Countershading

Countershading
Countershading employed by the grey reef shark.
The original drawings from Thayer's 1902 patent application
A photograph of a countershading study conducted by Thayer. The model on the left is camouflaged and visible whereas another on the right is countershaded and invisible[1]

Countershading, or Thayer's Law, is a form of camouflage. Countershading, in which an animal’s pigmentation is darker dorsally, is often thought to have an adaptive effect of reducing conspicuous shadows cast on the ventral region of an animal’s body. In essence the distribution of light on objects that are lit from above will cause unequal reflection of light on a solid body of uniform colour; such shadows could provide predators with visual cues to a prey's shape and projection. Countershading therefore reduces the ease of detection of prey by potential predators by counterbalancing the effects of shadowing.

Contents

Examples

Countershading is observed in a large variety of animals, such as pronghorn antelope, White-tailed deer, squirrels, birds, and various lepidopteran larvae.

Alternatively, in many marine animals (including various species of fish such as marlins and sharks, penguins and cephalopods) this form of camouflage may work through background matching; when seen from the top, the darker dorsal area of the animal blends into the darkness of the water below, and when seen from below, the lighter ventral area blends into the sunlight from the surface.

Furthermore, countershading could also result from differential selection pressures on dorsal and ventral surfaces, from the need to protect against the damaging properties of UV light or abrasion.

History

Abbott Handerson Thayer was one of the first to conduct extensive research on and to write about certain aspects of protective colouration in nature. In 1892, he wrote about the function of countershading in nature, in which he accounted for the white undersides of animals. For this reason countershading is sometimes called Thayer’s Law.

Military camouflage sometimes uses the same principle; Thayer even obtained a patent in 1902 to paint warships using a countershaded scheme.

Gallery

  • Anolis caroliensis showing blending camouflage and countershading

  • Countershading in Eyed hawk moth

  • Adelie penguins

  • Ringtailed lemur

See also

Notes

  1. ^ Behrens, Roy (27 February 2009). "Revisiting Abbott Thayer: non-scientific reflections about camouflage in art, war and zoology". Philosophical Transactions of the Royal Society B - Biology (Royal Society Publishing) 364 (1516): 497–501. doi:10.1098/rstb.2008.0250. PMC 2674083. PMID 19000975. http://rstb.royalsocietypublishing.org/content/364/1516/497.full#ref-18. Retrieved 2009-05-05. 

References

  • Edmunds, M. & R.A. Dewhirst (1994). The survival value of countershading with wild birds as predators. Biological Journal of the Linnean Society 51(4): 447-452.
  • Ruxton, G.D., M.P. Speed & D.J. Kelly (2004). What, if anything, is the adaptive function of countershading? Animal Behaviour 68(3): 445-451.
  • Speed, M.P., D.J. Kelly, A.M. Davidson, G.D. Ruxton(2005). Countershading enhances crypsis with some bird species but not others. Behavioral Ecology 16(2): 327-334.
v · d · eEvolutionary ecology
Patterns of evolution
Signals
v · Vision Fish surveying its world
Eyes
Evolution
Colouration
Related topics

Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • countershading — noun Date: 1896 cryptic coloration of an animal with parts normally in shadow being light and parts normally illuminated being dark thereby reducing shadows and contours …   New Collegiate Dictionary

  • countershading — condition of fish in the water column that are dark colored on top but light colored on the bottom. The effect is to obscure the image of the fish to predators by blending with the dark sea floor when viewed from above, the light sky when viewed… …   Dictionary of ichthyology

  • countershading — n. [L. contra, against; A.S. sceadu, shade] In camouflaging, an animal being dark dorsally and pale ventrally and therefore appearing evenly colored and inconspicuous …   Dictionary of invertebrate zoology

  • countershading — /kown teuhr shay ding/, n. Zool. the development of dark colors on parts usually exposed to the sun and of light colors on parts usually shaded, esp. as serving for protection or concealment. [1895 1900; COUNTER + SHADING] * * * …   Universalium

  • countershading — noun Zoology protective coloration used by some animals in which parts normally in shadow are light and those exposed to the sky are dark. Derivatives countershaded adjective …   English new terms dictionary

  • countershading — coun·ter·shading …   English syllables

  • countershading — coun•ter•shad•ing [[t]ˈkaʊn tərˌʃeɪ dɪŋ[/t]] n. zool. (of an animal) coloration that is dark on parts of the body surface that are usu. exposed to the sun and light on parts usu. in shade • Etymology: 1895–1900 …   From formal English to slang

  • countershading — /kaʊntəˈʃeɪdɪŋ/ (say kowntuh shayding) noun the presence (on an animal) of dark colours on parts usually exposed to the sun and of light colours on parts usually shaded, especially as serving for protection or concealment …  

  • countershading — |kau̇ntə(r)+ noun Etymology: counter + shading : coloration (as of an animal) with parts normally in shadow being light or parts normally illuminated being dark compare protective coloration …   Useful english dictionary

  • Dun gene — A bay dun, also called a classic or zebra dun A Blue dun, or Grullo …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”