Lichens, Beatrix Potter and Symbiogenesis

The unpresented paper 
In 1897 the eminent chemist Sir Henry E Roscoe, know for early studies on vanadium, presented a paper to the Linnaean Society in London on behalf of his then unknown niece, Beatrix Potter, a mycologist and gifted illustrator. Beatrix loved illustrating lichens and fungi and these detailed studies had led her to a definite conclusion with regard to the origin of lichens. However, neither scientific temper nor talent enabled her to present her research. Being a woman, she was barred from the precincts of the hallowed temple of Victorian science. Her paper, titled “On the Germination of Spores of Agaricineae", contained the radical suggestion that lichens are not a pure species (lower plants as they were then believed to be) but “a symbiotic relationship between fungi and algae”. In other words lichens are a compound species, a combination of fungi and algae.

Incidentally Charles Darwin and Alfred Wallace’s paper on natural selection titled “On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection” too had to be read to the Society on July 1, 1858 by its then  secretary John Joseph Bennett. Neither author was present. Darwin was attending the funeral of his son, and Wallace was still in Borneo. The gathered audience, among them many eminent men of science, lost no time in rejecting her paper. Her thesis ran against the very grain of scientific thought of the time, which was schooled to arrive at neat classifications of life forms in the tradition established by Carl Linnaeus himself (the author of Systema Plantarum and Systema Naturae also invented the index card). Moreover, the world was just coming to terms with Darwin’s radical thesis on evolution, and could ill-afford another paradigm shift. The idea had arrived, but not its time. The battle would be fought another day. 

What is a Lichen?

The dual theory of lichens was first proposed by Swiss botanist Simon Schwendener in 1867 but was rejected on the grounds that all living beings are autonomous entities. Post the second failed attempt by Beatrix Potter, it was finally in 1939 that Eugen Thomas established the dual nature of lichens. Lichens consist of a permanent merger of a fungus (called the mycobiont) and an photobiont (a partner capable of photosynthesis), which is usually a green alga or a cyanobacterium. The lichen is a new being, in the sense that it is different from either of the symbiotic partners. Neither partner can grow and survive independently in that natural environment (though they have been cultured separately under laboratory conditions).

The photosynthetic partner (or the photobiont) converts carbon dioxide to sugar using sunlight. These sugars are the food source for both the partners. The fungi provide the nitrates and sulphates to the photobiont. The two partners are hence metabolically linked; they survive as a single organism. In certain lichens a cyanobacterium may be present as the photobiont, or even in addition to the green alga (tripartite lichens). The relationship between the fungi and alga is never one to one. A particular fungus may form an association with a variety of algal species and vice versa. There are lichens in which one fungus is associated with two or even three algal species though the reverse configuration is extremely rare. Due to their unique metabolism and tolerance to extreme desiccation, lichens can survive climatic extremes. They are found from the poles to the equator and can survive for thousands of years. Due to the variety of associations possible they are extremely diverse. Tom Wakeford mentions that a particular British churchyard has been known to yield up to 180 species. They thrive in the deserts and have been found on Mount Everest. They can survive radiation and have been experimentally proven to be capable of surviving in space unprotected. 

In an interesting experiment conducted by the European Space Association, two species -- Rhizocarpon geographicum and Xanthoria elegans -- were sent to space aboard the Russian Soyuz space vehicle in 2005. In orbit the sealed capsules containing the lichens were open-ended and exposed to the vacuum of space, the extreme temperature fluctuations and the solar radiation. Two weeks hence, back on earth, no visible damage was discerned. 

Beatrix Potter in later life 
Spurned by the snooty scientific world, Potter retired to her farm in the English Lake District and devoted herself to writing, drawing and illustrating for children. Squirrel Nutkin, Peter Rabbi, Tom Kitten and Jemima Puddle-Duck were born and instilled love for nature in generations of children and still do as ballets, books, animations and cartoons. Later in her life she went back to her study of lichens but never tried to publish again. She did not need to. She used her considerable inheritance to buy farms and tracts of countryside. Eventually she left it all (4,000 acres) to the National Trust and now it is a part of the Lake District National Park. She died on Dec 22, 1943. 

Exactly one hundred years after her paper was rejected, the Linnean Society in 1997 formally apologized to her. By then another woman, Lynn Margulis, had battled scientific orthodoxy of a different kind and established not only that symbiotic mergers leading to new beings is far more common than admitted, but also spun a theory that looked at Symbiogenesis (Endosymbiotic Theory) at a much deeper level with radical implications for evolutionary theory. 

Other Composite Beings 
In nature composite beings like lichens abound. One such example is the flatworm Convoluta roscoffensis. These green flatworms are approximately 15 mm long and swarm in millions in seawater puddles near shallow beaches. What can appear as green water are indeed these flatworms swarming in the water, trying to catch the sun. It is not for themselves but for the symbiont Tetraselmis convolutae, a green alga that resides inside them. The worms are translucent to allow the sunlight to reach their symbionts. The algae are ingested in the juvenile stage but do not get digested. They get “trapped” inside the flatworm bodies and continue to thrive there – they grow, multiply and die inside the flatworm body. They produce food for the flatworm. The algae photosynthesize their food from sunlight (hence the sunbathing tendencies of the flatworms) and in turn feed the flatworms by leaking photosynthetic products (sugars). Algal waste products become food for the flatworm. The algae also use up the uric acid that the worms produce as waste, thus completing the loop. The flatworm's non-functional, superfluous mouth is an evolutionary adaptation since after the initial ingestion of the algal partner, the flatworm is a symbiotic being -- a miniature ecosystem. Such organisms are also called photoautotrophs and the algal partner the endosymbiont. 

Margulis writes: “Algae and worm make a miniature ecosystem swimming in the sun. Indeed, these two beings are so intimate that it is difficult, without very high-power microscopy, to say where the animal ends and the algae begin.” The idea of compound beings was quite unacceptable to the guardians of the Linnaean Society and the hostile reception was enough to keep Beatrix Potter out of the scientific society (a later attempt to present her work to the famous Kew gardens in London was also a failure due to similar apathy and gender bias). However the situation could not continue for long and in due course lichens were recognized as a symbiotic merger between fungi and alga. Symbiotic beings, when studied closely, defy the neat classification that the Victorian mind (and others later) associated with good science. Research describing such mergers was usually relegated to the dusty corners of  academia and its proponents often dismissed as freaks. Soon, thanks to the dogged and rigorous efforts of scientists like Lynn Margulis, symbiogenesis could be ignored no further. Like the evidence left behind at a crime scene, the clues kept showing up. Pointing out the pervasiveness of symbiosis and the futility of classifying the richness of life into clean slots Margulis writes: “Living beings defy neat definition. They fight, they feed, they dance, they mate, they die. At the base of the creativity of all large familiar forms of life, symbiosis generates novelty. It brings together different life-forms, always for a reason. Often, hunger unites the predator with the prey or the mouth with the photosynthetic bacterium or algal victim. Symbiogenesis brings together unlike individuals to make large, more complex entities. Symbiogenetic life-forms are even more unlike than their unlikely "parents." "Individuals" permanently merge and regulate their reproduction. They generate new populations that become multiunit symbiotic new individuals. These become "new individuals" at larger, more inclusive levels of integration. Symbiosis is not a marginal or rare phenomenon. It is natural and common. We abide in a symbiotic world.”
For an excellent account of Beatrix Potter’s brush with Victorian science and the role of Symbiotic relationships in evolution, you can read Tom Wakeford’s excellent book Liaisons of Life: From Hornworts to Hippos, How the Unassuming Microbe Has Driven Evolution. Lynn Margulis has written several readable books on SET (Serial Endosymbiotic Theory) describing her research into evolution. 

Symbiotic Planet: A New Look At Evolution: Lynn Margulis

What is Life: Lynn Margulis and Dorian Sagan 

Acquiring Genomes: The Theory of the Origins of the Species: Lynn Margulis and Dorian Sagan

Text and Photographs by Sahastrarashmi