Tag Archives: science writing

The wise trees stand sleeping

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photo credit: Winter Forest via photopin (license)

This year, winter has come late and with a vengeance. Snow lies in piles and drifts over every available surface, and movement through this landscape is muffled, strenuous. In the forest, the deciduous trees stand bare of adornments, their spindly limbs betraying no memory of summer. I’ve lived in a temperate climate my whole life, and though I’ve seen seasons come and go, the cycling of trees through the seasons retains a familiar mystery, year after year.

In the coldest months of the year, trees survive by becoming dormant, a condition in which tissue growth or elongation is paused. When the tree is dormant, all its biological processes–metabolism, growth, and energy production–are slowed or halted for a time. Dormancy isn’t a switch that turns on and off; rather, it is a gradual process that begins long before winter, cued by shorter day length and cooler temperatures.

Length of day is sensed by a specialized pigment called phytochrome. Phytochrome is a type of photoreceptor, which means that it is sensitive to light; in this case, light waves at the red end of the spectrum. Longer nights result in the production of a chemical called abscisic acid (ABA), which signals to the tree that it’s time to begin preparations for dormancy.

As the tree responds to these stimuli and growth slows, the production of chlorophyll slows, and leaves change color (for more on the color of fall leaves, see this post). A layer of cells grows between the branch and the base of the leaf stem, essentially cutting the leaf off from the tree so that it falls away. Since no food production is necessary during the dormant phase, the leaves are not needed until spring. As William Carlos Williams’ poem, “Winter Trees,” observes so eloquently:

All the complicated details
of the attiring and
the disattiring are completed!
A liquid moon
moves gently among
the long branches.
Thus having prepared their buds
against a sure winter
the wise trees
stand sleeping in the cold.

The shortening days of fall combined with increasing cold send the tree through this pre-dormancy phase into true dormancy, which begins a few weeks after growth has stopped. Nothing now can wake the tree until a genetically-determined number of “chill-hours” has been met. During this time, trees grow even more resistant to cold through such strategies as production of antifreeze compounds from sugars, evacuation of water from cells, and addition of fatty acids to cell membranes.

Over time, deciduous trees in temperate climates have evolved responses that ensure the highest chance of survival through recurring bitter winters. When spring comes, the trees will sense the warmth and begin to return to normal functioning. But for now, the wise trees  stand, sleeping in the cold.

REFERENCES

Campbell, Eileen 2012. “How do trees survive winter?” Mother Nature Network. Link

Krulwich, Robert 2009. “Why Leaves Really Fall off Trees.” NPR. Link

Shen Li 2011. “How Do Trees Know When to Wake Up?” Outside Story: Northern Woodlands. Link

“Winter Trees” by William Carlos Williams. Read it here.

Sex, which breaks us into voice

Photo by David Berkowitz.  http://commons.wikimedia.org/wiki/File:Galapagos_Tortoise_Mating.jpg

Photo by David Berkowitz, Wikimedia Commons

In all of nature, the tortoise is one of the most unlikely animals to be featured in a poem about sex. Yes, of course they are sexually reproducing organisms, and therefore in order for reproduction to occur, there must be an act of sex, but…tortoises? One curious aspect of the tortoise mating system is that it includes vocalizations. And not just any vocalizations: emphatic, rhythmic, sometimes roaring, sometimes human-like sounds. For an animal as, well, quiet as a tortoise, these vocalizations are definitely interesting. And to DH Lawrence, inspiring.

I thought he was dumb,
I said he was dumb,
Yet I’ve heard him cry.
 
First faint scream,
Out of life’s unfathomable dawn,
Far off, so far, like a madness, under the horizon’s dawning rim,
Far, far off, far scream.
 
Tortoise in extremis. 
 

The name “tortoise” generally refers to any land-dwelling, non-swimming member of the order Testudines (members of the order as a whole may be called “turtles”). All members of this order are characterized by a shell made of dermal bone that encases their organs and limb girdles (where the limbs attach to the trunk). The top part of the shell is called the carapace, the bottom part is the plastron, and the piece that connects the two is called the bridge. Though Testudines was once incredibly diverse, today only 260 species from 13 families remain.

I can't not include an image of "Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904

“Chelonia” from Ernst Haeckel’s Kunstformen der Natur, 1904

Tortoises, the land-dwelling subgroup of turtles, belong to the family Testudinae. They range in size from a few centimeters to two meters, and are one of the the longest-lived animals in the world; some individuals have been known to survive more than 150 years. Their age can be estimated by the concentric rings on the carapace, though this is not a definitive method.  Many species of tortoise are sexually dimorphic, which means that males and females have obvious physical (morphological) differences. Females tend to be slightly larger, and have shorter tails. In some species, females also have longer claws. Males often have longer tails, longer neck plates, and a plastron that is curved inward.

Which brings us to sex.

Male tortoise, cleaving behind the hovel-wall of that dense female,
Mounted and tense, spread-eagle, out-reaching out of the shell
In tortoise-nakedness,
Long neck, and long vulnerable limbs extruded, spread-eagle over her house-roof,
And the deep, secret, all-penetrating tail curved beneath her walls,
Reaching and gripping tense, more reaching anguish in uttermost tension
Till suddenly, in the spasm of coition, tupping like a jerking leap, and oh!
Opening its clenched face from his outstretched neck
And giving that fragile yell, that scream,
Super-audible,
From his pink, cleft, old-man’s mouth,
 

In tortoise mating, the female is on the bottom. The curvature of the male’s plastron fits neatly over the female’s carapace, enabling them to achieve the proper intimacy. Female tortoises have what is called a cloacaor vent, which is a single opening that serves both excretory and reproductive functions. Male tortoises also have cloacas, but within the cloaca is a hydraulic intromittent sexual organ, otherwise known as a penis. While tortoise penises are anatomically comparable (and evolutionarily convergent) to those of mammals, they can have dramatically different shapes and features. Some are pointed, some are flat, and some look like opening flowers. The penis is often disproportionately large (and by that I mean half the length of the plastron or more). Most likely these shapes and lengths have evolved in order to ensure genital contact with the female.

But what guides DH Lawrence’s poem is male tortoise vocalization during the act of mating. Tortoises rarely emit sounds, so when they do, it  is meaningful. Most likely, these vocalizations are auditory signals to females. It is thought that producing these sounds is energetically costly to males, so males who can produce more calls may be of higher quality. In Hermann’s tortoises, females have been shown to respond to recordings of male calls, and to prefer higher-pitched and faster rates of calling. In marginated tortoises, male mating success is positively correlated with the number of calls emitted during mounting. So the ability to produce these calls is advantageous to males.

His scream, and his moment’s subsidence,
The moment of eternal silence,
Yet unreleased, and after the moment, the sudden, startling jerk of coition, and at once
The inexpressible faint yell —
And so on, till the last plasm of my body was melted back
To the primeval rudiments of life, and the secret.
 
So he tups, and screams
Time after time that frail, torn scream
After each jerk, the longish interval,
The tortoise eternity,
Agelong, reptilian persistence,
Heart-throb, slow heart-throb, persistent for the next spasm.
 

 In “Tortoise Shout,” DH Lawrence recognizes something undeniably human in the call of the male tortoise. Strange as these creatures are, we share their reliance on sex, and more, the seeming enjoyment of the act. Lawrence hears the tortoise calling from the “horizon of life,” and it affirms his place in the universe by reminding him of our connection with all sexual beings.

Sex, which breaks up our integrity, our single inviolability, our deep silence
Tearing a cry from us.
 
Sex, which breaks us into voice, sets us calling across the deeps, calling, calling for the complement,
Singing, and calling, and singing again, being answered, having found.
 
 

REFERENCES

Galeotti, Paolo et al. 2004. Female preference for fast-rate, high-pitched calls in Hermann’s tortoises Testudo hermanni. Behavioral Ecology 16(1): 301-308. Link. 

Kelly, DA. 2004. Turtle and mammal penis designs are anatomically convergent. Proceedings of the Royal Society of London B 271 (Suppl 5), S293-S295. Link.

Lawrence, DH. “Tortoise Shout.” Read it here. 

McCurry-Schmidt, Madeline. 2011. “How turtles do it.” Link.

Meylan, Peter. 2012. Testudines: Turtles, Tortoises, and Terrapins. Tree of Life Web Project. Link. 

Niash, Darren. 2012. Terrifying sex organs of male turtles. Link. 

Sacchi, Robert et al. 2003. Vocalizations and courtship intensity correlate with mounting success in marginated tortoises Testudo marginata. Behavioral Ecology & Sociobiology 55:95-102. Link. 

Tortoise Calls: recordings by the California Turtle & Tortoise Club. Link. 

Because the wolves are shot

coyote

What do you really know about coyotes? Maybe you’ve heard the official line about the economic consequences of coyotes killing livestock. Maybe you know of a neighborhood cat that was taken. Maybe you’ve heard conservation groups protesting inhumane treatment of these animals, or recall Mark Twain’s “slim, sick, and sorry-looking skeleton…a living, breathing allegory of Want.” In reality, these animals are neither good nor evil, but are simply trying to survive the best they can in a world that is changing around them.

And as the coyote turns the cat to sweetness
in its mouth, a month-long stint of apricot
pit-, ant-filled scat, a month before of
birdseed, cricket, crappy sandwich; so,
 
don’t turn your back; befriend them; grab
and wave a stick; the twenty doses meant to still
their little ones were killed inside coyote,
and outcome: snapping infant death: your indoor
 
dogs, and bitten, squalling children
 

Karen Leona Anderson’s poem “Coyote” begins with a list of found items a coyote has eaten. Coyotes are omnivores and scavengers, meaning that they can and will eat just about anything.  Though they have a bad reputation as killers of sheep, chickens, and deer, coyotes also eat snakes, foxes, rodents, pet cats, sandwiches, and garbage, for a start. This could be the key to this species’ success in a country where the large predators are either killed outright or squeezed out by human population growth.

Which isn’t to say the coyote isn’t targeted. They are one of the most vilified animals in North America. The Wildlife Services division of the US Department of Agriculture specializes in “predator control,” killing thousands of predators to protect livestock and big game. The most common predator killed (at an estimated 512,500 between 2006-2012) is the coyote. Outcry by biologists and the public as well as a series of articles by Pulitzer-prize winning journalist Tom Knudson led to ongoing investigations into this organization.

The problem with killing coyotes is that in some systems they act as keystone predators. Remember ecology: everything (plant, herbivore, carnivore) is connected to everything else in the food web. When part of the web is removed, it affects every other organism that was connected to it. A keystone, literally, is the stone at the top of an arch that holds up the entire structure. A keystone predator, then, is at the top of the food web. When it is removed, the delicate balance between interacting species is destroyed.

edu_food_web

Removal of coyotes has an effect on smaller predator (mesopredator) populations; in the absence of coyotes, populations of animals such as raccoons and foxes (and housecats!) increase dramatically. These mesopredators then consume far more eggs, birds, mice, voles, and other small animals than they should, and the populations of these prey organisms plummet. (Housecats in particular decimate bird populations. More information here.) In a cascade effect, whatever plants or insects the birds or mice feed on are then released from predator pressure, and they, in turn, multiply. Replace the keystone predator in the system, and order is restored. This is called top-down regulation: maintaining the balance of the food web below and around the top predator.

dens
in rainpipes, basements, crawlspace, tenants’ dumpsters:
a fed coyote is a dead–what? Since they ate
even the stinging sugar-eaters, since when
 
they couldn’t eat they bred into your pets
a coyness, slipped behind the fence, endorphins,
dopamine sweeter than the kibble
                                                   –so what’s to want?
 

Whereas in the west, wolves, bears, and mountain lions act as apex predators, these animals have been almost entirely extirpated from the eastern US. In response, the sly coyote, omnivorous and adaptable, has taken the role formerly held by wolves. Genetic studies have shown that quite a few eastern coyotes are, in fact, coyote-wolf hybrids. As a result, they are larger than their western counterparts, and are behaviorally more wolfish. Unlike wolves and other large predators, however, coyotes aren’t picky about forests and open space. They easily adapt to live in suburban and even urban areas where food is abundant. Chicago, for example, has tracked hundreds of coyotes living in the city for the past 14 years, thriving off of the rodent population.

Though originally pushed out of rural areas by human expansion, biologists say that coyotes are equally at home in the city. They pose no danger to us so long as we allow them to remain wild. This means not feeding them, being sure to pick up your garbage, and taking pets inside at night. Don’t be so quick to judge an animal that is only surviving. Remember that every species has its part to play, and that designations of good or evil are restricted to those of us with morals and a conscience.

With eyes like lanterns out by the latticed gate,
a future soft-tanned pelt pulls up
and moves to the city, deceitful little trot,
about to whelp and, honey, because the wolves
 
are shot and wildcats museumed and moth-torn,
the city, hareless, knows it’s gone to them; omnivorous
I tell myself, so make yourself their home.
 
 

REFERENCES:

“Agriculture’s Misnamed Agency.” 2013. The New York Times.  Link.

Cart, Julie. 2014. “Congressmen question costs, mission of Wildlife Services agency.” Los Angeles Times. Link.

“Coyote: Canis latrans” by Karen Leona Anderson, from the collection Punish Honey. Buy it here.

The Humane Society. 2013. “Why Killing Coyotes Doesn’t Work.” Link.

Knudson, Tom. 2012.  Wildlife Services’ deadly force opens Pandora’s box of environmental problems.  The Sacramento Bee.

Stolzenburg, William. 2008. Where the Wild Things Were. Bloomsbury.

“Urban Coyote Ecology and Management.” The Cook County, Illinois, Coyote Project. Link.

USDA Publication. 2011. “Coyotes in Towns and Suburbs.” Link.

Way, J G. 2007. Suburban Howls: Tracking the Eastern Coyote in Urban Massachusetts. Dog Ear Publishing, Indianapolis, Ind.

THANKS:

Special thanks to Karen Leona Anderson for permission to use her work.  Please check out her lovely collection of poetry, Punish Honey, available here.  More information on Dr. Anderson is available here.