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Plant toxin levels in nectar vary spatially across native and introduced populations

Plant toxin levels in nectar vary spatially across native and introduced populations

Egan, Paul A., Stevenson, Philip C. ORCID: 0000-0002-0736-3619, Tiedeken, Erin-Jo, Wright, Geraldine A., Boylan, Fabio and Stout, Jane C. (2016) Plant toxin levels in nectar vary spatially across native and introduced populations. Journal of Ecology, 104 (4). pp. 1106-1115. ISSN 0022-0477 (Print), 1365-2745 (Online) (doi:

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1. Secondary compounds in nectar may function as toxic chemical defences and regulate floral antagonists, but can also mediate plant-pollinator interactions. Despite their ecological importance, few studies have investigated the patterns, causes and consequences of spatial variation in toxic nectar compounds in plant species, and none outside their native range.
2. Grayanotoxin I (GTX I) occurs in nectar of invasive Rhododendron ponticum where it is toxic to honeybees and some solitary bee species. We examined (i) geographic variation in the composition of nectar GTX I and GTX III (which is not toxic to these species) in the native and introduced range of R. ponticum, (ii) how their expression is structured at patch and landscape scales within ranges, and (iii) if climatic and environmental factors underpin spatial patterns.
3. While both GTXs varied within ranges, variation in GTX I, but not GTX III, was detected between ranges. GTX I expression was thus markedly lower or (in 18% of cases) absent from nectar in introduced plants. Spatial autocorrelation was apparent at both patch and landscape scales, and in part related to heat load interception by plants (a function of latitude, aspect and slope)
4. As expression of nectar GTXs was generally robust to environmental variation, and aggregated in space, this trait has the potential to be spatially discriminated by consumers. Given the specificity of change to GTX I, and its differential toxicity to some bee species, we conclude that its expression was likely influenced during invasion by pollinator-mediated selection and/or enemy-release from floral antagonists.
5. Synthesis. As the first demonstration of large-scale geographic variation and spatial structure in toxic nectar compounds, this work deepens our understanding of the chemical ecology of floral interactions in native and introduced species. Spatially explicit studies of nectar secondary compounds are thus required to show how the extent and structure of spatial variation may affect floral ecology. Future development of invasion theory should incorporate a holistic view of plant chemical defence, beyond antagonistic interactions, which integrates the consequences of chemically defended mutualist rewards.

Item Type: Article
Uncontrolled Keywords: chemical defence, grayanotoxins, invasion ecology, nectar chemistry, plant-herbivore interactions, pollination, spatial variation
Subjects: S Agriculture > S Agriculture (General)
Faculty / School / Research Centre / Research Group: Faculty of Engineering & Science
Faculty of Engineering & Science > Natural Resources Institute
Faculty of Engineering & Science > Natural Resources Institute > Agriculture, Health & Environment Department
Faculty of Engineering & Science > Natural Resources Institute > Chemical Ecology Research Group
Last Modified: 16 Oct 2019 08:59

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