Color Changes in Old Aposematic Thorns, Spines, and Prickles

Abstract

Of the various colorful plant/animal communication systems, adaptive color changes are known to take part in the two extensively studied gene dispersal systems: pollination by both invertebrates and vertebrates and seed dispersal via frugivory. Young and still unrewarding animal-pollinated flowers and young and unripe fleshy fruits are usually green and cryptic. Many flowers become colorful and visually conspicuous only towards anthesis, when they open and offer nectar and/or pollen, or other rewards to pollinators, because their still immature colorful petals are commonly covered by bracts or by green sepals. Many flowers retain their conspicuous advertising colors till they wilt. However, post-pollination floral color change is a well-documented phenomenon in various taxa and life forms on all continents except for Antarctica (Weiss 1991, 1995; Weiss and Lamont 1997; Bradshaw and Schemske 2003). Color change of individual flowers in an inflorescence may reduce their advertising intensity, and thus their detectability by pollinators. Retaining the attractive coloration after pollination, or after they turn unreceptive, may reduce pollinator visits to un-pollinated flowers because the pollinators learn that there is no reward and fly to other plants, thus diminishing the plant’s reproductive success. By the simultaneous reduction of both the reward after pollination and of attractiveness (advertisement) by changing their color, plants direct their pollinators to un-pollinated flowers within the same inflorescence or plant.