Spatiotemporal Variations in Nectar Robbing and Its Effects on Reproduction in Salvia castanea Diels (Lamiaceae)

TL;DR

This study explores how nectar robbing affects the reproduction of Salvia castanea plants in the Himalayan region.

Contribution

The study reveals that nectar robbing does not reduce seed set in Salvia castanea due to nectar replenishment and sufficient pollen deposition.

Findings

Nectar robbing rates did not affect seed set in Salvia castanea populations over multiple years.

Flowers maintained nectar volume and concentration regardless of robbing or pollination.

Only 5–10 pollen grains are needed for maximum seed set, with more than 10 ensuring high seed set.

Abstract

Nectar robbing typically reduces nectar availability to pollinators, damages flower structure, and/or induces secondary robbing. Consequently, it may reduce pollen deposition and seed set, increase pollination efficiency and outcrossing, and/or not affect reproduction in some species. However, spatiotemporal variations in nectar robbing and their effects on plant reproduction have received little attention. In this study, we assessed the effects of nectar robbing on floral visits, seed set, nectar volume and concentration, and flower longevity in two populations of Salvia castanea Diels (Lamiaceae) in the Himalayan region of Southwestern China in 2014–2020. We also examined whether one or a few visits by pollinators can result in the stigma receiving sufficient pollen to fertilize all ovules of S. castanea. We found that significant differences in the nectar robbing rate did not affect seed set in any of the years for either population of S. castanea. In the robbed and unrobbed flowers, nectar was consistently replenished every night at higher concentrations. Bagging, nectar robbing, and sufficient pollination did not affect flower longevity. Salvia castanea required only 5–10 pollen grains to achieve the maximum seed set. However, pollinators depositing more than 10 pollen grains after a single visit ensured a high seed set of >80%. Our results suggest that nectar availability, floral longevity maintenance, and sufficient pollen deposition mitigate the effects of nectar robbing on the reproductive success of S. castanea. These results are expected to further our understanding of plant–animal interactions and the ecological consequences of nectar robbing.

Figures