Plant-pollinator interactions are viewed as bipartite interactions. However, nectar-inhabiting microbes can modulate floral attractiveness and pollination success. This study sought to determine whether the functional group of flower visitors has consequences for nectar microbial community structure in western columbine (Aquilegia formosa). Columbine is pollinated by long-tongued visitors, including hummingbirds, bees, and hawkmoths. However, many insects including wasps and flies circumvent columbine’s specialized morphology by chewing holes in a nectar spur, or by taking advantage of already-existing holes to feed on nectar (nectar robbers).
We explored whether legitimate pollinators or nectar robbers disperse unique communities of nectar microbes by establishing five treatments (20 flowers/treatment): (1) no visitors: the base of nectaries were plugged with cotton to prevent pollinators, and spurs covered with plastic to prevent robbers, (2) no pollinators: nectaries were plugged with cotton, (3) no robbers: spurs were covered with plastic, (4) open robbed: spurs were pierced with a sterile implement to simulate the nectar robbing, and exposed to nectar robbers, and (5) rob control: spurs were pierced with a sterile then covered with plastic. Flowers were monitored for visitors for 30 observation hours to evaluate the efficacy of the treatments. Nectar was collected, frozen, and sequenced with Illumina sequencing.
Results/Conclusions
We observed aphids, ants, bees, wasps, lacewings and hummingbirds visiting columbine flowers. During the 30 observation hours of our experimental flowers, we found that there was no significant effect of treatment on the number of visit attempts. Nectar volume was not significantly correlated with flower size, as measured by corolla width or spur height. Treatment had a significant effect on the volume of nectar collected (F=4.14, p=0.001), where flowers that were experimentally robbed had less nectar. This is most likely due to the difficulty of collecting nectar from robbed flowers. So, nectar volume was likely similar across all treatments, and thus columbine flowers may replenish nectar rapidly after nectar has been consumed by pollinators or robbers.
Nectar microbe sequencing is currently underway (as of Feb 25, 2016). Sequencing data from the previous season suggests that columbine nectar microbe communities show variation across flowers. If columbine flowers that were exposed to pollinators and nectar robbers have different microbial communities then we will have empirical evidence that different functional groups of visitors vector unique microbe communities to flowers. Future directions include assessing whether microbe communities vectored by pollinators or robbers affect pollinator visitation rates, robber visitation rates, and plant fitness.