

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The team found that algae were slow to adapt to new climates, changing temperature preferences by less than 1°C every million years. This rate is “significantly lower” than the global temperature rise of 1°C to 4°C predicted over the next 80 or so years, Nelsen says.

“It’s surprising that it’s so low,” Nelsen says, noting that the rate is on the lower end of what’s been calculated for a wide range of plant and animal groups in previous studies. “It’s really disheartening to see actual numbers and data showing how discordant these two rates are: the predicted rate of global climate change, versus the rate at which [preferences] changed in the past.

James Lendemer of the New York Botanical Garden says having a longer generation time might make rapid evolution less likely, and that lichen biology may partly explain the slow evolution.

“What is the generation time of an organism that can essentially live forever, in many ways?” said Lendemer.

Nelsen predicts that lichens that depend on Trebouxia will disappear from many places where they are found today, although there may also be some migration of lichens to places where temperatures and humidity are tolerable.

“They’re going to have to change their distribution,” he said. “They’re going to have to spread out to take the hits.”

Then there’s the question of whether the migration destination habitat is even suitable for lichens, Lendemer says. Human-caused environmental degradation means that there are limits to the surface area available for the spread of lichens, no matter how welcoming the climate. Other lichens may need to form new algal-fungal partnerships to survive.

All of this could have considerable ecological impacts. Lichens play a crucial role in soil stabilization and moisture retention and can serve as food or shelter for animals.

“The overall picture of this representing a potentially dire situation is certainly real, as we know that lichens are strongly affected by rapid changes,” says Lendemer – for example, changes due to pollution or physical disturbance of the environment. environment by man.

For Nelsen, potential next steps include using this study’s approach to better understand the rate of climate adaptation of fungal partners and laboratory studies to verify the thermal limits of algal symbionts.

Journal reference: Frontiers in microbiologyDOI: 10.3389/fmicb.2022.791546

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