Despite the advantages of bearing a warning coloration established in the locality, the evolution of aposematism is not straightforward because proximal mechanisms seem to represent obstacles to its initial evolution. However, aposematic patterns are extremely diverse at all geographical and taxonomic levels, and this major discrepancy between theory and nature clearly suggests that positive frequency-dependent arguments are not as restrictive against the rise of novel warning colors. Similarly, predator generalization, which should not allow gradual shift of cryptic prey toward bright warning colors, does not seem to be efficient in restricting the rise of new conspicuous patterns.

In fact, both population dynamics and psychological arguments might well explain such spectacular diversification. First, positive frequency dependence would allow new local forms to be established through drift, relayed by other processes involving predator's cognitive biases. Second, the initial steps toward warning color are determined largely by which cognitive biases in the predators are exploited. That is, the initial pathway taken toward the evolution of warning coloration probably profoundly affects the aposematic phenotype that eventually evolves. Similarly, positive frequency dependence prevents deviations from the evolutionary pathway that is taken. In short, although aposematism is not expected predictably to evolve via Fisherian selection, it is such a powerful strategy once evolved that it is possibly inevitable in a contingent and varying world, where the nature and the height of the initial obstacles to its evolution fluctuate. It may thus follow a ratchetlike pattern of evolution, where more routes may lead toward aposematism than routes away from it.

See Also the Following Articles

Chemical Defense • Crypsis • Mimicry • Monarchs

Further Reading

Alatalo, R. V., and Mappes, J. (1996). Tracking the evolution of warning signals. Nature 382, 708-710.

Edmunds, M. (1974). "Defence in Animals. A Survey of Anti-predator Defences." Longman, New York.

Endler, J. A. (1988). Frequency-dependent predation, crypsis, and aposematic coloration. Philos. Trans. R. Soc. Lond. B 319, 505—524.

Guilford, T. (1988). The evolution of conspicuous coloration. Am. Nat. 131, S7—S21.

Lindström, L., Alatalo, R. V., Lyytinen, A., and Mappes, J. (2001). Strong antiapostatic selection against novel rare aposematic prey. Proc. Nat. Acad. Sci. U.S.A. 98, 9181—9184.

Mallet, J., and Joron, M. (1999). Evolution of diversity in warning color and mimicry: Polymorphisms, shifting balance and speciation. Annu. Rev. Ecolo. System. 30, 201—233.

Mallet, J., and Singer, M. C. (1987). Individual selection, kin selection, and the shifting balance in the evolution of warning colors: The evidence from butterflies. Biol. J. Linn. Soc. 32, 337—350.

Poulton, E. B. (1890). "The Colours of Animals." Trübner, London.

Rowe, C. (ed.). (2001). Warning signals and mimicry. Special issue of Evolutionary Ecology [1999, vol. 13, no 7/8]. Kluwer, Dordrecht, The Netherlands.

Sillen-Tullberg, B. (1988). Evolution of gregariousness in aposematic butterfly larvae: A phylogenetic analysis. Evolution 42, 293—305.

Sword, G. A., Simpson, S. J., El Hadi, O. T. M., and Wilps, H. (2000). Density dependent aposematism in the desert locust. Proc. R. Soc. Lond. B Biol. Sci. 267, 63—68.

Wallace, A. R. (1879). The protective colours of animals. In "Science for All" (R. Brown, ed.), pp. 128—137. Cassell, Petter, Galpin., London.

Apterygota is a subclass of the class Insecta in the phylum Arthropoda. It contains two orders, the Archaeognatha and the Thysanura.

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