Immediate Adaptation

IMMEDIATE ADAPTATION

Instantaneous Camouflage in the Animal Kingdom

COMPILED AND DESIGNED BY BRANDON LEE


IMMEDIATE ADAPTATIONInstantaneous Camouflage in the Animal Kingdom

780811984 398495937


COMPIlED AND DEsIgNED by brANDON lEE


IMMEDIATE ADAPTATION Instantaneous Camouflage in the Animal Kingdom

Book design copyright © 2010 by Brandon Lee

Published by Brandon Lee for course number GR.330,

Typography 3, taught online by Carolina de Bartolo

in Fall, 2010 at Academy of Art University, San

Francisco, CA. Printed at on Epson Stylus Photo

R1900. Bound at The Key, Oakland, CA, USA.

All rights reserved.


CONTENTs

1

17

33

51

65

ADAPTATION

CHrOMATOPHOrEs

CEPHAlOPODs

VErTEbrATEs

EVOlUTION

CHAPTEr 1

CHAPTEr 2

CHAPTEr 3

CHAPTEr 4

CHAPTEr 5

One of the biggest shifts in an animal’s surround-

ings occurs with the changing of the seasons. In

the spring and summer, a mammal’s habitat might

be full of greens and browns, while in the fall

and winter, everything can be covered with snow.

While brown coloration is perfect for a summer

wooded environment, it makes an animal an easy

target against a white background. Many birds

and mammals deal with this by producing different

colors of fur or feathers depending on the time

of year. In most cases, either changing amounts

of daylight or shifts in temperature trigger a

hormonal reaction in the animal that causes it to

produce different biochromes.

ADAPTATIONTHE ArT OF sUrVIVAl

1ADAPTION

ADAPTATIONs CAN bE ANy bEHAVIOrAl Or PHysICAl

characteristics of an animal that help it to sur-

vive in its environment. These characteristics fall

into three main categories: body parts, body cover-

ings, and behaviors. Any or all of these types of

adaptations play a critical role in the survival

of an animal.

FEW ADAPTATIONs CAN bE EITHEr PHysICAl Or bE

behavioral. A physical adaptation is some type of

structural modification made to a part of the body.

A behavioral adaptation is something an animal

does—how it acts—usually in response to some type

of external stimulus. When you look at an animal,

you usually can see some of its adaptations—like

what it is able to eat, how it moves, or how it may

protect itself. Different animals have many differ-

ent ways of trying to stay alive. Their adaptations

are matched to their way of surviving. Each group

of animals has its own general adaptations. These

groups are: fish, amphibians, reptiles, birds, and

mammals. Some of these adaptations make it easy to

identify which group an animal belongs to. A good

example of an animal adaptation is the way in which

an animal moves from one place to another.

AN ANIMAl’s bODy COVEr Is ONE ClEArly VIsIblE

adaptation. Body coverings help to protect animals

in diverse environments—from the land to water,

from the arctic to the desert. Mammals have hair,

or fur, that helps insulate their bodies. It keeps

them warm in winter and can protect specific areas

of the body, like eyelashes protecting the eyes.

Some mammals have different coverings: the arma-

dillo has plates, the porcupine has quills, and

naked skin covers the dolphin. All of these help

these mammals to survive in the different condi-

tions in which they live. Birds also have a very

protective covering: feathers. The feathers keep

the bird warm in winter, help it fly or swim, and

help fan the bird in hot weather.

2 IMMEDIATE ADAPTATION

CONCENTrATION OF PIgMENT IN THE HUMAN EyE

The makeup of the iris of the human eye. Pigment gets

more layered and dense the further away from the iris.

pupil

iris

sclera

fig 1.1

AMPHIbIANs AND rEPTIlEs HAVE bODy COVErINgs

that protect them as well. Amphibians have moist,

slick skin that is well suited for the water. Rep-

tiles have tough, dry skin covered by scales.

Insects, such as the cockroach, have coverings

that enable them to squeeze into very small places.

This allows them to find food and shelter. Many

insects build nests—a behavioral adaptation—or

cocoons—behavioral and structural adaptation—for

the winter because their body coverings alone do

not permit them to adjust to the cold. Many insects

also have other adaptations included in their body

coverings: cells that sense light and pigments that

allow some insects to change colors in order to

hide themselves from predators.

3ADAPTION

Crab spider

Anole

Tree Frog

golden beetle

sea Horse

Chameleon

blue ring Octopus

Flounder

Cuttlefish

Arctic Mammal

DUrATION PErIOD FOr APPEArANCE CHANgE

The amount of time that it will take a particular animal

to complete the cycle of changing their appearance. Note

that not all theses changes are equally drastic.

1sec

5wks

2sec

3sec

30sec

2min

5min

4mnths

2hrs

fig 1.2


2wks

AN ADAPTATION Is sOMETHINg AbOUT AN ANIMAl

that makes it possible for it to live in a par-

ticular place and in a particular way. It may be

a physical adaptation, like the size or shape of

the animal’s body, or the way in which its body

works. Or it may be the way the animal behaves.

Each adaptation has been produced by evolution.

As the environment changes, animals that cannot

adapt die out, and only the adapted ones survive

to produce babies. Because babies are usually more

or less like their parents, the whole species soon

contains only animals that have been adapted to

the new environment.

AN ANIMAl’s ENVIrONMENT CONsIsTs OF MANy

different things. The climate is important. Whether

it is hot, cold, dry, or wet will have an effect on

all the creatures that live in a particular place.

Another important part of an animal’s environment

is what kinds of food plants grow in it. The other

animals that live there also have an effect. If

there are predators around, the prey animals will

have to learn to defend themselves or run fast to

escape. These adaptations make it possible for a

great variety of creatures to live and thrive on

earth. animals adapt to the natural world.

THErE ArE ANIMAls WHO HAVE CErTAIN CHEMICAl

compositions that allow the microscopic pigments

in their external coverings called biochromes, to

absorb and chemically produce their color combina-

tions. The most apparent or visible colors trans-

mitted in the form of wavelengths refracted by the

light in the animal’s surroundings, will dictate

the color or appearance of the camouflage animal.

Hence, the amount of day light will also influence

the color that an animal will assume.

5ADAPTION

THE MOsT COMMON ExAMPlE OF THEsE TyPEs OF

animals is the chameleon with its remarkable abili-

ties to match the exact color of its surroundings.

Other species include insects that have the ability

to take the form of bird droppings or some butter-

flies that can resemble a leaf. Certain species of

fish have the ability to assume the form of a fallen

leaf in stream bed surfaces or become transparent

to effectively elude its predator as it swims away

to safety. The different ways by which camouflage

animals conceal themselves, is a manifestation that

disguising is the most effective way to survive in

their habitats.

POlAr bEArs HAVE HAIr THAT Is ACTUAlly ClEAr

while their skin is naturally black. They appear

white as the light bounces around once it makes

contact with the hair and is deflected back as white

since it is the predominant color of its snowy

surroundings. A zebra actually has dark brown and

white stripes and scientists call the zebra’s cam-

ouflage strategy, disruptive coloration. Zebras flee

from their predators and become a blur as they

blend in their surroundings, especially if the

heat of the desert creates some haze. At night, the

optical illusions that the shadows can play on the

zebra’s white stripes make them very hard to dis-

cern from the environment.

THE ACTUAl sTrUCTUrEs OF THE ANIMAl’s OUTEr

covering help in simple processes of concealment

like the squirrels with their coarse and uneven

fur as it can effectively resemble the bark of a

tree. Some animals have two different layers of

skin common among amphibians, snakes and fish. The

inner layer has a yellow pigment while the outer

layer can scatter light to assume a bluish hue.

As both yellow pigments and refracted blue lights

combine, the animal creates a green coloring as

its skin layers.


ANIMAls THAT CAMOUFlAgE AND THEIr AbIlITy

for concealment and deception have been put to a

test as their tool for survival is compromised by

certain changes in the environment. However, those

with superior camouflage characteristics have shown

great strategies in adaptation. Since some animals

have inherent biochromes that absorb the predomi-

nant colors refracted by the light, such animals

or insects could easily assume the appearance of a

dead leaf or a twig instead of green.

THErE ArE THE sO-CAllED DECOrATOr CrAbs

who decorate themselves with leaves as camouflage

devises. They have shown perceptual capabilities

as they know which leaves to select. They may carry

a plant for its value as food for sustenance but

they have been observed to carry the leaves of a

chemically toxic brown alga to elude a predatory

fish. In fact, these selective methods remain a mys-

tery to scientists which are known to them as the

perceptual mechanisms of camouflage animals.

As sOON As sOME ANIMAls PErCEIVE CHANgEs

in their environment, they relocate and select

an environment which closely matches their color.

This then increases their chances for survival.

They will be able to survive longer to physically

and chemically develop in order to adapt to their

surroundings. In time, these animals will have

offspring and pass on their coloration and will

gradually master the art of deception using their

camouflage machinations.

IT MAkEs HUMANs AlMOsT ENVIOUs THAT ANIMAls

that camouflage themselves have such capabilities

to survive no matter the changes the environment

may bring upon them. This is probably one of the

reasons why, there is renewed interests among sci-

entists and researchers in studying the camouflage

abilities of these animal species. Perhaps, they

will learn more strategies for survival that could

be used for other purposes.

7ADAPTION

fig 1.3

Chameleonblue ring Octopus FlounderCuttlefish

KINDS OF ANIMALS THAT CAN CHANGE COLOR

Peron’sTree Frog

ChameleonCuttlefish Blue RingOctopus

Flounder Golden TortoiseBeetle

Sea Horse Anole(Lizard)

rANgE OF APPEArANCE CHANgE AbIlITy

The effective range of color, texture and pattern a

particular animal can alter to its outward appearance

within a short period of time.

ANIMAls HAVE EVOlVED THEIr ADAPTATIONs. THIs

means a long period of slow change resulted in an

animal’s adaptation. The spots on the snow leopard,

for example, did not emerge overnight. Instead,

this process took generation upon generation of

snow leopards physically adapting to their envi-

ronment for characteristic spot patterns to evolve.

Those snow leopards with spot patterns were able to

hide more successfully, therefore surviving longer

than those without spots. This allowed the longer

surviving snow leopards to reproduce and create

more snow leopards with spot patterns like their

own. Indeed, this process of change over time is

the key to how many organisms develop adaptations.

Some adaptations can arise quickly through genetic

mutations; these mutations also may be deadly.


Anole (lizard)Peron’s Tree Froggolden Tortoise beetle sea Horse

KINDS OF ANIMALS THAT CAN CHANGE COLOR

Peron’sTree Frog

ChameleonCuttlefish Blue RingOctopus

Flounder Golden TortoiseBeetle

Sea Horse Anole(Lizard)

ANOTHEr rEMArkAblE ExAMPlE Is THE PEPPErED

moth of England, whom scientists initially studied

in the 1800s as having black scales on their wings

and body. They were notably specked with white;

hence, they were given the name peppered moths.

However, when England became highly-industrialized

and highly polluted, the trees became soot-black

making the peppered moths obvious and visible.

Thus, they were easily pounced upon by their bird

predators during mealtime. In subsequent years to

come, scientists were happy to discover that these

moths did away with their white specks and turned

almost black, thus they were able to reproduce and

survive in the harsh environment.

FEATHErs AND FUr IN ANIMAls ArE lIkE HUMAN

hair and fingernails—they are actually dead tissue.

They are attached to the animal, but since they are

not alive, the animal can do nothing to alter their

composition. Consequently, a bird or mammal has to

produce a whole new coat of fur or feathers in order

to change color. In many reptiles, amphibians and

fish, on the other hand, coloration is determined by

biochromes in living cells. Biochromes may be in

cells at the skin’s surface or in cells at deeper

levels in the dermis.

9ADAPTATION

sOME ANIMAls, sUCH As VArIOUs CUTTlEFIsH

species, can manipulate their chromatophores to

change their overall skin color. These animals

have a collection of chromatophores, each of which

contains a single pigment. An individual chro-

matophore is surrounded by a circular muscle that

can constrict and expand. When the cuttlefish con-

stricts the muscle, all the pigment is squeezed to

the top of the chromatophore. At the top, the cell

is flattened out into a wide disc. When the muscle

relaxes, the cell returns to its natural shape of

a relatively small blob. This blob is much harder

to see than the wide disc of the constricted cell.

By constricting all the chromatophores with a cer-

tain pigment and relaxing all the ones with other

pigments, the animal can change the overall color

of its body.

CUTTlEFIsH WITH THIs AbIlITy CAN gENErATE A

wide range of colors and many interesting pat-

terns. By perceiving the color of a backdrop and

constricting the right combination of chromato-

phores, the animal can blend in with all sorts of

surroundings. Cuttlefish may also use this ability

to communicate with each other. The most famous

color-changer, the chameleon, alters its skin color

using a similar mechanism, but not usually for

camouflaging purposes. Chameleons tend to change

their skin color when their mood changes, not when

they move into different surroundings.

sOME ANIMAl sPECIEs ACTUAlly CHANgE WHICH

pigments are in their skin. Nudibranches—a small

sea creature—change their coloration by altering

their diet. When a nudibranch feeds from a particu-

lar sort of coral, its body deposits the pigments

from that coral in the skin and outer extensions of

the intestines. The pigments show through, and the

animal becomes the same color as the coral. Since

the coral is not only the creature’s food, but also

its habitat, the coloration is perfect camouflage.


VIsIbIlITy OF ANIMAls IN ENVIrONMENT

The visibility of an animal changes drastically with the

environment that it is in. A second on a snow covered

field for a dark brown rodent can make the difference

between life and death.

Visibility

Camouflage

fig 1.4

When the creature moves on to a differently colored

piece of coral, its body color changes with the new

food source. Similarly, some parasite species, such

as the fluke, will take on the color of their host,

which is also their home.

MANy FIsH sPECIEs grADUAlly PrODUCE VArIOUs

pigments without changing their diet. This works

something like seasonal molting in mammals and

birds. When the fish changes environments, it

receives visual cues of a new surrounding model.

Based on this stimulus, it begins to release hor-

mones that change how its body produces pigments.

Over time, the fish’s coloring changes to match the

new surroundings.

11ADAPTATION

rAPID COlOr CHANgE Is AN AMAzINg NATUrAl

phenomenon that has evolved in several vertebrate

and invertebrate lineages. The two principal expla-

nations for the evolution of this adaptive strategy

are (1) natural selection for crypsis against a

range of different backgrounds and (2) selection for

conspicuous social signals that maximize detect-

ability to conspecifics, yet minimize exposure to

predators because they are only briefly displayed.

Here we show that evolutionary shifts in capacity

for color change in southern African dwarf chame-

leons are associated with increasingly conspicuous

signals used in male contests and courtship. To

the chameleon visual system, species showing the

most dramatic color change display social signals

that contrast most against the environmental back-

ground and amongst adjacent body regions. We found

no evidence for the crypsis hypothesis, a finding

reinforced by visual models of how both chameleons

and their avian predators perceive chameleon color

variation. Instead, our results suggest that selec-

tion for conspicuous social signals drives the evo-

lution of color change in this system, supporting

the view that transitory display traits should be

under strong selection for signal detectability.

THE AbIlITy TO CHANgE COlOr HAs EVOlVED IN

numerous vertebrate and invertebrate groups, the

most well-known of which are chameleons and ceph-

alopods—octopuses and their relatives. There is

great variation among species, however, in the

apparent capacity for color change, ranging from

limited changes in brightness to dramatic changes

in hue. What drives the evolution of this remark-

able strategy? Addressing this question by using

a combination of field-based behavioral trials in

which quantified color change, models of color per-

ception, and knowledge of phylogenetic relation-

ships for 21 distinct lineages of southern African

dwarf chameleons.


rEsUlTs OF CEll lAyErINg

When chromatophore cells use multiple layers of various

colors, the results are a wide range of shades and tones.

These cells can have a simple 2 layer build, to a more

diverse build of 6 layers.

1 cell 2 cells 3 cells 4 cells 5 cells 6 cells

fig 1.5

sHOWINg THAT EVOlUTIONAry CHANgEs IN THE

capacity for color change are consistently associ-

ated with the use of social signals that are highly

conspicuous to the visual system of chameleons.

Moreover, capacity for color change is unrelated

to variation in the environmental backgrounds that

chameleons must match in order to be camoufl aged.

Overall, results suggest that the evolution of

the ability to exhibit striking changes in color

evolved as a strategy to facilitate social signal-

ing and not, as popularly believed, camoufl age.

13ADAPTATION

fig 1.4lOCATION OF ANIMAls THAT

UTIlIzE CAMOUFlAgE

The worldwide ratio of animals who

possess the ability of instant adap-

tation, marked by the number of such

species within each location. Note

the higher density around warmer,

coastal regions.

ratio key

11+ species

8-10 species

6-8 species

4-6 species

2-4 species

0-2 species


15ADAPTATION

A chromatophore are specialized cells which can

contain or produce pigment, or reflect light in

a specific way to create a certain desired hue.

They are found in cold blooded animals like fish,

amphibians, reptiles, crustaceans, and cephalo-

pods, along with certain bacteria. Chromatophores

serve a number of functions—in addition to giving

color to the skin and eyes of these animals—the

cells can also help to protect the animals from

predators or radiation, and they are also used

to signal other creatures. Scientists also use

chromatophores to study various aspects of animal

life—the cells have been identified and studied

since the early 1800s.

CHrOMATOPHOrEsTHE bUIlDINg blOCks OF CHANgE

17THE CHrOMATOPHOrE

THE CHrOMATOPHOrE CEll

The cell contains the pigment sac in the center, which

in turn gets pulled and elongated by the muscles sur-

rounding it from all sides, creating the appearance of

a field of color.

radial Muscles

Nucleus

Pigment granules

fig 2.1

sOME bIOlOgIsTs brEAk CHrOMATOPHOrEs UP

into two rough categories: biochromes and schemo-

chromes. Biochromes actually contain and produce

pigment, while schemochromes can change the way

that light reflects from the skin of the animal,

thereby changing its color. Biologists may also

classify a chromatophore by the colors that it

produces—cyanophores, for example, produce colors

in the blue range. Iridescent animal coloring is

produced by iridophores.


IN ADDITION TO sIMPly CrEATINg FlAT COlOr,

many chromatophores can also be used to help an

animal change color. This trait is often observed

in animals like octopi, lizards, and some fish. The

cells can accomplish a color change by expanding or

contracting each individual chromatophore to cover

varying areas of the animal’s skin, in response to

stimuli like light. In addition to making excel-

lent camouflage, these color changing cells can

also help an animal regulate its body temperature,

or they can signal information to other animals of

the same species.

PEOPlE WHO HAVE ObsErVED THE rAPID COlOr

change of animals like octopi have probably noticed

that the color change spreads like a blush, rather

than happening all at once. This appears to be

caused by a sequential firing order for neurons in

the brain as they respond to a changing environ-

ment. Creatures like octopi with a highly refined

chromatophore control system can mimic the color

and texture of their environment remarkably well—

this camouflage technique is used to hide from

predators and also to pursue unsuspecting prey.

PHOTOsyNTHETIC bACTErIA OCCAsIONAlly AlsO

use chromatophores, to help them produce energy.

The pigments in bacteria may take the form of bac-

teriochlorophyll, and they are capable of photo-

synthesis. Different bacteria may use and arrange

their chromatophores in different ways, depending

on how they evolved and where they live. Depending

on the bacteria, the colors a chromatophore takes

can range from rich brown to bright green.

19THE CHrOMATOPHOrE

A PIgMENTED sTrUCTUrE Is FOUND IN ANIMAls,

generally in the integument. The term is usu-

ally restricted to those structures that bring

about changes in color or brightness. A majority

of chromatophores are single cells that are highly

branched and contain pigment granules that can

disperse or aggregate within the cell. However,

in coleoid cephalopod mollusks, the chromatophores

function as miniature organs, and changes in the

dispersion of pigment are brought about by muscles.

Although the mode of action of the two types of

chromatophore is completely different, the effect

is the same: pigment either is spread out over a

large area of the body or is retracted.

THE MOVEMENT OF PIgMENT TAkEs PlACE IN MANy

chromatophores simultaneously, so that the effect

is a change in the quality of light reflected from

the surface of the animal. The color change func-

tions as a camouflage from predator or prey, but it

may also serve for regulating temperature, protect-

ing against harmful radiation, and in signaling.

Light stimulates the responses of chromatophores,

generally indirectly via the eyes and central ner-

vous system.

sINglE-CEll CHrOMATOPHOrEs ArE FOUND IN sOME

annelids, insects, and echinoderms. They are much

more conspicuous in crustaceans, in fishes—espe-

cially in bony fish and teleosts—in anuran amphib-

ian, and in a few reptiles. The chromatophores may

be uniformly distributed in the skin (chameleons),

or they may occur in patches (flounders) or lines

(around the abdomen in shrimps). Chromatophores of

various colors may be distributed unevenly across

the body, and occur at different depths in the skin.

CHrOMATOPHOrEs WIll PrODUCE THEIr COlOrs

by reflection after absorption of light. Generally,

the light comes from above, but it may come from

below after reflection from an underlying structure.

The most common type of chromatophore contains


CHrOMATOPHOrE CEll ExPANsION

The amount of physical expansion a single chromatophore

can make within a split second, increasing the amount of

pigment visible on the skins surface. Note that the cell

will expand to roughly 100 times its relaxed state.

blue ring Octopus Cuttlefish

1.5mm

0.6mm

0.015mm

0.006mm

fig 2.2

melanin—and is, therefore, often called a melano-

phore—which absorbs all wavelengths so that the

chromatophore appears black; other types have red

(erythrophores) or yellow (xanthophores) pigments.

These pigments generally derive from carotenoids

in vertebrates.

CHrOMATOPHOrEs CONTAIN PIgMENT grANUlEs TO

move within them, giving them an appearance that

ranges from spotted to fibrous on the five-stage

scale that is widely used to measure the degree of

chromatophore expansion. If the pigment within the

particular cell is black or brown, the integument

takes on a dark appearance when most of the chro-

matophores are in the last stage of dispersion. If

the pigment color is yellow or cream, the animal

tends to look paler if all the chromatophores are

at that stage.

21THE CHrOMATOPHOrE

fig 2.3

There are 6 basic types of chromatophores that make

up the thousands of possible color combinations

within the skin of an animal.

MElANOPHOrE

These cells synthesize and contain black

and brown pigmentation known as melanin. There

are two kinds of melanophores present, dermal

and epidermal. Dermal melanophores are located

in the upper dermis, while epidermal melano-

phores are located in the lower epidermis skin

layers.

IrIDOPHOrE

These are tiny stacks of plates, which act as

a diffraction grating, and produce iridescent

colors. Iridescent blues in butterflies and birds

are also produced by diffraction, i.e. split-

ting and spreading out the different colors of

the spectrum. Depending on the spacing and the

angle of the observer, different colors are seen.

These are called structural colors, since they

depend on the structure of the material rather

than a pigment. In the cuttlefish, iridophore col-

ors are relatively fixed, but hormones do cause

some change.

lEUCOPHOrE

These are similar to iridophores, but are flat

and more orderly plates that reflect light rather

than diffract it. Their color matches the sur-

rounding light: white light will produce a white

shine, but if incoming light is a different

color, then that’s what will be reflected. This

helps with camouflage.

fig 2.4

fig 2.5


xANTHOPHOrE

Chromatophores that contain large amounts of

yellow pteridine pigments are named xantho-

phores; those with a preponderance of red/orange

carotenoids are termed erythrophores. Pteridine

and carotenoid containing vesicles are some-

times found within the same cell, in which case

the overall color depends on the ratio of red

and yellow pigments. Therefore, the distinction

between these chromatophore types is not always

clear.

EryTHrOPHOrE

The capacity to generate pteridines from guano-

sine triphosphate is a feature common to most

chromatophores, but xanthophores appear to have

supplemental biochemical pathways that result

in an excess accumulation of yellow pigment. In

contrast, carotenoids are metabolised from the

diet and transported to erythrophores. This was

first demonstrated by rearing normally green

frogs on a diet of carotene-restricted crickets.

The absence of carotene in the frogs’ diet meant

the red/orange carotenoid color ‘filter’ was not

present in their erythrophores. This resulted

in the frogs appearing blue in color, instead

of green.

PHOTOPHOrE

This actually emits light, rather than absorb

(pigment), diffract (iridophore) or reflect (leu-

cophore) already existing light. They use bio-

luminescence, or producing light from a chemical

reaction with very little heat. Sometimes, these

creatures have sacs containing bioluminescent

bacteria in a symbiotic relationship.

fig 2.6

fig 2.7

fig 2.8

23THE CHrOMATOPHOrE

lIgHTWAVE lENgTH

The length and duration of the 6 basic colors. The lon-

ger wavelength a color has, the further that color is

visible underwater, as it is not filtered out as quickly.

430 to 380 nm 700 to 790 THz

500 to 430nm 600 to 700THz

565 to 520 nm 530 to 580 THz

590 to 565 nm 510 to 530 THz

625 to 590 nm 480 to 510 THz

740 to 625 nm 405 to 480 THz

630 to 380 nm 480 to 790 THz

violet

blue

green

yellow

orange

red

full spectrum

fig 2.9


25THE CHrOMATOPHOrE

IN CrUsTACEANs, ElAsMObrANCH FIsHEs, ANUrANs,

and lizards, control of the chromatophores is

thought to be exclusively hormonal. Such hormonal

control is true also of some teleosts; in others

the control is part hormonal and part neural; while

in still others control is purely neural, as in the

chameleon. Where nerves are involved, the speed of

the response is faster, the chromatophores respond-

ing in minutes rather than hours.

EACH CEPHAlOPOD CHrOMATOPHOrE OrgAN HAs AN

elastic sac containing pigment granules. Attached

to the sac is a set of 15–25 radial muscles that

are striated and contract rapidly. Associated with

the radial muscles are axons from nerve cell bod-

ies that lie within the brain. Active nerve cells

cause the radial muscles to contract and the chro-

matophore sac expands—when the nerves are inac-

tive, energy stored in the elastic sac causes the

chromatophore to retract as the muscles relax. The

chromatophores receive only nerve impulses, and

there is no evidence that they are influenced by

hormones. The chromatophores are ultimately con-

trolled by the optic lobe of the brain under the

influence of the eyes.

TWO CONsEqUENCEs FOllOW FrOM THE FACT THAT

cephalopod chromatophores are under the direct

control of the brain. First, color change is

instantaneous. Second, patterns can be generated

in the skin in a way impossible in other animals.

Thus, cephalopods can use the chromatophores not

just to match the background in general color but

to break up the body visually so that a predator

does not see the whole animal. Because the chro-

matophores are neurally controlled and patterns

can be produced in the skin, they can also be used

for signaling.


red

orange

yellow

green

blue

violet

black

Photophore

Melanophore

xanthophore

Iridophore

leucophore

Erythrophore

COlOr rEPrEsENTATION OF CHrOMATOPHOrE CElls

The range of color that the various types of chromato-

phore cells reflect. This coloring comes from either

the type of pigment within the cells, or the reflective

surface of the cell and the wavelengths of light that it

transmits back.

fig 2.10

MANy sPECIEs HAVE THE AbIlITy TO TrANslOCATE

the pigment inside chromatophores, resulting in an

apparent change in color. This process, known as

physiological color change, is most widely studied

in melanophores, since melanin is the darkest and

most visible pigment. In most species with a rela-

tively thin dermis, the dermal melanophores tend

to be flat and cover a large surface area. However,

in animals with thick dermal layers, such as adult

reptiles, dermal melanophores often form three-

dimensional units with other chromatophores. These

dermal chromatophore units consist of an uppermost

xanthophore or erythrophore layer, then an irido-

phore layer, and finally a basket-like melanophore

layer with processes covering the iridophores

27THE CHrOMATOPHOrE

lIgHT rEFrACTION

The amount of light that is allowed to reflect back when

directed to an section of skin that is saturated with

chromatophores. Notice the jump at 700ppm.

Chromatophore saturation

THz//750

700

650

600

550

500

450

400

PPM4500 7000 9500

fig 2.11

bOTH TyPEs OF DErMAl MElANOPHOrEs ArE VEry

important in physiological color change. Flat der-

mal melanophores will often overlay other chromato-

phores so when the pigment is dispersed throughout

the cell the skin appears dark. When the pigment is

aggregated towards the centre of the cell, the pig-

ments in other chromatophores are exposed to light

and the skin takes on their hue. Similarly, after

melanin aggregation in DCUs, the skin appears

green through xanthophore filtering of scattered

light from the iridophore layer. On the dispersion

of melanin, the light is no longer scattered and

the skin appears dark. As the other biochromatic

chomatophores are also capable of pigment translo-


cation, animals with multiple chromatophore types

can generate a spectacular array of skin colors by

making good use of the divisional effect.

THE CONTrOl AND MECHANICs OF rAPID PIgMENT

translocation has been well studied in a number

of different species, particularly amphibians and

teleost fish. The regulation of motile activity in

fish chromatophores. It has been demonstrated that

the process can be under hormonal, neuronal con-

trol or both. Neurochemicals that are known to

translocate pigment include noradrenaline, through

its receptor on the surface on melanophores. Nor-

adrenaline and melatonin-mediated regulation of

pigment aggregation in fish melanophores. The pri-

mary hormones involved in regulating transloca-

tion appear to be the melanocortins, melatonin and

melanin concentrating hormone, that are produced

mainly in the pituitary, pineal gland and hypo-

thalamus respectively. These hormones may also be

generated in a paracrine fashion by cells in the

skin. At the surface of the melanophore the hor-

mones have been shown to activate specific G-protein

coupled receptors that, in turn, transduce the

signal into the cell. Melanocortins result in the

dispersion of pigment, while melatonin and results

in aggregation.

WHEN MUlTI-POTENT CHrOMATOPHOrE PrECUrsOr

cells develop into their daughter subtypes is an

area of ongoing research. It is known in zebrafish

embryos, for example, that by 3 days after fertil-

ization each of the cell classes found in the adult

fish—melanophores, xanthophores and iridophores—

are already present.

29THE CHrOMATOPHOrE

DUrINg THE VErTEbrATE EMbryONIC DEVElOPMENT,

chromatophores are one of a number of cell types

generated in the neural crest, a paired strip of

cells arising at the margins of the neural tube.

These cells have the ability to migrate long dis-

tances, allowing chromatophores to populate many

organs of the body, including the skin, eye, ear

and brain. Leaving the neural crest in waves,

chromatophores take either a dorsolateral route

through the dermis, entering the ectoderm through

small holes in the basal lamina, or a ventrome-

dial route between the somites and the neural tube.

The exception to this is the melanophores of the

retinal pigmented epithelium of the eye. These are

not derived from the neural crest, instead an out

pouching of the neural tube generates the optic cup

which, in turn, forms the retina.

CHrOMATOPHOrEs ArE AlsO FOUND IN MEMbrANEs

of phototrophic bacteria. Used primarily for pho-

tosynthesis, they contain chlorophyll pigments and

carotenoids. In purple bacteria, such as Rhodo-

spirillum rubrum the light-harvesting proteins

are intrinsic to the chromatophore membranes.

Although, in green sulphur bacteria they are gen-

erally arranged in specialized antenna complexes

called chlorosomes.

WHAT Is AN AlbINO? HOW CAN THErE bE sO MANy

types of albinism in reptiles? I thought albinos

were always white? All of these questions stem

from a fundamental difference in the ways pigmen-

tation are displayed between mammals and reptiles.

In mammals, there is only a single chromatophore,

the epidermal melanocyte. Therefore, if it fails

to function properly, any albino is all-white. In

reptiles, there are three types of chromatophores

present. This explains the numerous types of albi-

nos present in captive collections today.


lEVEl OF CHrOMATOPHOrE sATUrATION

The reliance of animals to survive on their chromato-

phore abilities depends heavily on the level of their

other self defense adaptations. generally, the less

defense they are equipped with, the higher level of

chromatophores in their skin.

Chromatophore saturationPPM4500 7000 9500

survival rate

fig 2.12

31THE CHrOMATOPHOrE

The cephalopod chromatophore system has fasci-

nated humans for millennia—in fact, Aristotle

described it in Historia Animalium 2,400 years

ago. The system is the only known example of

skin reflectance under direct neural control, as

opposed to the hormonal control utilized in the

chromatophore cells of flatfish or salamanders.

CEPHAlOPODsTHE METHOD OF INsTANT ADAPTATION OF MOllUsks

33CEPHAlOPODs

CHrOMATOPHOrE bEHAVIOr IN CEPHAlOPODs rANgEs

from intra-and inter-species communication to

camouflage and crypsis. Understanding cephalopod

behavior has applications to the fishing industry;

indeed cephalopods constitute only 3% of the global

fishery by weight, but are ranked only behind tuna

and shrimp in terms of the monetary value of the

catch. Furthermore, it has recently been calcu-

lated that world cephalopod biomass exceeds that

of humans.

THE bAsIC CHrOMATOPHOrE UNIT CONsIsTs OF A

pigment-filled elastic sac with muscle fibers attached

around the circumference. When these fibers are

contracted, the once-spherical sac stretches and

flattens into a disk, dispersing the pigment ommo-

chromes over a wide area more visible to surround-

ing organisms. As the muscles relax, the potential

energy stored in the elasticity of the sac retracts

the disk to its spherical default. Each muscle fiber

can be innervated by multiple nerves, all of which

emanate from motor neurons located in the chro-

matophore lobes of the central brain. Thus each

motor neuron controls at least one chromatophore

organ, and each organ may be affected by more than

one central neuron.

A rOUgH CHrOMATOPHOrE CONTrOl PATHWAy HAs

been elucidated, with relevant information start-

ing in the optic lobes and progressing in a series

through the peduncle and lateral basal lobes before

driving the motorneurons in the anterior and pos-

terior chromatophore lobes. The lobes are thought

to select a pattern, which the peduncle lobes then

modulate, while the lateral basal lobes then coor-

dinate the lower spatial frequencies of a given

pattern and the chromatophore lobes the higher.

These ascribed functions are very general indeed,

as the true purpose of any of these lobes is not

entirely clear.


VIsIblE COlOr sPECTrUM UNDEr WATEr

The depth at which wavelengths of color are no longer

visible under water. The shorter wavelengths of the warm

colors disappear first, while the longer wavelengths of

the cooler colors are visible at a greater depth.

red

sea level

25ft

50ft

75ft

100ft

125ft

Orange yellow green blue Violet

fig 3.1

35CEPHAlOPODs

IN ADDITION TO THE CENTrAl CONTrOl PrOVIDED

by the brain, chromatophores may influence each

other through an intra-skin network of unknown

mechanism. Evidence for this second control path-

way comes from following deceased animals held

under suitable conditions for a period of days

after their death, during which the skin chromato-

phores, retracted at the time of death, reawaken to

produce coordinated patterns. These patterns are

unlike any seen in life, with the notable exception

of animals with nerve lesions.

THE CHrOMATOPHOrEs OF CEPHAlOPODs DIFFEr

fundamentally from those of other animals: they

are organs rather than cells and are not con-

trolled hormonally. They constitute a unique motor

system that operates upon the environment with-

out applying any force to it. Each chromatophore

THE CEPHAlOPOD PrOCEss OF CHANgE

The process that a cephalopods system goes through when

adapting to its environment. The environment is taken

in through the eyes, then the signal is sent to the

brain, then to the muscle cells, which in turn tells the

neurons to contract around the Chromatophore cell. This

whole process happens in less than a second.

Environment Eyes brain

fig 3.2


organ comprises an elastic sac containing pigment,

to which is attached a set of obliquely striated

radial muscles.

WHEN ExCITED THE MUsClEs WIll THEN CONTrACT,

expanding the chromatophore; when they relax,

energy stored in the elastic sac retracts it. The

physiology and pharmacology of the chromatophore

nerves and muscles of squids are discussed in

detail. Attention is drawn to the multiple inner-

vation of dorsal mantle chromatophores, of cru-

cial importance in pattern generation. The size

and density of the chromatophores varies according

to habit and lifestyle. Differently colored chro-

matophores are distributed precisely with respect

to each other, and to reflecting structures beneath

them. Some of the rules for establishing this exact

arrangement have been elucidated by ontogenetic

studies. The chromatophores are not innervated

uniformly: specific nerve fibers innervate groups

of chromatophores within the fixed, morphological

array, producing ‘physiological units’ expressed

as visible ‘chromatomotor fields.’ The chromato-

phores are controlled by a set of lobes.

Muscle Neuron Chromatophore Cells

37CEPHAlOPODs

PATTErN rECOgNITION IN CUTTlEFIsH

The level of mimicking that a cuttlefish applies to its

skin when faced with various environments. Although

the cuttlefish is color-blind, it has incredible tonal

recognition, and can efficiently emulate the contrasting

environments that it's in.

3.31 Checker Pattern

3.32 Coarse substrate

3.33 Fine substrate

fig 3.3


AT THE HIgHEsT lEVEl, THE OPTIC lObEs, ACT

largely on visual information, select specific motor

programs (i.e. body patterns); at the lowest level,

motoneurons in the chromatophore lobes execute the

programs, their activity or inactivity producing

the patterning seen in the skin. In Octopus Vul-

garis there are over half a million neurons in

the chromatophore lobes, and receptors for all the

classical neurotransmitters are present, different

transmitters being used to activate (or inhibit)

the different color classes of chromatophore moto-

neurons. A detailed understanding of the way in

which the brain controls body patterning still

eludes us: the entire system apparently operates

without feedback, visual or proprioceptive. The

gross appearance of a cephalopod is termed its body

pattern. This comprises a number of components,

made up of several units, which in turn contains

many elements: the chromatophores themselves and

also reflecting cells and skin muscles.

HAVINg NEUrAl CONTrOl OF THE CHrOMATOPHOrEs

enables a cephalopod to change its appearance

almost instantaneously, a key feature in some

escape behaviors and during agonistic signal-

ing. Equally important, it also enables them to

generate the discrete patterns so essential for

camouflage or for signaling. The primary func-

tion of the chromatophores is camouflage. They are

used to match the brightness of the background

and to produce components that help the animal

achieve general resemblance to the substrate or

break up the body’s outline. Because the chromato-

phores are neurally controlled an individual can,

at any moment, select and exhibit one particular

body pattern out of many. Such rapid neural poly-

morphism (‘polyphenism’) may hinder search-image

formation by predators. Another function of the

chromatophores is communication. Intraspecific sig-

naling is well documented in several inshore spe-

cies, and interspecific signaling, using ancient,

highly conserved patterns, is also widespread.

39CEPHAlOPODs

ONE CUTTlEFIsH ADDED A PAIr OF EyE sPOTs TO

its back, a strategy cuttlefish will use to fool

predators. The spots lingered a few seconds, then

vanished. When Hanlon stuck his finger into another

tub, three squirrel-size cuttlefish turned to choco-

late, and one streaked its back and arms with wavy

white stripes. “Look at the pattern on that guy,” he

said with a smile as they lunged for his finger. In

other tubs, the cuttlefish put on subtler but no less

sophisticated displays. Hanlon’s students had put

sand in some tubs, and there the cuttlefish assumed

a smooth beige. On top of gravel, their skins were

busy fields of light and dark.

HANlON lIkEs TO sEE HOW FAr HE CAN PUsH

their powers of camouflage. He sometimes put black

and white checkerboards in the tubs. The cuttle-

fish respond by forming astonishingly sharp-edged

blocks of white. “We can give them any hideous

background,” he said, “and they will try to cam-

ouflage.” Cuttlefish and their relatives octopus and

squid are the world’s camouflage champions. But

Hanlon and his colleagues have just a rough under-

standing of how these animals, collectively known

as cephalopods, disguise themselves so well. Han-

lon, a senior scientist at the Marine Biologi-

cal Laboratory here, has spent much of the last

three decades studying them in his laboratory and

on thousands of ocean dives. He said he believed

that he finally had a theory for how they achieve

their magic. In fact, he said it could account for

all the camouflage patterns made by animals like

katydids and pandas. For all the variety in the

world of camouflage, there may be a limited number

of ways to fool the eye. Hanlon’s scientific career

was a foregone conclusion. At age 18, he took his

first dive in Panama and spotted an octopus hiding

on a coral reef. After serving as an army lieuten-

ant for two years, he entered graduate school at

the University of Miami, where he began to study

cephalopod camouflage.


Lionfish

Sea

Snak

e

Flatfi

sh

Sea Anemone

Stingray

Mantis Shrimp

Jelly Fish

Britle Star

Giant Crab

Sea Shell

Flound

er

Sand Goby

THE MANy FACEs OF THE MIMIC OCTOPUs

The various animals that the Mimic Octopus has been seen

to imitate, to varying degrees of success.

rate of occurrence

rate of success

fig 3.4

41CEPHAlOPODs

PATH OF CEPHAlOPODs

The range of migration taken by the various species of

cephalopods that move across the sea floor every year

miles traveled each year

fig 3.5

HE HAs sPENT MUCH OF HIs CArEEr UNDErWATEr,

swimming around coastal reefs and rocky coastal

waters from the Caribbean to South Africa to Aus-

tralia. Typically, Hanlon and his colleagues follow

a single cephalopod, filming for hours as it shifts

its skin. On some dives, Hanlon uses a spectrom-

eter to obtain precise measurements of the light

in the water and the reflections from the animal.

The tedium is interrupted now and then by acts

of spectacular deception. Cephalopods do not just

mimic the colors of the sea floor or coral reefs.

Sometimes, they make their arms flat and crinkled

and wave them like seaweed.


HANlON HAs WATCHED OCTOPI PErFOrM WHAT HE

calls the Moving Rock Trick. They assume the shape

of a rock and move in plain sight across the sea

floor. But they move no faster than the ripples of

light around them, so they never seem to move. Han-

lon’s jaw-dropping footage has appeared on a number

of documentaries. One pirated segment has wound

up on YouTube, where it has been viewed hundreds

of thousands of times. Hanlon approaches normal-

looking coral at Grand Cayman Island. When he is

a few inches away, half the coral suddenly becomes

smooth and white. An eye pops open, and an octopus

that has been clinging to the coral shoots away.

Despite thousands of dives, Hanlon still considers

himself a novice in spotting cephalopods. Once,

after following an octopus for an hour and a half,

he looked away a moment to switch cameras. When he

looked back, the animal was gone.

EVIDENTly, OCTOPI HAVE TO HIDE IN DArkNEss

from dolphins and other predators. Cuttlefish can

also use camouflage to deceive other cuttlefish, Han-

lon and his colleagues have found. A male cuttlefish

will typically guard several females from other

challengers. He does not often have physical fights.

It is enough for him to put on a powerful visual

display. But if another male disguises its skin to

look female, he can sneak up to the guarded female

and mate. The sneaky male’s disguise may be so good

that the other male may try to guard him as part

of his harem. Beyond documenting the varieties of

camouflage, Hanlon also wants to understand how

the animals produce them. At his lab, he studies

the powerful visual system of cuttlefish. Cephalo-

pods have huge eyes, and much of their brain is

dedicated to processing visual information. They

use this information to control their disguises

through a dense network of nerves running from the

brain to the skin.

43CEPHAlOPODs

ANIMAls UsE A NUMbEr OF sTrATEgIEs TO AlTEr

appearances. The skin layers can swell and con-

tract, changing the reflected colors. At the same

time, the cuttlefish can also control millions of

pigment-filled organs, causing them to flatten like

pancakes to add patterns to their skin. Edwin

Thomas, an engineer at the Massachusetts Insti-

tute of Technology, was so impressed by Hanlon’s

work on cuttlefish skin that he decided to mimic it.

Thomas and his colleagues created a thin layer of

gel that changes colors when it swells with water

and shrinks. “Roger’s animals can also do that,”

Dr. Thomas said, “but they’re doing it without sci-

entists involved.” For all the complexity of their

skin, Hanlon suspects that the cephalopods also

use mental shortcuts. “They don’t have time to ana-

lyze all this visual information,” he said. A clue

to how cephalopods disguise themselves so quickly

came to Hanlon when he and his colleagues reviewed

thousands of images of cuttlefish, trying to sort

their patterns into categories. “It finally dawned

on me there aren’t dozens of camouflage patterns,”

he said. “I can squeeze them into three categories.”

ONE CATEgOry Is A UNIFOrM COlOr. CEPHAlOPODs

take on this camouflage to match a smooth-textured

background. The second category consists of mottled

patterns that help them hide in busier environ-

ments. Hanlon calls the third category disruptive

patterning. A cuttlefish creates large blocks of

light and dark on its skin. This camouflage disrupts

the body outlines. To test this hypothesis, Han-

lon and his colleagues have been giving cuttlefish

carefully controlled background patterns to match,

natural patterns like sand and gravel as well as

artificial ones like checkerboards. The researchers

film the cuttlefish and classify them with image-

processing software. The three-category hypothesis

has been holding up, Hanlon said. He illustrates it

in spectacular fashion with a cuttlefish sitting on

sand. If he drops a few white rocks into the water,


rANgE OF CEPHAlOPOD EMUlATION by rEgION

The range of immediate adaption ability of cephalopods

seem to increase and decrease by region. Much of this

change in ability is seemingly random, although the

local predators and prey seem to have some direct rela-

tion in several cases.

PacificOcean

AtlanticOcean

Caribbean AfricanCoast

range

fig 3.6

the cuttlefish immediately inspects them and adds

what looks like a white rock to its skin, disrupt-

ing its outline.

rECENTly, HANlON AND sTUDENTs sOrTED THrOUgH

thousands of pictures of other camouflaged animals

and found that they appeared to fall into the same

three categories. A frog may have drab skin to

blend into the drab forest floor. A bird may have

mottled plumage, so that it matches the leaf and

branch pattern surrounding it.

45CEPHAlOPODs

INNEs CUTHIll, AN ExPErT ON CAMOUFlAgE AT

the University of Bristol, called Hanlon’s research

fascinating and inspiring. Cuthill agreed that

cuttlefish had limits to its camouflage. “It can’t

reproduce the Mona Lisa on its back,” he said. But

he still considers it an open question how much the

constraints come from cuttlefish brain wiring and

how much from the limited range of backgrounds that

cuttlefish encounter. What he learned from cephalo-

pods may apply throughout the animal kingdom. The

fact that cephalopods may need just three camou-

flage categories could mean that there are just a

few basic ways to fool predators.

MOsT ANIMAls WITH A FIxED Or slOWly CHANgINg

body pattern must move to the correct visual back-

ground, at the right time and lighting conditions,

to implement camouflage. Cephalopods have evolved

a different life history tactic: with their keen

vision and sophisticated skin—with direct neu-

ral control for rapid change and fine-tuned opti-

cal diversity—they move where they wish and can

adapt their body pattern for appropriate camouflage

against a staggering array of visual backgrounds:

colorful coral reefs, temperate rock reefs, kelp

forests, sand or mud plains, seagrass beds, and

others. How they choose the appropriate pattern

can tell us something about both cephalopod and

predator vision, and will lend understanding to

which visual cues are likely to play key roles

in accomplishing camouflage. First, the degree of

background matching can be superb. This Octo-

pus vulgaris in the Cayman Islands is mottled to

match the overall pattern, intensity, color and

three-dimensional physical texture of the algae

on this rock. Background matching does not always

require an exact match; in fact, this octopus more

often achieved a general background resemblance

while filmed it over 90 minutes as it foraged slowly

throughout this backreef area. Second, the speed

of change is rapid, as shown in the time lapse of


270 milliseconds between images one and two. The

total body pattern change as the octopus switched

from camouflaged to fully conspicuous took place in

2.02 seconds. Rapidity of visual change is accom-

plished by direct neural control of chromatophore

organs, which are cytoelastic sacs of pigment with

radial muscles attached around the periphery. Each

muscle is innervated by motoneurons that originate

in the lower motor centers of the brain, and they

travel without any synapse to each chromatophore

organ. Third, camouflage benefits from both opti-

cal and physical three-dimensional effects, the

latter being due chiefly to the changeable skin

papillae. Curiously, although papillae expression

is regulated by visual input, neither this nor the

biomechanics of how the papillae operate as a mus-

cular hydrostat in the skin has been studied in

any small detail.

HANlON ArgUEs THAT THE blACk AND WHITE

patches on a giant panda are a form of disruptive

camouflage. If a panda is up in a tree, the chunks

of black and white blend into the sunlight and

shadows. It may be able to hide on a snowy land-

scape this way, as well. Cephalopods are singular

for changing quickly among all three categories.

Chameleons can change between them, too, but they

shift slowly, as hormones spread across their skin.

Although he says he has found some rules, there is

much to figure out. To use disruptive patterning,

cuttlefish need to make sure that their color blocks

are on the same scale as the objects around them.

Hanlon has yet to figure out how they measure that.

Hanlon and his colleagues are also puzzled by the

many camouflage colors of the cuttlefish, which have

a single type of pigment in their eyes. Humans

have three. Experiments in Hanlon’s lab have shown

that they are color blind. They see a world without

color, but their skin changes rapidly to any hue

in the rainbow. How is that possible?

47CEPHAlOPODs

ONE OF THE MINOr sUrPrIsEs OF THIs WOrk Is

that that last item, the algorithm for generat-

ing camouflage, may not be that complex. By study-

ing many camouflaged organisms, they've categorized

camouflage techniques into just three different

strategies. The three are responses to the coarse-

ness of the patterns in the environment. If the

background is fine grained and simple, blend in by

generating a uniform skin pattern that matches

the average intensity. If the background is a mix-

ture of small objects of varying intensity, take

on a mottled appearance to blend in. And finally,

if there are relatively large objects with a fair

amount of contrast around, instead adopt a disrup-

tive camouflage scheme, which has the function of

breaking up the outlines of the body.

ONE OTHEr INTErEsTINg ObsErVATION Is THAT

cephalopods are thought to be color blind—they

have one visual pigment with a peak sensitivity

at 492nm—and that was tested with checkerboards of

various colors but similar intensity at 492nm, and

the cuttlefish can’t see them. A checkerboard of blue

and yellow squares that is painfully contrasty to

our eyes is seen as a uniform gray by the cephalo-

pod, which then adopts a uniform gray-brown skin

color. How they do any kind of color matching is

not known, but it may be that they simply don’t: in

an environment lacking many bright primary colors,

sticking with natural shades of gray and brown may

be adequate.


There is a wide spread opinion that the chameleon

changes its color according to its environment,

turning itself invisible to its predators. This

creates an individual able to shift its behavior

in accordance with different persons is compared

to a chameleon. But is that so? Science does not

confirm this idea at all.

VErTEbrATEsTHE METHOD OF INsTANT ADAPTATION OF skElETAl ANIMAls

51VErTEbrATEs

THE lAyErs OF PIgMENTED CElls IN THE CHAMElEON

The layers of various pigment colors in the skin of the

common Chameleon. The 5 layers of color can rearrange

to show an almost infinite range of color and tone

fig 4.1

CHAMElEONs ArE FAMOUs FOr THEIr AbIlITy TO

change their skin color to blend in with their sur-

roundings. But experts say camouflage is only half

the story of the tropical lizard’s remarkable trait.

One of the world’s foremost chameleon experts, Rax-

worthy has discovered several new species and is

actively engaged in protecting chameleon habitat

in Madagascar. Part of his research involves study-

ing what the lizards communicate with each other

via changes in their color. He’s found that the

color shifts often express territorial dominance or

unwillingness to mate. “Males become more brightly

marked to advertise their dominance,” Raxworthy

said. “Females become dark or flash red spots to

advertise their hostile response to males or their

non-receptive status. Aggressive chameleons may

become very dark.” Whatever the color signals mean,

the tropical reptiles’ unusual ability has earned

them a fan base among humans. He said chameleons

are rightfully considered masters of camouflage,

but that people often mistake color change as an

effort to blend in when in fact the lizards could

be showing signs of stress.


ACTUAlly, THE CHAMElEON CONsTANTly CHANgEs

its color. Chameleons possess in chromatophores two

types of pigments: one black (melanin) and another

one, of various colors. Chromatophores retire or

display their ramifications, changing this way

their color. Their movements are under the con-

trol of nerves or hormones (adrenaline secreted

by the adrenal gland and hormones of the hypophy-

sis). These colors respond perfectly to the needs

of their arboreal life: 130 species of chameleons

out of 156 live in trees. Colors displayed by the

chameleons vary from gray to whitish, black, vivid

green, green-yellow, olive or blue. Adding to their

natural colors their ability to stay still for

minutes and their wagging and extremely slow move-

ments—unusual for a lizard—that makes their later-

ally flattened bodies to look like a leaf or twig

shaken by wind.

OF COUrsE, THEy AFFOrD THEsE slOW MOVEMENTs,

due to their hunting technique, based on their

tongue, which is the longest in the world compared

to the body length. The tongue is launched and put

back in a fraction of second. The sticky tongue can

catch from insects to even small birds in the larg-

est species, than can be 70 cm long. This effective

hunting technique is also practiced by some newt

species from Americas. The chameleon does change

its color, but mostly for displaying its mood.

CHAMElEONs ArE sOlITAry AND ArE ExTrEMEly

territorial, rejecting even the company of other

chameleons. If two chameleons meet face to face,

they do all they can to impress each other, dis-

playing menacing postures—wagging, jaw clacking,

whistling, swelling of the body and the gizzard—

and menacing colors. The defeated one will adopt a

pale-gray color and will leave the territory. In

fact, if a chameleon is attacked by a predator, its

color turns reddish with brown and yellow stripes,

as their predators do not distinguish colors well.

53VErTEbrATEs

THE WAy THAT CHAMElEONs ACTUAlly DO THIs Is

really molecular—they’re molecular masterminds,

really. If you look at the skin of a chameleon,

you find that they have several layers of chro-

matophores and these are cells that can change

color. On the outer surface of the chameleon, the

skin is transparent and just below that is the

first layer of these cells, and they contain vari-

ous pigments. These are xanthophores, containing

particular specialized pigments that have a yellow

color. Beneath that are pigment cells which are

called erythrophores which have a red cooler in

them. Beneath that, another layer of cells called

iridiphores have a blue colored pigment called

guanine, which is actually also used in making

DNA. And underneath that is another layer of cells

called melanophores which have a brown pigment—

melanin—in them.

NOW, HOW DOEs THE CHAMElEON CHANgE COlOr?

Well those chromatophores are wired up to the ner-

vous system. What happens is that the coolers are

locked away in tiny vesicles, little sacs inside

the cells that keep them in one place, so the cells

don’t look colored. But when a signal comes in

from the nervous system or from the blood stream,

the granules or vesicles can discharge, allow-

ing the cooler to spread out across the cell, and

this alters the color of the cell. It’s rather like

giving the cell a coat of paint. By varying the

relative amount of activity of the different chro-

matophores in different layers of the skin, it’s

like mixing different paints together. So if you

mix red and yellow, you get orange for example, and

this is how chameleons do this. They mix differ-

ent contributions of these chromatophores. It’s a

bit like on your television screen. When you mix

different colors together on the screen to get the

color that the eye ultimately perceives and so,

that’s how the chameleon changes color, and usually

does so to convey mood.


HAbITAT HEIgHT AbOVE grOUND lEVEl

Out of the over 150 species of Chameleons, 130 of them

live in the trees. staying off the ground floor of the

forest increases survival rate, yet also generally

decreases the range of camouflage ability.

Calumma

nasuta

Furcifer

antimena

brookesia

decaryi

Furcifer

campani

Calumma

vencesi

250ft

200ft

150ft

100ft

50ft

fig 4.2.

COlOr CHANgE AlsO sIgNAls CHANgEs IN lIgHT

and temperature in the environment. In the morning,

after a fresh night, the chameleons will warm in

the sun, flattening their flanks, which turn black.

If a leaf is put on the back of a chameleon and

removed after a period, it will leave a color mark

on its back, following its shape, due to the shifts

in light and temperature. It is plausible that

the changing color ability developed in a remote

ancestor, during the dinosaur era. Thus, being a

chameleon won’t hide your real feelings. There are

in fact some other species that do copy their envi-

ronment, using chromatophores, like octopuses or

many flatfishes, like flounders.

55VErTEbrATEs

sPECIEs WITH ADAPTATION

Only a few classifications of vertebrates have adapted

instant adaptation. Mostly lizards and fish, these are

still pretty rare in the wild.

fig 4.3

ACCOrDINg TO ANDErsON, THE AbIlITy OF THE

chameleons to change color stems from chromato-

phores found in the upper layers of their skin.

These cells are filled with different kinds of pig-

ment. The lizards have three layers of chromato-

phores. The deepest layer contains melanophores,

which have black pigment. Cellular branches extend

from these cells and allow the pigment to flow up

to and interact with the pigment in upper lay-

ers. The middle layer of cells, called guanophores,

regulate blues shades, and cells in the uppermost

layer, called xanthrophores, contain yellow and red


pigments. “Basically there’s a neurological con-

trol mechanism that stimulates the pigments” to

move around and cause the chameleon’s skin color

to change, Anderson explained. Whether chameleons

are actively aware of their color changes is an

open question, Anderson said. He suspects that the

ability to do so is a trait borne out through the

process of natural selection.

rAxWOrTHy, THE AMErICAN MUsEUM OF NATUrAl

History herpetologist, says understanding why and

when chameleons change color is an ongoing sci-

entific pursuit that began with field observations

in the 1960s. He says the lizards’ rapid changes

in color, which can occur in about 20 seconds, are

most dramatic when chameleons are interacting with

one another. He adds, though, the changes also play

an important role in allowing the lizards to hide

or blend in with their environment. “Most of the

time, chameleons are behaving as highly cryptic

animals trying to avoid detection from predators,”

he said. In a broadcast of the Pulse of the Planet

radio program airing today, Raxworthy says the

best time to find chameleons is at night, because

they turn pale then and are easily illuminated with

a flashlight. When asked precisely why the lizards

turn pale at night, Raxworthy says, “We are not

sure. But it seems to be related to the closing of

the eyes.”

THE DEVElOPMENT OF CHrOMATOPHOrEs HAVE bEEN

studied extensively by using mouse coat-color

mutants. However, mammalian models do not permit

complete understanding of vertebrate pigmentation,

because mammals have lost most types of chro-

matophores (as well as their color vision), as a

result of long periods of nocturnal behavior dur-

ing evolution. Because body colors and patterns are

among the most variable and readily recognizable

features of animals, chromatophores should be a

suitable research subject to understand

57VErTEbrATEs

ANAlyzINg MEDAkA MUTANTs, WHICH HAVE UNIqUE

defects in proliferation and morphogenesis of cer-

tain types of chromatophores on skin, and identi-

fied a mutation in the gene encoding somatolactin,

a hormone of growth hormone, prolactin family, as

the cause of the mutant phenotypes. This study

provides genetic evidence of somatolactin function,

and further investigation using the medaka will

provide insights into development and regulation

of chromatophores.

INVErTEbrATE VIsUAl CElls OFTEN CONTAIN FEW

pigment granules and they control light scatter-

ing by redistributing their pigment granules. In

some invertebrates and in vertebrates, photore-

ceptor cells of the retina do not contain pigment

granules and the screening function is provided by

neighboring pigment cells, which develop from the

same tissue as photoreceptor cells. In the moth

Deilephila elpenon, migration of retinal screening

pigment within the pigment cell is independent of

visual cell activity and is controlled by the pig-

ment cell itself. Maximal pigment movement is seen

after exposure of the pigment cell to wavelengths

between 352 and 443 nm. In vertebrate eyes, the

retinal pigment epithelium, which is composed of

pigment cells, lies adjacent to the photoreceptor

cells and probably performs a number of functions

critical for the viability and activity of the ret-

ina. Recently, a retinal protein-coupled receptor,

which is present in the intracellular membranes of

cells in the retina, and peropsin, a visual pig-

ment-like protein-coupled receptor, which is local-

ized to the apical microvilli, have been identified

in mammals. purified from bovine binds to all-trans

retinal and absorbs both visible and ultraviolet

light. Whether it as a signal-transducing light

receptor and/or participates in the visual cycle

as a retinal isomerase is not known.


sUrVIVAl rATE WITH CAMOUFlAgE

The survival rate ration increases substantially when a

vertebrate has the ability of camouflage. The more adapt

at adaptation, the higher the chances of survival are.

survival rate

Camouflage adaptation

fig 4.4

PErOPsIN MAy PlAy A rOlE IN PHysIOlOgy, EITHEr

by detecting light directly or by monitoring the

concentration of retinoids or other photoreceptor-

derived compounds. As for lower vertebrate cells,

within which pigment granules migrate, detailed

examination at the molecular level has not been

carried out. When a hypophysectomized horned toad,

whose left lateral margin has been cut for denerva-

tion, is placed in a dark box and a beam of light is

projected through a hole in the box to impinge on

the denervated left edge of the animal for a period

of time, the denervated side is always found to be

noticeably darker than the normal side.

59VErTEbrATEs

WHEN THE DENErVATED lEFT sIDE OF THE TOAD Is

shielded by a zinc cover and the animal as a whole

is exposed to a general bright illumination, the

covered side becomes as pale as the uncovered side.

Isolated pieces of skin from the species of Anolis

become brown in direct sunlight and remain green

in ordinary diffuse illumination. In these cases,

however, the differences in coloration, which were

assumed to result from direct stimulation, are so

slight that a conclusive decision is by no means

easy. The primary response probably plays a very

minor role in the normal chromatic activities of

most lizards.In amphibians, the direct response of

some melanophores to light stimulation has been

described. Melanophores in the posterior part of

the tail fin of Xenopus tadpoles at later stages are

in the fully aggregated state under normal condi-

tions of illumination, which leads to the paleness

of the tails. In darkness, however, pigment disper-

sion occurs in those melanophores causing the tail

to become black. This phenomenon was first observed

by Bagnara, who used hypophysectomized tadpoles

and referred to it as the tail-darkening reaction.

By the use of isolated tails, it was concluded that

melanophores in that tissue are themselves sensi-

tive to changes in illumination.

CHAMElEONs FINE-TUNE CAMOUFlAgE TO THEIr

predator’s vision. Chameleons’ mastery of camou-

flage goes further than anyone expected—it seems

they can fine-tune their color changes to the visual

systems of specific predators. Devi Stuart-Fox at

the University of Melbourne, Australia, and col-

leagues studied the Smith’s dwarf chameleon (Brad-

ypodion taeniabronchum), which lives in South

Africa. This critically endangered chameleon can

alter its color palette in milliseconds, either

for camouflage or for social signaling. The team

captured eight males and eight females of the spe-

cies. They placed them on a branch and presented

them with realistic models of two of their biggest


predators: the fiscal shrike—a bird that impales

chameleons on thorns before eating them—and a ven-

omous tree snake called the boomslang.

UsINg A sPECTrOMETEr, THE TEAM TOOk rEADINgs

of the color shades and brightness of the back-

ground and the chameleon. Then, after the chame-

leon had spotted the model predator and changed

color, they took another set of readings. The cha-

meleons color-matched their backgrounds much more

closely when presented with a bird than a snake,

the team found. However, when the team modeled the

visual systems of both predators, they found that

the chameleon still appeared better camouflaged to

the snake than the bird, thanks to the snake’s

relatively poor color vision. In the presence of

a snake, it seems, the chameleons just don’t have

to try as hard. The researchers noticed that the

chameleons were also consistently paler, compared

with their background, when presented with the tree

snake. “This is probably because while birds usu-

ally approach from above, putting the chameleon

against a dark background, snakes usually approach

from below, putting it against a background of a

light, bright sky,” says Stuart-Fox.

61VErTEbrATEs

bradypodion adolfifriderici

bradypodion caffer

bradypodion carpenteri

bradypodion damaranum

bradypodion dracomontanum

bradypodion excubitor

bradypodion fischeri fischeri

bradypodion fischeri multitu

bradypodion fischeri uluguruensis

bradypodion gutturale

bradypodion karrooicum

bradypodion melanocephalum

bradypodion mlanjense

bradypodion nemorale

bradypodion occidentale

bradypodion oxyrhinum

bradypodion pumilum

bradypodion setaroi

bradypodion spinosum

bradypodion taeniabronchum

bradypodion tavetanum

bradypodion tenue

bradypodion thamnobates

bradypodion transvaalense

bradypodion uthmoelleri

bradypodion ventrale

bradypodion xenorhinum

brookesia ambreensis

brookesia antakarana

brookesia bekolosy

brookesia betschi

brookesia bonsi

brookesia brygooi

brookesia decaryi

brookesia dentata

brookesia ebenaui

brookesia exarmata

brookesia griveaudi

brookesia karchei

brookesia lambertoni

brookesia lineata

brookesia lolontany

brookesia minima

brookesia nasus

brookesia perarmata

brookesia peyrierasi

brookesia stumpffi

brookesia superciliaris

brookesia therezieni

brookesia thieli

brookesia tuberculata

brookesia vadoni

brookesia valerieae

Chamaeleo Chamaeleo africanus

Chamaeleo Chamaeleo anchietae

ChamaeleoChamaeleo calyptratus

Chamaeleo Chamaeleo chamaeleon

Chamaeleo Chamaeleo dilepis

Chamaeleo Chamaeleo etiennei

Chamaeleo Chamaeleo gracilis

Chamaeleo Chamaeleo laevigatus

Chamaeleo Chamaeleo monachus

Chamaeleo Chamaeleo quilensis

Chamaeleo Chamaeleo roperi

Chamaeleo Chamaeleo ruspolii

Chamaeleo Chamaeleo senegalensis

ArbOrEAl AND grOUND CHAMElEONs

Most Chameleon species live in the safety of the trees

and their branches, however there are few species that

have adapted to life on the forest floor. These particu-

lar chameleons oddly enough are generally less adept at

color change.

arboreal

ground

both (lays eggs on forest floor)

fig 4.5


Chamaeleo Chamaeleo zeylanicus

Calumma andringitraensis

Calumma boettgeri

Calumma brevicornis

Calumma capuroni

Calumma cucullata

Calumma fallax

Calumma furcifer

Calumma gallus

Calumma gastrotaenia

Calumma glawi

Calumma globifer

Calumma guibei

Calumma guillaumeti

Calumma hilleniusi

Calumma linota

Calumma malthe

Calumma marojezensis

Calumma nasuta

Calumma oshaughnessyi

Calumma parsonii

Calumma parsonii cristifer

Calumma peyrierasi

Calumma tigris

Calumma tsaratananensis

Calumma vatosoa

Calumma vencesi

Chamaeleo Trioceros affinis

Chamaeleo Trioceros balebi

Chamaeleo Trioceros bitaeniatus

Chamaeleo Trioceros camerunensis

Chamaeleo Trioceros chapini

Chamaeleo Trioceros conirostratus

Chamaeleo Trioceros cristatus

Chamaeleo Trioceros deremensis

Chamaeleo Trioceros eisentrauti

Chamaeleo Trioceros ellioti

Chamaeleo Trioceros feae

Chamaeleo Trioceros fuelleborni

Chamaeleo Trioceros goetzei

Chamaeleo Trioceros harennae

Chamaeleo Trioceros hoehnelii

Chamaeleo Trioceros incornutus

Chamaeleo Trioceros ituriensis

Chamaeleo Trioceros jacksonii

Chamaeleo Trioceros merumontanus

Chamaeleo Trioceros johnstoni

Chamaeleo Trioceros kinetensis

Chamaeleo Trioceros laterispinis

Chamaeleo Trioceros marsabitensis

Chamaeleo Trioceros montium

Chamaeleo Trioceros oweni

Chamaeleo Trioceros pfefferi

Chamaeleo Trioceros quadricornis

Chamaeleo Trioceros rudis

Chamaeleo Trioceros sternfeldi

Chamaeleo Trioceros schubotzi

Chamaeleo Trioceros tempeli

Chamaeleo Trioceros tremperi

Chamaeleo Trioceros werneri

Chamaeleo Trioceros wiedersheimi

Furcifer angeli

Furcifer antimena

Furcifer balteatus

Furcifer belalandaensis

Furcifer bifidus

Furcifer campani

Furcifer cephalolepis

Furcifer labordi

Furcifer lateralis

Furcifer major

Furcifer minor

Furcifer monoceras

Furcifer nicosiai

Furcifer oustaleti

Furcifer pardalis

Furcifer petteri

Furcifer polleni

Furcifer rhinoceratus

Furcifer tuzetae

Furcifer verrucosus

Furcifer willsii

rhampholeon marshalli

rhampholeon boulengeri

rhampholeon chapmanorum

rhampholeon moyeri

rhampholeon nchisiensis

rhampholeon platyceps

63VErTEbrATEs

The ability to change color and appearance in

response to environmental stimuli has evolved

in numerous vertebrate and invertebrate lineages

including fish, amphibians, reptiles, crusta-

ceans, and cephalopods. In most lineages, color

change occurs over a period of minutes or hours

and is primarily under hormonal control, whereas

in some lineages, most notably cephalopods and

chameleons, chromatophores are under direct neu-

ral control, enabling the animals to respond

extremely rapidly to changes in their natural

or social environments. For this reason, color

change in cephalopods and chameleons has fea-

tured in popular culture, myth and legend since

first described in Aristotle’s Historia Animalium.

THE DEVElOPMENT OF CAMOUFlAgE

EVOlUTION

65EVOlUTION

IN MOsT lINEAgEs THAT HAVE EVOlVED COlOr

change, however, the apparent capacity for color

change varies greatly. For instance, among the

more than 150 species of the family Chamaeleonidae,

color change in some is primarily limited to shifts

in brightness, while others show remarkable chro-

matic change, including striking combinations of

blues, greens, oranges, yellows, and black. Despite

the animals’ marked variation in the ability to

change color, processes driving the evolution of

this adaptive strategy have never been examined.

TWO PrIMAry PrOCEssEs DrIVE THE EVOlUTION

of color change: natural selection for the abil-

ity to camouflage against variety of backgrounds

and selection for conspicuous social signals. Like

colorful hidden insect wings or plumage ornaments

in some birds, color change in a social context

enables the use of signals that can be briefly

exposed or flashed to intended receivers—usually

conspecifics—but concealed from potential predators

at other times. Because such “transitory signals”

are only briefly exposed, they are expected to be

under strong selection to maximize detectability

to conspecifics, potentially explaining the evo-

lution of dramatic color change in some species.

In many color-changing lineages, color change is

known to facilitate both crypsis and social commu-

nication. As color generally serves more than one

purpose in color-changing species, evolutionary

processes underlying the ability to change color

per se cannot be inferred from functional studies

of particular color patterns. To infer underlying

evolutionary processes requires experimental stud-

ies on closely related populations or taxa, which

differ in their ability to change color, or com-

parative tests based on phylogeny.


EVOlUTION Is MADE POssIblE by THE VArIATIONs

that exist with animals. It exists because animals

compete with each other for the limited amount of

resources that are available, space and food. Those

animals with the more useful characteristics and

features will survive whereas the weaker animals

will find it difficult to exist. This ‘weeding out’

process is called selection and natural selection

operates on a continuous basis. An example of this

is camouflage which is a valuable aid to an animal’s

survival. Natural selection will ensure that any

improvements that are made to an animal’s camouflage

are passed onto the next generation, increasing its

chances of survival and also its chances of produc-

ing its young.

ANIMAls UsE CAMOUFlAgE TO MAkE DETECTION

or recognition more difficult, with most examples

associated with visual camouflage involving body

coloration. However, in addition to coloration,

camouflage may make use of morphological struc-

tures or material found in the environment, and

may even act against senses other than vision.

In nature, some of the most striking examples of

adaptation can be found with respect to avoiding

being detected or recognized, with the strategies

employed diverse, and sometimes extraordinary. Such

strategies can include using markings to match the

color and pattern of the background, as in various

moths, and to break up the appearance of the body,

as in some marine isopods. Camouflage is a tech-

nique especially useful if the animal can change

color to match the background on which it is found,

such as can some cephalopods and chameleons. Fur-

ther remarkable examples include insects bearing

an uncanny resemblance to bird droppings or fish

resembling fallen leaves on a stream bed, to even

making the body effectively transparent, as occurs

in a range of, in particular, aquatic species.

67EVOlUTION

In order for evolution to occur then there has to

be a change in a species genotype. This can happen

in a number of ways:

MUTATION

Sections of the DNA strand passed on from parent

to offspring can mutate, producing new genes. Not

all mutations are beneficial, indeed the majority

inhibit rather than enhance survival chances.

Statistically however given enough incidences of

mutation one will occur that leads to a survival

benefit. Mutations occur all the time, meaning

that species have been are still are constantly

evolving in this manner.

gENE FlOW

Say two distinct populations of the same rodent

live in different environments and have devel-

oped different traits, then due to environmental

change one population migrates and encounters

the other. Sexual reproduction between the two

species will cause genes to flow between the two

populations creating new variations in the same,

but separate species.

HybrIDIzATION

This is akin to gene flow, except it occurs between

two different species. For example, a Labrador

mating with a Collie produces a hybrid offspring

that inherits characteristics from both.


EVOlUTION by MUTATION

EVOlUTION by gENE FlOW

EVOlUTION by HybrIDIzATION

fig 5.1

fig 5.2

fig 5.3

69EVOlUTION

THE DNA sTrAND

breakdown of the DNA strand within every living animal.

The seemingly minute differences in each strand makes

multitudes of variation.

kb21

14

6.4

5.1

4.5

1.9

fig 5.4

kb0-25


71EVOlUTION

ExAMPlEs sUCH As lEAF MIMICry IN bUTTErFlIEs

helped convince, for example, of the power of natu-

ral selection. Other strategies may even stretch

to the use of bioluminescence to hide shadows

generated in aquatic environments, and include

decorating the body with items from the general

environment, such as do some crabs. This diver-

sity of camouflage strategies is a testament to the

importance of avoiding predation, as this is surely

one of the most important selection pressures an

organism can face. Concealment represents one of

the principal ways to do so.

WHAT DrOVE THE EVOlUTION OF COlOr CHANgE

in chameleons? Chameleons can use color change to

camouflage and to signal to other chameleons, but

a new paper shows that the need to rapidly signal

to other chameleons, and not the need to camouflage

from predators, has driven the evolution of this

characteristic trait.

IN WHITE sANDs, N.M., TWO sPECIEs OF brOWN

lizards have evolved white scales in order to blend

in with their environment. By studying the genetic

mechanisms at work in this adaptation, scientists

are able to observe evolution as it happens. The

study illuminates the mechanics of not only adap-

tation, but also speciation, or how species form.

CHAMElEONs FOr ExAMPlEs CAN DO slIgHT COlOr

changes in their skin but not as radical color

changes as some might think though some species

might be better at it then others. They might use

camouflage to hide away from potential predators as

one option. I’m sure if you were faced with a lion

you’d like to blend in with a tree too as yelling

and running doesn’t always do the trick. They might

use camouflage when scared or frightened. Sometimes

there isn’t any actual threat however they feel

frightened or threatened and decide to use the cam-

ouflage. It’s sort of like when you feel threatened

and hide under your bedsheets covers.


sUrVIVAl rATE WITH ENVIrONMENT EMUlATION

representation of the survival of species who evolve

to include instant adaptation, as opposed to their

counterparts without.

adopted crypsis not adopted crypsis

survival rate

fig 5.5

EVEry sPECIEs HAs ITs OWN gENETIC MAkEUP,

known as a genotype. A genotype governs all the

possible genes that can go into making an indi-

vidual of the species. The exact observed char-

acteristics of a species can also depend on the

environment—such as skin color in humans exposed

to the sun—but the possible range of response is

still governed by genetics.

FOr CAMOUFlAgE TO DEVElOP IN A sPECIEs THEN

a new gene set for the species pigmentation needs to

find its way into a population via one of the meth-

ods above. The new pigmentation improves survival,

slowly at first but with an exponential increase,

find its way into the whole population.

73EVOlUTION

FOrEIgN sPECIEs INTrODUCTION

With the changes to the world that modern man has made,

almost every species alive is effected. Introducing

foreign animals into isolated areas has created species

takeover in that evolution can’t keep pace with.

time

dominance

fig 5.6

FOr ExAMPlE, sAy A sPECIEs OF rODENT WITH

black pigmentation lives in a savannah type envi-

ronment. One of the rodents is born with patches

on it’s skin. The patches have the side effect of

helping it blend in with the savannah grass. The

rodents are hunted by a variety of predators, but

the patchy rodent survives into maturity because

its siblings are more visible targets. The rodent

has a litter of its own. Six of its fourteen off-

spring have patchy skin. These offspring also have

higher survival chances than the other rodents and

so a greater proportion than average survives to

maturity. They also breed.


sOON, THE skIN PIgMENTATION Is PrEVAlENT IN

the majority of the population. But the gene is

still not fixed—the genes governing skin pigmenta-

tion are complex and there are a number of varia-

tions. Within the population of patchy skinned

rodents, the ones with patches more like stripes

have an even better survival chance. So soon it is

stripy rodents that are most prevalent. This pro-

cess continues until the gene becomes fixed—that is,

100% of the members of a population have the gene.

IT DOEs NOT MATTEr THErEFOrE HOW THE gENE

was originally introduced to the population, it is

statistics and the laws of survival which govern

how it spreads. Many new gene configurations have

no benefit whatsoever and these evolutionary dead

ends are quick to die out. It is simply the law

of averages that dictates that, eventually, a new

gene spread will provide an evolutionary benefit and

thus become endemic in a species.

ANIMAls rEMAIN CONCEAlED WHEN THEIr COlOr

resembles or matches the natural background of

their environment. This phenomenon, also known as

general color resemblance, includes crypsis, in

which overall body color resembles the general

color of the habitat, or pattern blending, in which

color patterns on the body match patterns of light

and dark in the environment. Background match-

ing may change seasonally—termed variable back-

ground matching—or with age. Concealment may also

be achieved through disruptive coloration by con-

trasting colors or irregular marks that break up

the body’s outline. Finally, animals may attain

concealment if they have a lighter ventral surface,

because this may counteract the sun’s effects-

lightening the dorsum and shading the ventrum when

it shines from above.

75EVOlUTION

ADAPTATIONs sUCH As CAMOUFlAgE CAN ONly lAsT

as long as they are useful. If an animal’s life-

style changes, the path of evolution will also

change. This has happened with birds; some lin-

eages have evolved the power of flight but have lost

this when they have taken up life on land.

CryPTIC ANIMAl COlOrATION, Or CAMOUFlAgE,

is a common adaptation that serves to decrease its

bearer’s risk of detection. It has been used as a

classic example of evolution, but surprisingly lit-

tle is known about how it actually works. Camouflage

has been considered to be tightly related to the

resemblance of an animal to its visual background,

the better the animal matches its background, the

less it is expected to be detected by a predator.

Regarding camouflage as synonymous to background

matching allows a relatively easy way to estimate

camouflage through the measurement of the degree of

visual match between the animal and its background.

This approach appears logical when only the recep-

tion of visual information is considered. However,

if not only the reception, but also the processing

of such information by the predator affects the

detection probability, the approach may be bio-

logically unrealistic. The evidence supporting the

significance of background matching for camouflage

is correlative and some empirical studies show that

cryptic animals do not necessarily match their

background very closely. Thus, although background

matching certainly is an important determinant of

camouflage, other phenomena may be involved as well.


red

blue

yellow

black

green

orange

violet

COlOr VIsIbIlITy OF PrEDATOrs

The various colors that common predators can view. Very

often in the Animal kingdom, a predator can see several

colors, but not the full spectrum. These are generally

adapted to their environment. For Instance, a preda-

tor in deep waters will likely not be able to sense red

orange and yellow because those colors are filtered out

by the water.

fig 5.7

77EVOlUTION

THErE Is OVErWHElMINg EVIDENCE OF MAMMAls’

pelage coloration matching their backgrounds, both

between and within species. Across species, at

least five different coat colors appear to match

the typical background on which they are found

among carnivores, artiodactyls, and lagomorphs,

the three orders in which statistically and phylo-

genetically controlled comparisons have been made

to date. Thus, species that are white or become

white in winter are found in arctic and tundra

biomes, pale species in desert and open environ-

ments, red and gray species in rocky habitats, and

dark species in closed environments and in dense

or tropical forests. Unfortunately, these robust

associations do not make a clear-cut case for con-

cealment, because coats of different color have

differing thermoregulatory properties. White fur

might scatter solar radiation toward the skin and

hence be expected in cold climes; pale fur that

reflects light might be expected in very hot envi-

ronments such as deserts; and dark fur might be

expected in the tropics, because it enhances water

evaporation more readily than cool surfaces or

because it protects against ultraviolet radiation.

THE rEsEArCH, CONDUCTED by DEVI sTUArT-FOx

and Adnan color, shows that the dramatic color

changes of chameleons are tailored to aggressively

display to conspecific competitors and to seduce

potential mates. Because these signals are quick—

chameleons can change color in a matter of milli-

seconds—the animal can afford to make it obvious,

as the risk that a predator will notice is lim-

ited.This finding means that the evolution of color

change serves to make chameleons more noticeable,

the complete opposite of the camouflage hypothesis.

The amount of color change possible varies between

species, and the authors cleverly capitalism on

this in their experiments.


sTUArT-FOx AND MOUssAllI MEAsUrED HAVE COlOr

change by setting up chameleon duels”: sitting two

males on a branch opposite each other and measur-

ing the color variation. By comparing species that

can change color dramatically to those that only

change slightly, and considering the evolutionary

interrelationships of the species, the researchers

showed that dramatic color change is consistently

associated with the use of color change as a social

signal to other chameleons. The degree of change

is not predicted by the amount of color variation

in the chameleons’ habitat, as would be expected

if chameleons had evolved such remarkable color

changing abilities in order to camouflage.

PrOgrEss OF MOVEMENT

The progress of movement that an evolutionary change in

a species brings. Having gradual evolution often brings

with it expanded migration to new territory.

fig 5.8

79EVOlUTION

AArbOrEAl ....................... 53

ADAPTATION ................... 1-15

AggrEgATION ................. 28-29

AlbINO ..................... 30, 33

AlgAE .......................... 46

AMErICAN MUsEUM OF

NATUrAl HIsTOry ................ 57

AMErICAs ....................... 53

AMINO ACID ................. 46, 48

AMPHIbIAN ............ 2, 6, 17, 60

ANOlE ........................ 4, 9

ANNElID ........................ 20

ArIsTOTlE .................. 33, 65

ArMADIllO ....................... 2

ArTIODACTyls ................... 78

AUsTrAlIA .................. 42, 60

bbACTErIA ........... 17, 19, 23, 30

bAgNArA ........................ 60

bIlATErAl sIgNAlINg ............ 21

bIOCHrOME ........... 1, 5, 7, 9, 18

bIOlUMINEsCENCE ............ 23, 72

blOOD sTrEAM ................... 54

blUE rINg OCTOPUs .........4, 8, 21

bOOMslANg sNAkE ................ 61

bOVINE ......................... 58

brAIN .............. 19, 24, 43, 48

brIsTOl, UNIVErsITy OF ......... 46

CCArIbbEAN ...................... 42

CArNIVOrE ...................... 78

CArOTENE ....................... 23

CArTENOIDs ..................... 45

CEllUlAr brANCH ................ 56

CEPHAlOPOD ............ 5, 9, 32-49

CHAMElEON .......... 2, 6, 9, 50-63

CHlOrOsOME ..................... 30

CHrOMATOPHOrE ............ 8, 16-31

COlD-blOODED ................... 17

COlOrATION ....... 1, 6-7, 9-10, 60

COrAl ............ 10-11, 42-43, 46

CrAb sPIDEr ..................... 4

CryPsIs ............ 12, 34, 66, 75

CrUsTACEAN ......... 17, 20, 26, 35

CUTHIll, INNEs ................. 46

CUTTlEFIsH .... 2, 8, 10, 22, 33-38

CyANOPHOrE ..................... 18

CyTOElAsTIC sAC ................ 47

DDECOrATOr CrAb .................. 7

DEIlEPHIlA ..................... 58

DErMIs .............. 9, 22, 27, 30

DNA .................... 54, 68, 70

DOlPHIN ..................... 2, 43

DOrsAl MANTlE .................. 37

DOrsUM ......................... 75

DWArF CHAMElEON ............ 12, 60

EEMbryO ..................... 29, 30

ENVIrONMENT .......... 1-19, 34, 71

EPITHElIUM ................. 30, 58

EryTHrOPHOrE ....... 21, 23, 27, 54

EVOlUTION ........ 5, 12, 57, 64-79

EyE .................17, 30, 46, 54

INDEx

80

FFEATHEr ................... 1, 2, 9

FIsH.................. 9-12, 19, 36

FlOUNDEr ............. 4, 8, 20, 25

FOOD ............. 3, 5, 7, 10,, 67

FrOg ................. 4, 9, 23, 45

FUr ................. 4, 15, 23, 71

gg-PrOTEIN ...................... 29

gENE FlOW ...................... 68

gENOTyPE ................... 68, 73

gOlDEN TOrTOIsE bEETlE .......... 9

grAND CAyMAN IslAND ............ 43

HHANlON, rOgEr ............... 40-47

HIsTOrIA ANIMAlIUM ......... 33, 65

HOrMONEs ....... 11, 22, 26, 29, 53

HOrNED TOAD .................... 59

HybrIDIzATION .................. 68

IIgUANA

IllUMINATION ................... 60

INsECT ............ 6-7, 20, 53, 57

INVErTEbrATE ..... 2, 12, 51-63, 65

IrIDOPHOrE .......... 18, 22, 27-29

IrIs............................. 3

JkATyDID ........................ 40

kElP FOrEsT .................... 46

klAgOMOrPHs ..................... 78

lIgHT ......... 5-7, 17-22, 38,, 72

lINEAgE .............12, 65, 66, 76

MMADAgAsCAr ..................... 52

MAMMAl ........... 4, 9, 30, 57, 78

MArINE bIOlOgICAl lAbOrATOry ... 40

MIT............................. 44

MATUrITy ....................... 74

MEDAkA ......................... 58

MElANI ................. 21, 57-59

MElANOPHOrE ..... 21, 27-29, 54, 60

MElATONIN ...................... 29

MElbOUrNE, UNIVErsITy OF ....... 60

MIAMI, UNIVErsITy OF ........... 40

MIgrATE ................ 30, 59, 68

MIlITAry ....................... 65

MOllUsk .................... 20, 33

MOOD ................... 10, 53, 54

MOrPHOgENEsIs .................. 58

MOUssAllI, ADNAN ............... 79

MUsClE ......... 10, 18, 29, 36, 47

MUTANT ..................... 57, 58

MUTATION ................ 8, 58, 68

NNATUrAl sElECTION .......12, 57, 66

NEUrAl CONTrOl ..... 33, 39, 56, 65

NEUrOMUsCUlAr .................. 36

NEUrON ............. 19, 29, 36, 47

NUDIbrANCH ..................... 10

NOCTUrNAl ...................... 57

NOrADrENAlINE .................. 29

81

OOCTOPUs VUlgArIs ........... 39, 47

OFFsPrINg ............... 7, 68, 74

OPTIC lObE ............. 26, 34, 39

OsMOTIC TrANsFEr ............... 35

PPANAMA ......................... 40

PANDA ...................... 40, 47

PATTErN ...... 38-41, 45-47, 56, 79

PErON’s TrEE FrOg ............ 3, 9

PErOPsIN ................... 58, 59

PHENOTyPE ...................... 58

PHOTOrECEPTOr .............. 58, 59

PHylOgENETICAlly ............... 78

PHylOgENy ...................... 66

PIgMENT ... 18-22, 26-30, 48, 54-61

POlAr bEAr ...................... 6

POrCUPINE ....................... 2

PrEDATOr ...... 5-9, 20, 39, 53, 72

PrEy ................ 5, 19, 20, 45

PrOlACTIN ...................... 58

PrOlIFErATION .................. 58

PUlsE OF THE PlANET ............ 57

rrADIAl MUsClE .......18, 26, 37, 47

rAxWOrTHy, CHrIsTOPHEr ..... 52, 57

rECEPTOr ........... 29, 39, 58, 59

rEFlECT ........ 17, 22, 33, 42, 78

rEPTIlE .......... 2, 9, 20, 27, 39

rETINA ..................... 30, 58

rHODOsPIrIllUM ................. 30

rOCk rEEF ...................... 46

rODENT ................. 11, 74, 75

ssAlAMANDEr ..................... 33

sCHEMECHrOME

sEA HOrsE .................... 4, 9

sENsITIVITy .................... 48

sHElTEr ......................... 3

sHrIMP ..................... 20, 34

sIgNAls ........ 12, 52, 55, 65, 78

sNOW lEOPArD .................... 8

sOMATOlACTIN ................... 58

sOUTH AFrICA ............... 42, 60

sPECTrOMETEr ............... 42, 61

sTIMUlUs .................... 2, 11

sTUArT-FOx, DEVI ........... 60, 78

syMbIOTIC ...................... 23

TTEMPErATUrE ............. 1, 19, 55

TErrITOry ...................... 53

TExTUrE ............. 8, 19, 44, 46

THOMAs, EDWIN .................. 44

TONgUE ......................... 53

TrANsITOry sIgNAls ......... 12, 66

TyrOsINAsE NEgATIVE

TyrOsINAsE-POsITIVE

UUlTrAVIOlET ................ 58, 78

VVENTrAl sUrFACE ................ 75

VIsUAl INFOrMATION ..... 39, 43, 76

WWAVElENgTH ...... 5, 21, 27, 35, 58

WEATHEr ......................... 2

WINTEr .................... 1-3, 78

WHITE sANDs, N.M ............... 72

82

xxANTHOPHOrE ..... 21, 23, 27-29, 54

xENOPUs ........................ 60

yyOUTUbE ........................ 43

zzEbrA ........................... 6

zEbrAFIsH ...................... 29

83

COlOPHON

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Instantaneous Camouflage in the Animal Kingdom




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