Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Wednesday, May 31, 2023

Analysis of a partnership

You probably recall from biology class the word symbiosis -- when two organisms share living space.  This sort of relationship can result in a fused life form where even so, the two participants retain a discernible separateness.  (Remember the Trill from Star Trek?)  The melding can go deeper, though; lichens, commonly seen growing on rocks and tree trunks in damp areas, are an example of such a composite, in this case between one or more types of fungus and photosynthetic cyanobacteria.  Deeper still are mitochondria -- the organelles in all eukaryotic cells that conduct cellular respiration and provide the majority of the energy required by the organism -- which are the descendants of single-celled aerobic bacteria that billions of years ago formed a partnership with their host cells so mutually beneficial that now, neither can live without the other.

Symbiosis is usually broken down into three broad classes.  The distinction is how the participating organisms fare.  That one of them benefits in some way is a given; if both were harmed, the relationship would be strongly selected against and probably wouldn't persist very long.  It's what happens to the other that determines what kind of symbiosis it is:
  • parasitism -- one organism benefits, the other is harmed (an example is disease-causing bacteria)
  • commensalism  -- one organism benefits, the other breaks even (such as the bacteria passively riding on our skin)
  • mutualism -- both organisms benefit (such as a good many of the bacteria in our gut, which have increasingly been found to be absolutely essential for health)
The trouble is, nothing in biology is clear-cut.  Our commensal skin bacteria occupy niches that, if they were eradicated, might be taken over by pathogenic species.  (Thus the adjuration by doctors not to overuse topical antibiotics and hand sanitizers.)  So are they actually mutualistic?  Then there are the species that help in some ways and harm in others -- or, perhaps, help one species and harm another.

This, in fact, is why the whole topic comes up today.  Scientists in New Zealand have been working to preserve endangered species on the islands.  There are quite a few, owing to the country's geological (and thus biological) isolation -- it's developed a singular group of endemic species that are uniquely vulnerable to loss of habitat from agriculture and from the introduction of exotic species like cats, pigs, and the ubiquitous sheep.  One such species is the rare Cooper's black orchid (Gastrodia cooperae), which is nearly invisible for most of the year -- the only above-ground part is a long, creeping stem -- and puts on a flower stalk once during the growing season.

[Image licensed under the Creative Commons Kathy Warburton/INaturalist (CC BY 4.0)]

Orchids are notorious for being difficult to grow from seed.  The seeds are minute, and most orchid species are extreme specialists, able to survive only in a very narrow range of conditions.  The result is that conservation efforts are fraught with difficulty.  Trying to germinate the seeds in the lab requires knowing exactly what that particular species needs, which can mean a lot of trial-and-error, and the potential loss of batches of seeds when the efforts fail.

The Cooper's black orchid is no exception.  It's so rare it was only identified in 2016, and is known to live in only three sites in New Zealand.  Fortunately for this species, there is a related orchid species, Gastrodia sesamoides, that is quite common and appears to need many of the same conditions that the Cooper's black does, so scientists have been trying to identify what those conditions are so they can be replicated in the lab.

And it turns out that one of the conditions is the presence of a symbiotic fungus -- Resinicium bicolor.  The fungus infiltrates the roots of the orchid, creating a greater surface area for nutrient and water uptake, much like the mycorrhizae familiar to organic gardeners that can increase crop yields without the addition of inorganic fertilizers.

Where it gets interesting is that Resinicium bicolor was already known to botanists -- as a plant pathogen.  It's a deadly parasite on Douglas firs, an introduced tree in New Zealand that is much used for lumber, causing "white-rot disease."

So is Resinicium a mutualist or a parasite?  The question is, "with respect to what?"  It's lethal to Douglas firs, but essential to the Cooper's black orchid (and, presumably, other native orchid species).

Biology, as I mentioned before, isn't simple.

That, of course, is why it's so endlessly fascinating.  The more we look into the complexity of the natural world, the more it brings home the truth of the quote from Albert Einstein: "Life is a great tapestry.  The individual is only an insignificant thread in an immense and miraculous pattern."


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