Impact of Spatial Distance and Pollinators on Floral and Fruit Bacterial Communities of Solanum carolinense

Fruits and flowers house microbial communities that are unique from the rest of the plant. While a great deal is known about a handful of symbiotic microbes associated with roots and leaves, the microbial communities of fruits and flowers have received considerably less attention. Fruits are reproductive tissues that house, protect, and facilitate the dispersal of seeds, and thus they are directly tied to plant reproductive success. Fruit and flower microbial communities may, therefore, also impact plant fitness. This dissertation examines how fruit bacterial communities, as determined using the 16S rRNA gene marker, are shaped across spatial and environmental gradients and the role of pollinators in shaping floral bacterial communities among natural populations of Solanum carolinense. There have been limited studies on how spatial distance influences bacterial communities found in and on fruit tissue and the role of pollinators in shaping floral bacterial communities. The first study addresses how bacterial communities in fruit change across similar environmental conditions at fine spatial scales (2 to 450 m). Overall, no differences were found in observed richness or bacterial community composition. Next, the role that generalist pollinators might play in shaping these communities was tested using pollinator exclusion cages. Here we found that generalist pollinators do not play a large role in shaping floral bacterial communities in Solanum carolinense. Comparing bacterial community diversity between caged and uncaged flowers, via PCoA we found no significant clustering of samples. In contrast, significant clustering was detected between flowers and bee pollen baskets. Together these results suggested that environmental factors may be more important in shaping floral bacterial communities. To test this, we sampled 9 populations along a 337 km latitudinal transect and again used the 16S rRNA gene to characterize bacterial communities. We did not identify a significant correlation between distance and bacterial community composition in either the total nor endophytic community in the fruit. Results from these studies suggest that while there is some evidence for environmental effects shaping fruit and flower communities, other factors such as host selection (e.g., secondary compounds in fruit) also likely play an important role in shaping bacterial communities.