Little Cities

Learning about nature always makes me happy, but it’s mutualisms that really give me the warm fuzzies. Whether it’s anemones and clownfish, hummingbirds and flowers, or rhinos and oxpeckers, these collaborations are a nice reminder that nature isn’t always red in tooth and claw.

So when I went to search for samples, I was immediately drawn to the lichens growing on tree trunks outside the library. I slid a fingernail under a splotch of green lichen, peeling it from the bark. Its underside was rich and dark.

Lichens are really two organisms– a happy marriage between and alga and a fungus. Like any good relationship, it’s a balance of give and take. The alga can do photosynthesis, providing nutrients to the fungus. In return, the fungus shelters and anchors the alga in its filaments, also gathering minerals from the environment. Variations on the happy couple can be found all over the world, from the tops of mountains to the ocean shores.

The sample was so dense that it was difficult to image with the Foldscope, resulting in this image, which reminds me of the view out an airplane window when I’m flying back to Princeton. The piece of lichen looked completely homogeneous to the naked eye, but zooming in revealed these tiny variations, almost like little cities seen from above, housing the algal and fungal cells.

I tried to gather another sample from a different tree, but those lichens were not as cohesive as the ones pictured above, and they crumbled when I peeled them off. I assume that those might be a different species. It made me wonder what the relationship was between the lichen and the tree– if specific species are paired together, and if so, could the mutualism extend beyond the alga and fungus to include the tree itself somehow?

I conducted this project as part of Professor Pringle’s EEB321 class at Princeton University.

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