The role of plant-pollinator interactions in structuring nectar microbial communities

1. Floral nectar harbours a diverse microbiome of yeasts and bacteria that
depend predominantly on animal visitors for their dispersal. Since
pollinators visit specific sets of flowers and carry their own unique
microbiota, we hypothesize that plant species visited by the same set of
pollinators may support non-random nectar microbial communities linked
together by the type of pollinator. 2. Here we explore the importance of
plant-pollinator interactions in the assembly of nectar microbiome and
study the role of plant geographic location as a determinant of microbial
community composition. We intensively sampled the nectar of 282 flowers of
48 plant species with beetles, birds, long-tongued and short-tongued
insects as pollinators in wild populations in South Africa, one of the
world’s biodiversity hotspots, and using molecular techniques we
identified nectar yeast and bacteria taxa. The analyses provided new
insights into the richness, geographic structure and phylogenetic
characterization of nectar microbiome, and compared patterns of
composition of bacteria and yeast communities in relation to plant and
pollinator guild. 3. Our results showed that plant-pollinator interactions
played a crucial role in shaping nectar microbial communities. Plants
visited by different pollinator guilds supported significantly different
yeast and bacterial communities. The pollinator guild also contributed to
the maintenance of beta diversity and phylogenetic microbial segregation.
The results revealed different patterns for yeast and bacteria; whereas
plants visited by beetles supported the highest richness and phylogenetic
diversity of yeasts, bacteria communities were significantly more diverse
in plants visited by other insect groups. We found no clear microbial
spatial segregation at different geographical scales for bacteria, and
only the phylogenetic similarity of yeast composition was correlated
significantly with geography. 4. Synthesis. Interactions of animal vector,
plant host traits and microbe physiology contribute to microbial community
assemblages in nectar. Our results suggest that plants visited by the same
pollinator guild have a characteristic nectar microbiota signature that
may transcends the geographic region they are in. Contrasted patterns for
yeast and bacteria stress the need for future work aimed at better
understanding the causes and consequences of the importance of plants and
pollinators in shaping nectar microbial communities in nature.