Floral symmetry and nectar guides: ontogenetic constraints from floral development, colour pattern rules and functional significance

The accord between symmetries of flower shape (external contours) and nectar guides (internal contours) was examined using the bulbous flora of South Africa, and in the general floras of Britain, Alpine Colorado, Canadian Arctic and Israel. It was found that radially symmetrical flowers have radially symmetrical nectar guides whereas bilaterally symmetrical flowers have bilaterally symmetrical nectar guides. It is suggested that the complementarity between the external and the internal contours of the flower increases the probability that, and efficiency with which, a bee moves into the flower's centre and towards the sporophylls and access to floral rewards, regardless of the flower's form and the bee's previous experience. Patterns of coloration of tepals against background and nectar guides against tepals also accord with behavioural and sensory characteristics of pollinators. It is suggested that the complementarity of contours is probably constrained by floral development, but patterns of coloration of tepals against background and nectar guides against tepals is constrained by pollinators' sensory physiology.