Coincident disruptive coloration

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Hugh Cott's drawings of 'coincident disruptive coloration' in the frog then called Megalixalus fornasinii formed "persuasive arguments" for natural selection. Left: active; right: at rest, marks coinciding. Cott coincident disruptive coloration Megalixalus fornasinii.jpg
Hugh Cott's drawings of 'coincident disruptive coloration' in the frog then called Megalixalus fornasinii formed "persuasive arguments" for natural selection. Left: active; right: at rest, marks coinciding.

Coincident disruptive coloration or coincident disruptive patterns are patterns of disruptive coloration in animals that go beyond the usual camouflage function of breaking up the continuity of an animal's shape, to join up parts of the body that are separate. This is seen in extreme form in frogs such as Afrixalus fornasini where the camouflage pattern extends across the body, head, and all four limbs, making the animal look quite unlike a frog when at rest with the limbs tucked in.

Contents

A special case is the disruptive eye mask that camouflages the most conspicuous feature of many animals, the eye.

Camouflage mechanism

Cott noted the mechanism when he saw Dendropsophus leucophyllatus, the clown treefrog, and saw its similarity with the distantly related Megalixalus. Dendropsophus leucophyllatus.jpg
Cott noted the mechanism when he saw Dendropsophus leucophyllatus , the clown treefrog, and saw its similarity with the distantly related Megalixalus.

Historical description

The English zoologist and camouflage expert Hugh Cott explained, while discussing "a little frog known as Megalixalus fornasinii" in the chapter on coincident disruptive coloration in his 1940 book Adaptive Coloration in Animals , that [2]

Forewing pattern of many moths such as Biston strataria, the oak beauty moth, coincides with pattern on the narrow margin of hindwing visible at rest. (1930) Oak Beauty (Biston strataria) (cropped).jpg
Forewing pattern of many moths such as Biston strataria , the oak beauty moth, coincides with pattern on the narrow margin of hindwing visible at rest.

It is only when the pattern is considered in relation to the frog's normal attitude of rest that its remarkable nature becomes apparent... The attitude and very striking colour-scheme thus combine to produce an extraordinary effect, whose deceptive appearance depends upon the breaking up of the entire form into two strongly contrasted areas of brown and white. Considered separately, neither part resembles part of a frog. Together in nature the white configuration alone is conspicuous. This stands out and distracts the observer's attention from the true form and contour of the body and appendages on which it is superimposed. [2]

Cott concluded that the effect was concealment "so long as the false configuration is recognized in preference to the real one". [2]

Taxonomic range

Coincident disruptive coloration is seen in other amphibians including the common frog, Rana temporaria , in which the dark and light bands that cross the body and hind legs coincide in the resting position, joining separate anatomical structures visually and breaking up and taking attention away from the body's actual outlines. [3]

Disruptive patterns on underside of orange-tip butterfly Anthocharis cardamines coincide across fore- and hind-wings. Anthocharis cardamines female MichaD.jpg
Disruptive patterns on underside of orange-tip butterfly Anthocharis cardamines coincide across fore- and hind-wings.

Several moths and butterflies make use of the mechanism; these include the oak beauty moth Biston strataria and the scalloped oak moth Crocallis elinguaria , in which the pattern on the forewing coincides with the pattern on the narrow strip of the hindwing which is visible in the moth's habitual resting position. Many moths and butterflies which often rest with the wings closed, such as the orange-tip Anthocharis cardamines , do the same but on the cryptically-coloured underside of the wings. [4] [3]

Disruptive eye mask

The jack-knifefish, Equetus lanceolatus, has a strongly disruptive pattern on body and through the eye, forming a disruptive eye mask. Equetus lanceolatus in Madagascar Reef.jpg
The jack-knifefish, Equetus lanceolatus , has a strongly disruptive pattern on body and through the eye, forming a disruptive eye mask.

One form of coincident disruptive coloration has special importance. Disruptive eye masks camouflage the eyes of a variety of animals, both invertebrates such as grasshoppers and vertebrates such as fishes, frogs, birds and snakes; some mammals have similar patterns. The eye has a distinctive shape and dark coloration dictated by its function, and it is housed in the vulnerable head, making it a natural target for predators. It can be camouflaged by a suitable disruptive pattern arranged to run up to or through the eye, in other words to coincide with it, such as the camouflage eyestripe of the Mexican vine snake and certain fishes. [2] [5] [6]

Created in active camouflage

Sepia apama actively creating a coincident disruptive pattern across its body parts Sepia apama creating coincident disruptive pattern.jpg
Sepia apama actively creating a coincident disruptive pattern across its body parts

Cephalopods are capable of active camouflage, by day used for signalling as well as camouflage. At night, 86% of giant Australian cuttlefish, Sepia apama , were seen to select camouflage patterns. Most often (41%), these were disruptive, the patterns coinciding across the cuttlefish's body parts. [7]

Experimental test

The effect was tested in two experiments in 2009 by Innes Cuthill and Aron Székely. The first experiment presented wild insect-eating birds with edible pastry targets resembling moths, with or without coincident disruptive patterns. The second experiment showed similar targets to humans on computer screens. They found in both experiments that coincident disruption was "an effective mechanism for concealing an otherwise revealing body form". [8] [9]

Evidence for natural selection

In the words of the camouflage researchers Innes Cuthill and A. Székely, Cott's book provided "persuasive arguments for the survival value of coloration, and for adaptation in general, at a time when natural selection was far from universally accepted within evolutionary biology." [1] In particular, they argued, Cott's category of "Coincident Disruptive Coloration" "made Cott's drawings the most compelling evidence for natural selection enhancing survival through disruptive camouflage." [1]

Such patterns, Cott stressed, embody considerable precision. The markings must line up accurately between the folded limbs and body for the disguise to work. Cott's description and in particular his drawings convinced biologists that the markings must have survival value, rather than occurring by chance. Further, as Cuthill and Székely indicate, the bodies of animals that have such patterns must therefore have been shaped by natural selection. [1]

Related Research Articles

<span class="mw-page-title-main">Camouflage</span> Concealment in plain sight by any means, e.g. colour, pattern and shape

Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the battledress of a modern soldier, and the leaf-mimic katydid's wings. A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate, as well as making general aiming easier. The majority of camouflage methods aim for crypsis, often through a general resemblance to the background, high contrast disruptive coloration, eliminating shadow, and countershading. In the open ocean, where there is no background, the principal methods of camouflage are transparency, silvering, and countershading, while the ability to produce light is among other things used for counter-illumination on the undersides of cephalopods such as squid. Some animals, such as chameleons and octopuses, are capable of actively changing their skin pattern and colours, whether for camouflage or for signalling. It is possible that some plants use camouflage to evade being eaten by herbivores.

<span class="mw-page-title-main">Motion camouflage</span> Camouflage by choosing path to avoid seeming to move against background

Motion camouflage is camouflage which provides a degree of concealment for a moving object, given that motion makes objects easy to detect however well their coloration matches their background or breaks up their outlines.

<span class="mw-page-title-main">Hugh B. Cott</span> English zoologist and camouflage expert (1900–1987)

Hugh Bamford Cott was a British zoologist, an authority on both natural and military camouflage, and a scientific illustrator and photographer. Many of his field studies took place in Africa, where he was especially interested in the Nile crocodile, the evolution of pattern and colour in animals. During the Second World War, Cott worked as a camouflage expert for the British Army and helped to influence War Office policy on camouflage. His book Adaptive Coloration in Animals (1940), popular among serving soldiers, was the major textbook on camouflage in zoology of the twentieth century. After the war, he became a Fellow of Selwyn College, Cambridge. As a Fellow of the Zoological Society of London, he undertook expeditions to Africa and the Amazon to collect specimens, mainly reptiles and amphibians.

<span class="mw-page-title-main">Countershading</span> Camouflage to counteract self-shading

Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and insects, both in predators and in prey.

<i>Afrixalus fornasini</i> Species of amphibian

Afrixalus fornasini is a species of frog in the family Hyperoliidae and is native to Africa. Its common name is Fornasini's spiny reed frog or the greater leaf-folding frog

<span class="mw-page-title-main">Animal coloration</span> General appearance of an animal

Animal colouration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. Some animals are brightly coloured, while others are hard to see. In some species, such as the peafowl, the male has strong patterns, conspicuous colours and is iridescent, while the female is far less visible.

<span class="mw-page-title-main">Cuttlefish</span> Order of molluscs

Cuttlefish, or cuttles, are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.

<span class="mw-page-title-main">Underwater camouflage</span> Camouflage in water, mainly by transparency, reflection, counter-illumination

Underwater camouflage is the set of methods of achieving crypsis—avoidance of observation—that allows otherwise visible aquatic organisms to remain unnoticed by other organisms such as predators or prey.

<span class="mw-page-title-main">Disruptive coloration</span> Camouflage to break up an objects outlines

Disruptive coloration is a form of camouflage that works by breaking up the outlines of an animal, soldier or military vehicle with a strongly contrasting pattern. It is often combined with other methods of crypsis including background colour matching and countershading; special cases are coincident disruptive coloration and the disruptive eye mask seen in some fishes, amphibians, and reptiles. It appears paradoxical as a way of not being seen, since disruption of outlines depends on high contrast, so the patches of colour are themselves conspicuous.

<i>Adaptive Coloration in Animals</i> 1940 textbook on camouflage, mimicry and aposematism by Hugh Cott

Adaptive Coloration in Animals is a 500-page textbook about camouflage, warning coloration and mimicry by the Cambridge zoologist Hugh Cott, first published during the Second World War in 1940; the book sold widely and made him famous.

<i>Concealing-Coloration in the Animal Kingdom</i> Book by Abbott Handerson Thayer

Concealing-Coloration in the Animal Kingdom: An Exposition of the Laws of Disguise Through Color and Pattern; Being a Summary of Abbott H. Thayer’s Discoveries is a book published ostensibly by Gerald H. Thayer in 1909, and revised in 1918, but in fact a collaboration with and completion of his father Abbott Handerson Thayer's major work.

<span class="mw-page-title-main">Deimatic behaviour</span> Bluffing display of an animal used to startle or scare a predator

Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. The term deimatic or dymantic originates from the Greek δειματόω (deimatóo), meaning "to frighten".

<i>Animal Coloration</i> (book) 1892 book by Frank Evers Beddard

Animal Coloration, or in full Animal Coloration: An Account of the Principal Facts and Theories Relating to the Colours and Markings of Animals, is a book by the English zoologist Frank Evers Beddard, published by Swan Sonnenschein in 1892. It formed part of the ongoing debate amongst zoologists about the relevance of Charles Darwin's theory of natural selection to the observed appearance, structure, and behaviour of animals, and vice versa.

<span class="mw-page-title-main">Multi-spectral camouflage</span> Camouflage designed to work at multiple frequencies, not just visible light

Multi-spectral camouflage is the use of counter-surveillance techniques to conceal objects from detection across several parts of the electromagnetic spectrum at the same time. While traditional military camouflage attempts to hide an object in the visible spectrum, multi-spectral camouflage also tries to simultaneously hide objects from detection methods such as infrared, radar, and millimetre-wave radar imaging.

<span class="mw-page-title-main">Coloration evidence for natural selection</span> Early evidence for Darwinism from animal coloration

Animal coloration provided important early evidence for evolution by natural selection, at a time when little direct evidence was available. Three major functions of coloration were discovered in the second half of the 19th century, and subsequently used as evidence of selection: camouflage ; mimicry, both Batesian and Müllerian; and aposematism.

<span class="mw-page-title-main">Distractive markings</span>

Distractive markings serve to camouflage animals or military vehicles by drawing the observer's attention away from the object as a whole, such as noticing its outline. This delays recognition. The markings necessarily have high contrast and are thus in themselves conspicuous. The mechanism therefore relies, as does camouflage as a whole, on deceiving the cognition of the observer, not in blending with the background.

Martin Stevens is a British sensory and evolutionary ecologist, an underwater photographer and a natural history and popular science writer. He is known for his work on disruptive coloration in animal camouflage.

<span class="mw-page-title-main">Disruptive eye mask</span> Camouflage to conceal the eye

Disruptive eye masks are camouflage markings that conceal the eyes of an animal from its predators or prey. They are used by prey, to avoid being seen by predators, and by predators to help them approach their prey.

<i>Dazzled and Deceived</i> Camouflage book by Peter Forbes

Dazzled and Deceived: Mimicry and Camouflage is a 2009 book on camouflage and mimicry, in nature and military usage, by the science writer and journalist Peter Forbes. It covers the history of these topics from the 19th century onwards, describing the discoveries of Henry Walter Bates, Alfred Russel Wallace and Fritz Müller, especially their studies of butterflies in the Amazon. The narrative also covers 20th-century military camouflage, begun by the painter Abbot Thayer who advocated disruptive coloration and countershading and continued in the First World War by the zoologist John Graham Kerr and the marine artist Norman Wilkinson, who developed dazzle camouflage. In the Second World War, the leading expert was Hugh Cott, who advised the British army on camouflage in the Western Desert.

References

  1. 1 2 3 4 Cuthill, I. C.; Székely, A. (2011). Stevens, Martin; Merilaita, Sami (eds.). Animal Camouflage: Mechanisms and Function. Cambridge University Press. p. 50. ISBN   978-1-139-49623-0.
  2. 1 2 3 4 5 Cott, Hugh B. (1940). Adaptive Coloration in Animals. Methuen. pp.  68–72.
  3. 1 2 Cloudsley-Thompson, John Leonard (1989). "Some Aspects of Camouflage in Animals" (PDF). Qatar University Science Bulletin. 9: 141–158.
  4. Evans, David L. (1983). "Relative Defensive Behavior of Some Moths and the Implications to Predator-Prey Interactions". Entomologia Experimentalis et Applicata. 33 (1): 103–111. doi:10.1111/j.1570-7458.1983.tb03240.x. S2CID   85407476.
  5. Barlow, G. W. (1972). "The attitude of fish eye-lines in relation to body shape and to stripes and bars". Copeia. 1972 (1): 4–12. doi:10.2307/1442777. JSTOR   1442777.
  6. Gavish, Leah; Gavish, Benjamin (1981). "Patterns that conceal a bird's eye". Z. Tierpsychol. 56 (3): 193–204. doi:10.1111/j.1439-0310.1981.tb01296.x.
  7. Hanlon, Roger T.; Naud, Marie‐José; Forsythe, John W.; Hall, Karina; Watson, Anya C.; McKechnie, Joy (2007). "Adaptable Night Camouflage by Cuttlefish" (PDF). The American Naturalist. 169 (4): 543–551. doi:10.1086/512106. hdl: 2440/45458 . PMID   17427123. S2CID   850591.
  8. Cuthill, I. C.; Szekely, A. (2009). "Coincident disruptive coloration". Philosophical Transactions of the Royal Society B: Biological Sciences. 364 (1516): 489–496. doi:10.1098/rstb.2008.0266. PMC   2674087 . PMID   18990668.
  9. Stevens, Martin; Cuthill, Innes C.; Alejandro Párraga, C.; Troscianko, Tom (2006). "Chapter 4 The effectiveness of disruptive coloration as a concealment strategy". Visual Perception - Fundamentals of Awareness: Multi-Sensory Integration and High-Order Perception. Progress in Brain Research. Vol. 155. pp. 49–64. doi:10.1016/S0079-6123(06)55004-6. ISBN   9780444519276. PMID   17027379.