SIGNALING FUNCTIONS OF FLORAL COLOR PATTERNS FOR INSECT FLOWER VISITORS

The diversity of floral colour patterns in angiosperms is known to be an adaptation aimed at the pollinators' capacity for learning and disc riminating colours. The species-specific labelling of colour signals i mproves pollen transfer between the flowers of a species caused by the flower constant foraging behaviour of pollinators. The initial flower detection of inexperienced flower visitors, however, requires non-spe cies-specific, standardized cues among potential food plants fitting t o the innate preferences of flower visitors. It was shown that the col our patterns of many melittophilous angiosperm blossoms closely match the colour signals releasing innate responses of bumble bees and hover flies which exhibit very different kinds of innate colour preferences. In this comparative study, physiological, morphological, phylogenetic al and functional aspects of the construction of visual signalling uni ts in melittophilous plants are investigated. The various levels of th e representation of colour patterns are described, such as the spectra l reflection of flower colours, the relative quantum absorption of the photoreceptors of a flower visitor, and the representation of floral colour patterns in the colour triangle as well as in a perceptual colo ur space. With respect to the flower parts which display the optical r eleasers of innate colour preferences there is a great morphological d iversity. The signalling function of the androeceum as the primary foo d signal highlights the evolution of innate colour preferences in flow er visitors. The androeceum, floral guides or central colours of bloss oms offer standardized optical releasers corresponding to innate colou r preferences of pollen-feeding insects. Plant species with polymorphi c flowers are used as a study case in order to demonstrate the standar dization of colour signals at the species level. In summary, floral co lour patterns serve multiple functions: They offer species-specific as well as standardized signals and they may address themselves at the s ame time to flower visitors with fundamentally different visual system s and innate colour preferences.