A nectar-inhabiting bacterium may not influence female fitness in Ipomopsis aggregata
Abstract
Hummingbirds are known to select which floral resource to utilize based on visual and olfactory cues. The role that microbes play in mediating the mutualism between hummingbirds and flowers is mostly unexplored in the field of microbial and pollination ecology. Bee pollinators are known to be deterred by high concentration of bacterial nectar, and the same has been shown for hummingbirds but only in one highly controlled setting with artificial flowers. There is limited evidence on how bacterial nectar influences hummingbird pollination, especially in wild systems. We tested if the presence of Pantoea sp., a plant generalist bacterium, in floral nectar influences the female fitness of Ipomopsis aggregata, a hummingbird-pollinated wildflower. Plants were inoculated with sterile or bacterial nectar, at the end of the growing season, seed set, fruit set, and fly larval predation were calculated to test the effects of bacterial nectar on plant fitness. Floral and vegetative plants were also accounted for in our fitness models. We found no significant differences in seed set, fruit set, or predation between our Pantoea-treated plants and sterile nectar treatments. We found that larger floral and vegetative traits of I. aggregata were associated positively with seed set and predation, but not fruit set. Pollen limitation was found to be minimal or absent, hand pollination did not prove to significantly improve seed or fruit production. Hummingbird pollination or female fitness of Ipomopsis aggregata was not affected by Pantoea sp. in floral nectar in field realistic conditions. Plant morphology was found to play a more important role in reproductive success than microbial nectar dynamics. These results suggest that microbial mediation of plant-pollinator mutualisms may be context-dependent and not universally disruptive.
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