Pollination of Anemopaegma album (Bignoniaceae) with focus on floral nectar as the mediator of interactions with mutualistic and antagonistic bees

Abstract

We focused our study on the pollination of Anemopaegma album, a Bignoniaceae species from and on the features of primary attractive, the nectar, which mediate the interaction with mutualists and antagonists bees. We investigated the floral biology and identified pollinators and nectar robbers through field observations; we determined the mating system by performing controlled experiments; we described the floral structure with emphasis on the arrangement of reproductive structures and on the floral nectary and nectar chamber using scanning electron microscope for surface micromorphology and optical microscope for nectary histology; we monitored nectar production during the first day of anthesis and the weather conditions around plants. We registered medium and large-sized bees visiting A. album flowers throughout the daylight period acting as pollinators (Euglossini and Bombini) and as nectar robbers (Oxaea and Xylocopa). Plants from the focal population showed obligate outcrossing depending on bees for sexual reproduction; and flowers showed herkogamy mechanisms that favour outcrossing. The nectar chamber is formed by the constriction caused by the dilated basis of filets covered densely by trichomes and the nectary showed histological features related to the production of high amount of nectar in a short period. In fact, the highest volume of nectar is available when flowers open; after this, just small quantities are added along the day. The hottest and driest period was around midday, when just the nectar robber bee from genus Oxaea visited the flowers. Bees that Keywords: flower-bee interactions, seasonally-dry habitats, floral nectary, hercogamy, mating system. a seasonally dry habitat, promote A. album outcrossing used diluted nectar as a floral resource and concentrated their visits during the morning when the highest volume of nectar was available and the weather conditions were more suitable.