Hawkmoth Pollinators Decrease Seed Set of a Low-Nectar Petunia axillaris Line through Reduced Probing Time

SummaryAlthough deception of floral pollinators is well known among orchids [1 and 2], the majority of animal-pollinated plants secure pollination by nectar rewards. The costs and benefits of nectar production remain poorly understood [3, 4 and 5]. Here, we developed a crossing design to introgress a low-nectar-volume locus of Petunia integrifolia into the genetic background of P. axillaris. The resulting introgression line resembled P. axillaris but produced only one-third of the nectar volume. When exposed simultaneously to low-nectar and wild-type P. axillaris plants, hawkmoth pollinators reduced their probing duration on low-nectar plants but otherwise did not show any signs of discrimination against these plants. However, reduced probing duration resulted in reduced seed production in the low-nectar plants despite their higher reproductive potential as evidenced by hand pollination. In line with this interpretation, we found a positive correlation between probing duration and seed set, and hawkmoth pollination of low-nectar plants that were manually supplemented with nectar to parental levels yielded seed sets similar to hand pollination. Thus, a simple self-serving pollinator behavior—the adjustment of probing time in response to nectar volume—may select against reducing nectar and protect many plant-pollinator mutualisms against a drift toward parasitism.Video Abstract To view the video inline, enable JavaScript on your browser. However, you can download and view the video by clicking on the icon belowHelp with MP4 filesOptionsDownload video (16574 K)

► A Petunia axillaris line containing one-third of the regular nectar volume was bred ► Moth pollinators significantly reduced probing time on the low-nectar line ► The low-nectar line produced fewer seeds than its parent in moth-pollination assays ► Seed set was positively correlated with moth probing time