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Among different mechanisms of adjusted effectiveness of amimetic visual stimuli matched with the corresponding receptive fields, bilateral symmetry of spots and spatial symmetry of gratings play an exceptionally inportant role (e.g., Kenward et al., 2004). The effectiveness of pair stimuli is determined by the bilateral symmetry of visual system and visual perception evolved during millions of years in the field of Earth gravitation, but the causes of the evolution of repetitive stilmuli and the corresponding receptive fields are unclear. Kenward et al. (2004) consider about ten factors that might lead to the evolution of repetitive visual stimuli and the corresponding receptive fields, including the highest detectableness of repetitive stimuli on the background of environmental optic noises.

In particular, crosswise striped patterns and lengthwise striped patterns play an important role in fish behaviour.

For example, in swordtail fish, Xiphophorus cortezi, and some other poeciliids, females show preference for males with artificially manipulated symmetrical vertical bars (Schlüter et al., 1998; Morris et al., 2001). In the same context, in pipefish, Syngnathus typhle, males prefer ornamented females, with crosswise striped patterns (that work as amplifiers of female body size) over lengthwise ones (Berglund & Rosenqvist, 2001).

Fig.1 (read text)

Coss (1979) has conducted laboratory experiments with early fry of jewel fish, Hemichromis bimaculatus, and artificial models of head of adults (Fig.1) equipped with symmetric and asymmetric spots. It is shown that models with two horizontal spots (Fig.2) induce the most intensive fright responses of fry than any others. According to Blest (1957), pair horizontally arranged crosses, spots and eye-spots induce fright responses in birds. It is shown in experiments with naïve chicks, Gallus gallus domesticus, that any asymmetry in size, shape and color of pair stimuli (Fig.3) affects their effectiveness (Forsman & Herrström, 2004).

Fig.2 (read text)

Fig.3 (read text)

As shown in experiments with fry of jewel fish, three and four spots are bilaterally symmetric but less effective than two horizontal spots (Coss, 1979). It may mean that fry must spend more time to recognize the more complicated stimuli and, finally, to make the corresponding decisions.

Basic References

Berglund A., Rosenqvist G. 2001. Male pipefish prefer ornamented females. Animal Behaviour 61, 345-350

Blest A.D. 1957. The function of eyespot patterns in the Lepidoptera. Behaviour 11, 209-256

Coss G.R. 1979. Delayed plasticity of an instinct: Recognition and avoidance of 2 facing eyes by the jewel fish. Developmental Psychobiology 12, 335-345

Forsman A., Herrström J. 2004. Asymmetry in size, shape, and color impairs the protective value of conspicuous color patterns. Behavioral Ecology 15, 141-147

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Category: Ethology | Views: 842 | Added by: nickyurchenko | Date: 2012-08-17

By virtue of an evolutionarily determined feature of color vision, insects, fish and other animals see fast-moving objects as colorless (Gehres & Neumeyer, 2007; Stojcev et al., 2011). In animals, the fastest moving parts are wings (in insects and birds: e.g., see Schön, 2009). So styding natural coloration of wings allows to understand deeper the phenomenon of color blindness in respect of fast-moving objects.

In insects,  strong correlation between the presense of eye-catching, signalling marks in wing coloration and the frequency of wing-beats is observed.

In particular, wasps, horneybees and other stinging insects have among all insects ones of the fastest beating wings, which are transparent or semi-transparent and have no eye-catching marks. The frequency of wing-beats, F, in the stinging insects is ranged approximately within 100-250 beats per second. For example, for common wasp, Vespa vulgaris, F = 140 b/s, for European honeybee, Apis mellifera, F = 240-250 b/s (Byrne, 1988). These wings beat too quickly to be used as the right location of signalling marks. In the stinging insects, the elements of aposematic coloration, with black, yellow and red colors, are located mainly on the relatively immobile belly (that can be seen in the flight).

The numerous dragonflies and damselflies can be included into the second group with two subgroups. Fast-wingbeating dragonflies (Anisoptera), with the frequency of wing-beats more than 15-20 beats per second (Rüppell, 1989), form the first subgroup. Slow-wingbeating damselflies (Zygoptera), with the frequency of wing-beats less than 15-20 beats per second (Rüppell, 1989), form the second subgoup Unexpectedly, dragonflies and damselflies have the transparent and decorated wings with signalling color patterns.

For example, aposematic coloration in fast-wingbeating (F = 24-25 beats per second) golden-ringed dragonfly, Anotogaster sieboldii (transparet wings, black & yellow belly) (Ishizawa, 2005), is designed similar to that in the stinging insects.

Finally, the numerous butterflies as well as moths can be aggregated into the third group of insects, which have the slowest beating and decorated wings with the cryptic or signalling color patterns. In these insects, the mean frequency of wing-beats is about 5-15 beats per second (Byrne, 1988). It is important in our context that signalling marks, varied from primitive dots to high quality concentric eye-spots, are most developed just in the group af slow-wingbeating butterflies and moths.

For example, the frequency of wing-beats in large emperor moth, Saturnia pyri, with four eye-spots (Fig.1) is about 8 beats per second ((Byrne, 1988).

Fig.1 (read text)

The detailed analysis of signalling coloration in dradonflies and damselflies allows to select the following 4 basic rules that lie at the heart of signalling coloration in fast-moving natural and artificial objets.

Rule #1. An evolutionarily optimal solution

Signalling color patterns must be bilaterally symmetric (both in the fast-moving and slow-moving objects). It is shown experimentally (e.g., Forsman & Herrström, 2004) that even small asymmetry in size, shape and color impair the effectiveness of silnalling stimuli.

In general, the effectiveness of bilaterally symmetric stimuli is determined by the bilateral symmetry of visual system and visual perceprion evolved during millions of years in the field of Earth gravitation.

Rule #2. An evolutionarily optimal solution

Color stimuli must be located closer to the base of the wings or the center of rotation. These stimuli move with the lower linear velocity than stimuli located at the wingtips.

In accordance with this rule, wings of American rubyspot damselfly, ... Read more »

Category: Ethology | Views: 893 | Added by: nickyurchenko | Date: 2012-08-04

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