Monthly Archives: August 2011

Visualizing trophic interactions in an urban aquatic mesocosm

Variations in how to display the trophic interactions of an ecosystem—the food web, the regulating pressures between organisms of a particular space—have existed since the roots of the idea in community ecology. Nature—or, in particular, the relationships between organisms—has long been described as a web by many. Take, for example, the now-classic food web of Bear Island, the southernmost island of the Norwegian Svalbard archipelago, by Victor Summerhayes and Charles Elton in their seminal 1923 paper. In their illustration below, organisms are grouped into functional clusters, and arrows depict one organism being consumed by another, outlining a basis from which these systemic illustrations would build upon for decades.

Victor Summerhayes and Charles Elton's 1923 food web of Bear Island, Norway.

But this depiction of life wasn’t quite so scientifically until Charles Darwin published his On the Origin of Species in 1859, in which he wrote,

I am tempted to give one more instance showing how plants and animals remote in the scale of nature, are bound together by a web of complex relations. I shall hereafter have occasion to show that the exotic Lobelia fulgens is never visited in my garden by insects, and consequently, from its peculiar structure, never sets a seed. Nearly all our orchidaceous plants absolutely require the visits of insects to remove their pollen-masses and thus to fertilise them. I find from experiments that humblebees are almost indispensable to the fertilisation of the heartsease (Viola tricolor), for other bees do not visit this flower […] Hence we may infer as highly probable that, if the whole genus of humble-bees became extinct or very rare in England, the heartsease and red clover would become very rare, or wholly disappear. The number of humblebees in any district depends in a great measure upon the number of field mice, which destroy their combs and nests; and Col. Newman, who has long attended to the habits of humble-bees, believes that “more than two-thirds of them are thus destroyed all over England.” Now the number of mice is largely dependent, as every one knows, on the number of cats; and Col. Newman says, “Near villages and small towns I have found the nests of humblebees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice.” Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!

Darwin also described this web of complex relations as an entangled bank, “clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth,” and he reflected on how each of these forms, different they may be, are dependent on one another in direct and indirect pathways while at the same time producing the kinds of ecological pressures that lead to adaptation and the rise—or elimination—of species.

A species web of a slightly different kind: Charles Darwin's 1837 sketch of an evolutionary tree.

On the Origin of Species and Darwin’s subsequent writings were foremost about natural selection, the non-random process by which biological traits become more or less common in a population. But Darwin’s idea can be, and was, applied the same to how organisms themselves become more or less common in an ecosystem—the question became the following: what are those forces and relationships that allow some species to foster in a particular environment, while others only play a minor role? Community ecologists divide these species into two initial groups: autotrophs, which produce organic matter from inorganic substance to compose the primary level of an ecosystem (the first trophic level), and the heterotrophs (1+ trophic levels), which cannot fix carbon and thus must consume organisms from the initial or subsequent trophic bases. In terms of the relationships between the autotrophs and heterotrophs, food web ecology polarizes the dynamic between which group regulates the other. In bottom-up control, also known as donor control, the autotrophs (i.e., plants and algae) produce the primary resources, thereby maintaing the nutrient availability that organisms at higher trophic levels are dependent upon. Contrasting bottom-up control is the top-down dynamic, also known as a trophic cascade, in which predation and herbivory are the factors that dominate whether a species will thrive in an environment. More typically, however, analyses in community ecology strive for some middle ground between the two.

While the organization of a food web is inherently more complex—incorporating the movement of energy and mineral nutrients; dividing the heterotrophs into carnivores, herbivores, decomposers; delineating even further between competitor species, generalist consumers, specialist predators, etc—this basic model holds steady. Because this organization is predominantly a visual one—spatial and temporal patterns and variations are a large part of community dynamics in ecological research, as outlined in a recent review by Massol et al.—an interesting aspect of studying trophic interactions lies in the possibilities for visualizing data. The first graphical interpretation of a food web was published in 1880 by Lorenzo Camerano, in a manuscript entitled “On the equilibrium of living beings by means of reciprocal destruction.” Frustrated by his time’s scientific divide over which animals are useful or beneficial to agriculture, Camerano wrote the following.

To have an exact and clear idea, I repeat, of the relations between, for example, insectivorous birds and phytophagous insects, and between these and plants, these groups cannot be studied separately. Rather it is necessary to study each in relation to all other animals to see the general laws governing the equilibrium of animal and plant species.

While Camerano’s reasoning for the paper, published in the Accademia delle Scienze di Torino, was particular and applied towards the practical, his ultimate goal in the article and its resulting visualization was of general and theoretical concern.

Plate 1, Camerano 1880. Theoretical web of plant and animal interactions.

Compare that template of trophic relationships among organism groups—including primary producers, predators, ectoparasites, endoparasites, and carnivores—with a particular illustration of an ecological community of individual species with regard to enemies of a specific phylogenetic order, Coleoptera.

Plate 2, Camerano 1880. Web of interactions between Coleoptera, enemies of Coleoptera, and ecological enemies of those enemies.

In the former, more-theoretical visualization, Camerano sides with the theory of bottom-up control—vegetation is the base layer of the trophic sphere, with interactions between higher trophic levels expanding in outward rings. In the latter, allying with top-down ideas of control, complex relations are derived not from primary production, but rather from multiple pressures of predation, forming direct and indirect influences between heterotrophs. It is the latter depiction—with its emphasis on predator–prey relationships and linear–nonlinear associations between species—that has most influenced how many visualizations of trophic dynamics are drawn. In Summerhayes and Elton’s depiction of Bear Island, the first illustration in this article, the ecologists organized the biota with priority on that relationship between predator and prey—protozoa eat the bacteria, polar bears eat seals. Even where nutrients and zooplankton entered the situation, their connection to the rest of the system was given within the framework of consumption dynamics—bacteria consume nitrogen, worms eat dead plants, algae take in mineral salts.

And nor is this choice of visualization a poor or incorrect one. However, an interesting note lies in the shift between how to organize a food web in the 19th and early 20th centuries  and what kind of information should and can be included in more sophisticated images now. When one adds in the more quantitative turn in food web analysis—such as with ecological pyramids and trophic dynamics, both of which incorporate the second law of thermodynamics to consider how energy is conserved or lost as it passes between organisms—the complexity inherent in the early food webs above exponentially increases in magnitude.

The question in producing a food web is, then, how to produce a visualization of that complexity without overwhelming our perception of reality. Sacrifice quantitative rigor, and the illustration instead appears as illusion, an over-simplification. Introduce too much information, and the traceable dissolves into surplus. Such are the balancing acts Edward Tufte outlines in his 1983 The Visual Display of Quantitative Information. In the book, the statistician argues that good information design reveals the greatest number of ideas in the shortest time, with the least ink, in the smallest amount space, akin to what Italo Calvino described as lightness in literary prose—both must, in the end, tell not only a good story, but a proper one, without sacrificing either extreme of this information equilibrium.

As some of the first illustrations of food webs came from aquatic systems, bodies of water, as simultaneously self-contained microcosms and hubs in ecological networks, are good places to look for growing trends in data visualizations. An interesting and successful  update on the classic food web comes from a paper by Kevin Caillouët et al. in a 2008 paper on enclosed aquatic communities in New Orleans, Louisiana. After Hurricane Katrina flooded 80% of the city in August of 2005, floodwater from Lake Pontchartrain to the north inundated the urban terrain for over three weeks. By completely covering most regions of the city in brackish water, flooding resulted in the production of novel aquatic habitats in lowlands, depressions, and artificial containers, to name a few. Much as a forest fire produces a blank template from which previously occupied niches can be reclaimed and monocultures overthrown, Hurricane Katrina produced a blank template from which new food webs—new trophic interactions, in new magnitudes and organizations—could be drawn. In particular, on the back of research suggesting correlations between flooding and increased mosquito populations, Caillouët et al. sought to examine how these new aquatic communities would work for or against local mosquito populations, and how this in turn could influence the human risk of mosquito-borne diseases such as that caused by West Nile virus. In particular, the team examined the quasi-contained ecosystem of abandoned swimming pools, the largest of artificial containers and one of the most prone habitats to support mosquito larval development.

Caillouët et al. sample a flooded abandoned swimming pool in the Lakeview neighborhood of New Orleans.

By sampling pools in two flooded neighborhoods of New Orleans near the 17th Street Canal levee breach, the researchers were looking at this artificial environment as a mesocosm of sorts. Unlike the simplified microcosm, a controlled, laboratory-based ecosystem used to simulate and predict the behavior of its natural counterpart, a mesocosm instead brings the natural under controlled conditions, providing a link between observational field study and the artificiality of the laboratory. These mesocosms, which were being colonized by various invertebrates, fish, and mosquito species, allowed the team to ask the following questions about the composition of these new and temporary environments: if mosquito larvae were using the pools for development; if fish moved in from Lake Pontchartrain and were able to establish populations; if predatory invertebrates migrated to and colonized pools; and, lastly, if and to what extend these latter organism groups regulated mosquito populations.  To explore how these questions translate into science, Caillouët et al. relied on a conceptual model, the first step in transforming idea into design, the prerequisite for collecting and interpreting data.

Models and interpretations of aquatic community colonization post-Hurricane Katrina. Caillouët et al. 2008.

The conceptual model (A) of Caillouët et al. is not all too different, as a theoretical insight, from the initial plate by Camerano in 1880. Just as Camerano endeavored to clearly illustrate the relationships that draw together insectivorous birds and phytophagous insects, and between these and plants, the modern model food web illustrates the general relations between four main groups of organisms: the top predators, the specialist predators, the competitor species, and the prey. Much as Summerhayes and Elton used arrows in their 1923 depiction of an aquatic food web to illustrate the direction of the relationship between two or more organisms, the above model demonstrates a direct (and negative) effect of one group on another with solid lines, while dotted lines indicate an indirect (and therefore positive) effect. Continue reading

Metaphor of microglia: the maintenance amoeba of the brain’s neural network

[Here on out, eukaryography will have weekly or so examples and discussions of creative metaphors used by writers of scientific phenomena. Today’s imagery comes from Mo Costandi at Neurophilosophy]

It is said that the human brain contains roughly 10 billion neurons, each of which is connected to those other neurons through 10,000 synapses. This figure, massive as it may be, is also an understatement—Mo Costandi at The Guardian notes that in actuality the numbers come in closer at hundreds of billions of neurons and glial cells, those non-neuron cells—also known as neuroglia—that maintain homeostasis in the brain and provide support and protection of neurons. In turn, this quantity of cells produces more like  a quadrillion synapses.

To maintain some control over this complex information processing system, our brain generates more neurons and neuroglia than necessary, ensuring a surplus of connections. To reduce noise in this system, the brain relies on a process known as pruning. Also known as neuro-structural reassembly, pruning can occur through several interrelated scenarios. In one, the brain must replace simpler associations with a matured understanding of complex relationships—as we mature from childhood, our brain does as well, and needs reconsideration of the economy of neurons to do so. This process is part of the more general act of the network’s housekeeping. Neurons that have been damaged, are decaying, or are no longer necessary are removed to improve the overall functioning of the organ. Costandi writes that although neuroscience has know this process continues into and somewhat through our adult lives, the field has been in the dark in regards to the mechanisms—the how of X connecting to Y—of pruning. Costandi reports that now, a team of Italian researchers has been able to clarify this void in our understanding. Pruning, they have found, occurs through the actions of cells called microglia, which scour the developing human brain and engulf unnecessary synapses.

Microglial cell from the mouse brain expressing green fluorescent protein. Photograph by EMBL/ Rosa Paolicelli.

The microglia are related to the macrophages of the innate immune system, and functionally are very much the same. A variety of macrophages exist,  and their roles include ingesting foreign material, releasing cytokines to stimulate other macrophages, and presenting antigens. In the same way, microglia act as the initial defense against invading pathogens and substances and performing maintenance tasks. But Costandi doesn’t limit his definition of microglia to the vocabulary of immunology—he also draws on a personal favorite, that of protozoology. Microglia, he writes,

crawl, amoeba-like, through the spaces between neurons, using their protrusions to detect viruses and microbes that have infiltrated the brain and quickly engulf those they find.

Amoeba, members of the genus Amoeba, were discovered by early cell biology in 1757 by  entomologist August Johann Rösel von Rosenhof. In his Insecten-Belustigung (Recreation among the Insects),  Rösel described, sketched, and discovered that one species of these organisms, which he called “the little Proteus,” when touched, drew its octopus-like figure together.

Engraved colored figures of Volvox and amoeba, August Johann Rösel von Rosenhof (1757).

This form-changing ability, which became the characteristic of amoeba that gave the group its 18th century name, Proteus animalcule—after the Greek god Proteus, who could shift his shape—is an aspect that allows these organisms to feed. Amoeba have cytoplasmic extensions called pseudopodia that accout for this shape shifting–like imagery. This process is the prerequisite for phagocytosis, the act of engulfing other organisms or matter in the pseudopodia and bringing them into the amoeba’s body to be metabolized. This “cell eating” phenomenon is also exibited by the macrophages and microglia that Costandi notes in his article:

Phagocytosis means “cell-eating” and is the process by which microglia and other cells take up solid materials. First, the material is pulled towards the cell membrane, which then begins to invaginate, or fold in on itself, to envelop the material. As the in-folding continues, the outer edges of the membrane are drawn together until they eventually meet, producing a globule (the vesicle), which then buds off and moves into the cell. The contents of the vesicle are then processed appropriately—microbes are destroyed and membrane proteins and other cellular components recycled.

Below, an amoeba, Vannella sp., engulfs an unspecified cell through this meticulously described process.

And returning to the first part of the metaphor, that of the microglia-as-macrophage, in the following video a white blood cell chases bacteria through a maze of erythrocytes.

Through the experiment performed by Rosa Paolicelli et al.the details and methods of which are explained in full by Costandi at his Neurophilosophy blogmicroglia in the brain tissue of mice were found to be engulfing, in much the same way as an amoeba or macrophage, fragments of a protein known as PSD-95, which is major part of the protein network found in active synapses of the brain. In the following video from Nimmerjahn et al. (2005), we can visualize microglial cells patrolling synapses for functional deficits.

Therefore, Costandi writes, “the developing brain treats unwanted synapses as if they were unwanted invaders. It dispatches microglial cells to survey the state of synapses in their surroundings and to dispose of the ones that are wired incorrectly or superfluous.” To the microglia in our neural network, unnecessary and outdated synapses are akin to pathogens in the bloodstream, particles of algae to a grazing amoeba in a drop of lake water in Rösel’s German countryside.

Charles Darwin on beauty

[From The Voyage of the Beagle (1839), Chapter III: Maldonado]

July 26th, 1832

Maldonado is situated on the northern bank of the Plata, and not very far from the mouth of the estuary. It is a most quiet, forlorn, little town; built, as is universally the case in these countries, with the streets running at right angles to each other, and having in the middle a large plaza or square, which, from its size, renders the scantiness of the population more evident. It possesses scarcely any trade; the exports being confined to a few hides and living cattle. The inhabitants are chiefly landowners, together with a few shopkeepers and the necessary tradesmen, such as blacksmiths and carpenters, who do nearly all the business for a circuit of fifty miles round. The town is separated from the river by a band of sand-hillocks, about a mile broad: it is surrounded, on all other sides, by an open slightly-undulating country, covered by one uniform layer of fine green turf, on which countless herds of cattle, sheep, and horses graze. There is very little land cultivated even close to the town. A few hedges, made of cacti and agave, mark out where some wheat or Indian corn has been planted. The features of the country are very similar along the whole northern bank of the Plata. The only difference is, that here the granitic hills are a little bolder. The scenery is very uninteresting; there is scarcely a house, an enclosed piece of ground, or even a tree, to give it an air of cheerfulness. Yet, after being imprisoned for some time in a ship, there is a charm in the unconfined feeling of walking over boundless plains of turf. Moreover, if your view is limited to a small space, many objects possess beauty. Some of the smaller birds are brilliantly coloured; and the bright green sward, browsed short by the cattle, is ornamented by dwarf flowers, among which a plant, looking like the daisy, claimed the place of an old friend. What would a florist say to whole tracts, so thickly covered by the Verbena melindres, as, even at a distance, to appear of the most gaudy scarlet?

Jean-Henri Fabre on bees

The victuals are now collected: honey and flower-dust. If there is a pink carpet of sainfoin anywhere in the neighbourhood, tis there that the Mason goes plundering by preference, though it cost her a four hundred yards‘ journey every time. Her crop swells with honeyed exudations, her belly is floured with pollen. Back to the cell, which slowly fills; and back straightway to the harvest-field. And all day long, with not a sign of weariness, the same activity is maintained as long as the sun is high enough. When it is late, if the house is not yet closed, the Bee retires to her cell to spend the night there, head downwards, tip of her abdomen outside, a habit foreign to the Chalicodoma of the Sheds. Then and then alone the Mason rests; but it is a rest that is in a sense equivalent to work, for, thus placed, she blocks the entrance to the honey-store and defends her treasure against twilight or night marauders.

—Jean-Henri Fabre, “The Tribulations of the Mason Bee,” Mason Bees (1925)

"first contact," photograph by author.

Fictionalizing science writing and “The Distance of the Moon”

Italo Calvino’s Cosmicomics, a collection of short stories of a science-inspired nature, is one of my favorite pieces of literature. Calvino was a fantastically imaginative writer, and his Cosmicomics highlight his ability like no other. The stories in Cosmicomics exemplify what Miroslav Holub implied when he commented that play allows the artist to “avoid the aridities of rationalism”—Calvino’s imaginings are anything but dry. Each takes its origin from some brief, abstract concept drawn from the hard sciences. In the case of the collection’s first story, “The Distance of the Moon,” Calvino opens with the following excerpt:

At one time, according to Sir George H. Darwin, the Moon was very close to the Earth. Then the tides gradually pushed her far away: the tides that the Moon herself causes in the Earth’s waters, where the Earth slowly loses energy.

From this deduction, Calvino injects the statement with life, character, a host of emotions and interactions. He plays with the feminization of the moon, why, from a storyteller’s point of view, She might have been pushed away from the Earth and what effort Earth’s inhabitants might have made to re-reach Her. The tale begins, in effect, to describe Calvino’s greater reinterpreting of how the universe was created, how forms so numerous came into being:

How well I know! — old Qfwfq cried,– the rest of you can’t remember, but I can. We had her on top of us all the time, that enormous Moon: when she was full — nights as bright as day, but with a butter-colored light — it looked as if she were going to crush us; when she was new, she rolled around the sky like a black umbrella blown by the wind; and when she was waxing, she came forward with her horns so low she seemed about to stick into the peak of a promontory and get caught there. But the whole business of the Moon’s phases worked in a different way then: because the distances from the Sun were different, and the orbits, and the angle of something or other, I forget what; as for eclipses, with Earth and Moon stuck together the way they were, why, we had eclipses every minute: naturally, those two big monsters managed to put each other in the shade constantly, first one, then the other.

To me, Calvino performed something through these stories—12 in the original collection—that the sphere of science writing, as a general whole, has seemed to have neglected or perhaps even forgotten. Cosmicomics was published in 1965—when the author was 43 years old—and in the decades since, few writers have produced the same form of fictionalized “toying” with scientific fact, making of empirical research something new, what Michel de Certeau conceptualized as reappropriation. In his pivotal The Practice of Everyday Life, de Certeau wrote of the public’s interpretation of information and texts—scientifically based or not—as acts of consumption, and as such, likened to everyday resistance against a top-down dynamic between information producers and consumers. The consumer of information, the theorist wrote, “takes neither the position of the author nor an author’s position. He invents in texts something different from what they intended.” In this case, the information drawn from science, to de Certeau, did not have to be the final frontier—instead, one could formulate fact into new configurations.

Discussing Cosmicomics, Jeanette Winterson described Calvino as an adamant believer that art is a force that can unite various and seemingly disconnected parts of the self and the social body. Science, as one element of this greater unit, should be only the starting point in bringing together strands of thought and creativity. Winterson wrote, “For him [Calvino], literature as a force going forward, postwar, would be a literature that could encompass everything—science, history, politics, fantasy—but would be in thrall to none of these.”

What has become of this encompassing since Calvino’s time? Science writing today is undoubtedly creative, clear, communicative, to name a few characteristics of the craft. Yet foremost as an educative endeavor—to foster scientific literacy, to raise societal awareness, to bridge scientific practice and everyday life—current science writing is, and in some ways, as practiced, must be, thrall to the worldview and positivism of science and its methodology. Any effort to produce scientifically inspired fiction is given the label of “sci-fi,” when in fact is was Calvino who redefined the term to mean something entirely different. Most recently, Verlyn Klinkenborg’s Timothy; or, Notes of an Abject Reptilean imagining of the musings of an 18th-century Turkish female tortoise in Selborne, England—stands out as an example that fulfills this niche of literature. Of the book and its author, The Washington Post Book World writes, Klinkenborg “rescues us from dailynessfrom, as Timothy would say, our terrible speedand makes our world again large and wondrous.”

Calvino’s Cosmicomics is about making our would wondrous, even those elements of that world we typically relegate to laboratories, observatories, and remote field sites instead of being seen as inspirational sources of creativity. Of Cosmicomics, Salman Rushdie wrote that “Perhaps only Calvino could have created a work that combines scientific erudition, wild fantasy and a humane wit that prevents the edifices of these stories from toppling into whimsy.” I would hope, for one, that Rushdie was incorrect in making such a suggestion, that Calvino’s work was only the beginning of a movement in literature, in particular the short story form. The products of Cosmicomics continually inspire my own thoughts on writing and literature, serve as the best kind of example of something to strive for in words. And they do so for others as well, in varied formats and mediums. Take for example, and enjoy, the following short filmby an Israeli visual communications student, dubbed “shulamitsitself a reimagining and reappropriation of Calvino’s “The Distance of the Moon.”

Kalevi Kull on biosemiotics

Biosemiotics can be defined as the science of signs in living systems. A principal and distinctive characteristic of semiotic biology lays in the understanding that in living, entities do not interact like mechanical bodies, but rather as messages, the pieces of text. This means that the whole determinism is of another type […] The phenomena of recognition, memory, categorization, mimicry, learning, communication are thus among those of interest for biosemiotic research, together with the analysis of the application of the tools and notions of semiotics (text, translation, interpretation, semiosis, types of sign, meaning) in the biological realm.

Kull K. (1999). Biosemiotics in the twentieth century: a view from biology. Semiotica 127(1/4), 385–414.

The painted lives of ciliates and schistosomes

Art has always been one way to mediate tensions, tensions such as those between the logic-driven mind of scientific inquiry and the subjective experience of the non-human, what Jakob  von Uexküll called an organism’s umwelt. Thomas Nagel famously argued that we can never know what it is like to be a bat, or any non-human organism, but whether through experimental-minded writings on what the world might be through a tortoise’s point of view  or through watercolor paintings, the artistic hopes to bridge various umwelten more so than a declaration of scientific understanding—the difference lies within the distinction of this is how a starling sees the spectrum of light and thus the world (science) and this is how a starling might see the world (art). Might opens possibilities, a window into creative endeavor.

The paintings of Emilie Clark might be one answer to Nagel. Clark, a painter based on Brooklyn, NY, has worked on a series of projects involved in life on a microscopic scale. In a 2004 gallery showingPondering the Marvelous, Clark responds to the writings of Mary Ward, a 19th-century Irish natural historian and painter, specifically Ward’s A World of Wonders Revealed by the Microscope. In imagining Ward’s writings as personal letters to the artist, Clark produced two series of her own watercolors—the first based on Ward’s description of Ireland’s microscopic landscape, and the second on Clark’s own collection.

Untitled MW-#50. Painting by and courtesy of Emilie Clark.

Untitled MW-#12. Painting by and courtesy of Emilie Clark.

The paintings are not meant in their entirety to be illustrations of these organisms’ umwelten, and nor do they achieve this ideal. But these paintings play with the possibility of “what if?” And it is this play that creates an opening in our imagining of the umwelt of other species. Perhaps best said by the poet–immunologist Miroslav Holub, the act of play allows us, simply, to “avoid the aridities of rationalism.” Yet this is not Clark’s first foray into toying with the lifeworld of other microorganisms.

In a previous post, I briefly touched on the topic of cover art for scientific journals—in this case, a watercolor of a stag beetle by Albrecht Dürer for a 2005 issue of Emerging Infectious Diseases. One of Emilie Clark’s projects, which one can find on her webpage, is likewise producing watercolor medical illustrations, many of which have found their way onto the covers of The Journal of Experimental Medicine. The JEM, since its beginnings in 1896, publishes original research on the physiological, pathological, and molecular mechanisms that are encountered by or reactions of the host in response to disease. In the case of a November 2005 issue of the journal, the target pathogenic organism of Clark’s illustration was Schistosoma mansoni, one of three causative agents of human schistosomiasis.

From the cover caption of JEM 2005; 202 (10). Emilie Clark's watercolor of S. mansoni eggs. The eggs secrete a chemokine binding protein, thereby suppressing the inflammatory response.

Schistosomes are blood flukes (trematodes) that belong to the genus Schistosoma. In addition to S. mansoni, the other two members of this genus that cause disease in humans are S. hematobium and S. japonicum. The disease itself, caused by human contact with water home to schistosome cercaria, is a definitive chronic condition whereby the mature schistosomes, after reaching the final stage of their life cycle, migrate to the mesenteric or rectal veins and begin to mate, thereby producing up to 300 eggs per day for the rest of their reproductive lives—which can be as long as 4–20 years. A proportion of these eggs will become lodged in the target veins, where they mature and secrete antigens that elicit an intense immune response in the host. It is this immunological reaction, which can continue as long as the mating worms and the eggs continue to exist in the body, that characterizes schistosomiasis. It was the point of the primary research communication by Philip Smith et al., the inspiration for the choice of Clark’s watercolor, to demonstrate one way in which S. mansoni modifies the human host to tolerate decades-long chronic infection without causing death. In particular, the researchers demonstrated that S. mansoni eggs secrete a protein into host tissues that binds certain chemokines—proteins that induce directed chemotaxis, how certain cells direct their movements according to particular chemicals in their environment, in nearby responsive cells—and inhibits their interaction with host chemokine receptors and their biological activity.

Now, compare Clark’s interpretation of the organisms and this phenomenon with a direct realistic representation through a microscope. Continue reading