Pollinator selection against toxic nectar as a key facilitator of a plant invasion

• Published in: Philosophical transactions of the Royal Society of London. Series B. Biological sciences Vol. 377; no. 1853; p. 20210168
• Main Authors: Egan, Paul A., Stevenson, Philip C., Stout, Jane C.
• Format: Journal Article
• Language: English
• Published: England The Royal Society 20.06.2022
• Subjects: Animals; Bees; Ecology; Ekologi; Evolutionary Biology; Evolutionsbiologi; Flowers; Herbivory; Plant Leaves; Plant Nectar - chemistry; Pollination; plant–herbivore–pollinator interactions; phenotypic selection; post-invasion evolution; toxic nectar
• ISSN: 0962-8436; 1471-2970; 1471-2970
• DOI: 10.1098/rstb.2021.0168

Plant compounds associated with herbivore defence occur widely in floral nectar and can impact pollinator health. We showed previously that Rhododendron ponticum nectar contains grayanotoxin I (GTX I) at concentrations that are lethal or sublethal to honeybees and a solitary bee in the plant's non-native range in Ireland. Here we further examined this conflict and tested the hypotheses that nectar GTX I is subject to negative pollinator-mediated selection in the non-native range, but that phenotypic linkage between GTX I levels in nectar and leaves acts as a constraint on independent evolution. We found that nectar GTX I experienced negative directional selection in the non-native range, in contrast to the native Iberian range, and that the magnitude and frequency of pollinator limitation indicated that selection was pollinator-mediated. Surprisingly, nectar GTX I levels were decoupled from those of leaves in the non-native range, which may have assisted post-invasion evolution of nectar without compromising the anti-herbivore function of GTX I (here demonstrated in bioassays with an ecologically relevant herbivore). Our study emphasizes the centrality of pollinator health as a concept linked to the invasion process, and how post-invasion evolution can be targeted toward minimizing lethal or sub-lethal effects on pollinators. This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.