University of Crete

Introduction

Most animals around as are coloured .Other with common , plain patterns and other with intense colours and remarkable patterns. Some of them can even change colour in front of our very eyes. To most of them colour is not just a simple product of metabolism but an adaptation for survival .Coloration helps them :

• to hide
• to warn of potential predators
• to deceive by mimicry
• to communicate with other organisms
• to regulate body temperature or even
• to protect from mutations
   

Camouflage

or

Concealing or protective or cryptic coloration

Implies Iam not here !!!

 

 

 

• crypsisà to hide
• enables the organism to blend with its background and be less visible
• It may be assumed by :
• animals in order to avoid their predators (which renders them less likely to be attacked )
or
• by a predator in order to be unnoticed by his potential prey. (helps them sneak up on prey more effectively)

 

Defence by camouflage

 

• In many cases a sufficient method is to adopt the color and general background pattern (usually against a plain background )

eg the white coats of arctic mammals

 

• Although a uniformly colored rounded or cylindrical object when viewed from above is conspicuous ,even against a background of the same color ,because of the highlight on its upper surface and the shadow on its lower surface

• .In many animals this effect is overcomed by countershading : surfaces of the animal that are turned towards the light are dark and those on the underside are pale.

   

• The dark pigment dulls the intensity of the highlight and the pale color lightens the shadow ,thereby reducing the appearance of three-dimensional form
• In aerial or aquatic environments: the pale lower surfaces tend to blend with the sky or water surface and the dark upper parts with the ground or bottom .

 

• In mottle backgrounds with different lightning conditions and shadows ,color patterns with stripes and spots are very common.

Such an animal moving ,through the underbrush ,dappled by spots of sunlight is very hard to see .

eg tigers ,leopards ,zebras , and giraffes.

 

• Sometimes cryptically colored animals have violently contrasting colors and disruptive markings to deceive a predator .The predator observes the pattern and does not distinguish them immediately, giving its pray a chance to escape .
• eg the clownfish

   

• Many species including reptiles , amphibians and insects try to fright off their attackers when they are discovered .This is accomplished by brightly colored areas or eyespots that were previously hidden and are suddenly revealed. This serves to startle the predator or at least give them enough time to react.

Many insects have realistic —looking eyespots ,which frighten off small birds because they simulate the presence of their own predators

eg the emperor moth

 

Experiments have shown that birds are more frightened of such realistic eyes than than of two concentric circles-confirming that natural selection for increasing realism is possible

• Not all eyespots are for scaring off predators. Some serve to deflect attack from the animals head ,by providing a more noticeable target at the wing tip

eg the meadow brown butterfly

 

• Concealing coloration is not only noticed in animals but also in their eggs when they nest on bare places

eg shorebirds have eggs that are protectively colored ,closely resembling their average surroundings .

 

 

 

• Changes in color

• Certain animals can change color patterns or they can alter in shade, slowly or rapidly , as they move

eg frogs ,flounders ,chameleons , crabs and others .

• By changing colors ,the animal can blend to different surroundings and lightening conditions

• .Many lizards can change color in response to light and temperature changes ,excitement or other factors .Many assume the dark phase when cold and in darkness ,but some are pale on warm nights .Excitement or fright may cause paling ,darkening or both ,depending on the species .
• Color changes are under hormonal and nears control .Responses to light may be initiated through the eyes and brain or directly by the skin ..

 

Survival value of Concealing coloration

. Concealing coloration does have survival value.

When grasshoppers with different body colors were fastened to plots of different colored soils —light ,dark , sandy and so on ,and then exposed to predators , it was found that there was a significantly higher percentage of survivors among those grasshoppers that matched their backgrounds .

 

 

         

Warning or aposematic coloration .

Implies :Stay back!Don’t eat !Don’t touch !!!

• apostasy (being different )

• Many insects and other animals have evolved warning colors as a signal to predators that they are toxic ,or taste nasty . California’s Garibaldi uses its orange aposematic coloration as awarning that you are entering its territory .

• The most common fom of warning are bold patterns of yellow ,orange or red combined with black

• Aposematic coloration has at least three protective properties

1. certain colors may be less attractive or appetizing for the predator

.eg humans tend not to regard blue things as edible

2. Bright colors may startle a predator (neophobic response )
3. Striking colors help the predators to learn quickly about the link between color and taste

 

• gregarious behavior: the tendency to crowding of aposematic creatures

As seen by the lack of any difference between naïve and experienced birds it is not to increase learning speed or to increase the neophobic response of the predator .

Instead it seems to increase the signaling effectiveness of the warning colors. A large mass of classical warning colors is naturally more repellent than a small patch .

Researchers suggest that aposematism encourages the evolution of gregariousness , because grouping has a dual benefit : safety in numbers and safety by dazzling

 

 

   
Mimicry .

Implies :Iam someone or something else !!!

 

• Some animals resemble specific objects such as twigs , leaves ,stems ,flowers ,pieces of bard e.t.c

eg the leaf —mimicking katydid from Central Amerika

• Batesian mimicry : a mechanism in which a harmless or palatable mimic survives by evolving to resemble a dangerous or distasteful model..

eg Hover flies have striped bodies resembling wasps but have no sting on their own .

The viceroy butterfly itself delectable to birds mimics the appearance of the unpalatable monarch .

 

• Batesian mimicry poses an interesting ecological problem .It is clearly an advantage to the mimic and a disadvantage to the model

If a predator encounters mimics first it will keep feeding on similar animals and will probably have to kill several models before it changes its habits .

 

• .One of Jane Brower’s experiments is instructive on this point .

• She fed mealworms ,some of which had been made bitter with quinine (the models ) and some with no quinine (the mimics) .

• These were all painted with green bands
• Οther mealworms with orange bands were offered as an alternative food source .

• Αfter a few experiences with bitter mealworms , the birds learned to fed only on those with orange bands and avoid all green-banded worms .

• The mimics were still largely protected even when they constituted 60 percent of the model-mimic population ,but not at higher levels .

 

• Thus Batesian mimicry works quite well if the proportion of mimics is not too high and the predators have an alternative food source

_t is to the advantage of models to change so they do not resemble mimics .

   

• Mullerian mimicry :the evolution of similar shapes and color patterns by two species both of which are noxious.

eg the pattern of black and yellow stripes common to many types of wasps and bees

• The advantage is that a predator learn to avoid a single pattern .It does not have to threaten representatives of all these species and learn many different warning signals.

• Thus a painful encounter with one kind of bee helps to protect all those that resemble it even though they belong to different species

 

 

   

Color signals

• Visual signals are more common among animals at the high levels of organization especially arthropods and vertebrates. This is because well developed eyes are needed for effective visual communication.

 

Visual communication .Functions

 

• intraspecific communication-between the sexes ,parents and offspring ,members of a flock ,rivals
• identification and threat display
• defence of territory
• to divert attack from the nest and young
• as an indication of maturation

eg in guppies both the size and number of colored spots increases on average with age in some males

• Colors in fishes may be advertising a willingness to remove parasites from another fish.
• Color signals are often used to attract a mate

(In some species both sexes acquire a nuptial plumage )

e.g. the reddened rump areas in female chimpanzees and baboons during estrus.

To these animals attracting a mate is more important than blending in Therefore they depend on their quick reflexes and high maneuverability or other methods to escape predators .

 

• Color signals reach their greatest variation in birds

.In almost all birds species the males are more brightly colored than the females ,since the male doesn’t usually have to stay by the nest to protect the young .

Some males require camouflage for protection .In such cases the color spots are usually displayed only under certain circumstances .

e.g. the robin is perfectly camouflaged from above .It is only his red stomach that is threatening usually to other males of his species .

 

Body temperature/Heat loss

 

• Coloration also help some animals to control their body temperature more effectively by influencing the rate of dermal absorption and reflection of sunlight
• Solar radiation has its peak intensity in the visible range .It is important to the heat balance whether this light is absorbed or reflected. When exposed to solar radiation dark colored skin or fur absorbs more of the indecent energy than light colored skin or fur
• It has been suggested that black colored animals lose heat by radiation faster than white colored ones . .No such differences have been found

 

 

protection from mutations

Tropical radiation is physiologically damaging .Under these conditions the darker animals might enjoy an advantage as their heavy pigmentation could filter the sunlight

e.g. the black peritoneum’s of many desert lizards seem to function primarily in absorbing mutation —inducing ultraviolet light

 

   

Natural selection

Animal camouflage is a striking example of the workings of natural selection .Today we see the result of many years of survival by those animals best adapted to their surroundings .Through slight variations in form and color ,certain individuals came to resemble their surroundings more than others .They had a better chance to survive and produce more of their kind .It has taken millions of years for the animals just mentioned to develop .In the process countless ill-adapted life forms must have perished.

A modern phenomenon of quick adaptation in a changing environment

• melanism is the ability to form dark pigments in the wings and body .It is a genetically inherited trait .
• Industrial melanism among moths ,It was first observed in factory districts of England ,Germany and other European countries and is now widespread,wherever air pollution is taking place.
• The moths rest by day on trunks and branches of trees .
• Originally their colors blended with the pale background of bark and light colored lichens.
• Lichens are sensitive to air pollutants and die off as the fumes and soot increase.
• Darkening of the trees results from their death and accumulations of soot .In areas of Britain where air pollution has been reduced the frequency of carbonaria has declined.

 

END

The reality of the selective advantage of color adaptations has been debated .It has been argued that animal vision may be so different from human vision (certain animals are colorblind or may be able to see ultraviolet or infrared light that an animal that appears to be protectively colored to a human may be quite evident to its natural predators .However many experimental studies such as the experiments with grasshoppers and moths have shown that coloration does have as survival value .