A new study has revealed that thousands of species of plant-like microorganisms may evolve too slowly to keep pace with Earth’s changes as the climate crisis continues.
This is small Organisms are algae, something you’d likely imagine floating as a green film over a pond or lake.
But when algae and fungi combine, they form colonies of lichen — those light-colored, squiggly patches that grow on rocks and trees in your backyard. With lichen as their medium, algae are adept at inhabiting a wide variety of ecosystems around the world, inhabiting anywhere from arctic tundra to the most arid desert. Lichen is the dominant vegetation, covering 7% of the planet’s surface.
Lichen grows within millimeters per year and can be up to thousands of years old. Even if the middle of the lichen begins to collapse and decompose, the outer edge will continue to spread out like a ring.
But these slow-growing lichens also move at a snail’s pace when it comes to evolutionary change: they are not adapting fast enough to match the pace of our planet’s change, especially as it warms.
Trace evolutionary change
In order to understand how lichen might adapt, the researchers looked at the genetic relationships of different types of algae for comparison, as well as their diverse environments.
By creating family trees from algae, researchers can track evolutionary changes. Scientists have realized how long it takes algae to get used to the environment, temperatures, amount of precipitation and seasonal changes. According to the new study, the algae inside a lichen can take hundreds of thousands, if not millions, of years to adapt to their preferred climates.
“I was shocked,” said study senior author Matthew Nielsen, a research scientist at the Chicago Field Museum. “I should have known better than the other papers I’ve read, but I was upset to see it. It’s so close to home, to a group of living creatures near and dear to my heart.”
When it comes to lichen, algae provide food in the form of sugars while the fungus acts as a habitat, creating a symbiotic relationship. Over time, lichen has evolved to appear in the most extreme environments, including around volcanoes.
Their purpose varies depending on where you live, but lichen produces oxygen, prevents erosion, provides nesting material, retains moisture, and contributes to the water cycle in ecosystems. They also serve as a food source for many species including some mammals, such as reindeer.
“When you see lichen, you’re basically looking at all the fungal tissue, with some algal cells hidden and protected inside,” Nielsen said. “Loosely speaking, it’s like a greenhouse — mushrooms create a more hospitable environment for algae.”
The level of diversity is just part of what makes lichen so attractive to Nielsen. There are about 20,000 species of fungi that help form lichens – more than all types of mammals and birds combined.
“It might be a little more subtle and not nice, but it still represents a great deal of variety out there,” Nielsen said. However, he pointed out that lichen can appear spectacularly and of a mundane nature.
a changing world
If the planet continues to warm at its current rate, it will exceed what many Trebouxia species can adapt to, potentially causing ripple effects.
“In this study, we set out to find out how quickly the climate preferences of these algae evolve over time, and correlate them with predictions about future rates of climate change,” Nielsen said.
“We found that the projected rate of modern climate change greatly exceeds the rate at which these algae evolved in the past. This means that certain parts of their range are likely to become inhospitable to them.”
Algae and lichen have managed to survive previous shifts in global Earth temperatures, but climate change is causing this to happen more quickly.
“Closely related algal species tend to have similar climatic preferences, as predicted by their evolutionary relationships,” Nielsen said. “Maybe the more closely related species live in really similar climates, while the more distantly related species may differ more in their climate tolerance.”
When the climate changes, it is not uncommon to see plants or animals emerge in new environments, as they compete with existing species. While this does not mean that the 7,000 algae will simply disappear, it does indicate that changes are looming. If the algae partner of the lichen begins to die, the fungus may also be taken out, or the algae may have to slowly move to another area.
“I think we’re going to see the scopes of these things change, and that might lead to some confusion in the relationships with fungi — we might get partnerships that didn’t exist before,” Nielsen said.
“Since algae are the food source for the fungus, they are the ones who do photosynthesis and make sugars to give to the fungus. If they are forced to move, the fungal partner will have to either move as well, or develop a new partnership.”
Going forward, Nielsen wants to determine how this lichen survives and even thrives in extreme and diverse environments, test the limits of the temperature range of the algae that it can tolerate, and understand more about the mushroom component of lichen and how it reacts to change.
Nielsen believes that lichen research can be applied to other aspects of understanding how climate change is evolving.
“They have interesting stories behind them, and it’s kind of up to us to try and figure out exactly what they’re doing out there in nature,” Nielsen said.
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