Plant Diversity ›› 2023, Vol. 45 ›› Issue (03): 315-325.DOI: 10.1016/j.pld.2022.11.002

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Floral trait variation across individual plants within a population enhances defense capability to nectar robbing

Shuang Tiea, Yong-Deng Heb,c,d, Amparo Lázaroe, David W. Inouyef,g, You-Hao Guoa, Chun-Feng Yangb,c   

  1. a. College of Life Sciences, Wuhan University, Wuhan 430072, China;
    b. CAS Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China;
    c. Center of Conservation Biology, Core Botanical Gardens, Chinese Academy of Sciences, Wuhan 430074, China;
    d. University of Chinese Academy of Sciences, Beijing 100049, China;
    e. Global Change Research Group, Mediterranean Institute for Advanced Studies (IMEDEA; UIB-CSIC), Esporles, Balearic Islands, Spain;
    f. The Rocky Mountain Biological Laboratory, Post Office Box 519, Crested Butte, CO 81224, USA;
    g. Department of Biology, University of Maryland, College Park, MD 20742, USA
  • Received:2022-06-10 Revised:2022-11-01 Published:2023-07-06
  • Contact: You-Hao Guo,;Chun-Feng Yang,
  • Supported by:
    We thank Ming-Fang Du for assistance in the field, Jia-Xing Huang for identifying the bumble bees, and Michele Dudash for improvement on an earlier manuscript. The research was supported by the National Natural Science Foundation of China (No. 31970253 and 32270243) and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB31010000). AL was also supported by a Ramón y Cajal contract (RYC-2015-19034) from the Spanish Ministry of Science, Innovation and Universities, the Spanish State Research Agency, European Social Funds (ESF invests in your future) and the University of the Balearic Islands, and by the project PRPPID2020-117863RB-I00, financed by the Spanish Ministry of Science and Innovation and the Spanish Research Agency (MCIN/AEI/10.13039/501100011033).

Abstract: Floral trait variation may help pollinators and nectar robbers identify their target plants and, thus, lead to differential selection pressure for defense capability against floral antagonists. However, the effect of floral trait variation among individuals within a population on multi-dimensional plant-animal interactions has been little explored. We investigated floral trait variation, pollination, and nectar robbing among individual plants in a population of the bumble bee-pollinated plant, Caryopteris divaricata, from which flowers are also robbed by bumble bees with varying intensity across individuals. We measured the variation in corolla tube length, nectar volume and sugar concentration among individual plants, and evaluated whether the variation were recognized by pollinators and robbers. We investigated the influence of nectar robbing on legitimate visitation and seed production per fruit. We found that the primary nectar robber (Bombus nobilis) preferred to forage on plants with long-tubed flowers, which produced less nectar and had lower sugar concentration compared to those with shorter corolla tubes. Individuals with shorter corolla tubes had comparatively lower nectar robbing intensity but higher visitation by legitimate visitors (mainly B. picipes) and higher seed production. Nectar robbing significantly reduced seed production because it decreased pollinator visits. However, neither pollination nor seed production differed between plants with long and short corolla tubes when nectar robbers were excluded. This finding suggests that floral trait variation might not be driven by pollinators. Such variation among individual plants thus allows legitimate visitors and nectar robbers to segregate niches and enhances population defense against nectar robbing in unpredictable conditions.

Key words: Bumble bees, Caryopteris divaricata, Corolla tube, Intraspecific variation, Plant reproductive success, Pollination