Flower visitors are thought to be key vectors of bacteria and fungi that colonize floral structures. Floral microbes can play a strong role in shaping plant – flower visitor interactions such as pollination success. Although plants and flower visitors exist in integrated communities, and flower visitors aside from primary pollinators may vector microbes, plant – flower visitor – floral microbe interactions have yet to be considered in a network framework, or beyond a pollinator-centric view of flower visitation.
We explored whether flower visitor frequency, diversity, or interaction structure drives floral microbial community structure by collecting all flower visiting arthropods (regardless of their perceived pollination efficiency) and isolating floral microbes from 20 flowering plant species in a high elevation wet meadow in Tahoe National Forest near Truckee, CA. Visitors were collected during 30-minute time windows over two weeks. Concurrently, 30 flowers of each species were collected and frozen. In the lab, arthropods were identified to the lowest taxonomic level possible with help from specialists. For each plant species, DNA was extracted from six pools of five flowers from each species. Isolated DNA was sent for sequencing of the fungal and bacterial communities.
During the 140 observation hours of the 20 focal plant species, we collected 4,346 arthropods. The most commonly collected arthropod orders by far were Coleoptera and Hymenoptera, followed by Diptera, Thysanoptera, Aranae, and Hemiptera. Rare arthropod orders included Lepidoptera, Neuroptera, and Odonata. Across plant species, there was significant variation in visitation frequency (ANOVA F19=15.82, P<0.001). The five plants with the highest average arthropod abundance per collection window were Lingusticum grayi, Erigeron glacialis, Drymocallis lactea, Bistorta bistortoides, and Aquilegia formosa. Arthropod communities (grouped by order) were significantly different across plant species (adonis F19=7.698, R2=0.38, p=0.001). Sequencing of nectar-inhabiting microbes from five of the focal plant species in the previous field season revealed a significant effect of plant species on microbe community composition.
The observed variation in visitor communities and visitor frequencies across the 20 species in this community combined with floral microbe sequencing data from all 20 plant species will allow us to assess whether 1) flower visitor frequency and/or diversity is correlated with microbial OTU diversity, and 2) whether the plant – flower visitor network is structurally correlated with the plant – floral microbe network. Floral microbe sequencing is currently underway (samples are at the Integrated Microbiome Resource as of Feb 23, 2017).