Visual function of red staminal filaments in a bee-pollinated plant

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.

KEYWORDS:

• Bee colour vision
• contrast colour pattern
• floral colour evolution
• flower-pollinator interaction
• Hypericum ascyron

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

The work was financially supported by the Plateau Scientific Expedition and Research (STEP) program (2019QZKK0502), West Light Foundation of The Chinese Academy of Sciences and Yunnan Ten Thousand Talents Plan Young & Elite Talents Project (to Y. Niu) and State Key Laboratory of Phytochemistry and Plant Resources in West China and Yunnan Key Laboratory of Natural Medicinal Chemistry (E0230211Z1).

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).