Thursday, September 28, 2017

I’m Likin’ The Lichen

Biology Concepts – symbiosis, mutualism, lichens

The lycan is a subject better relegated a cryptozoology
blog. Along with the Loch Ness Monster, vampires, and
the Easter Bunny, cryptids are those animals for
whom there is little or no solid evidence, yet the search
for them by some devotees continues.
A current movie craze has been to replace werewolves with lycans, animals that can control there physical changes to wolf, and can survive under difficult conditions. I know of another organism that has even greater powers, but wouldn’t make a great movie monster – they don’t move and are very slow growing.

Lichens (not lycans) are some of the most intriguing species on Earth, and may very well be the most amazing organisms off Earth as well. Lichens don’t necessarily break a lot of biological rules; they just refuse to acknowledge that our rules apply to them. They write their own rulebook, and humans can’t come close to playing by their rules. They make us look like such wimps. In lichen gym class, we wouldn’t be picked last - we wouldn’t picked at all.

Lichens are symbiots of two completely unrelated organisms; one is the mycobiont, which is always a fungus. The other component is the photobiont, and can be either a green algae or a cyanobacteria. The fungal partner of the lichen makes up about 80% of the mass, but the algae or bacterial component is photosynthetic. Therefore, when they become a mutualistic symbiot, the mycobiont provides a structure and a foothold to a surface, while the photobiont supplies energy through photosynthesis.

Lichens provide food for many animals. For instance, the
Cladina Stellaris grows in the desolate Arctic. It provides
food for the resident reindeer, who we know from past posts
can disconnect its biological clock and feed all through the
day. The reindeer must be particular though, because it will
take the reindeer lichen decades to recover from grazing,
since it grows only 3-5 mm each year.
This is the first exception when dealing with lichens – what are they? They certainly aren’t plants, since they contain a fungal element and not plant element. But they aren’t fungi, since they also contain a bacterial (the cyanobacteria) or protist element (the algae). They are kings in search of a kingdom. Just like Lady Gaga, they defy classification as normal life!

Fungi are decomposers; they break down organic materials to produce nutrients and carbohydrates. But in the lichen, the photobiont produces glucose by photosynthesis, so there is no need for the fungi to decompose for energy. The lichen stores most of its soluble carbohydrate as sugar alcohols, which are made by the fungal component from the algae/cyanobacteria-produced glucose. Therefore, the fungus provides a carbohydrate storage mechanism as well as a structure. These aspects give lichens the ability to live where neither the fungus nor the algae could live on its own.

The second amazing aspect of the lichen symbiosis is that the lichen doesn’t look like either the fungus or the algae that makes it up. It also doesn’t look like a mix of the two. The lichen creates a whole new morphology, with the photobiont housed below a layer of the modified fungus. In the case of lichens, you add 2 + 2 and get a Chevy.

The thallus is the body of the lichen (latin for “green shoot”). In most cases, the thallus is a layer of the fungus, called a cortex, with the photobiont house just below the cortical layer. Enough light still reaches the algae or cyanobacteria in order to make photosynthesis possible.  Below the photobiont layer is the medulla, and can include a stringy (hyphal) fungus layer or maybe just the gelatinous photobiont. Finally, some lichens will have a lower cortex layer of fungus as well. The take home message is that neither the fungus nor the algae or cyanobacteria take on any of these forms UNLESS they are part of a lichen – it is a completely different structure.

Not every lichen has a lower cortex layer, but almost all
have the top cortical layer of tough fungal material. This
layer protects the lichen from predation and dessication
(it does nether spectacularly well). The photobiont lives
primarily in the subcortical symbiont layer, while the
medulla is spongy and has many fungal filaments. The
rhizine connects the lichen to its substrate, but many
lichens are erhizinate, they do not have rhizines.
The mycobiont is the more flexible of the two components; literally thousands of different fungi can act as the mycobiont. On the other hand, only 100 or so different photobionts exist. Most common of these are of the species Trebouxia. They are green algae which rarely live on their own, they have become specialized for symbiotic life as a lichen.

The combination of these two components yields the over 17,000 different lichens that have been identified. The combinations are also flexible, a lichen may use different photobionts during its life, and identical lichen types may use different photobionts even within the same general area.

The combinations of decomposer and autotroph that make up lichens are hearty and diverse. Fully 8% of the Earth’s surface is covered with lichens, not bad for something so small. More amazing is that lichens can survive in places that support almost no other life. Lichens and endolithic bacteria are only living things in the McMurdo Dry Valleys of Antarctica, as well as the Atacama desert of Chile, often called the two driest places on Earth (I think they forgot about Lynchburg, TN).

The McMurdo Valleys (4,800 sq. km) are a cold desert environment (Water, Water, Everywhere). They are almost ice and snow free, even though they are on the frozen continent of Antarctica. Less than 200 mm (8 in) of precipitation is available each year, and most of this is from summer glacier melt.

The Atacama Desert in Chile is a desolate wasteland,
no offense to any inhabitants. It probably has its
nice parts too.  Parts of the desert have had no
recorded rainfall..... ever. This leads to some
interesting formations, like these geometric salt
patterns, very appropriate for this series of posts.
The average rainfall in the entire Atacama Desert is even less, only about 1mm (0.04 in) per year, and many weather stations have never recorded any precipitation at all. The lichens survive on the water vapor that reaches them from the coastal fog,which comes from 150 km (80 miles) and a mountain range away. Interestingly, an extreme Antarctic cold front brought 80 cm (31.5 in) of snow to the plateau in July of 2011! This was enough to bring wildflowers to the Atacama, in places they had never been seen before.

Despite (or perhaps because of) these arid environments, lichens are the major form of life in the Atacama Desert and McMurdo Valleys. Most organisms cannot survive a loss of 20% moisture, but lichens can do just fine when 90% dehydrated. While their growth may be retarded, they quickly make up for it by absorbing up to 35x their mass in water when it is available. Lichens dry out slowly because of the dense cortex of fungus on the outside, so they can still photosynthesize despite long arid periods.

Even more exceptional, the lichen symbiot is less than 50% water, even on a good day. Mushrooms are 92% water, and algae or bacteria are typically 96% water, but when you put them together as a lichen, their normal water content is some 40-45% lower. This is how the lichen can live in places that would not support either of its components on their own – amazing.

The deserts, both cold and hot, allow the lichens to show off another of their skills. Lichens can withstand extreme temperatures and wild swings in temperature. Scientists keep thinking up new ways to torture them. Lichens survived a bath in liquid nitrogen at -195 ˚C. Not satisfied that they had been treated harshly enough, European Space Agency scientists strapped some lichens to a rocket and exposed them to the cold and radiation of outer space for 14.6 days. Cold, hot (shielded re-entry), vacuum, UV, cosmic rays – the lichens survived just fine. Because of this will to live, exobiologists (scientists who study what life on other planets might be like) study lichens as a model alien life form or as an organism with which we might seed other planets.

Lichens (or something similar to them) are likely to be found on other planets, but they also may affect other forms of life off Earth. A recent study by performed in Italy and the UK has shown that the few animal types (rotifers, nematodes) that are able to survive dessication as lichens can are influenced greatly by their environment. They may have different ways to survive drought, but statistical modeling shows that the type of lichen they are found in has more to do with their survival in drought or even in space than their own tolerance mechanisms.

Lichenometry is the art and science of investigating
how long a surface has been exposed. For example,
moraines are gatherings of stones at the edges of
glaciers. How long has it been since the glacier receded
from that spot? Lichens grow at a predictable rate given
a known environment, so measuring the size of a lichen
will give good estimate of how long the surface has been
available to be lichenized (just made up that word).
As a result of the poor environments where lichens can be found (although they also grow just fine in temperate areas- just look outside your front door), lichens are the slowest growing life forms on Earth. Usnea sphacelata, which looks like a small forest of bonsai, grows about 0.01-1 mm per year. Usnea can only grow on about 120 days per year, but they live a very long time. An age of 200 years is not unusual, the record is about 4500 years.

In a defined area with a defined weather pattern, lichens may grow at a very slow rate, but it is a very consistent rate. This predictability makes them good for dating other structures, a process called lichenometry. For instance, lichens can be use to estimate how long a rock face has been exposed by a retreating glacier. Once the rock is uncovered, lichens will soon colonize it and grow at a consistent rate. Once you know the size of the lichen, identify the type of lichen, and know its growth rate for that area, an age for the exposure can be calculated.

Next week we will talk more about the amazing properties and abilities of lichens, but one last tidbit for today. For anyone who has read Peter Rabbit or Benjamin Bunny to their child, Beatrix Potter is a familiar name. Before becoming a famous author, Beatrix made a living by illustrating other author’s books and doing some scientific illustrations. She was an outdoorsy girl, and her pictures of lichens led her to study them on her own.

Beatrix Potter wrote more than 20 childrens classics; the
illustrations were her own and are perhaps more iconic than
her prose. But she started out working on lichens, and was a
devout “Schwendenerist,” a follower of Simon Schwendener’s
idea of lichen symbiosis. I got the chance to collaborate with
one of Simon’s distant relatives a few years ago. Hi Reto!
While the dual hypothesis of lichens had already been put forth by Simon Schwendener, it was not well received in England. Potter used microscopy and her drawings to generate evidence for Schwendener’s hypothesis. However, she was not a scientist, and worse, she was a woman – so she couldn't present her evidence to the botanists of her time. Her uncle was Sir Henry Roscoe, the eminent scientist who developed the first flashbulbs for photography (along with another scientist named Bunsen – name sound familiar?). He supported her and read her papers into the scientific record, but she could never make name for herself as a scientist in that environment, so she turned to writing. It was a lucky thing for us all – a world without Flopsy and Mopsy is too horrible to imagine.

Fontaneto, D., Bunnefeld, N., & Westberg, M. (2012). Long-Term Survival of Microscopic Animals Under Desiccation Is Not So Long Astrobiology, 12 (9), 863-869 DOI: 10.1089/ast.2012.0828
For more information or classroom activities on lichens, exobiology, or lichenometry, see:

Lichens -

Exobiology –

Lichenometry –

Thursday, September 21, 2017

Water, Water Everywhere, But….

Biology concepts – symbiosis, mutualism, water storage

“Gobi” means desert in Ural-Altaic,
so when you say, “Gobi Desert,” you
are really being redundant.
Sometimes the places with the most water are the most lifeless areas. Everyone thinks of sand and heat, but Lawrence of Arabia wouldn’t even recognize most biological deserts.

The term biological desert is misleading, since places like the Gobi Desert in Asia support over 600 species of plants and hundreds of animal species, vertebrate and invertebrate. Death Valley in the USA has over 100 plants species; it could hardly be called dead! A biological desert has less to do with the climate and more to do with the adaptability of organisms to adverse conditions of oxygen, salt, water, light, or too often - pollution.

Take for instance the South Pacific Gyre. This area of about 34 million square kilometers (10 million sq. miles) has very little life in the pelagic zone (the below the surface waters to just above the sea floor). In the last posts we learned why water and salts are crucial for life, and the extreme evolutionary adaptations that have occurred in many organisms in order to conserve body water and maintain safe salt levels. But here we are in the ocean – water everywhere, salt everywhere, but almost nothing lives in the gyre.

The north and south Pacific gyres represent
a huge portion of the Earth’s surface, and
these are relatively life free areas, the largest
deserts on Earth.
The reason for this paucity of life has more to do with nutrients than with water or salt. Because the current moves counter-clockwise, the center of the gyre is isolated from the upwelling of nutrients from the ocean floor, and the winds can’t help to churn the waters. Even if they could, it would help little. The waters of the gyre are rigidly layered due to salt and temperature differences (stratification, I Am Your Density), so nutrients find it difficult to travel to the surface from below. Adding to the problem, there is little landmass in the South Pacific, so windblown organic material and terrestrial runoff are limited. Nutrients are coming from neither above nor from below.

With limited nutrients, there is a ceiling to the amount of primary productivity of phytoplankton (phyto = plant, and planktos = wandering in Greek) that can take place. Fewer producers means that few primary consumers can be supported, and so forth up the food chain. Little life on the surface means few nutrients drop to the ocean floor (waste and dead organisms), and so on.

The ocean gyres have little upwelling if nutrients
and therefore little plankton production. The bad
news - with global climate change, the gyre-related
low productivity zones are growing in size.
Strangely enough, the lack of producers in the gyre has benefited humans in at least one aspect. The chlorophyll of the producers changes the color of the ocean, and this affects the trapping of heat and the wind currents. With a loss of living things in the North pacific gyre, a 2010 study states that typhoon formation has decreased in this region by more than 70%............Don’t get too excited, global surveying also says that the biological deserts of the gyres are growing much faster than global warming models would predict. As they grow, global productivity will be reduced, and that can’t be good for any of us.

We don’t make things any easier by letting chemicals run into the oceans either. Man made dead zones from increased nitrogen and phosphorous. These nutrients are needed for growing phytoplankton, but you can have too much of a good thing. The overgrowth of phytoplankton and algae in these areas, along with the decomposers they support, deplete O2. The result is that there is no oxygen left for succession organisms, so larger animals cannot live there (neither can the plankton or algae after a while).

Man made dead zones correspond to areas of
runoff from sprayed fields. For instance, the estuary
of the Mississippi River in the Gulf of Mexico forms
the second largest man made dead zone in the world
each summer. Not to be outdone, the Baltic Sea dead
zone in Northern Europe is the largest, and it is
present all year round.
So the gyres are “almost dead” zones, and some polluted estuaries are considered dead zones. What about a body of water with dead in its name, the Dead Sea? At 423 meters (1388 feet) below sea level, the Dead Sea is officially the lowest body of water on Earth. Water flows into it, but not out of it, so all the salts and minerals just accumulate.

The temperature of the desert surrounding the Dead Sea is warm enough that evaporation plays a factor in increasing the salinity and mineral content of the remaining water. Only certain types of bacteria and algae can survive in the 33.7% saline waters (~8.6 x the salinity of the Mediterranean Sea).

 Dunaliella salina algae are particularly abundant in the Dead Sea after the rainy season. These green algae produce antioxidant carotenoids to protect themselves from the intense sun exposure of the Jordan Rift Valley as well as huge amounts of glycerol (a three carbon carbohydrate) to counteract the osmotic pressure which would otherwise move all the freshwater out of the algal cells.

The algae is a good food source for halophilic (salt-loving) bacteria. However, during dry years, both the alga and bacteria are present in much lower numbers. But isn’t just the high salt that prevents larger plants and animals from living in the Dead Sea. The minerals that accumulate, such as magnesium chloride, calcium chloride, magnesium bromide, and calcium sulfate, are toxic to animals that drink the water. Fish from the freshwater feeders of the Dead Sea sometimes swim into the mineral-laden waters and are killed almost instantly.

The Dead Sea has receded a mile in the past twenty
years, and environmentalists warn it could be
completely gone by 2050. As it recedes, it leaves
salt on the rocks after the water evaporates.
The exception to this is the recently discovered freshwater springs that also feed the Dead Sea. Along the sea bottom near these vents lives a multitude of Archaea (often called extremophiles) that used to be classified as bacteria, but are now known to be a different kingdom of life. Spreading along the seafloor, mats of Archaea form biofilms, previously unknown in the Dead Sea.

The Great Salt Lake in Utah is similar to the Dead Sea biologically, but the lower salinity (some places are 5% salt, while others are 25 %; a railroad causeway has separated it into a more saline north arm and less saline south arm) allows more types of organisms to thrive in the water. Still no fish, but more types of algae, as well as some brine shrimp and brine flies.

Surprisingly, there is abundant flora and fauna around both the Great Salt Lake and the Dead Sea. The Jordan Rift Valley boasts camels, leopards, and ibexes, as well as fig trees and the rose of Jericho. In the western hemisphere, the Great Salt Lake has millions of shore birds, mostly fed by the 100 billion brine flies that hatch each summer. It is just the exception that here you have to move away from the water to find the life.

The above two examples indicate areas that have a lot of water, but too much salt for it to be useful. There is another place on Earth that has plenty of H2O, but not enough liquid water to support much life – does that make sense?

Antarctica. It is hard to believe that with all that ice, miles thick in some places, there is not enough free water to keep plants and animals alive, but in many parts of the continent, that is the case.

McMurdo Station is the largest community on
Antarctica, if you don’t count the penguins. It is
located near the McMurdo Dry  Valleys, the driest
places on Earth. This is due to the katabatic winds.
Cold air is more dense, and is pulled downhill. The
wind can reach speeds of 200 mph, and as it warms,
it evaporates all the moisture on the ground and in the air.
Some areas of Antarctica do support a little life; two vascular plants exist on the frozen continent, hair grass (Deschampsia antarctica) and the pearlwort (Colobanthus quitensis). These plants only grow on the west coast peninsula.

In the McMurdo Dry Valleys, east of McMurdo Station and the Ross ice sheet, almost nothing grows. There are hypersaline lakes here that put the Dead Sea to shame, including the Don Juan Pond that is 18x the salinity of the ocean.  

There are no vertebrate animals in the valleys; microbes make up all the biology there. In all of Antarctica, only 67 species of insect are found, and most of these live as parasites on penguins.

The exception is the wingless midge (Belgica antarctica). At an average of 6 mm long, this fly is the largest purely terrestrial and year-round animal on the entire continent (penguins only live on the continent for part of the year).  This flightless fly relative lives in algae mats, on rocks, and in the mud… just about anywhere it wants to. There are no competitors on Antarctica; this walking fly reigns supreme!

Belagica is well adapted to life in Antarctica. It is
black to absorb heat, and it is wingless so it won’t
be blown out to sea by the strong winds. It has a
short egg laying time and adult life span so that it
can complete its life cycle in the highly variable
summer season.
Other adaptations allow B. antarctica to thrive in this harsh environment. While the vast majority of plants and animals die with a relatively low level of dehydration (5-25%), these midges can survive a 70% water loss event - I suspect they can’t expectorate! In the winter…… WINTER? Isn’t it always winter there? Well, no; there is a colder season....the midge can react to winter by dehydrating and then coming back to life in the spring.  Something like having a piece of beef jerky moo after you start salivating on it. Amazing.

Recent evidence shows just how adapted B. antarctica is for the dehydration. The midge has one genetic response to thermal stress, whether it be hot or cold. They turn off some pathways and increase glucose metabolism pathways.

But in dehydration, it has different responses to different patterns of dessication. If it is a rapid dehydration, glucose metabolism pathways are up regulated, but if it is slow and steady, a whole different set of pathways are upregulated, including those for different osmoprotectant molecules (trehelose and proline).

The dry valley temperatures (-10˚C to -51˚C) could easily cause havoc with the midge’s protein function, including the pathways that protect it from dehydration stress. Heat shock proteins help to stabilize protein function in temperature extremes, usually they are expressed (transcribed from DNA and translated from mRNA) for short periods of time, only when there is an abnormal event. But Belgica’s heat shock proteins are expressed all the time. This is a huge energy investment, and an investment that few animals are willing to make. But in areas with too much salt or too little water, sacrifices must be made.

Next time we will talk about one of the greatest exceptions in biology, an organism that can live in the Atacama Desert, the Jordan Rift Valley, the Great Salt Lake, and even at Antarctica. It's not a bacteria, not a fungus, not a plant, not an animal – this is one heck of an exception.

Teets NM, Kawarasaki Y, Lee RE Jr, Denlinger DL. (2012). Expression of genes involved in energy mobilization and osmoprotectant synthesis during thermal and dehydration stress in the Antarctic midge, Belgica antarctica. J Comp Physiol B DOI: 10.1007/s00360-012-0707-2  

For more information or classroom activities on biological deserts, life in the Dead Sea, and life on Antarctica, see:

Biological deserts and gyres –

Life around the Dead Sea –

Life in Antarctica -