JIM CONRAD'S
NATURALIST NEWSLETTER
Issued from the valley of the Dry Frio River on the
southern slope of the Edwards Plateau, northern
Uvalde County, southwestern Texas, USA

February 24, 2013

COTTONTAIL MYSTERY SOLVED
In this area at dusk and dawn you see large Black-tailed Jackrabbits as well as much smaller cottontails. I've tried many times to photograph the cottontails but in such dim light it's been impossible to get a good picture. However, this week a bit before dusk a cottontail streaked across the road, then froze beneath an Ashe Juniper a stone-toss away, apparently thinking his camouflage made him invisible. You can see him at http://www.backyardnature.net/n/13/130224ct.jpg.

A rear view -- the black patch on the back apparently being a wound -- is at http://www.backyardnature.net/n/13/130224cu.jpg.

I've wanted a picture because in this part of the world we have two very similar cottontail species and I've not been sure which one is so abundant around the cabin. Now with such fine views I'm pretty sure I know: The pictures show a Desert Cottontail, SYLVILAGUS AUDUBONII. The other cottontail species also occuring here is the Eastern Cottontail, Sylvilagus floridanus, the common cottontail of eastern North America. Our Desert Cottontail differs from the Eastern in that its ears are relatively larger, and our environment is more like what's described for the Desert Cottontail than for the Eastern.

In western Kansas the two cottontail species' distributions similarly overlap. A University of Kansas webpage says that "The desert cottontail is difficult to distinguish externally from the eastern cottontail, but is paler, and has longer and more thinly haired ears. Its upperparts are pale grayish brown heavily lined with black and with some yellow."

It continues, "Desert cottontails are usually found in dry, open upland habitats, whereas eastern cottontails in the same areas of western Kansas are restricted to riparian thickets along streams."

Desert Cottontails are distributed throughout much of western North America, from Montana and northern California south into the arid parts of south-central Mexico. Here we're close to their eastern boundary.

Each morning a little before dawn I jog by a neighbor's house where numerous dogs perpetually bark and chase whomever passes down the road. The neighbors also set rabbit traps for rabbit stew, though mostly they trap only their own dogs. The amazing thing is that every morning several cottontails can be seen grazing the grass lawn there and along the road, peacefully coexisting with these hysterical, neurotic dogs.

*****

SACHEM
The other day I placed the potted Calendulas outside and within a few minutes a skipper butterfly had landed on a flower, as shown at http://www.backyardnature.net/n/13/130224sk.jpg.

Volunteer butterfly identifier Bea in Ontario confirms that it's the Sachem, ATALOPEDES CAMPESTRIS, which we've met many times. The Sachem is a good species with which to start off the new season of adding species to our Selected Butterflies of Uvalde County Page, which already has a handsome selection of photos from last year, as shown at http://www.backyardnature.net/n/a/uvalde/.

Sachems are found throughout the US southern states from coast to coast, and in late summer it migrates into the northern states. It also extends southward through Mexico and Central America to Brazil in South America. Over most of its range it's one of the most common, conspicuous and attention-getting of all skippers.

Besides being so common, one way Sachems draw our attention is that they are so big-headed and thick-bodied that we're surprised to see that with such small wings they can fly so robustly. Those robust flights are another reason to notice them, because during most of the day males perch on or near the ground, often in conspicuous spots, waiting for females to fly by. When a female does zip past, a swirling mid-air commotion takes place as they figure out if they're meant for one another.

One reason Sachems are so common is that their caterpillars feed on grasses, including grass species benefiting from human disruption of the landscape, such as crabgrass, Bermuda grass, St. Augustine and Goosegrass. Adults also take nectar from many kinds of common flowers, from milkweeds and peppermint to clover and marigolds. As might be expected of such a dynamic, aggressive species, it appears to be expanding its distribution northward, maybe as a response to global warming.

The name Sachem is based on similar-sounding terms used to signify chiefs or leading people in tribes of several northeastern American indigenous people.

*****

WATER BEARS
During this week's microscopic expedition into a drop of water from the little Dry Frio River behind the cabin I came to a part of the slide upon which a diffuse gob of mushy, decaying plant material lay, in which were found the slow-moving critters shown at http://www.backyardnature.net/n/13/130224br.jpg.

Compared to other organisms on the slide, these were fairly large, seen here at my lowest magnification. The largest of the three shown is about one millimeter long (3/32nd inch). Keeping in mind that we're looking down on the tops of the two individuals at the top of the image, notice that the largest one's rear end is deeply divided. The small one in the picture's lower left is on its side, showing leg-like structures on its belly side. In short, these tiny creatures appear to be structured very much like the thumb-sized, juicy caterpillars found in the summer munching on tree leaves or garden tomato plants. Could such small, aquatic organisms be the caterpillar stage of an insect?

I'm glad I didn't have to wrestle with that question because I might have wasted lots of time trying to figure out which insect species produce such caterpillars. Instead, because they're so unlike the daphnia, rotifers and other microorganisms we usually see, and because they have such a cute name, I remembered from my student days that these little beings are called water bears or sometimes moss piglets. More technically they're referred to as tardigrades.

That's interesting because all by themselves tardigrades constitute a whole phylum of the Animal Kingdom. Phyla are top-level taxonomic divisions right below kingdom, so we're dealing with a whole other kind of animal than normally we see or hear about. Our little water bears have nothing to do with insect caterpillars. Despite their uniqueness, water bears are exceedingly common, occurring in many marine, freshwater, and semiaquatic terrestrial environments worldwide. In the submerged, decaying vegetative ooze ours inhabited they were doing the job of breaking down organic matter into simpler components to be made available to less complex organisms.

Science finds tardigrades especially interesting because as a group they are one of the most complex of all known organisms known as "polyextremophiles." Extremophiles, without the "poly" prefix, are organisms capable of thriving in extreme physical and/or chemical condition. Polyextremophile such as water bears can thrive in a variety of extreme conditions. For example, certain tardigrades can withstand temperatures ranging from just above absolute zero to well above the boiling point of water. They can survive pressures greater than that in the deepest ocean trenches and have survived the vacuum of outer space. They survive solar radiation, gamma radiation and ionic radiation at doses hundreds of times higher than would kill a human. They can go without food or water for nearly 10 years, drying to the point where they are 3% or less water, but then rehydrate, forage, and reproduce.

Something else curious about tardigrades is that they are "eutelic," which means that all adult tardigrades of the same species possess the same number of cells. Some species have as many as 40,000 cells in each adult, while others have far fewer.

To me it seems that tardigrades are so exotic that they might as well be from some other planet. However, they've been on Earth for a long time, with fossils showing up from the Cambrian of some 500,000,000 years ago. In fact, some specialists regard tardigrades as ancestors of arthropods, which includes everything from insects and spiders to shrimp and barnacles. In a sense, then, when we see water bears lumbering across stems of aquatic milfoil, we're witnessing a scene from the distant, distant past.

*****

AGARITA FLOWERING
A very common head-high, much branched, woody shrub in this area is one the ranchers don't like because its silvery-green, trifoliate leaves are so tough and spiny-margined that they can't be eaten by cattle -- even deer don't much care for them. You can see a typical one in a natural prairie opening in the woods, surrounded by Little Bluestem grass, at http://www.backyardnature.net/n/13/130224bb.jpg.

For about a month clusters of small, reddish flower buds have been enlarging along the woody stems, and this week some of the buds on plants in sheltered spots with a southern exposure released their flowers, as shown at http://www.backyardnature.net/n/13/130224bc.jpg.

This is such a conspicuous shrub in our landscape that among English speakers it goes by several mostly Spanish names, including Agarita, Agarito, Algerita, Agritos, Currant-of-Texas, Wild Currant, and Chaparral Berry. It's BERBERIS TRIFOLIOLATA. The name Agarita surely is based on the Spanish verb agarrar, which means "to grab." The ending "-ita" is added to little things, to the Agarita "grabs a little," which might be said of a brush with scratchy but not very dangerous spines.

Agarita is a member of the Barberry Family, the Berberidaceae. In North America the Barberry Family is mostly known among wildflower admirers for its spring wildflowers, the May-Apple and Twinleaf, and among gardeners for such handsome ornamentals as the Nandina and barberries. Some authorities place Agarita in the genus Mahonia, but not the Flora of North America.

Walking down the road on a sunny day the sweet aroma of their half-inch-wide flowers is wonderful, like warm honey. Bees love them. The blossoms have six sepals and six petals, which is a little unusual for a dicot. Normally flowers with parts in multiples of three are monocots, such as the lilies and irises. However, the Barberry Family is a smallish one, so unusual flower features might be expected. You can see a freshly opened blossom with widely spreading sepals but with its corolla not yet fully expanded at http://www.backyardnature.net/n/13/130224bd.jpg.

A view into a blossom showing more atypical features is at http://www.backyardnature.net/n/13/130224be.jpg.

Few flowers possess such huge stigmas atop their ovaries -- stigmas being the female parts where pollen grains germinate. You can see that the ovary also is plumply oval. But what really is striking is how the six stamens are T-shaped, each arm of the Ts being one of the bags, or "valves," of the pollen-producing anther. You can see how yellow, sticky pollen adheres to the valves. Another unusual feature of anthers in the genus Berberis is that they are "irritable." When an insect leg or other object disturbs a ripe, unopened anther valve, the valve responds by releasing its pollen.

Agarita, like other barberry species, is susceptible to infection by Puccinia graminis, which is a fungus causing the Stem Rust disease of such agriculturally important Grass Family members as wheat, barley and triticale. A feature of the life cycle of Puccinia graminis is that it features "alternation of generations," which means that during part of its life it lives on grass species, and the other part on an entirely different species, in this case barberry plants such as Agarita. In some places where wheat, barley and triticale are grown people root out every barberry they can find, hoping to diminish their problems with Stem Rust. Here we're too arid for those crops so, fortunately for Agarita and us who are glad to have Agarita in the neighborhood, there is no such effort.

Agarita's red, pea-sized fruits are described as good tasting, though it's a pain to pick them through all those spiny leaves. Quail and other small mammals use the spiny plant for cover.

Agarita inhabits rocky, limestone soil in most of Texas, southern New Mexico, a tiny bit of Arizona, and much of arid northern Mexico.

*****

BLACK PIT LICHEN
Along the little Dry Frio River running behind the cabin, here and there horizontal beds of limestone outcrop. Sometimes the limestone's surface is smooth and flat but other times it's very roughly pitted. That's because different geological formations are involved, and each formation reacts differently to physical and chemical erosion. Often in small cavities of pitted limestone a certain black, crustose lichen can be found, as shown at http://www.backyardnature.net/n/13/130224ln.jpg.

An even more roughly pitted surface with pits lined with black lichen is shown at http://www.backyardnature.net/n/13/130224lo.jpg.

Anatomically, there's not much to this lichen. Spore-producing, bowl-like apothecia such as those seen on all the lichens we've looked at so far are missing in this species. Its spores are produced in microscopic cavities called perithecia, which are mostly to entirely sunken into the lichen's body, or thallus. Up close you see that the lichen surface fragments into irregular little islands, and that the thallus constituting each island's surface is very warty, as shown at http://www.backyardnature.net/n/13/130224lp.jpg.

Beneath the dissecting scope there's still not much to see, other than that the "warts" sometimes sprout rootlike appendages that snake out onto the naked limestone, as seen at http://www.backyardnature.net/n/13/130224lq.jpg.

Using the "Dynamic Key" at http://lichenportal.org to make a list of species it might possibly be, then on the Internet comparing our pictures with other pictures of each species, my best bet is that our black, limestone-loving, pit-living lichen is VERRUCARIA NIGRESCENS, which doesn't seem to have a common English name. However, I've seen the name Black Pit Lichen applied to certain Verrucaria species, and that name seems so appropriate for this species that that's the English name I'll begin using. Fact is, the genus Verrucaria contains numerous species, they're very hard to distinguish, and even lichenologists are uncertain how to classify the species, so Verrucaria nigrescens is just an educated guess.

Verrucaria nigrescens is described as living on limestone, walls and mortar, and occasionally on siliceous rocks (like sandstone) in western Eurasia, China, North Africa, North America, and Australia.

Verrucaria species in general help break down limestone rocks by secreting acids that dissolve cement holding together the rock particles. This produces an environment -- the pits -- in which mosses and higher plants eventually take root. This process is slow. A study in Estonia found that it took about 34 years for an average colony of Verrucaria nigrescens to grow 35mm (1-3/8ths inch). I would guess that to form pits such as those in our pictures, centuries if not millennia are required.

*****

CESSPIT GEOLOGY
Each day I do enough physical labor to keep my body exercised and my hands callused. During recent weeks I've been digging trenches and pits with pick, shovel and iron bar for a building. Recently I've been excavating a cesspit. You can see me standing in my masterpiece at http://www.backyardnature.net/n/13/130224gr.jpg.

Digging that pit exposed interesting insights into the location's geology.

First of all, I knew that I was digging into the geological unit known as the Glen Rose Formation, thanks the Geologic Atlas of Texas, San Antonio sheet - 1982, freely accessible online -- along with hundreds of other such publications covering all of the US -- from the US Geological Survey at http://ngmdb.usgs.gov/Prodesc/proddesc_19384.htm.

A portion of the map available on the above page shows my digging location -- designated by the greenhouse icon in the center of the page -- in the Glen Rose at http://www.backyardnature.net/n/13/130224.gif.

Knowing what formation I was working in, I could look up "Glen Rose Formation" on the Internet, where I learned that I was digging through material deposited 108-113 millions of years ago, during the Early Cretaceous when dinosaurs roamed the area. Glen Rose material consists mostly of various forms of limestone, but also there are layers of quartz siltstone, sandstone, marl, dolomite and other rock types. There's more about the Glen Rose Formation than a person can digest at http://www.northtexasfossils.com/glenrose2.htm.

In the cesspit, the deeper you go, the older the rocks become. That's just how sedimentary geology works, with newer material being piled atop older. Sometimes faulting and other violent forces flips rock strata upside-down or shoves younger rocks below older ones, but that hasn't happened in our area.

Mostly from fossil findings, Glen Rose strata are known to have been deposited in a "transitional marine" environment -- the zone between open ocean and shore. Consequently, digging through the Glen Rose you pass through material ranging from that deposited in deep ocean water, to beach sand in which dinosaur footprints might be found.

In the picture of me in the cesspit, in the bottom of the pit the brownish stratum with white splotches is sand in which white balls of clay are suspended. Sand normally gathers in beach and shallow water environments where relatively strong water currents can carry the sand there, and clay usually settles in quiet waters such as in lake bottoms, so somehow material from two distinct sources was mingled and deposited by floodwaters. Various scenarios enabling such a layer can imagined. Conceivably a hurricane or tsunami ripped away not only a sandy beach but also the clay platform it lay upon, mingled the contents, and dumped them where I'm standing, though that spot would have been underwater then.

Above the sand with white mudballs you see a layer of solid, white limestone, suggesting that after sand and mudballs were deposited, for a long time the area where I'm standing was under deep ocean water where fine-textured mud settled to the ocean bottom eventually to lithify into the limestone. Such mud very largely consists of microscopic organisms encased in calcium-rich shells.

This long period of mud accumulation eventually was interrupted by some kind of catastrophic event powerful enough to mingle fairly large broken fragments of shattered limestone rock with silt to form the layer even with my shoulders in the picture. That layer looks like the contents of a landslide and one can only imagine what event put such a shattered mix of rocks and silt there.

Above the jumble of large rocks and silt there's the typical dark soil our woods and prairies root in, the results of mere centuries, not millions of years, of complex soil chemistry and biology.

Really, there in the cesspit looking at the geological profile around me, I felt as if I were in a museum where only the most majestic of the Earth's activities are referenced.

*****

FEATURED ESSAYS FROM THE PAST:

"Sparrow Colors," from the February 16, 2003 Newsletter, at http://www.backyardnature.net/n/p/030216.htm.

"Sparrow Tao," from the January 31, 2010 Newsletter, at http://www.backyardnature.net/n/p/100131.htm.

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.

Visit Jim's backyard nature site at http://www.backyardnature.net