Comparison of floral traits and pollinator assemblages of insular and mainland varieties of Lilium auratum

Abstract

Abstract Lilium auratum var. platyphyllum, which is endemic to the Izu Islands, has white petals and emits a strong floral scent, typical of moth‐pollinated plants. Moths might be important pollinators within the Izu Islands because swallowtail butterflies are absent or rare there. Therefore, we investigated insular var. platyphyllum and widespread L. auratum var. auratum on the mainland of Japan to clarify the relationship between floral characteristics and pollinators. Measurement of floral scent intensity using an odor sensor indicated that the intensity increased in the evening and at night in var. platyphyllum, whereas intensity increased at night in var. auratum. Total sugar weight in nectar, which was calculated by nectar volume and sugar concentration, showed that the flowers of var. platyphyllum secreted nectar abundantly both in the evening and at night, whereas those of var. auratum secreted an almost constant amount of nectar throughout the day. Flower visitor assemblages and their frequencies studied using digital cameras suggested that crepuscular and nocturnal hawkmoths are important pollinators for var. platyphyllum. In contrast, both diurnal swallowtail butterflies and nocturnal large hawkmoths are important and effective pollinators for var. auratum. These conclusions were also supported by the exclusion experiments of either diurnal or nocturnal flower visitors using mesh bags. The rates of seed sets of var. platyphyllum were significantly higher from nocturnal pollination than from diurnal pollination. Thus, this study revealed that floral traits of var. platyphyllum show more adaptation for crepuscular and nocturnal hawkmoths, which are relatively abundant in the Izu Islands, than those of var. auratum.