Cardenolides in nectar may be more than a consequence of allocation to other plant parts: a phylogenetic study of Asclepias

Détails

ID Serval
serval:BIB_40481963EA6C
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
Cardenolides in nectar may be more than a consequence of allocation to other plant parts: a phylogenetic study of Asclepias
Périodique
Functional Ecology
Auteur(s)
Manson J.S., Rasmann S., Halitschke R., Thomson J.D., Agrawal A.A., Johnson M.
ISSN
0269-8463
Statut éditorial
Publié
Date de publication
2012
Volume
26
Numéro
5
Pages
1100-1110
Langue
anglais
Résumé
The primary function of secondary plant metabolites is thought to be defence against herbivores. The frequent occurrence of these same noxious compounds in floral nectar, which functions primarily to attract pollinators, has been seen as paradoxical. Although these compounds may have an adaptive purpose in nectar, they may also occur as a nonadaptive consequence of chemical defence in other plant parts. If nectar chemistry reflects physiological constraints or passive leakage from other tissues, we expect that the identity and relative concentration of nectar cardenolides to be correlated with those of other plant parts; in contrast, discordant distributions of compounds in nectar and other tissues may suggest adaptive roles in nectar. We compared the concentrations and identities of cardenolides in the nectar, leaves and flowers of 12 species from a monophyletic clade of Asclepias. To measure putative toxicity of nectar cardenolides, we then examined the effects of a standard cardenolide (digoxin) on the behaviour of bumblebees, a common generalist pollinator of Asclepias. We found that the average cardenolide concentrations in nectar, leaves and flowers of the 12 Asclepias species were positively correlated as predicted by nonadaptive hypotheses. However, significant differences in the identities and concentrations of individual cardenolides between nectar and leaves suggest that the production or allocation of cardenolides may be independently regulated at each plant part. In addition, cardenolide concentrations in leaves and nectar exhibited no phylogenetic signal. Surprisingly, bumblebees did not demonstrate an aversion to digoxin-rich nectar, which may indicate that nectar cardenolides have little effect on pollination. Although the idea that discordant patterns of secondary metabolites across tissue types may signal adaptive functions is attractive, there is evidence to suggest constraint contributes to nectar secondary chemistry. Further work testing the ecological impacts of such patterns will be critical in determining the functional significance of nectar cardenolides
Mots-clé
Asclepias, cardenolide, milkweeds, optimal defence theory, pollinator preference, secondary metabolites, toxic nectar
Web of science
Open Access
Oui
Création de la notice
14/09/2012 12:30
Dernière modification de la notice
20/08/2019 14:38
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