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

Kenward B., Wachtmeister C. A., Ghirlanda S., Enquist M. 2004. Spots and stripes: the evolution of repetition in visual signal form. Journal of Theoretical Biology 230, 407-419

Morris M.R., Elias J.A., Moretz J.A. 2001. Defining vertical bars in relation to female preference in the swordtail fish Xiphophorus cortezi (Cyprinodontiformes, Poeciliidae). Ethology 107, 827-837

Schlüter A., Parzefall J., Schlupp I. 1998. Female preference for symmetrical vertical bars in male sailfin mollies. Animal Behaviour 56, 147–153