The evolution of visual fruit signals: concepts and constraints.

Abstract

This chapter considers the different selective factors and outlines the recent developments in the field of communication between fruiting plants and visually oriented animals (e.g. primates and birds). Instead of viewing fruit colours simply as colours, they are viewed as signals. This shift of emphasis offers more general insights into the selective pressures between plants and their frugivorous consumers.

Unripe red fruits may be aposematic

“…14 The poisonous or otherwise unpalatable species presented here, which have unripe red fruits and the two other types of defensive aposematic coloration (mimicry of caterpillars and spines), which have recently been proposed to occur in fruits and repel large herbivores 44,47,70 seem to represent a widespread but still almost unexplored phenomenon. The aposematic unripe fruit hypothesis is further supported by the fact that birds detect red fruits from a longer distance than black fruits.…”

“…Following the recent discussions that many colorful thorny or poisonous plants might be aposematic [36][37][38][39][42][43][44][45][46][47][48][49][50][51][52][53][55][56][57]66,67 and that several colorful fruits are aposematic because they are poisonous, 13,14,47,[60][61][62]65 mimic poisonous caterpillars, 37,46,70 or mimic aposematic colorful spines, 37,44,46,47 a new hypothesis should be considered, namely, that unripe red fruits might also be aposematic. To explore this issue, we have screened the plants in the flora of Israel that have unripe red fruits and discuss their potential of being aposematic.…”

“…[5][6][7][8][9][10] Fruit color is the typical visual signal that plants use to communicate with frugivores, 5,6,8,[11][12][13][14] although other plant parts (branches of the raceme, panicle or leaves) may also contribute to this signaling system. 5,7 Multicolored fruit displays, where fruits first change their color from green to a conspicuous color when they have reached full size but are still unripe and later to a second conspicuous color upon ripening, have been studied in plants of several ecosystems.…”

“…[40][41][42] The similarity between aposematic colors in poisonous insects and ripe fruits has already been demonstrated, 68,69 but their aposematic role in fruits was not considered by Herrera 68 and was not found to operate in artificial fruit-like objects introduced to domestic chicks. 69 Several types of defensive aposematic coloration have been proposed to occur in fruits that repel large herbivores: (1) brightly colored poisonous fruits; 13,14,60,65 (2) pods of several wild annual legumes (Lathyrus ochrus, Pisum humile, P. elatius and Vicia peregrina) have conspicuous reddish spots arranged along them that appear to mimic aposematic lepidopteran caterpillars and may repel various herbivores; 37,46,47,70 (3) colorful (yellow, red, purple or various combinations of these) aposematic thorn-like unripe soft fruits in several wild Erodium species and in Sinapis alba growing in Israel. 44 Here we report that conspicuous red but unripe fruit of several plant species are poisonous or unpalatable.…”

“…40-42), has recently been shown to be common also in thorny plants and in plants that mimic them 39,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] as well as in certain poisonous plants, some of which proposed to be aposematic earlier. 13,14,[36][37][38]46,47,51,[58][59][60][61][62][63][64][65][66][67] In animals, aposematic coloration is usually red, orange, yellow, black and white or combinations of these, which protect unpalatable, dangerous or poisonous prey species. [40][41][42] The similarity between aposematic colors in poisonous insects and ripe fruits has already been demonstrated, 68,69 but their aposematic role in fruits was not considered by Herrera 68 and was not found to operate in artificial fruit-like objects introduced to domestic chicks.…”