Compendium 5.1: Worthy miscellany

Compendium Volume 5 Number 1 July 2021

Symbiosis: Structure and Functions, Ecological and Evolutionary Role, Sélosse 2000

(La Symbiose : Structures et Fonctions, Rôle Écologique et Évolutif)

Book review by Ehsan Kayal

What is symbiosis? How is it defined? What does it involve? And how did it come to be? These are some of the questions French Biologist Marc-André Sélosse explores in this book.

It is not simple to define “symbiosis,” which differs between the English and French languages. Sélosse focuses on the narrower French definition, which involves “long-term coexistence of two different organisms throughout their life with reciprocal benefits” [Sélosse 2000: 22]. In English, the term “symbiosis” refers not only to mutualism (reciprocal benefits), but also to parasitism or commensalism (one partner benefit without impacting the other partner). One important aspect of the study of mutualistic symbiosis is exploring reciprocal physiological exchanges that happen between symbionts (organisms involved in symbiosis). Such exchanges are facilitated by morphological changes in one, the other or both partners.

Sélosse offers readers a glimpse of the breadth of symbiotic relationships found in nature. For example, there are bacteria living inside worms around deep-sea vents in the ocean that use chemical energy seeping from the earth to create organic compounds that nourish their worm hosts. The author also highlights the case of lichen, which appears to be a single species, but is actually formed by a symbiosis between fungi and algae. Sélosse focuses especially on symbiosis involving mycorrhiza, which are the “symbiotic organs formed by a root and a fungus” [Sélosse 2000: 140], and on root nodules, the “symbiotic organs of legumes, often around roots, containing bacteria of the Rhizobiaceae family responsible for fixing nitrogen” [Sélosse 2000: 140].

Leguminous plant hosts provide their Rhizobia symbionts with carbon, while protecting these bacteria from harmful oxygen, in exchange for nitrogen. The efficiency of these symbiosis is such that the “rhizobiaceae-containing root nodules fix as much atmospheric nitrogen per year as the fertilizer industry” [Sélosse 2000: 54]. Similarly, plants with mycorrhizal associations supply their symbionts with carbon in exchange for water, phosphate and other nutrients furnished by the fungi. Studies have linked “an increasing diversity of mycorrhiza” with “increasing diversity of plants” [Sélosse 2000: 67].

Symbiosis can short-circuit the mineralization-immobilization cycle (conversion of inorganic compounds to organic compounds by micro-organisms or plants) by bringing together partners that thrive on each other’s by-products. This results in a “concentration of resources” [Sélosse 2000: 49] that allows organisms to conquer new ecological niches as exemplified by lichen and corals, but also playing a key role in the evolution of the soil that promotes vegetation successions [Sélosse 2000: 60]. For example, lichen is the first to colonize bare rock, where it produces citric acid and holds water, slowing altering the rock in the early stage of soil creation. Rhizobial symbioses then pitch in by fixing nitrogen, otherwise absent in a rocky substrate.

The book also flips some of the common understandings of organismal biology. For instance, many herbivores lack digestive enzymes to break down plant material. Rather, they feed on the population of microorganisms of their rumen, or the “pocket situated upstream of the stomach in ruminants that harbors a symbiotic microflora” [Sélosse 2000: 141]). The rumen is a large organ, whose volume can represent “8 to 15% of total body weight” [Sélosse 2000: 32]. That makes those microorganisms (protists, fungi and bacteria) the “true” herbivores, while the ruminants are secondary consumers.

The older traces of symbiosis predate the origin of the eukaryotic cell (cell with a nucleus enclosed within a nuclear envelope), where the mitochondrion (the energy-producing organelle of the cell) are descendants of a likely unique endosymbiotic event occurring some two billion years ago. In that event, an anaerobic archaean (third kingdom of life composed of unicellular organisms lacking a nucleus; the other two kingdoms are eukaryotes and bacteria) captured a facultative aerobic type of bacteria, which became mitochondria. Similarly, the acquisition by some eukaryotic cells of a chloroplast originating from cyanobacteria gave way to photosynthetic plants.

In some sense, “no organism lives alone, and each carries a symbiotic cortege without which one cannot understand neither the physiology nor the ecological success of the organism” [Sélosse 2000: 134].

Biophilia: the human bond with other species, Wilson 1984

A book review by Rachel West

As I read the first chapter, Wilson brought me far into the forests of the Amazon Basin to encounter canopy-dwelling birds and frogs found nowhere else on Earth; he showed me the life cycle of a tiny moth so specialized that the adult lives only in the fur of the 3-toed sloth, and held up fistfuls of forest soil teeming with tiny life to demonstrate that “the woods were a biological maelstrom of which only the surface could be scanned by the naked eye.”

With his astonishing eye for detail and his fluid prose, he fascinated me, he drew me in, he fed my curiosity…and then he reminded me: “Eliminate just one kind of tree out of hundreds in such a forest, and some of its pollinators, leaf eaters, and wood borers will disappear with it, then various of their parasites and key predators, and perhaps a species of bat or bird that depends on its fruit… and when will the reverberations end?”  

Throughout this book, Wilson brought me close to the beauty of living systems across the world. He taught me enough about them to make me curious, and then to make me care; and then, when he showed me how easily that entire system could be disrupted, he had my undivided attention. This kind of understanding and connection, Wilson argues—this human bond with other species—is an essential ingredient in motivating us to change our behaviors in order to slow the rate at which “the wildernesses of the world [are shriveling] into timber leases and threatened nature reserves.”

One of the challenges with building these connections and then acting upon them, Wilson suggests, is that we are programmed to operate in physiological, not ecological, time; that our minds “travel back and forth across hours, days, or at most a hundred years. The forests may all be cut, radiation slowly rise, and winters grow steadily colder, but if the effects are unlikely to become decisive for a few generations, very few people will be stirred to revolt.” But in recent times, our impact on ecosystems has been compressing “ecological time” to align with “physiological time,” and the results are becoming visible in the span of single generations; the massive Florida manatee die-off due to the destruction of their seagrass pastures is but one starkly visible example of the reverberation felt by the loss of a single species from an ecosystem.

In the chapter “The Conservation Ethic”, near the end of the book, Wilson explores the relationship between the human drive to perpetually expand—and the related desire for personal freedom, at least in Western cultures—and the necessity for conscious stewardship of the environment to ensure our ultimate survival—not only our physical survival, but our spiritual survival. He writes “The only way to make a conservation ethic work is to ground it in ultimately selfish reasoning.”  In other words, it is likely that wild species and places will be best understood and protected with respect to their perceived value, such as the vast array of plant compounds that have shown promise as anti-cancer compounds, or, as has been increasingly recognized in recent years, for the ability of wild places to improve the emotional and spiritual well-being of the people who spend time there.

This book is even more relevant now than it was when it was released in 1984, and thus has the potential to reach a broader audience today. More people may be ready to hear some of the truths held in this book because now, more than ever before, the human race is seeing, and feeling, the long-term effects of the way we have treated the planet.

An Okanagan Worldview of Society, Armstrong 2020

Jeannette Christine Armstrong is a Canadian author, educator, artist, and activist, who wrote this article about the traditional decision-making process in Okanagan, called “enowkinwixw,” which demonstrates a great practice of biophilia.

Okanagan, the Penticton Indian reservation in Canada where the author was born and raised, has a very fragile ecosystem. However, the author discovered that this community treats the land differently compared to other communities. They treasure natural resources and believe that the land is the people. They bear in mind that everything they have came from the land and that their every decision has a possibility to destroy the land. Therefore, they not only pay attention to the relationship among human beings but also how human relationships affect the land.

When the author was searching to understand how the community developed this form of interaction, the traditional decision-making process enowkinwixw caught her attention. The model is accomplished with four criteria:

This word demands four things from us: 1) that we solicit the most opposing views; 2) that we seek to understand those views using non-adversarial protocols; 3) that we each agree to be willing to make adjustments in our own interests to accommodate diverse needs expressed; and 4) that we collaboratively commit to support the outcomes [Armstrong 2020: 166].

Through this process, the minority voice is valued as it could point out the most important things that have been ignored. It is how the Okanagan could bring the minority into balance with the majority, minimize the conflicts and bring everyone to work together.

If we begin to think about the minority, about why there is a minority, why there is poverty, then we should be able to find creative ways to meet the needs of the minorities [Armstrong 2020 : 167].

The author believes that this is why the Okanagan community could add preservation of land into the decision-making process. By adopting enowkinwixw, the community respects every opinion from every perspective. Therefore, they train people to speak for different components that make up their existence, such as the children, the elders, and the water; while the author herself was appointed as a land speaker, who thinks and speaks for the land. In this way, the people realize that material things are not as important as the power of the land, which is what sustains them.

This mindset is meant to help the world achieve a harmonic relationship between people and nature.

Armstrong, Jeannette, 2020, An Okanagan worldview of society, Living Earth Community: Multiple Ways of Being and Knowing, Mickey, Tucker & Grim (eds), Cambridge, UK: Open Book Publishers, 

Sélosse, Marc-André, 2000, La Symbiose : Structures et Fonctions, Rôle Écologique et Évolutif, Paris: Librairie Vuibert. (Symbiosis: Structure and Functions, Ecological and Evolutionary Role)

Wilson, E.O., 1984, Biophilia: The Human Bond with Other Species, Cambridge: Harvard University Press.

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 5 Number 1 July 2021