The Demeaning of Life...Chapter 22: Camouflage and Mimicry

Some of these resemblances are perfectly staggering—to me they are a source of constant wonder & thrilling delight. It seems to me as though I obtain a glimpse of an intelligent motive pervading nature, as well as of the mighty, never-resting wonder-working laws that regulate all things.

Henry Walter Bates, letter to Darwin, 1861

Of all the myriad varieties of physical adaptation that play a part in aiding survival, two stand above the pale for their sophistication and a certain sly genius concealed within their unmistakable utility: defense mechanisms and protective (or cryptic) coloration.

Plant and animal defenses are products of evolutionary arms races. The first predator was presumably a single celled organism that hit on the idea of engulfing some smaller cell, thereby inventing “food.” Since that game-changing event transpired, most living things have taken part in what amounts to an endless contest in which winners manage to postpone being eaten—whether by means of running faster, growing a thicker shell to deter stronger teeth, or simply going into hiding. Means of defense go well beyond the no-frills stings and bulky shells, the diverse spines and vile excretions. Some creatures rely on the use of smoke screens, electrocution, and self-evisceration—forceful displays of nature’s creative prowess. And among those slow-moving creatures without such defenses, many styles of protective coloration exhibit a subtlety of rendition that in some instances is almost beyond belief.

These attributes have long been a source of wonder and cause for heated debate thanks to a shared quality of overtly appearing designed, in a manner that exceeds the “appearance” of design in other natural features. Nonetheless, it is widely held that these things can all be accounted for solely by the slow-turning wheels of gradualistic evolution. In spite of this widespread conviction, to this day there are no definitive explanations for marvels that have the appearance of being intentionally shaped by an intelligent agency. And there are some good reasons to question prevailing accounts.

Animals marshal an array of stratagems to defend themselves in a world teeming with sharp-eyed predators. These defenses also help relieve the stress of constantly being on the lookout. In fact, many creatures can go about their lives virtually unmolested thanks to their built-in defenses including what amount to flashing warning signs.

 Here is a partial listing of strategies, including a few singular cases:

• Many varieties of poisonous stings and bites. (Though used for securing prey these are often solely for protection.) Many insects are unpalatable as a result of concentrating toxic compounds from food plants in their own flesh. On the other hand, animals (such as frogs and newts) synthesize their own poisonous chemicals.

• A fearsome assortment of spines, spurs, spikes, and detachable quills. These can be poison-tipped or capable of causing potentially fatal infections.

• Diverse noxious, sticky, toxic (or just plain foul) excretions and emissions are employed throughout the animal kingdom. The chemical elements are often altered versions of  substances having other, completely unrelated physiological roles.

• Along with their remarkable camouflage systems, cephalopods (squid, octopuses, and cuttlefish) deploy opaque “smoke screens” by expelling clouds of a black inky substance.

• Many lizards and salamanders can voluntarily shed their tails, which (advantageously) then flail wildly, distracting the predator while the real prize escapes…and grows a new tail.

• Sea cucumbers (a soft-bodied mollusk) perform a related trick. When threatened they expel several internal organs. A portion of the eviscerated tissue consists of tubular elements from the sea cucumber’s respiratory system. This material expands many fold, elongating greatly and becoming sticky, disabling predators. The organs are regenerated within days.

• Warning coloration: bright colors or stripes, often in combination with black stripes or against a black background, which indicate toxicity or other dangerous defenses.

• The electric eel (actually, a type of fish) can deliver brief shocks of up to 850 volts.             
• As well as being highly camouflaged, some species of the slow-moving horned lizards can spray blood for up to several feet from a special pore near the eyelid. In addition to the element of shock and surprise, their blood is reported to have a repellent effect.
• The bombardier beetle stores a mixture of hydroquinones and hydrogen peroxide in a special chamber near its anus. If threatened, the beetle empties the contents into another sealed chamber where the chemicals mix with a catalyst, triggering a violent reaction that raises the temperature of the mixture to near the boiling point. Resulting pressure forces the hot fluid through a turret-like nozzle that the beetle can aim in a chosenn each of its claws. The anemones’ stinging tentacles provide protection to the otherwise defenseless crab, which also scrapes off food particles captured in the tentacles for its own benefit.          
• The bizarre Malaysian “exploding ant,”suicide bomber of the insect world. It belongs to a  group of forest-dwelling ants that are often attacked by marauding weaver ants. Workers have hugely enlarged mandibular glands running the length of their bodies. As a last resort in battle, worker ants violently contract their abdominal muscles, causing the poison-filled mandibular glands to rupture, spraying a sticky and corrosive fluid in all directions. This toxic glue can ensnare all nearby attackers, immobilizing them.

            Then there are the “passive” protective devices of cryptic coloration. This encompasses both camouflage and mimicry, of which there are a number of distinct subcategories (several being named after their discoverers). These include:

                 

• Cryptism: The commonest form of camouflage: an organism resembles a leaf, flower part, twig, rock, or the surface upon which it typically resides or rests. With ever increasing frequency, photographic images are appearing of exotic animals whose cryptism elicits gasps of amazement: walking-stick insects, caterpillars, katydids, mantises…geckos, toads, bizarre sea-horses such as the leafy sea dragon and other reef-dwelling fishes.

• Active camouflage: Some animals can, through various physiological means, alter their coloration to match different backgrounds. 

• Disruptive coloration: Patterns of bold spots or stripes that serve to “break up” an animal’s outline against a complex backdrop (as is the case with leopards and zebras). In combination with cryptic coloration, an animal “disappears” against its background.

• Batesian mimicry: The “sheep in wolf’s clothing” trick: a harmless animal resembles a toxic or dangerous one.

• Müllerian mimicry: Two or more unpalatable species come to resemble one another, reinforcing their warning coloration patterns.

• Automimicry: One part of an organism’s body resembles another part (snakes whose blunt-tipped tails resemble a head; butterflies and other insects whose hind-ends mimic heads.) If attacked, they may escape with non-fatal injuries. Also, various butterflies, moths, birds, and fish possess “eye-spots” which, when presented, may startle a predator, allowing escape.

• Wassmannian mimicry: The mimic lives alongside the model (usually social insects such as ants, bees, or termites) within its colony or nest, producing pheromones that make their  presence acceptable.

The phenomenon of protective coloration has always elicited wonder and admiration and has frequently been held up as proof of the existence of an intelligent creator. Even after Darwin, certain scientists have admitted doubts as to whether a naturalistic explanation could account for certain particularly vexing cases. In fact, the discovery of mimicry (as a biological phenomenon) was considered the first truly convincing demonstration of the powers of natural selection.

Henry Walter Bates, along with Alfred Russel Wallace, embarked on an expedition to Brazil in 1848. Bates and Wallace—only in their mid-twenties at the time—were both avid collectors of beetles and butterflies, a fashionable hobby in Victorian England. Each had been inspired by Darwin’s The Voyage of the Beagle, first published in 1839. Insect collectors (Darwin being one himself) were ideally suited to probe evolution’s mysteries, being particularly attuned to the variety and extreme diversity of the creatures they studied. The question of how such diversity arose was a much-discussed topic. Hoping to finally solve the problem of the origin of species, the two young men traveled up the Amazon River, together and then separately. Wallace, sick and exhausted, was forced to return to England in 1852. On the journey home, Wallace’s ship caught fire and sank—with all his specimens and notes. Bates remained abroad for seven more years. Having collected almost 15,000 animal species (8000 of them unknown to science) he arrived back in England, his body likewise ravaged by sickness and deprivation. Just months later Origin of Species was published. Bates became an enthusiastic supporter of Darwin’s new theory and the two became fast friends and life-long allies.

Bates’ most important contribution was the discovery of a previously unrecorded form of mimicry that now bears his name. In Brazil he noted many instances of one butterfly species that had taken on the colors and wing patterns of another. Typically, these markings were patches and stripes of vivid primary colors against a dark background (a key design theme in warning devices used by animals). After careful study, Bates found that one of the two—he termed it the model—was avoided by predators due to a diet of toxic plants while its mimic was safe to eat. Even more intriguing: during his travels, Bates repeatedly found distinct varieties of one of the unpalatable (model) species being impersonated by different varieties of the same mimic species. To further complicate matters, in some regions he found numbers of separate species (even day-flying moths) all sporting similar flashy wing patterns. And all along the way he came across instances of remarkable protective coloration. The sheer complexity and degree of sophistication of all these things captivated him.

Back in England, Bates promoted his findings as the clearest-yet demonstration of natural selection at work. He described his discoveries in Darwinian terms, explaining them in words similar to these: Through chance mutation, some varieties of butterflies acquire a purely fortuitous, crude resemblance to an unpalatable species. Over time this resemblance increasingly grows more refined, with selection favoring the offspring of superior mimics. And ever since, books have offered up the explanation proposed by Darwin and Bates as consummate illustrations of natural selection in action. But is it as simple as this? Time and again, such matters have proven to be more complex than originally thought. Perhaps other influences are at work here.

Much has been learned about butterfly wing patterns through laboratory rearing and cross-breeding experiments. It was recognized that these colors and patterns on two-dimensional surfaces (as opposed to more complex three-dimensional structures) were more readily modified by genetic alteration. In the 1920s and 30s biologists determined that, in at least one major  group, individual species’ markings were variations on a basic ground plan consisting of “pattern elements”—rows of stripes and spots confined to specific wing-vein-bound subregions. An important observation was made: these subregions are modular and, as such, can not only evolve independently of other elements but do so readily. The established theory explaining butterfly mimicry is based on a two step hypothesis. Initially, mutations in those regulatory genes responsible for wing coloration result in morphological changes that bestow a chance resemblance. The second step involves further small scale mutations which, when subjected to natural selection, progressively result in ever-closer resemblances. Modifications to wing patterns, being modular and subject to point mutations (changes in a single nucleotide base), occur readily. And often.

More recently—thanks to advances in evolutionary developmental biology (evo-devo)—a fairly detailed understanding of the genetic aspects of coloration and pattern development has been reached. Specific genes, previously found in Drosophila and known to have additional functions, were identified as being responsible for eye-spot formation as well. Location of such features is set by the ground plan. When, if, and for how long the genes are switched on determines whether any one locus develops into a simple spot or something more elaborate—like one of those markings that bears an astonishing resemblance to a vertebrate eye (complete with a tiny silvery dot near its center to create the convincing illusion of a reflection on an eye’s glassy surface).                                                

While it is recognized that many such developmental issues are far from settled, researchers expect to make great strides in coming years. However, this conventional mechanistic approach to these matters will not likely account for the evolutionary “need” for such things as the butterfly wing mark that captures, with the realism of a trompe l’oeil painting, a beaded raindrop—complete with a line on the wing that, where it passes beneath the “raindrop,” is offset a bit to perfectly match the refraction such a spheroid lens would produce.

Of all the graphic illustrations of the raw power of organic evolution, I find specific instances of cryptic coloration to be among the most amazing due to their refined subtleties, sheer ingenuity, and aesthetic appeal: the squid-like cuttlefish, which can alter its color, pattern, and skin texture in an instant to match virtually any backdrop…the wide variety of insects that are essentially invisible against the leaves, bark, or ground upon which they hide….those birds and mammals of northern latitudes that turn white in the fall.[1] The list is a long one. While so many people have wondered how such things have come about, the answers offered by Darwinian theory paint a simple picture: The occasional minor, random mutation—a frilly edged wing, a slightly different color, a seemingly inconsequential bump—provides a chance advantage and, if passed on to offspring, improves (even if ever so slightly) their odds of surviving. Through time, by way of additional random changes, these features grow or are enhanced and become ever more subtly realistic.

In the case of cryptism—bearing in mind the perils of “the argument from personal incredulity”—I nonetheless find myself unmoved by this stock explanation. In the case of the many forms of protective coloration, however, it seems to lack real substance or a feel of scientific authenticity. My use of such language clearly reveals a response  that is intuitive and emotional and is thus not a valid approach to a scientific question. Most people with scientific backgrounds, aware of the issues, find the matter of cryptism not only unmystifying, but a model demonstration of Darwinism in action.

 One particular experience when I was sixteen was pivotal in a burgeoning comprehension that nature has certain qualities that defy rational explanation. While hiking in a brushy canyon near my home, I came across a sizeable gopher snake—at almost five feet long, the largest I had yet seen. (As to the emotional impact of encounters with wild animals: when it comes to serpents, “size matters.”)

            The snake was hidden under an old board and, with the sudden loss of cover, it speedily assumed a defensive posture. I felt a rush of adrenaline when it coiled like a rattlesnake, head reared and tongue flickering. Staring me down, the mostly harmless reptile had become a rattlesnake. The species has brown markings with paler interiors on a golden-colored background so gopher snakes look somewhat similar to their dangerous relatives to begin with. However, the transformation of its appearance went beyond simply looking like a rattlesnake. Its head became flattened and the jaws were flared—distinguishing viper traits. The snake inflated its lungs, which had the effect of markedly increasing its girth. (Rattlers are conspicuously thick-bodied snakes.) Its slender tail, held aloft, vibrated in a hazy blur—nearly indistinguishable from the blur of rapidly buzzing rattles. Simultaneously, air was forcefully expelled from the snake’s lungs with a dull hiss that credibly reproduced a certain instantly recognizable sound. The imposter faced me squarely, weaving its head slowly from side to side. Those who have faced down an angry rattlesnake while on full adenal alert will attest that the net effect triggers a compelling instinctive fear; keeping one’s distance is an involuntary, unquestioned response. (Of course, being an adolescent male of my species, it was compulsory that I locate a stick and wave it in front of the snake’s face, provoking multiple vigorous strikes.) All in all, the entire display was a thrilling demonstration of plucky menace and I left completely cowed. The memory remains vivid.

            Later, in view of what I had witnessed, it was a shock to realize that in addition to the diamond shaped pattern imitating that of pit vipers, this snake had displayed a total of seven discrete traits and behaviors that copied ones displayed by its dangerous relative: the pile of sinuous coils…reared head held flat, jaws flared…tail borne vertically behind the coils, tip raised and vibrating in a blur…inflated body…exhaled air that sounded amazingly similar to that viscerally fear-inducing rattle…the spirited strikes. Later I learned that these things are all known defensive responses (and that many gopher snakes have died by human hands as a result of their subterfuge). However, the thing that most amazed me was the realization that all these responses were unlearned and purely instinctive. Snakes do not rear their young—no mother snake imparted these skills. Nor is it likely that gopher snakes learn such things through observing their cousins. No: they are born with this remarkable talent for mimicry. How do they know? I pondered this question for years. And still do.

Few literary people are aware that the acclaimed expatriate Russian novelist Vladamir Nabakov was equally famous among butterfly fanciers around the globe. Prior to his career as a writer, Nabakov was a curator of Lepidoptera (butterflies and moths) at the Harvard  Museum of Comparative Zoology. A recognized expert in his field, Nabakov was mindful of contemporary neo-Darwinian thought when he wrote this oft-quoted passage in his autobiography Speak, Memory:

The mysteries of mimicry had a special attraction for me. Its phenomena showed an artistic perfection usually associated with man-wrought things. Consider the imitation of oozing poison by bubblelike macules on a wing (complete with pseudo-refraction) or by glossy yellow knobs on a chrysalis (“Don’t eat me—I have already been squashed, sampled and rejected”)…. When a certain moth resembles a certain wasp in shape and color, it also walks and moves its antennae in a waspish, unmothlike manner. When a butterfly has to look like a leaf, not only are all the details of a leaf beautifully rendered but markings mimicking grub-bored holes are generously thrown in. “Natural selection,” in the Darwinian sense, could not explain the miraculous coincidence of imitative aspect and imitative behavior, nor could one appeal to the theory of “the struggle for life” when a protective device was carried to a point of mimetic subtlety, exuberance, and luxury far in excess of a predator’s power of appreciation.

            Nabakov wrote about these matters in a similar vein in several non-fiction works, often imparting the same attitude of skepticism toward a Darwinian explanation. This has puzzled many of those who knew Nabakov as a credible scientist, fully aware of the heresy he was committing in suggesting there was something more than natural selection at work. Nabakov was certainly not alone—being a member of that skeptics camp he wondered how something that so clearly showed signs of deliberate design could be the end result of slowly accumulating random mutations. But through what naturalistic means does an animal manage to contrive an invisibility cloak?

            Despite claims to the contrary, this is a question that has not yet been answered satisfactorily. But here is an excellent example of how mimicry is explained, from Peter Forbes’ Dazzled and Deceived: Mimicry and Camouflage:

Very often we fall into circular arguments when we speculate on evolution because there is no purpose to it—no end in sight. We see that some organisms have survived, so we say that these must have been the fittest. And which are ‘the fittest’? Those which have survived. But in mimicry one creature has led and another has, through selection, copied it. The old problem of attributing to nature a goal when it has none dissolves in the face of mimicry because, although there is no purpose to the whole of it, for the mimicking species there is a goal: to copy the model. So we have an index of the success of evolution in producing the match. Similarly with the butterflies that mimic dead leaves. Success is demonstrable.

            This is a striking but not atypical example of a phenomenon discussed in the last chapter: readers are warned of circular reasoning’s pitfalls, which the unwary often fall prey to. But the author proceeds to promptly stumble into that very trap. How can we explain camouflage and mimicry from an evolutionary standpoint? Answer: Through the process of natural selection working on genes. How do we know that natural selection accounts for these features? Because, writes Forbes, “in mimicry one creature has led and another has, through selection, copied it.” Their success, as he asserts, “is demonstrable.”

            Odd, that the fallacious reasoning so often glides by unnoticed…that the feature or phenomenon in question is never actually “explained.” Much progress has been made in describing mechanisms behind wing pattern evolution and they are well-supported and make perfect sense. And yet, the real issue—How are these mimicries achieved?—is never directly confronted. The same is true of many remarkable instances of camouflage. How, through gradualistic processes, have genes been modified to the extent that a butterfly so perfectly resembles a fallen leaf that it even includes gnawed-looking edges and dark patches that appear exactly like the decayed places on a dead leaf? What “codes” for a tiny, perfectly placed silver dot that imparts a sense of the moist reflectivity of an eye’s surface? And although this is a different matter, I wonder how moths and other insects that rely on a specific body-axis orientation when hiding on a background of leaf or bark have learned to rotate their bodies so that instead of conspicuously standing out they vanish into thick tropical air. In some instances, this behavior also involves a specific way of positioning legs and antennae. These are simply inherited, instinctive behaviors, we are informed. No doubt this is correct but the fact remains that inherited behaviors—one of biology’s great mysteries—have continually eluded scientific explanation.

            Other unanswered queries: Why, if protective coloration is so readily achieved by way of modular genetic mutation and selection, do more species not “take advantage”of such a highly effective adaptive capacity? And this: If Batesian mimicry is to remain a successful tactic, the mimic has to be significantly less abundant than the model. (If mimics were as common or more abundant than their models, predators “sampling” both species would not learn which were to be avoided.) So how are populations of Batesian mimics world-wide regulated to maintain rarity relative to the populations of their models? Another question, one of those posed by Nabakov: It is widely recognized that specific instances of camouflage and mimicry are often not perfect and need not be so to succeed. Why then does natural selection, throw in such unbelievably subtle and apparently superfluous details? Not only has my research failed to yield answers to these hard questions but thus far I have yet to find askers.

            Such puzzles are little more than distraction in the face of a deeper issue. The phenomena of defense mechanisms and protective coloration are directly entwined with the survival imperative. They recapitulate in the clearest fashion to what lengths life will go in order to further survival. Life always finds a way and its solutions are always something to behold. In the cases of camouflage and mimicry, the artistry and sophistication and sheer variety of the material devices are one of the stronger demonstrations of Natural Design’s creative imperative. Almost all forms of protective coloration show signs of nature’s signature flair, its tendency toward over-embellishment and whimsy combined—paradoxically—with spareness and practicality. And, always, there is that thing Nabakov (with his uncanny knack for language) called “exuberance.” Natural selection, in contrast, is a conceptual tool that makes no attempt to the underscore the enigmatic richness and depth that are immaterial elements of all biological features.

By the same token, positing Natural Design as an explanation goes no further toward elucidating the mechanisms involved. It makes no such claims, being little more than a guidepost. Natural Design offers a way of viewing nature in its entirety as having a capacity to elicit broad-brush changes and somehow speed the arrival of crucial structures and vital processes. Its subtle influence has helped bring about life’s greatest necessities—things like ribosomes and chloroplasts, respiration and photosynthesis, retractable claws and binocular vision.

             As with many of nature’s other countenances, in its highly successful expressions of camouflage and mimicry life becomes (or at least mimics) art. In the case of such utilitarian features, this seems an over-the-top extravagance, a needless addition of fringe and filigree. Perhaps what some of us find a bit unnerving about this esthetic profligacy is the lingering suspicion that this particular form of natural beauty bears a veiled message. What we attempt to explain in utilitarian terms exists in nature as something more than simple practicality. Meanwhile, we are staring directly at the biological message while it remains invisible…hiding in plain sight.                                                                                         

    

     ©2017 by Tim Forsell      draft                                    15 Oct 2017

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[1] This crucial adaptation has been independently “discovered” by ptarmigan, foxes and wolves, hares, and weasels (the mammals being in three separate orders). The mechanisms behind the process have not yet been identified or explained aside from there being a connection to day length.