Herbivore-induced effects on floral microbiome assembly and consequent pollination

 
Conserved phytohormone signaling allows plants to maximize finite resources available for growth, defense, and reproduction. Under adverse conditions however, conserved signaling results in unintended tradeoffs that affect plant fitness. For example, herbivory can elicit differential plasticity in a host’s phenotype, resulting in ecological costs potentially mediated through labile flowers and the mutualists they attract. Flowers, which are inherently linked to reproduction, facilitate interactions with other community members, including microbes that colonize floral organs, rewards, and ultimately, seeds. Additionally, herbivory can shift floral metabolism by altering floral reward chemistry, potentially shifting patterns of floral microbe colonization that indirectly effects pollinator preferences. We tested how timing of herbivory impacts pollinator preferences and consequent floral colonization in the mustard Brassica juncea. Plantswere either damaged by the caterpillar Tricoplusia ni, the aphid Brevicoryne brassicae, or left as controls. While herbivory alone had no effect on pollinator attraction, timing of herbivory significantly impacted pollinator foraging bouts and consequent fruit production. B.brassicae damaged plants were visited less often relative to control plants and while T.ni plants were unaffected. Interestingly, herbivore damage from B.brassicae damaged resulted in decreased bacterial colonization relative to T.ni damaged and control plants. To determine if these affects were related to defense induction, we conducted invitro tests with synthetic nectar and found that salicylic acid reduced bacterial performance. While we’ve demonstrated that herbivory reduces pollination that may affect floral colonization, much work still needs to be done to tease apart herbivore-induced effects on microbe assembly and consequent floral phenotypes.