Lichens are in danger of losing the evolutionary race with climate
change
The algae part of many common lichens can't adapt to temperature change
as fast as the Earth is warming

Date:
February 15, 2022
Source:
Field Museum
Summary:
To learn how lichens might be able to adapt to climate change,
researchers examined the evolutionary history of the algae that's
a part of 7,000 kinds of lichens. By studying genetic relationships
between algae and building a giant family tree to show how different
algae are elated to each other and how quickly they evolve, the
scientists found that this algae can take hundreds of thousands
of years to adapt to the changes in temperature that we expect to
see over the course of this century. That means that these lichens
are in dire trouble when it comes to climate change.



FULL STORY ========================================================================== Algae are more than just the green scum that shows up on aquarium
walls. The tiny plants, when teamed up with a fungus, can form a composite structure called lichen. Lichens grow everywhere, from tundras in the
Arctic to the bark of the tree in your yard, and they do everything
from creating oxygen to serving as food for reindeer. But a new study characterizes their preferred climates and concludes that their ability
to change these climatic preferences happens slowly, over the course of millions of years. That means that these algae are likely to be impacted
by rapid climate change the Earth is currently undergoing -- and they
might take lots of common lichens with them.


==========================================================================
"In this study, we set out to learn how rapidly the climate preferences
of these algae have evolved over time, and relate them to predictions
about future rates of climate change," says Matthew Nelsen, a research scientist at the Field Museum and the lead author of the new paper in
Frontiers in Microbiology.

What'd the researchers find? "Terrible, awful things," says Nelsen. "We
found that the predicted rate of modern climate change vastly exceeds
the rate at which these algae have evolved in the past. This means that
certain parts of their range are likely to become inhospitable to them."
The group of algae that Nelsen and his colleagues examined is called Trebouxia.When the tiny algae take up residence inside a lichen, they
live together with the fungus as one; the fungus provides the physical structure, while the algae provide food through photosynthesis. "When
you see a lichen, you're basically looking at all fungal tissue, with
some algal cells hidden away and protected inside," says Nelsen. "Loosely speaking, it's like a greenhouse -- the fungus creates a more hospitable environment for the algae." There are more than 7,000 kinds of
lichen powered by Trebouxia, making it the most common algal partner
in lichens. If the Earth continues warming at the rates predicted,
it'll be too hot for many Trebouxia species in parts of their ranges,
and this could have downstream impacts on other organisms.



==========================================================================
But the Earth's climate has always undergone changes, and lichens
(including the algae that fuel them) have been able to survive by adapting
to new temperatures. The question for Nelsen and his colleagues was
whether Trebouxia can evolve fast enough to keep up with modern climate
change, which is happening way, way faster than normal.

To figure it out, Nelsen and his colleagues (including Field Museum
curator Thorsten Lumbsch, Field Museum Intern Kati Heller, and Field
Museum research associate Steve Leavitt) compared the DNA-based
relationships of different species of modern algae to one another
and looked at the environments they live in. "Closely related algal
species tend to have similar climatic preferences, as predicted by their evolutionary relationships," says Nelsen. "The most closely related
ones might live in really similar climates, whereas distantly related
species might differ more in their climatic tolerance." Essentially, it
takes a lot of time for the climatic preferences of algae to change. To determine how much time it takes algae to make such big evolutionary
leaps, the researchers created family trees showing how different algae
are related to each other and calibrated the tree by using age estimates
from previous work. "We lack any useful fossils in this group, so we had
to use age estimates of this group from a previous study that included
some plant and algal fossils to timescale a bigger group (plants and
green algae) that includes Trebouxia," says Nelsen.

After a whole bunch of statistical analyses, the upshot was that it
could take hundreds of thousands, if not millions of years, for Trebouxia
to adapt to the temperature changes that we're on course to see in the
next century.

"I was shocked," says Nelsen about the team's findings. "I should have
known better from the other papers I've read, but I was disturbed
to see it. It's so close to home, on a group of organisms near and
dear to my heart." Plus, Nelsen notes, lichens (or any organisms)
surviving climate change isn't solely about being physically capable
of tolerating new temperatures, different amounts of precipitation,
or changes in seasonal extremes. When the climate changes, animals and
plants can spread into new environments, where they compete with native species. "Another new species might come in that is competitively more
dominant than you, and you could get out-competed in that environment. And
that could also lead to your disappearance from that area."


==========================================================================
All this doesn't necessarily mean that the 7,000 Trebouxia lichens are all destined for extinction. "I think we're going to see the ranges of these
things shift, and that could lead to some shuffling of the relationships
with fungi - - we might get partnerships that weren't there previously,"
says Nelsen. "Since algae are the food source for the fungus, they're
the ones photosynthesizing and making sugars to give to the fungus. If
they're forced to move, then the fungal partner would either have to
move too, or develop a new partnership." Losing lichens could have a
profound effect on their ecosystems, says Nelsen.

"Lichens are the dominant vegetation on 7% of the Earth's surface. They
play roles in ecosystem hydrology by retaining moisture. They also play
roles in carbon and nitrogen cycling, and some of them are used by animals
for food or nesting materials." Despite the study's bleak predictions,
Nelsen hopes the research is a step in the right direction for learning
how to predict climate change's effects, which can in turn possibly help scientists looking for solutions. "A lot of papers looking at climate
change response are taking an organism's current range, estimating
its current climate preference, and projecting that into the future,"
says Nelsen. "Instead, we estimated the rate at which these organisms
have changed in the past and compared that with the anticipated rate
of future climate change to make predictions about whether they would
be able to evolve rapidly enough without moving, which not as many
people have done. And I think we're the first ones to look at lichens
this way." And he hopes the study provides us all with the motivation
to take climate change seriously and work towards systemic change to
curb its worst effects. To sum it up, says Nelsen, we need to "be better." ========================================================================== Story Source: Materials provided by Field_Museum. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Matthew P. Nelsen, Steven D. Leavitt, Kathleen Heller, Lucia
Muggia, H.

Thorsten Lumbsch. Contrasting Patterns of Climatic Niche Divergence
in Trebouxia--A Clade of Lichen-Forming Algae. Frontiers in
Microbiology, 2022; 13 DOI: 10.3389/fmicb.2022.791546 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215075122.htm

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