Eye spot (defense)

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Eye spots of the elongated tail feathers in the plumage of the male blue peacock ( Pavo cristatus )

An eye spot , also known as ocellus or ocelle (from the Latin "ocellus" = small eye), is an eye-like pattern on the surface of an animal whose function can vary. Eye spots are found in fish , insects , birds, and mammals , among others , and have evolved independently of one another in different taxa . Many German and scientific species names refer to the eye spots, for example that of the evening peacock ( Smerinthus ocellatus ).

description

Eye spot on a copper-striped tweezer fish ( Chelmon rostratus )

Eye spots appear as circular, oval or egg-shaped areas on the outside of the body of animals. They are of different sizes, even in a living being with several eye spots they can differ considerably from one another in terms of extent. They can be designed as a black or dark circle, edged with a ring of light color, or vice versa.

In order to increase the authenticity of eye spots, total reflections (also called highlights) are imitated, which express themselves as white sickles and are usually directed upwards. The highlight imitations of butterflies reflect UV light and therefore also appear white to birds and reptiles. Using dummies, it was found that eye spots with imitation highlights were attacked less often than those without highlights. It was also crucial that the highlights were directed upwards in order to simulate a natural situation. Fish do not form any highlights in their eye spots, because the similar refractive index of the cornea and water does not result in any highlights in the real eye.

Ecology and behavioral biology

"Deception" function

In the evening peacock butterfly ( Smerinthus ocellatus ) the eye spots are on the upper side of the hind wings
Caligo memnon feignsa conspecific tothe territorial predator, an anole lizard.
The caterpillar of Papilio bianor looks like a snake's head with its eye-spots on its shoulders.

Often the eye spot serves to ward off predators and is then assigned to the secondary (active) defense mechanisms . The evening peacock butterfly, for example, suddenly spreads its camouflaged fore wings when threatened and lets the eye spots appear on the upper side of the hind wings. The moment of fright in the predator is used by the evening peacock butterfly to warm up - a prerequisite for escape. Although small birds tend to attack small spots, they shy away from large eye-spots like those of the peacock's eye , especially if the eye-spots appear three-dimensional or are concentric and additionally move slowly through slow wing movements in order to imitate creeping predators. The caterpillar of the wine hawk ( Deilephila elpenor ) also increases mimicry when there is danger with the help of behavior: it retracts its head so that the eye spots widen and the head resembles that of a snake thanks to the thickening. Moving the body back and forth intensifies the effect. In the real miracle perch ( Calloplesiops altivelis ), the eye spot results in a change in swimming behavior: the fish swims backwards out of its hiding place in danger, for example a crevice, because the eye spot sits on the oversized dorsal fin , which in its proportions resembles the dangerous net and pearl moray equals.

Eye spots do not necessarily mimic predators of predators to act as a deterrent: The wing image of some Caligo TYPES appears as head imitation of Anolis -Echsen, a predator of butterflies, behaves very territorial and therefore avoids counterparts primarily. The picture is characterized by a large eye spot and a smaller eye spot that could represent the eardrum. There is also a dark color to imitate the body of the lizard. Furthermore, the eye spot is on the underside of the wing, so it cannot represent the frontal view of a predator, but rather a lizard sitting upside down on the tree.

Eye spots are also used to direct predator attacks , which primarily target the head, onto insensitive parts of the body. Butterflies with eye spots are more likely to have injured wings as a sign of attack by birds and consequent survival than butterflies without eye spots. Animals that use eye spots for this function have sensitive body parts that are well camouflaged, which are then primarily not attacked and allow the animal to flee after an attack. To enhance the illusion, can in butterflies, for example, representatives of Bläulingen be formed at the rear end also "wrong sensor", leading to Kopfmimikry leads. In addition, this type of deception can lead the predator to escape in a certain direction. In fact, the prey flees in the opposite direction and has a higher chance of escape.

Field experiments with dummies of gnome pygmy owls ( Glaucidium gnoma ) reinforced the hypothesis that eye spots on the back of the head influence hating . The reason is probably that hating birds attach more relevance to the large eye-spots on the back of the head than to the smaller eyes and therefore do not hate the gnome pygmy owl from behind. Because the hating birds attack the gnome pygmy owl from the front, they are observable for the gnome pygmy owl, easier to attack and can even be captured.

"Communication" function

The eye spots can also be a product of intersex selection . For example, females of blue peafowl ( Pavo cristatus ) prefer males with the most iridescent and contrasting eye spots. This behavior is explained with the handicap principle , because the complex eye spots and the male's wheel are expensive to produce and maintain, but also because they hinder the peacock during the escape.

Also in butterflies there is a strong sexual dimorphism in the expression of the eye spots, for example in Hypolimnas bolina . The dimorphism is probably due to sexual selection and is used by the males to recognize female conspecifics.

literature

  • Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt 2011, ISBN 978-3-534-23212-3 .

Individual evidence

  1. ↑ Caroline Deppe et al .: Effect of northern Pygmy-Owl ( Glaucidium Gnoma ) Eyespots on avian Mobbing , The Auk 120 (3): 765-771, 2003. doi : 10.1642 / 0004-8038 (2003) 120 [0765: EONPGG ] 2.0.CO; 2 . P. 765.
  2. ^ A b Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt, ISBN 978-3-534-23212-3 . Pp. 52, 53.
  3. ^ Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt, ISBN 978-3-534-23212-3 . Pp. 54-55.
  4. ^ Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt, ISBN 978-3-534-23212-3 . P. 57.
  5. ↑ a b Konrad Dettner et al .: Textbook of Entomology . 2nd Edition. Spectrum Academic Publishing House, 2003, ISBN 978-3-8274-2617-8 . P. 573.
  6. ↑ Donald M. Broom et al .: Biology of behavior: mechanisms, functions and applications . Cambridge University Press, 1981, ISBN 0-521-23316-X , pp. 38 ( limited preview in Google Book search). Retrieved February 26, 2011.
  7. ^ Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt, ISBN 978-3-534-23212-3 . P. 54.
  8. ↑ Ellen Thaler: "Look into my eyes, little one!" , Biology in our time, Volume 27, January 1997, p. 21. doi: 10.1002 / biuz.960270113 ; ISSN  0045-205X
  9. ^ Matthias Schaefer: Dictionary of Ecology . 4th edition. Spectrum Akademischer Verlag GmbH, Heidelberg, Berlin 2003, ISBN 3-8274-0167-4 . P. 174
  10. ↑ David L. Evans et al .: Insect defenses: adaptive mechanisms and strategies of prey and predators . State University of New York, 1990, ISBN 0-88706-896-0 , pp. 5 ( limited preview in Google Book search). Retrieved February 26, 2011.
  11. ^ Robert K. Robbins: The "False Head" Hypothesis: Predation and Wing Pattern Variation of Lycaenid Butterflies (English; PDF; 196 kB). American Naturalist 118, pp. 770-775.
  12. ^ Klaus Lunau : Warning, camouflaging, deceiving . Completely revised new edition 2011 of the 1st edition. Scientific Book Society, Darmstadt, ISBN 978-3-534-23212-3 . P. 55.
  13. ↑ Caroline Deppe et al .: Effect of northern Pygmy-Owl ( Glaucidium Gnoma ) Eyespots on avian Mobbing , The Auk 120 (3): 765-771, 2003. doi : 10.1642 / 0004-8038 (2003) 120 [0765: EONPGG ] 2.0.CO; 2 . Pp. 769 and 770.
  14. ↑ Adeline Loyau et al .: Iridescent structurally based coloration of eyespots correlates with mating success in the peacock , Published by Oxford University Press on behalf of the International Society for Behavioral Ecology, 2007. doi: 10.1093 / beheco / arm088 . P. 7.
  15. ↑ Ullasa Kodandaramaiah: Eyespot evolution: phylogenetic insights from Junonia and related butterfly genera (Nymphalidae: Junoniini) , Department of Zoology, Stockholm University, 2009. doi: 10.1111 / j.1525-142X.2009.00357.x . P. 496.