Shade avoidance and Zahavi's handicap principle in dense plant populations
I propose that tall plants ‘show off’ and that the shade avoidance syndrome is a case of spectral communication among plants in dense populations, enabling the operation of Zahavi's handicap principle in plants. The costly signal triggering shade avoidance is composed of: (1) the far-red (FR) irradiation that plants emit as a by-product of photosynthesis, and (2) the phytochromes and the down-stream factors that respond to phytochrome signalling that evolved to analyse the FR emission and respond. This is a special case of a complex system serving as a signal. Because various types and levels of shade avoidance are common in most, if not all, dense plant populations, it seems that the operation of Zahavi's handicap principle in plants is a common phenomenon. Although plants do not see, they can use light for interplant communication about their relative strength. Unlike the many types of species-specific operations of Zahavi's handicap principle in animals, the handicap signal in plants is not species-specific, like prey–predator interactions. This difference probably stems from the fact that plants are sessile, have no animal-like vision, and compete with individuals of many other species. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 313–319.