ABSTRACT
Background
Floral colour is a primary signal in plant-pollinator interactions. Presumably because bees lack red receptors, bee-pollinated flowers are rarely red. Hypericum (Hypericaceae) is a genus, with yellow flowers and filaments, mainly pollinated by bees. However, one species, H. ascyron exhibits unique red filaments.
Aims
We tested whether the red filaments influence pollinator visitation frequency and colour perception.
Methods
We examined whether H. ascyron require pollinators for seed set and compared insect visitation rates of H. ascyron with those of a sympatric yellow-filamented congener. Colour perception by bees was also estimated.
Results
Pollinator visitation substantially enhanced seed set under natural conditions and flowers of H. ascyron had similar rates of visitation by bees as their yellow-filamented congener. Red filaments per se absorbed ultraviolet light and therefore should not be perceived as a chromatic colour by bees. The chromatic contrasts between filaments and petals as perceived by pollinators was similar between species, whereas achromatic contrasts were higher in H. ascyron.
Conclusions
Pure-red staminal filaments work as well in attracting potential pollinators as the yellow filaments of congeners. Based on our findings, we suggest that the evolution of red filament colour may have been driven by factors other than pollinator attraction.
Acknowledgements
We thank Li-Shen Qian and Ze-Min Guo for the help with field experiments, Hao-Yi Li and Hui-Hui Xi for counting seeds, and Fei Zhao for identification of Hypericum species. This research was undertaken on Haba Mountain and we are grateful for the welcome we received from the people (as well as the cattle and horses) there.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Author contributions
All authors conceived and designed the study and experiments. Y.L.H. conducted the field experiments and wrote the original draft. Y.N. designed the strategies for plant sample collection, took photos and revised the draft. Z.C. designed the strategies for colour analyses. J.J.Z. collected and counted plant seeds. Y.L.H and Y.N. processed data, analysed results and prepared display items. G.X. and Y.N. provided financial aid to this study. All the authors reviewed the manuscript.
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.
Additional information
Funding
Notes on contributors
Ya-Li Hu
Ya-Li Hu investigates the chemical constituents of Hypericum ascyron and is interested in natural products and their functions in ecological interactions and in biology.
Zhe Chen
Zhe Chen is trained in evolutionary ecology and has a reserach interests in plant-animal interactions.
Jian-Jun Zhao
Jian-Jun Zhao is a natural products chemist and has interests in pharmacology and biology.
Yang Niu
Yang Niu is an evolutionary ecologist with a long-standing interest in plant reproductive ecology and colour evolution using multidisciplinary methods.
Gang Xu
Gang Xu has long been investigating natural products (especially polycyclic polyprenylated acylphloroglucinols, PPAPs) from Hypericum (Hypericaceae).