Symbiology

In the rural parts of Thailand, it's common to see livestock grazing in the fields surrounded by tall white egrets or, as in the photo above, with smaller birds such as these mynahs perched on their backs.

The birds are there to take advantage of easy prey; insects stirred up by the grazing buffalo as they move through the field. Local people say that the birds also eat ticks and flies which bother their cattle. This relationship between birds and grazing animals is a clear illustration of symbiosis, a habitual association between dissimilar species.

"Symbiology", the title of this post, is the study of these relationships and how they work to the benefit or detriment of the involved species.

There are several kinds of symbiotic relationships going on in the scene: with ticks clinging to the buffalo's hides to draw blood, it's parasitism. When birds catch and eat insects, that's of course predation. If the birds really do remove parasites from the buffalo, so that both benefit from the association, that's mutualism.

There's another example of symbiosis occuring in the picture, more vitally and clearly mutualistic than that between the buffalo and birds, but it's happening out of sight, hidden away in the gurgling guts of the buffalo. Ruminants are able to eat and digest grass and other high-cellulose plant material only through the fermenting action of symbiotic microorganisms living in their digestive systems.  Grazing animals provide habitat and a steady supply of fodder for their tiny symbionts while the bacteria break down cellulose to provide nutrition for the host animal.

Early interpretations of evolutionary theory tended to emphasize  competition for survival between individual organisms and between species; "the struggle for existence" (Darwin). While competition is an important factor in evolution, it's not the whole story. More recently, there has been a shift toward acknowledging the importance of symbiotic coevolution of species with cooperation providing key adaptive advantages for most species.

I remember learning about symbiosis as a child in school; how plants give off oxygen that animals need and then animals exhale carbon dioxide that plants need. Pretty neat, I thought.

Black Bee foraging in our garden.

Mutually beneficial associations between larger plants and animals are relatively easy to see and to study. It is well known, for example, that flowering plants display their reproductive organs in attractive blossoms with a reward of sugar deep within. Insects, just going about the business of survival and searching for food, pick up pollen and carry it to other blossoms, aiding in the cross-fertilization of the plant. Clearly, flowering plants and flying insects co-evolved in such a way as to benefit each other.

When frugivorous  birds and animals eat the tasty nutritious fruit produced by plants, they are not harming the plants at all. That's exactly what the fruit is for because in this way the plant seeds are carried away and dispersed in a nice deposit of fecal fertilizer, enabling the species to propagate itself at some distance from the parent plant.



Life is solar powered. The sun is the primary source of energy for nearly every form of life on earth. Only photosynthetic organisms, though, can use the sun's radiant energy directly to synthesize chemically reactive organic compounds (carbohydrates). Chloroplasts are the tiny organelles in plant cells that enable photosynthesis.    

Electron Microscope Image of Chloroplasts 

These chloroplasts have been found to contain their own DNA, separate and different from the DNA of the plant, suggesting that this is an example of an ancient symbiotic relationship between a host microorganism and cyanobacteria which found a way to survive and reproduce within it.

Plants lift the chloroplasts in their leaves toward the sun and the chloroplasts feed the plant with carbohydrates that build plant structure.

Animals obtain energy from the sun indirectly by eating plant matter (or other animals). In animal cells (including human, of course), organelles called mitochondria provide energy through a process called cellular respiration.  These organelles appear to be another example of ancient symbiosis whereby bacteria capable of respiration found a home in a host cell that was not. This was an association that proved advantageous for both organisms.

If we look into life in the soil, again the more readily apparent organisms such as termites and earthworms are fairly well known.  Earthworms eat dead plant matter in the soil, leaving castings which are rich fertilizer for local plants; another mutually beneficial arrangement.

Compost with "Effective Microorganisms"

The soil is alive with microorganisms much too small to be ordinarily seen but which comprise most of the soil biomass. These fungi, bacteria etc. perform vital ecosystem  services, breaking down dead plant matter and releasing nutrients for further use.
 

One extremely important instance of symbiosis has to do with nitrogen, an element fundamental to life on all levels. Nitrogen is a necessary component of all structural cell proteins, regulatory enzymes, and of nucleic acids (DNA/RNA).
Nitrogen is plentiful in the atmosphere in a relatively non-reactive form (N2) which cannot be used by plants or animals. Nature has evolved a way around this obstacle in the form of nitrogen fixing microorganisms which transform N2 into ammonium compounds. Before the advent of synthetic fertilizers nearly all the nitrogen in the cells of living organisms was supplied by these bacteria.

Rhyzobium nodules  (our garden)

In terrestrial ecosystems, rhyzobium bacteria living in nodes on the roots of leguminous plants perform a vital service in taking nitrogen from the air and making it available to plants  and, through plants, to animals.

 

The industrial approach to providing for human needs, both basic and perceived, is an experiment still in progress.  Early successes were impressive enough that zealotry to imitate the developed "west" is strong throughout the world. While industrial development does provide superficial security, comfort and pleasure, the questionable benefits and punishing costs of all this are only recently coming to light.

Desertification and famine is a heavy price to pay for excessive consumption but it has been paid before and will be paid again. Deforestation and overgrazing disrupts the hydrological cycle, causes  drought and soil erosion, reducing the carrying capacity of any given ecosystem. This pattern has brought about the collapse of societies and civilizations before our modern era. Earth is a limited ecosystem.

Industrial food production might justly be termed "petrochemical agriculture".  Inputs such as synthetic fertilizer, pesticides, and fuel for mechanized cultivation, harvesting and transportation, are all derived from oil and gas.
Over time, their use destroys the life processes in the soil which are vital for plant health.  The resulting plants are sick and addicted, needing ever more of these inputs to produce even nutritionally depleted outputs. The precarious dependence on affordable petrochemicals to feed us is a foolish gamble.

Like the buffalo in the picture at the head of this entry, and as with all animals, we humans too, provide habitat to teeming populations of microflora in our digestive tracts which supply us with numerous nutrients and other healthful benefits that researchers are currently busy discovering.  Ever increasing evidence links chronic diseases of developed societies; obesity, depression/anxiety, autoimmune disorders, metabolic syndrome, cancer, etc., with disturbed microbial ecology, chiefly in the lower intestine.  It turns out that many factors of life in industrial societies ( refined foods, antibiotics, antiseptic cleaners, etc ) reduce the biodiversity of the human biome to the detriment of our health.

Ecological insight is a relatively new way of understanding the world and our place in it. I believe it carries unbounded potential to revolutionize our attitude to life.