OfAposematic Coloration in Thorny Spiny and Prickly Plants

There is very strong indirect evidence for the operation of aposematic coloration in thorny and spiny plants and its convergent evolution in the fact that conspicuous thorn and spine coloration is found in angiosperm taxa that have mutually exclusive biochemical pathways of pigmentation. For instance, taxa belonging to the Caryophyllales (e.g., Cactaceae, Caryophyllaceae, Chenopodiaceae) produce yellow and red pigments via the betalain pathway (Stafford 1994) . Most other angiosperm families use anthocyanins for similar patterns of coloration. The fact that spines of cacti are usually conspicuous because of their coloration (Lev-Yadun 2001), commonly including yellow, orange and red coloration resulting from betalain derivatives, indicates that this group of pigments may, among their various functions, be involved in aposematic coloration. By contrast, in Rosaceae, Asteraceae and Fabaceae as well as in many other angiosperm families that use anthocyanins for yellow, orange, pink, red, blue and black coloration of thorns, spines and prickles, the chemical origin of the aposematic coloration is different (Lev-Yadun 2001, 2006b; Lev-Yadun and Gould 2008). It seems therefore that the aposematic coloration of thorny, spiny and prickly plants is a good case of convergent evolution.

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