Effects of nicotine on the digestive performance of nectar-feeding birds reflect their relative tolerance to this alkaloid.
The paradox of secondary metabolites, toxic defence compounds produced by plants, in nectar and fruits is well known. Deterrence of feeding by nectarivorous and frugivorous birds is better understood than the effect of these chemicals on the digestive performance of birds. Digestive parameters such as transit time and sugar assimilation are important in assessing nutrient utilization and deterrence may be related to post-ingestive effects involving these parameters. Nectar and many fruits contain mainly sugars and water, and avian consumers compensate for low sugar content in their diet by increasing food intake: this may also increase their intake of secondary metabolites. We investigated how the alkaloid nicotine, naturally present in nectar of Nicotiana species, influences compensatory feeding and digestive performance of nectar-feeding birds. High nicotine concentration negatively affected compensatory feeding and apparent assimilation efficiency of white-bellied sunbirds Cinnyris talatala and Cape white-eyes Zosterops virens; but nicotine slowed gut transit time only in the latter species. In contrast, food intake and digestive performance of dark-capped bulbuls Pycnonotus tricolor was unaffected by nicotine up to a concentration of 50μM. Bulbuls are primarily frugivorous; hence, they are more exposed to secondary metabolites than sunbirds and possibly white-eyes. Because their diet is richer in toxins, frugivorous birds may have evolved more efficient detoxification strategies than those of specialist nectar-feeding birds.
Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa. Electronic address: slerch@zoology.up.ac.za.
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Lerch-Henning
Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
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Nicolson
D000818:Animals; D019422:Dietary Sucrose / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D004063:Digestion / Q000187:drug effects* / Q000502:physiology; D004361:Drug Tolerance; D002149:Energy Intake / Q000187:drug effects; D005243:Feces / Q000737:chemistry; D005247:Feeding Behavior / Q000187:drug effects; D005765:Gastrointestinal Agents / Q000633:toxicity; D041981:Gastrointestinal Tract / Q000187:drug effects* / Q000502:physiology; D005772:Gastrointestinal Transit / Q000187:drug effects; D008658:Inactivation, Metabolic; D007408:Intestinal Absorption / Q000187:drug effects*; D009538:Nicotine / Q000633:toxicity*; D018722:Nicotinic Agonists / Q000633:toxicity*; D046109:Passeriformes / Q000502:physiology*; D057048:Plant Nectar / Q000009:adverse effects / Q000737:chemistry; D013019:South Africa; D013045:Species Specificity; D066007:Toxicokinetics
D019422:Dietary Sucrose; D005765:Gastrointestinal Agents; D018722:Nicotinic Agonists; D057048:Plant Nectar; D009538:Nicotine
Apparent assimilation efficiency; Bird pollinators; Foraging behaviour; Gut transit time; Secondary metabolites