Thursday, March 29, 2012

Life in the Extremes

Extreme places I have gone,
But never seen any light.
      ~ lyrics from Extreme Ways by Moby

I have become inured to the news story, breathlessly delivered, about some organism found living in an extreme environment where life is “totally unexpected.”  It now seems to me that life, usually, will find a way.

Over the past few years, we have discovered organisms surviving, indeed, prospering in such extreme places as the mouth of hot geysers at Yellowstone National Park, the water of Spain’s Rio Tinto which is heavily acidic and polluted with heavy metals and other toxins, or the bottom of a lake in Antarctica where cold temperatures are married to a lack of oxygen.  These creatures are the extremophiles, forms of life (typically microbes) that have evolved the means of living under what we would consider rather inhospitable conditions.

The reach of extremophiles into such places is broad; consider the following list of names, drawn from the Microbial Life Education Resources website, for those organisms living or experiencing optimal growth under specific kinds of extreme conditions (the nature of those conditions is noted in parentheses):

* acidophiles (high acidity levels)
* alkaliphiles (high alkaline levels)
* anaerobes (no oxygen) {includes facultative anaerobes (live with or without oxygen present) and
                                             obligate anaerobes (cannot grow in presence of oxygen)
* endoliths (within rocks)
* halophiles (high salinity)
* methanogens (anoxic or low oxygen environments – these are methane-producing organisms)
* oligotrophs (limited available nutrition)
* piezophiles or barophiles (high pressure)
* psychrophiles (low temperature – 15ºC or lower)
* thermophiles (high temperature – 40ºC or higher)
* hyperthermophiles (extremely high temperature – 80ºC or higher)
* toxitolerants (high levels of toxic waste)
* xerophiles (little available water)

“We know that we are only scratching the surface of what is out there,” asserts biologist Kenneth Stedman of Portland State University’s Center for Life in Extreme Environments.  (John Roach, “Miracle” Microbes Thrive at Earth’s Extremes, National Geographic News, September 17, 2004.)

The proximate spark for this posting is the piece that ran in early March on the PBS NewsHour about researchers from Oregon State University finding life in yet another hostile, extreme place – farmers’ fields in Oregon’s Willamette Valley.

Okay, it’s not the place that was intended to be surprising, rather it's the combination of place and life form – fish.  Perhaps the true surprises were the complex, though temporary, ecosystems in the farmers' fields supporting spawning fish, immature fish, amphibians, and myriad invertebrates.  (Oregon Farmers Surprised to Find Fish in Fields, PBS NewsHour, March 8, 2012.)

For more than a century and a half, efforts have been made to mitigate seasonal flooding in the Willamette Valley, which is a river flood plain.  Wetlands have been filled, stream channels diverted, and acres of the flood plain that once connected to the Willamette River have been lost.  Still, winter flooding occurs in these fields on an annual basis, reestablishing seasonal wetlands.  Water fills the ditches that cross the fields, linking the fields with seasonal streams that ultimately feed into the river.  (L.A. Wyss, et al., Grass Seed Agriculture and Invertebrate Communities of Seasonal Wetlands in the Southern Willamette Valley, Seed Production Research at Oregon State University.  2010-Ext/CrS 130, 3/11.)  Significantly, a substantial portion of the agriculture involved is grass seed production; nearly all of Oregon’s grass seed is grown in this valley.  Those farms growing perennial grass seeds till their fields with reduced frequency, much to the advantage of the fish “hatcheries,” compared to fields growing annual varieties which are tilled every year.

The diversity of fish species (some 13 in all) found by Oregon State University researchers in the waterways in these fields from the fall to the spring is striking, particularly given that nearly all are native to Oregon.  This suggests that these fields may play a key role in sustaining native fish, providing them with relief from the non-natives and a sanctuary in which to spawn.  Among the native species found here are rainbow trout, cutthroat trout, and Chinook salmon.  (G.R. Giannico, et al., Fish and Amphibian Use of Intermittent Agricultural Waterways in the South Willamette Valley, Oregon Seed Extension Research Program, Seed Production Research Report 2005.)

During summer these ditches are dry, the fish have worked their way to the river, and these seasonal ecosystems are gone . . . until the next wet months.

This NewsHour story would have garnered just a passing “that’s interesting” from me were it not that the piece makes specific mention of an invertebrate inhabitant of those ecosystems.  That was the hook for me – not the fish or the combination of fish and farmers’ fields.  One of my favorite invertebrates is an important member of those ecosystems and it gets about three seconds of fame beginning at 4:13 of the video.  At that moment, two of the researchers are examining some of the various invertebrates in a flooded ditch.  One says, “Oh, man, there’s a lot of ostracods.”  The other replies, “Oh, beautiful.”

That’s a wonderfully apt response when coming upon ostracodes (I’ll get to the differences in spelling in a moment), and one that I’ve voiced aloud often during countless hours spent peering through a microscope on the hunt for their fossilized shells (I’ll get to the fossil record in a moment as well).

These shrimp-like creatures are crustaceans, members of their own Class, the Ostracoda.  I have seen estimates of between 20,000 and 25,000 extant species.  (These estimates, possibly high, appear in two of the sources cited below – the chapter Ostracoda by Anne Cohen, et al., and the Preface by Noriyki Ikeya, et al.)  They live within two shells and usually don’t exceed two millimeters in length, often coming in at under half a millimeter.  The shells, frequently oval or almond shaped, are shed periodically as the animal grows to maturity.  The variety in shell ornamentation is remarkable.  The shell surfaces of some ostracodes are elaborately ornate with ridges, knobs, and grooves, some sport protrusions like wings, others are plain and smooth.  Among the Ostracoda are scavengers, herbivores, predators, and suspension feeders.

Ostracodes appear in a variety of YouTube videos.  A particularly informative one can be found here.  It shows the shell arrangement of some of these animals (fresh water ostracodes, I believe), their mode of locomotion, and variety of sizes (juveniles and adults appear).  The shells of these particular ostracodes are relatively plain.

To get a sense of the intricate patterns that may appear on ostracode shells, here are pictures of shells of extant marine species from the Atlantic Ocean.  (These were downloaded from the Smithsonian Institution and used under the terms of copyright “fair use” as defined by the Smithsonian.)  The first is of Henryhowella cf. asperrima; the second is of Cytheropteron perlaria.  (In terms of size, the first shell shown is 200 microns (μm) or 0.2 millimeters.  The second is even smaller.  A micron is one millionth of a meter or a thousandth of a millimeter.  An inch equals 25,400 microns.)

One of the most distinguishing attributes of these organisms is their ubiquity in water.
They are found today in almost all aquatic environments including hot springs, caves, within the water table, semi-terrestrial environments, in both fresh and marine waters, within the water column as well as on (and in) the substrate.  In fact almost anywhere that’s wet, even if only for a brief period!
This quotation is from Ostracods, found on the Microfossil Image Recovery And Circulation for Learning and Education (MIRACLE) website of the University College London’s Micropalaeontology Unit.  Other basic information about ostracodes can be found in various sources on the web, including Anne C. Cohen, et al., in their chapter Ostracoda in The Light & Smith Manual:  Intertidal Invertebrates from Central California to Oregon (edited by James T. Carlton, 2007).

After this digression regarding sources, I suppose it’s appropriate to address the spelling (and pronunciation) issue.  Ostracode or ostracod?  Either will do.  The scientists managing the listserv for the International Research Group on Ostracoda, a list for the exchange of research on Ostracoda, made it clear that both spellings of the “vernacular” name would be acceptable on the list (“and any others your keyboard may happen to substitute”), though they admit they prefer ostracode.  They really wanted to forestall any replay of the “bitter controversy” over the spelling – “We are as unlikely to settle the issue as we are to unite all religions and stamp out all disease.”  That said, when it’s in my control, I use ostracode.

In the fossil record, ostracodes are known by their shells from the Ordovician – over 450 million years of fossil evidence – not too shabby.  Fossil shells from ostracode-like animals go back even further.  One source asserts that “[o]stracods have the best fossil record any arthropod group,” and that includes the trilobites.  Not surprisingly, given how long they’ve been around, the number of ostracode species that have been identified in the fossil record greatly exceeds the number of extant species.  (Noriyki Ikeya, et al., Preface:  The phylogeny, fossil record and ecological diversity of ostracod crustaceans, in Evolution and Diversity of Ostracoda, Hydobiologia, 2005, p. xi.)  As paleontologist Donald Prothero notes, “A small sample of almost any Phanerozoic [the eon from the Precambrian to the present] biogenic sediment yields ostracodes in abundance.”  (Bringing Fossils to Life:  An Introduction of Paleobiology, 1998, p. 267.)

No question about it, ostracodes are survivors.  Their history is long and their reach is broad.

And fossil ostracode shells are beautiful.  To suggest some of their beauty as fossils, here is a photograph of a Cretaceous fossil ostracode shell, Cythereis ornatissima.  (As with the previous pictures, this one was downloaded from the Smithsonian website.)

I draw some of the fossil ostracodes I find.  As I do, my appreciation for the intricacy of some of the shell surfaces only increases.  This Cretaceous ostracode is a case in point; it’s Fissocarinocythere pidgeoni.

I’ll conclude with a question triggered by NewsHour piece about fish and farming in the Willamette Valley.
How do the ostracodes return each year to the seasonal wetlands and farmers’ ditches in the Willamette Valley?
This question doesn't include any sense of surprise that they do return – never be surprised by these little survivors.  Rather, it just reflects an interest in the means they use in this instance.  Perhaps the species found darting in these watery environments (and helping to feed the fish) are those whose eggs dry out when water goes, only to be revived and hatch when water returns.  I think it unlikely the animals can swim the necessary distance on their own, but, perhaps the force of the water flowing into and out of the fields is sufficient to carry the juvenile and mature ostracodes back and forth.  Prothero’s description of ostracodes suggests a couple of additional, possible methods ostracodes might use to populate the fields.  “Although they cannot fly, freshwater ostracodes can disperse through the air when their tiny eggs are carried in the mud stuck to the feet of birds, or [are] blown from pond to pond.”  (Bringing Fossils to Life, p. 267.)

A pretty neat little critter.

From the plethora of extremophiles to the abundance of ostracodes occupying nearly all watery niches, it's  hard to escape the conclusion that life usually does manage to make an appearance.

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