Ants and Plants: Symbiotic Living

The first known farmers were apparently…ants. Leafcutter ants have been growing fungus on chopped up leaves for at least 50 million years. It is an amazingly long time.  Yet, when one thinks of the astonishing range of different “breeds” of animals and crops which humankind has created through artificial selection during the 10 millenia or so years since we started farming, the ants seem a bit lackluster.  For all of their workaholic zeal, ants are not as relentless as us in selecting for traits in their crops.

Yet, as we learn more about the ants and their empire, the amazing extent of their symbiosis with the plants they use is beginning to become more apparent to us.   Because of the vastly greater timeline of their endeavors, they have coevolved in astonishing ways. An example of this can be found in the homes of Philidris nagasau, a species of leaf cutterant native to Fiji.  These ants literally grow their homes out of Squamellaria, an epiphytic plant which grows on tropical trees.

The Economist described the mechanism through which the ants grow a home (or, alternately, the way the epiphytic plant obtains an army of insect servants):

P. nagasau worker ants harvest seeds from their epiphytic homes, carry them away, and then insert them into cracks in the bark of suitable trees. That done, they patrol the sites of the plantings to keep away herbivores, and also fertilise the seedlings as they grow by defecating into hollow structures called domatia that develop in the bases of the plants’ stems. As a Squamellaria grows, its domatium swells (see picture) and develops galleries that can accommodate ants—which then move in. This, and the plant’s habit of growing flowers that generate nectar long after they have been pollinated, provide the evolutionary quid pro quo that makes the relationship between insect and epiphyte work.

It is incredible that the ants grow their own houses.  Yet, as one looks more closely at familiar domestic arrangements with this story in mind, they start to seem less familiar.  Is farming really as unique as we make it out to be, or does it resemble mutualistic arrangements found throughout the natural world.

We would never say we co-evolved with goats, cows, and horses: their domestication seems like a one way exchange to us. Yet an outside observer might look at our leather sofas, cheeseburgers, cavalry charges, or angora sweaters and come to a different conclusion.

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Painting by Robert Steven Connett

ZOOOIDS – Underworld II (Robert Steven Connett, 2009, Acrylic on canvas)

Here is an amazing painting of fantastic glistening underworld creatures.  I greatly admire the artist, Robert Steven Connett, a self-taught contemporary painter who crafts baroque landscapes of dark lifeforms and gleaming spirit-things.  At their best his works come together to portray life as an interwoven web of symbiotic appetite and need—a phantasmagorical ecosystem of amalgamation and ingestion.   It is as though Giger were a gifted mycologist or invertebrate zoologist.  As far as I can tell, Connett has made few inroads in reality, where art is controlled by a click obsessed with fatuous celebrity and tiresome naval-gazing deconstructionism.  However he has created his own strange markets online (in much the same way that he builds his own imaginary underworld ecosystems).  It almost gives a person hope.

I realize this has been an art-heavy week…but I will make it up to you next week when, in celebration of Halloween, we have a whole week dedicated to a unifying theme of macabre terror.  The Halloween themes of years past–the children of Echidna, the Flowers of the Underworld, even the spiritual and ontological horrors of the undead–raised no eyebrows on the internet, so I am ratcheting up the dreadful violence this year.  Steel yourself for the frightful flesh-cutting terror…uh, and for more art too I guess.

Arbor Day Thoughts

Magical Tree
by JourneyArtist (deviantart)

Today is Arbor Day, the annual international celebration of trees. Like my distant heathen ancestors, I partake in a bit of tree worship.  Because of their immense size, strength, beauty and longevity, trees are an obvious metaphor for the numinous.  However there are also more subtle and compelling reasons that trees are the ideal symbol of divinity.

Trees are at the center of a vast web of commensal relationships between living things.  They rely on large mutualistic collections of organisms to survive. Trees cannot live without an unseen world of symbiotic organisms in the soil. The towering plants rely on nitrogen fixing bacteria, fungi, and actinomycetes to take nutrients from the earth.  Likewise trees communicate through fungal networks which link them together in improbable ways we are only now learning about.

Trees utilize bees, flies, monkeys, and birds for pollination…and to disseminate their seeds.  They call on different parasitoid wasps for defense through elaborate biochemicals. We should really envision a tree not as a big spiky discreet thing sitting in the lawn, but as a vast flow chart/rolodex of connections with other living organisms.

Of course trees are not unique in being an interconnected node within a vast web of life—that is really the way all life is.  It is a grotesque human conceit that humans stand outside and above nature.  I have always thought of humanity as a problematic youngest child.  We are the favorite (for the moment). We have such gifts…but we are so arrogant, unhappy, and unstable.  And we are so so monstrously greedy.  I sometimes like to imagine trees as a gentle stable elder brother.

Actually though, mammals are much older than flowering trees.  For hundreds of millions of years our pathetic little ancestors cowered beneath the roots of conifers, cycads, ginkgoes, tree-ferns and such.  Then, at the end of the Mesozoic, the ascent of mammals happened at the same time that the angiosperms took over the land.  Our shrewlike ancestors evolved into arboreal primates as the angiosperms themselves were becoming the forests.

We grew up together! While the great angiosperm forests of the Eocene may not have required much from our squirrel-like grandparents, today’s forests desperately require our good graces so that they are not all converted into parking lots. Plywood, and ugly discount furniture.

Anyway, my thoughts are getting away from me.  I only wanted today’s post to be a reminder of Arbor Day and how wonderful and beautiful trees are. Here is a small gallery of lurid yet evocative images of sacred trees!  I especially like the pictures of trees together with outer space or the cosmos (like the big portal tree at the top).  Happy Arbor Day!

Space Tree by MartijnVn on DeviantArt

Ant Farmers

Agriculture is almost unknown in the natural world. Human beings are the only vertebrates known to grow crops or keep livestock (with the possible exception of damselfish which carefully tend little algae gardens).  And yet we were not the first animals to invent the concept.  Ants have farmed fungi within their tunnels for tens of millions of years.  Ants also keep aphids in captivity in order to “milk” them of sugary secretions–or to eat them outright.  It is possible that beetles, termite, or snails came up with the concept first, but most evidence points to ants as the first farmers.

An Ant Milking Aphids

Ants do not have a shabby operation either. Leaf cutter ants form the largest and most complicated animal societies known on Earth (other than our own) and a single colony can have over 8 million individuals.  Leaf cutters are an ideal example of how adept ants are at farming fungi.  Four different castes of worker ants work together to bring back leaf fragments and integrate them into huge fungal gardens. Different species of leafcutters cultivate different fungi from the Lepiotaceae family.  Certain bacteria with antifungicidal and antibacterial properties grow within the metapleural glands of the ants.  The worker ants use these bacteria to “prune and weed” dangerous or unproductive organisms out of their gardens.  Older (more expendable) worker ants carry waste products from the hive to a waste pile where they stir the hive wastes together to aid in decomposition.  The waste-management job brings the danger of fungal or bacterial contamination and contaminated ants are exiled to certain death in order to keep the gardens safe.  Additionally dead ants from within the hive are carefully placed around the waste pile so as to protect the hive from their decomposition.

Leaf Cutter Ants at the Cameron Currie Lab arrange cut-up leaves into their fungal garden.

According to geneticists who study the rates of mutation within the various fungal cultivars, ants began their farm relationship with fungi around 50 million years ago in the warm Eocene epoch (an era which saw many of the critical relationships in modern ecosystems begin).

 

Digital Cut-away of an underground leaf-cutter nest

Scientists are also beginning to understand the means by which ants herd their little flocks of aphids.  The aphids are smaller insects which feed on the saps and juices of plants (which they suck out by means of specialized mouthparts called stylets).  The ants prevent the aphids by flying away by tearing off their wings.  The feet of the ants produce chemicals which tranquilize and subdue the aphids and keep them from escaping the “pastures” near the ant colonies.  It is believed that aphids also derive certain benefits from this arrangement since the aggressive ants protect them from many of their natural predators.

An Ant with a “herd” of Aphids

For years naysayers belittled the farming achievements of ants suggesting they were little more than symbiotic arrangements.  However as entomologists study the ants more carefully they increasingly discover just how complicated and sophisticated those relationships are (involving as they do numerous symbiotic relationships with bacteria in order to produce the chemicals necessary for agricultural control).  Additionally, what are humankind’s relationships with our crops and animals if not huge harrowing examples of symbiosis?

Lichens, the Great Colonizers

Lichen (by WiseAcre)

Cast your imagination back half a billion years ago to the Cambrian geological period.  Although Earth’s oceans were seething with strange experimental life forms, the alien continents were bleak and empty.  Huge brown mountains sloughed away into giant canyons. Black volcanoes eroded into naked black beaches. Great flash floods poured over a landscape bare of plants and animals. No horsetails grew.  No dragonfly buzzed.  Not even a miserable liverwort crouched by the empty streams. But were the ancient continents entirely bare? No—bacterial films and single cell algae were believed to have covered the land, and looming above that primitive slime were the first lichens, symbiotic life forms so hardy that they alone thrive on continental Antarctica today.

Red Lichen living in Antarctica (photo by Gerhard Hüdepohl from Atacamaphoto.com)

Lichen is a bizarre composite organism in which a fungus is paired with a photosynthesizing partner (either green algae or cyanobacteria).  The thallus of lichen (which makes up the organism’s body) is very different from either the fungal or algal components living on their own.  The fungi surround and hold up the algae by sinking tendrils through the algal cell walls (in much the same manner parasitic fungi attack their hosts).  By sharing the resources of the two different partners the organism is capable of surviving extreme desiccation, and, when the lichen is again exposed to moisture, a flood of nutrients becomes available to both partners.

Lichen (from "Art Forms of Nature" E. Haeckel)

The partnership makes for an extraordinarily resilient organism which can be found everywhere on land from the rainforests to the deserts to the highest mountains to the harsh frozen rocks of Antarctica. The European Space agency explored the durability of lichen by blasting living specimens into outer space where, to quote the ESA, the organisms were “exposed to vacuum, wide fluctuations of temperature, the complete spectrum of solar UV light and bombarded with cosmic radiation. During the Foton-M2 mission, which was launched into low-Earth orbit on 31 May 2005, the lichens…(Rhizocarpon geographicum and Xanthoria elegans) were exposed for a total 14.6 days before being returned to Earth….Analysis post flight showed a full rate of survival and an unchanged ability for photosynthesis.”

Lichen dot the face of a Song Dynasty statue on Qingyuan Mountain, China.

Lichens’ strange partnership also creates strange morphological forms. In many circumstances these organisms resemble exotic corals, sponges, or plants. Additionally, many lichens are brightly colored.  The result is often a miniature landscape of bizarre beauty.  I have included some photos from sundry sources but you should check out the lichen photos at Stephen Sharnoff’s site (even disfigured by the trademark, his lichen photos are the best on the net).

Competing Lichens Growing on a Rock

Since it involves both algae and fungi, lichen reproduction can be complicated and takes many different forms depending on the species and the circumstance.  Some lichens form soredia, small groups of algal cells surrounded by fungal filaments which are dispersed as a group by wind. Others produce isidia, elongated outgrowths from the thallus which break away.  During the dry season, certain lichens crumble into dusty flakes which are blown across the landscape.  When the rains come the flakes burst into full growths.  In the most interesting and complicated pattern of reproduction, the fungal portion of the lichen produces spores (as a result of sexual exchange and meiosis) these spores are disseminated across the landscape and then must find compatible algae or cyanobacteria with which to partner.

 

Community Lichens is in the Sawtooth Mountains (photo by Mark Dimmitt)

Lichens are probably long lived and it is possible that somewhere there are those that make the bristlecone pines seem young and have lasted as long as Pando, but who knows?  We have not explored and documented the world’s lichens very completely…or even fully understood the mechanisms of their partnership.  What is certain is that they are one of life’s most efficient colonizers: in areas such as the Atacama Desert and Antarctica, plants cannot grow unless lichen lived there previously (in fact I am going to include this post in my “invaders” category for just this reason). Lichens are also efficient at exchanging carbon dioxide for oxygen, and they are a critical link in the carbon cycle capable of fixing elemental carbon back into the soil and into the ecosystem.  When you look at a tundra landscape and savor the beauty of reindeer, mountains, and arctic birds, spare a thought for the ancient lichen, one of the first organisms on the land and still one of the most important.

Lichen slowly colonize a New England gravestone from the 1700's.