Gut microbiome of nectarivorus birds in relation to nectar microbiome and secondary metabolites: ecological and evolutionary perspectives

The presence of plant secondary metabolites (PSMs), frequently considered as `toxins`, in floral nectar is a widespread phenomenon. The traditional hypothesis is that the evolutionary interactions between flowering plants and their nectar consumers (legitimate pollinators as well as nectar robbers) are mediated by nectar PSMs. Our central hypothesis is that PSMs are indeed mediators of the interactions between flowering plants and nectar consumers but mainly through the functions of the nectar microbiota and the gut microbiome of nectar consumers.

We studied various factors that determine microbiome composition in nectar. Nectar microbial community were found to be distinct for each plant species while there were no significant differences between nectar microbial communities within nectars taken from different plants of the same species within the same region. Analyses of Nicotiana glauca nectar microbiome at different sites (a) along Israel and (b) across the globe revealed that both geographical and environmental factors govern the nectar microbiome composition.

By using nicotine-free nectar of transgenic N. attenuata we have demonstrated that floral nectar microbiome is affected by pyridine-type alkaloid composition. We also showed that the presence of PSMs in nectar shapes the nectarivorous (Orange-tufted sunbirds, Cinnyris osea) gut microbiome. We also demonstrated that sunbird gut microbiome contains bacteria which are able to degrade the N-containing pyridine alkaloids.

Our studies therefore showed that the complicated interactions between nectar microbiome and nectar consumers’ gut microbiomes might affect flower visitation by pollinators and nectar thieves and thus affect plant fitness.