Floral Longevity and Attraction of Arctic Lupine, Lupinus arcticus: Implications for Pollination Efficiency

Abstract

Pollination by insects is a mutualistic relationship in which flowers receive pollen for reproduction while pollinators are rewarded with pollen or nectar. Floral longevity (the period an individual flower blooms) and floral attraction (the period during which pollinators are attracted to the flower, often indicated by petal colour) both play prominent roles in plant and pollinator success. This study investigated whether floral longevity and floral attraction were mediated by pollination type in arctic lupine (Lupinus arcticus S. Wats.), a common herbaceous perennial in northwestern North America. Flowers were either open to pollinators, cross-pollinated by hand, or bagged to prevent cross-pollination, and floral longevity, seed set, and flower colour were observed. Open and hand-pollinated flowers had significantly shorter floral longevities and higher percent fruit sets than bagged flowers. A colour change of the banner petal marking from white to pink occurred in some flowers and was a signal of floral attraction, as pollinators preferentially visited pre-change flowers. Pre-change flowers contained more pollen and were less likely to have been injured by herbivory than post-change flowers, yet the colour change was not related to pollination type or fruit set. Pollination-induced shortening of floral longevity is likely an adaptation to limited plant resources and pollinator visitation rates. For L. arcticus, this could be influenced by short growing seasons and low annual temperatures in the study area. In the face of climatic changes and shifting species phenologies, the mediation of floral longevity by pollinators could decrease temporal mismatch between plants and their pollinators, yet the many factors at play make this difficult to accurately predict.