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Animalia >Chordata >Osteichthyes >Gasterosteiformes >Gasterosteidae >Gasterosteus >

During the reproductive season, a male three-spined stickleback prepares a nest and defends the area surrounding it (a territory). The male chases away any intruding males by directing aggression toward them: opening the mouth and rushing toward the intruders.

A factor that induces innate behavior in an animal is called 'a releaser,' and the specific element of the releaser that actually induces the behavior in question is called 'a sign stimulus.' In the three-spined stickleback, intrusion of a strange male into a territory is a releaser that induces aggressive behavior in the territorial male. Aggressive behavior, however, is induced in the territorial male even when the male does not see the entire body of the intruder. Rather, the territorial male shows aggression just seeing a red color - male nuptial coloration. In other words, the key stimulus that releases aggression in territorial males of the three-spined stickleback is red coloration.

It is Tinbergen who first showed experimentally the concept of this key stimulus. He showed two models to a territorial male: a complex model that looked like a real stickleback but lacked a red belly, and a simple model that did not look like a stickleback but had a red belly. The complex model without a red belly did not induce any aggression in the male whereas the simple model with a red belly did.

In this video picture, we duplicated the Tinbergen's experiment. A male was preparing a nest at the far-left end of the aquaria. We showed three models to the male: a complex model that looked like a real stickleback but lacked a red belly, a simple spindle-shaped model with a red belly, and a much simpler model with a red belly. The male showed aggression only toward the two simple models with a red belly.

The video picture also shows that the territorial male rushes toward the eye painted on the models, suggesting that the male is recognizing the eye as the focus of its attacks.

(This video picture was prepared by Friends of Fukui City Museum of Natural History during a project 'Educational Videos on the Three-spined Stickleback.' http://www.nature.museum.city.fukui.fukui.jp/friends/itoyo/)
(translated by Asoh)

(Data No.momo050707ga01b)

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