The Pioneers: Archaea and Bacteria

phylogenetic tree wikipedia

Animals and Plants, in the upper right corner, no longer headline the Tree of Life.         (Wikipedia)

The most basic categories of living things are not what they used to be. In the past they included Plants and Animals, but no longer. Today the three Domains are all named for organisms too small to see. Plants and Animals, including humans, have become small print within a Domain called Eukaryotes (you-CARRY-oats), meaning cells with a nucleus.

A second Domain is Bacteria. The third is the Archaea. Not sure how to pronounce Archaea? I wasn’t either. It’s AR-kee-ah or ar-KY-a; both are acceptable. That noun is plural; the singular is AR-kee-on, an Archaeon, sounding faintly of Star Wars.

Archaea are like Bacteria in that they have no nucleus and are simpler, smaller and older than Eukaryote cells. So how are these Archaea so different from Bacteria that they get their own Domain? Biologist Carl Woese in 1977 argued successfully they are indeed a different form of life. I’ll describe a few features that Archaea and Bacteria have in common and then others that seem unique to Archaea.

Both Archaea and Bacteria are small, unstructured, and simple compared to the Eukaryotes that evolved. But one achievement they both share has been to try out nearly every possible chemical or environmental source to get their energy. Sunshine, salty water, temperatures ranging from volcanic to polar, even radioactive settings—varieties of Bacteria and especially Archaea have found ways to draw energy from, and live off of, these and other environments.

Another similarity is that Archaea and Bacteria don’t reproduce sexually; two cells don’t mingle their genes to form a new individual. Instead, individual cells just multiply their insides by two and then divide to form identical daughter cells. To put some variety into their DNA, they both use a technique other than reproduction. A Bacterium or Archaeon can pump some of its DNA into another cell. Or a cell can just pick up a bit of DNA floating near it. No merging, just some sharing. This gene-sharing is called lateral gene transfer. It is important to know about.

archaea hot springs yellowstone nationa park (earth-chronicles.com)

Archaea at home in a Yellowstone hot spring.       (earth-chronicles.com)

For starters, gene sharing is one reason that antibiotic-resistant bacteria in hospitals can spread their immunity to other bacteria so quickly. And gene sharing  doesn’t have to take place between members of the same species, as sexual reproduction usually does. Instead, DNA can be transferred from any species of Bacterium or Archaeon to any other species within the same Domain if the conditions are right.

If plants and animals could carry on such gene swapping, the mind boggles. Squirrels could transfer some of their DNA over to dandelions. Or vice-versa. Such promiscuity helps explain how Bacteria and Archaea have evolved so many different ways to live in extreme environments, as well as so many different colors.

But Archaea are also distinct from Bacteria in notable ways:

  • Archaea were first discovered in extreme settings where even Bacteria fear to tread: geysers, intensely salty water, even thermal vents at 251 degrees F, the hottest place any organism has been found living.
  • Another feature is that, while some varieties of both Archaea and Bacteria get their energy from light, Archaea do it their own way, through a process unrelated to the photosynthesis going on around us in plants. Importantly, too, only Archaea produce methane, essential to organic decomposition.
  • Finally, while many Bacteria can make us sick—Lyme, Cholera, Syphilis—Archaea may be nicer: No pathogenic Archaea have been discovered––so far.

Archaea and Bacteria had the Earth to themselves for over a billion years. Then about two billion years ago, Eukaryotes appeared, evolving from their single-celled predecessor but larger and internally more developed. By then, Archaea, like Bacteria, had carried out much of the groundwork for living, pioneering what it takes to survive in different conditions, experimenting with energy sources, trying out each other’s genetic parts.

And they succeeded. They didn’t fade away after the sophisticated Eukaryotes began evolving into countless large species like us. Today, their total mass is right up there with all the plants and animals combined. Humans each carry around a few pounds of them.  They got the basics right. We are among the beneficiaries.

What Birds Are Saying

Sitting on a wood piling at a marina, a motionless Herring Gull stared out over the boats. Humans strolled by on one side of him (?), boats purred by on the other.

High overhead, two other gulls appeared, flying lazily toward the ocean. Without looking up at all as far as I could tell, the Herring Gull squatted slightly, thrust its neck downwards and its head upwards, and let out several very loud, prolonged squawks, then resumed his silence. The other gulls, if they noticed, didn’t show it.

I was surprised that the Herring Gull was unfazed by the people and boats moving close by but reacted loudly to the two others far above. Was he saying “Beat it”? Or “Hey, good lookin'”? Or did the other gulls have nothing to do with his alarm?

Herring Bull (Wikimedia Commons)

Wikimedia Commons

Judging partly from the gull’s hunkered position, I thought at first that I had heard the Herring Gull’s “choking call,” an emphatic defense best rendered as “No, I’m not moving!” But after more googling, I wasn’t so sure. The call could have been the familiar “long call” of gulls, a series of raucous, trumpeted yawks that assert their territory.

But gulls don’t ever really “sing.” Most of the singers among birds, the makers of trilled, often complex melodies, are closer to home. The Robins, Sparrows, Wrens, Cardinals, Mockingbirds, and other backyard birds that perch on branches and at feeders, hop on the ground, and take flight together are among the maestros. With a vocal organ, the syrinx, that divides where the windpipe forks into the lungs, song birds can produce rapid trills and even two notes at the same time.

Debbie Ackerman in The Genius of Birds (2017) describes the difference between calls and songs. Calls “are typically short, simple, succinct, and innate (like a human scream or laughter), uttered by both sexes to make their point.” Perching birds call to “warn of predators and to identify family, friends, and foes. [Males also] sing to defend their territory—to stake it out or fence it in—and to woo a mate” (141).

The Britannica adds this:

Bird song is best considered the vocalization that is used in courtship and breeding, chiefly by the male, to advertise that he is ready to mate, to attract the female and perhaps stimulate her sexually, to keep the pair together, and to inform rival males that he has established a territory from which they will be excluded. The male’s call are also part of a threat display that take the place of actual combat in repelling intruding rivals. (“Songbird”)

I’ve wondered about the connections between the modest size of such birds, their vocal skills, their perching, and their reproductive success. As a a sophisticated instrument for social communication, their songs may have made them fitter for the flying, flocking, and perching life.  I suspect the subtexts of their singing are as untranslatable as the nuances of human song and conversation.

In any event, their combination of size, sociability, and song has flourished: Today the perching birds number more than half of the 200 to 400 billion individual birds worldwide, and their 5,000 species account for more than all other bird species combined. Not bad for feathery successors of the dinosaurs.*

Wren singing (Wikimedia comm)

Wikimedia Commons

I’m reminded that no type of organism alive now, including ours, has come down from its start as a fixed package of parts and abilities. We living things are the history of our changing survival strategies. Gulls, insects, flowers, trees, apes, humans––we are works in progress, ongoing creations. While we are alive, we are only the current versions.

 

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*Cheery little birds descended from dinosaurs! Ackerman puts her finger on some similarities:

It’s easy to catch the reptilian in birds. You can see it in their beady eyes and quick darting movements; in the pterodactyl-like wings of a rhinoceros hornbill; in a robin holding up his head in frozen alertness to catch a sound, his expressionless face remindful of a lizard’s; or in a great blue heron—the slow heavy wing beat, the snaky finesses of its neck, the hoarse squawks, are all a throwback to dinosaur lagoons. But it baffles the imagination to think that the tiny flashlike chickadee could have arisen from the big beasts of vanished ages. (45)

In addition to sources mentioned, Wikipedia, Quora,  Earbirding, and Cornell University’s All About Birds have been useful sources.