Iridescence as a form of coloration in animals
Jan Snyder, Ed.D.
Arizona State University GK-12 Project Manager
Background
Animal coloration is a commonly noted feature that helps us differentiate species.
However, coloration in animals provides a variety of functions that include camouflage to
displays. In some cases, animals benefit when they blend in to their immediate environments
such as to avoid predation. For others, being able to stand out can promote attraction of a mate,
hence, greater potential for success in reproduction.
In some species, as with the female collard lizard (Crotophytus collaris), a seasonal color
appears as a signal to members of the opposite sex when mating time has arrived. Sexual
dimorphism in color patterns is common especially with certain bird species.
Most animal colorations are due to pigments in the hair, feathers, scales etc. However, in
some cases colors are exhibited due to physical structures at the molecular level in the form of
iridescence. Whereas students will typically find color patterns that promote camouflage
relatively easy to understand, how might they interpret iridescence? If anything, iridescence
causes an animal to stand out. If we consider that a given species exhibits colors due to
iridescence, why might this feature be desirable?
This lesson requires student access to the Internet
Grade Level: 5-8
National Standards
Content Standard C: Life Science
•Structure and function in living systems
•Diversity and adaptations of organisms
Arizona State Standards
Strand 4: Life Science
Content 3: Populations of Organisms in an Ecosystem (Grade 7)
PO 2. Explain how organisms obtain and use resources to develop and thrive in:
• niches
• predatory/prey relationships
PO 3. Analyze the interactions of living organisms with their ecosystems:
• limiting factors
Overview
Whereas students will probably understand that color patterns in animals provide
adaptive features that promote survival, they might not consider the mechanisms that exist to
provide the color. Through guided efforts on the part of the teacher, students will probably
realize that most colors in animals, like those objects most familiar to them (e.g. clothes,
buildings, cars, etc), are a result of certain light waves being reflected from pigments. Although
levels of understanding of pigments, and their capacity to absorb some light waves as they reflect
others, will vary the basic concept should be readily understood. Indeed, most colors we see in
nature are a result of this light-absorption/ reflection interaction with pigments.
This activity allows students to investigate iridescence and its role in nature. Students are
provided with web-based images of animals along with accompanying information. A question
to explore might be, “Why does iridescence exist in nature when most coloration patterns are due
to pigments in the outer surface layers of animals?” Students consider various animals examples,
their environments and, in some cases, their behavior, in an effort to answer this question.
Materials
Computers with access to the Internet
The following are optional for use as displays during the lesson
Morpho butterfly1
Peacock Feather2
Key Words
Iridescence
Coloration
Adaptations
Environment
Lesson
1]
You are no doubt aware that animals have different color patterns that are typically
characteristic of their species. Look at the accompanying photo of a leopard and list those
features of its coloration pattern that you think are important to its survival.
Just before this photo
was taken, the leopard was
lying on the rock in the
shadow and it was difficult
to see. What features of the
leopard’s coloration pattern
do you think made it difficult
to see?
Share your ideas in a
class discussion and list them
on the board.
Do you know what
makes colors on leopards,
trees, your dog, house, your
clothes, or almost anything
you know about?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
South African Leopard. Photo by the author  2004
1
2]
If you do not know the
Available on the web:
http://www.google.com/products?client=safari&rls=en&q=Morph+Butterfly&ie=UTF8&oe=UTF-8&um=1
2
Available on the web: http://www.tonyhill.net/productCat85987.ctlg
answer to this question, take a moment to turn on your computer and open the web browser. Go
to: http://answers.yahoo.com/question/index?qid=20080120181903AA8Fh8Z
At this site you will find a basic description of the principals behind what makes objects have
color. Discuss this phenomenon in class to make sure you know how light interacts with
pigments so that an color-sensitive observer can see color.
Not all animals see color. In fact amongst mammals only humans and a few other higher
primates, like chimpanzees and gorillas, can see color. On the other hand, birds, fish, insects and
reptiles see color and they are the animals that often include species that have very bright color
patterns.
3]
However, not all colors on animals are due to the interaction of light waves and pigments.
Take a look at a photo of the Dogbane Beetle. What do you see in the color pattern of this
species of insect that is different from what you normally see in animals? How would you
describe the color pattern other than by naming the colors (e.g. red, green, yellow, etc)
themselves? What word can you think of that best describes the special feature of the colors of
this insect? ______________
4]
Now look at the Magnificent frigate bird. It may not be just like the beetle but the purple
color of this bird is due to something similar to what you see in the beetle. Actually, if you were
to see this bird at the right angle, it too would have that same quality to its coloration—that is
why it is called, “Magnificent.”
5]
There are many animals that display colors with the same sort of effect. The term used to
describe this effect is, “Iridescence” and it is the not due to light waves bouncing off of
pigments. Instead, iridescence is due to light hitting extremely small, prism shaped molecules in
the surface of the feather (birds), scale (fish and reptiles) or exoskeleton (insects). You may have
seen a prism at a science museum or an earlier science class. Rainbows result from tiny water
droplets acting like billions of prisms. When the sun is behind you its light waves are refracted
through the tiny water droplets to cause a rainbow to appear.
6]
Now that you have a basic understanding of iridescence in animals spend some time
looking at various examples of color patters that appear due to this phenomenon. Keep in mind
that the observer only sees the iridescent effect if the animal is seen at a particular angle relative
to the light source (generally the sun) and the viewer.
• Butterflies
• Beetles
• Cichlid Fish
• Hummingbird
You have probably seen a peacock. Males of this species
are very colorful. If you look at individual peacock feathers you
can see details of what are known as, “eye spots.” If you have
ever seen a peacock spread his tail feathers, describe what it looks
like to other members of the class.
Even the head and body are an iridescent color. Why do
you think male peacocks have such iridescent colors in their tail
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Tony Hill
feathers?
A research article, published in February of 20073,
hypothesizes that butterflies that exhibit iridescent colors tend to
live in dark forested areas.
A feature of iridescence is that color is evident to the
viewer even in low light and as long as the angle of sight is
oriented from a particular direction.
What does this information suggest about the probable
natural habitat for peacocks?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
For an example of a butterfly that lives in the South
American rainforest view the photo of a Blue Morpho. Read the
description for further discussion of this species and its
iridescent colors.
Tony Hill
Cichlid Fish
In south Central Africa lies one of the deepest lakes in the
world. Lake Malawi lies between Malawi and Mozambique and it covers approximately one
third of the Country of Malawi. The lake is the home of well over 100 endemic species of
Cichlid Fish—even now, many of these fish have not been described by scientists who name new
species.
Lake Malawi at Dawn
Photo taken by author © 2006
3
Douglas, J., Cronin, T., Chiou, T. and Dominy, N. (2007). Light habitats and the role of
iridescence in the sensory ecology of neotropical nymphalid butterflies (Lepidoptera:
Nymphalidae). Journal of Experimental Biology 210, 788-799. Available on the web:
http://jeb.biologists.org/cgi/content/full/210/5/788?maxtoshow=&HITS=10&hits=10&RESULT
FORMAT=&author1=Douglas&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspe
c=relevance&resourcetype=HWCIT
Many of the species of Cichlid fish have iridescent coloring. Use the links, below, to
view a few of the species of this group of fish that are known for breeding their young in their
mouths (mouth breeding).
Labeotropheus trewavasae
Maylandia crabro
Rhamphochromis species
You can also view a video of Cichlid mating behavior. When you watch this video, pay
special attention to the fin on the back of the female (larger of the two fish). What do you notice
about the color of that dorsal fin?
Since Lake Malawi is very deep many places in it have low light conditions. Even in
many of the shallow areas, there are large rocks resting on the bottom so it is shaded from the
sunlight and the fish live in low light conditions.
7]
Now that you have learned about iridescence, its occurrence in some animals, and the
types of environments where most of those animals live, propose a hypothesis to explain why it
occurs as a form of color in only select groups. Use examples provided from this lesson or from
another authoritative source.