One major obstacle to studies of defensive plant coloration in general and apose-matic coloration in particular is provided by the fragmentary and inconsistent descriptions of plant coloration, especially of vegetative organs. Taxonomists have usually referred only to flower colors, and even this character has not always been fully described. Thorn, spine and prickle color, unripe and ripe fruit color, leaf colors, bark color and color changes in all of these organs have usually not been systematically described. In his seminal book on plant demography, Harper (1977) commented as follows on the possibility that defensive plant coloration operates: "botanists were reluctant to accept things that are commonplace for zoologists." The surprisingly small number of papers in botany related to defensive coloration as compared to zoology is clearly reflected in the annotated bibliography by Komarek (1998), which has thousands of related publications on animals and only a few about plants. The significant progress made in understanding the defensive role of pigmentation in zoology and the basics of the genetic mechanisms involved took over a century to achieve (e.g., Majerus 1998; Ruxton et al. 2004; Hoekstra 2006), and the effort needed to reach the same level of progress in botany is probably not any smaller. Lev-Yadun and Gould (2008) emphasized that in spite of all of the current difficulties involved in accepting, understanding and proving defensive plant coloration, there is no reason to continue with the long tradition of botanists (or, to give them their current popular name, "plant scientists") of neglecting the study of defensive plant coloration including aposematism. Moreover, even zoologists studying animal aposematism who studied plant-animal interactions related to herbivory overlooked this issue. An intermediate stage of imperfect explanations, which in any case are common in many areas of biology and other sciences, will still allow progress to be made in the issue of aposematic coloration and may stimulate thinking by other scientists who may develop even better theoretical or experimental ideas than the ones that exist today.
Aposematic (warning) coloration is a biological phenomenon in which poisonous, dangerous or otherwise unpalatable organisms visually advertise these qualities to other animals (Cott 1940; Edmunds 1974; Gittleman and Harvey 1980; Ruxton et al. 2004). The evolution of aposematic coloration is based on the ability of target enemies to associate the visual signal with risk, damage, or nonprofitable handling, and thus to avoid such organisms as prey (Edmunds 1974; Gittleman and Harvey 1980; Ruxton et al. 2004). Typical colors of aposematic animals are yellow, orange, red, purple, black, white and brown, or combinations of these (Cott 1940; Edmunds 1974; Wickler 1968; Savage and Slowinski 1992; Ruxton et al. 2004). The common defense achieved by aposematic coloration has resulted in the evolution of many mimicking animals. The mimics belong to two general categories, although there are intermediate situations. One is Mullerian mimics: here, defended animals mimic each other, sharing the cost of predator learning among more participants. The other is Batesian mimics, which are undefended animals that benefit from the existence of common defended aposematic models (Cott 1940; Edmunds 1974; Wickler 1968; Savage and Slowinski 1992; Ruxton et al. 2004).
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