By LESLIE BISHOP, guest columnist
I have been looking closely at tree bark for years, noticing the textures, the colors, the ridges, valleys and the patterns bark creates as it travels up a tree.
Tree bark is enhanced by the presence of lichens that add texture and color to a winter landscape. When I look closely at lichens, I appreciate the variety of shapes and colors and am reminded of their fascinating and complex biology.
Lichens are a combination of different types of organisms living in a beneficial symbiotic relationship.
All lichens contain a fungus and a photosynthetic partner. The fungal part provides structure and protection for the lichen, and the algal or cyanobacterial part provides sugars produced from energy of the sun via photosynthesis.
The type of fungus — whether it is a leafy structure or a spreading crust — affects the type of lichen. Biologists have recognized this two-partner symbiotic relationship for more than 100 years.
This long-standing recognition recently was challenged by a new discovery. In a paper published in the journal Science in July 2016, biologists reported that with genetic testing they found a third organism present in lichens — a yeast.
The yeast apparently provides protection from the invasion of pathogenic microbes. Even the authors of the research were surprised by this result.
In a news release, co-author M. Catherine Aime, professor of botany and plant pathology at Purdue University, said, “These yeasts comprise a whole lineage that no one knew existed, and yet they are in a variety of lichens on every continent as a third symbiotic partner. This is an excellent example of how things can be hidden right under our eyes and why it is crucial that we keep studying the microbial world.”
Other surprises are hidden in lichens as well.
On a warm winter day, Jeff and I were hiking at Yellowwood Lake. We walked in silence and could hear only the sound of our boots crunching dry leaves on the trail. Occasionally we would hear the familiar screech of the red-shouldered hawk circling above the treetops, and out-of-season peeps and croaks from thawed tree frogs.
When we stopped for a snack, Jeff was drawn to a tree, gnarly with age. He pointed to a knot in the bark — “an eye,” he said. It did look like an eye; I saw an elephant’s eye with folds of leathery hide.
I continued around the back of the huge old tree to explore the lichens on its bark: flat leafy lichens, tiny, crusty lichens and thin branching lichens that look like little trees.
All of a sudden, I noticed movement. A small patch of bluish green lichen, about the size of a dime, was rocking back and forth. Once I saw one, I saw more — lichens in a herky-jerky back and forth motion, and other lichens moving slowly up the tree.
I gently scooped one into my hand and looked closely with my pocket magnifying glass to see six spindly legs waving frenetically on a tiny bristly body with long curved biting jaws — an insect larva with lichens attached to its back.
I moved from tree to tree and see more. Tiny camouflaged bodies moved up and down the tree trunks. Were they hiding from predators or were they hiding from the prey they will stab with those sharp jaws?
Later, I learn that the green lacewing larva, Leucochrysa pavida, in the family Chrysopidae (order Neuroptera), constructs a debris packet from available lichens and attaches it to specialized bristles on its back with a silk-like substance. The lichen covering allows the larva to be cryptic as it moves along the tree trunk searching for insect prey. The covering will later provide a protective cocoon when the insect goes into the pupa stage of metamorphosis. Brilliant!
I am filled with questions and have to keep bringing myself back to the simple joy of observation. Once again, nature teaches me that that there is always more to discover.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She is a volunteer interpretive naturalist at Brown County State Park. She can be reached through the newspaper at [email protected].
