Lerch-Henning S, Nicolson S W
Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
Comp Biochem Physiol A Mol Integr Physiol. 2015 Dec;190:47-53. doi: 10.1016/j.cbpa.2015.08.015. Epub 2015 Sep 6.
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.
植物产生的次生代谢产物（即花蜜和果实中的有毒防御化合物）的悖论是众所周知的。与这些化学物质对鸟类消化性能的影响相比，花蜜和果实对食蜜鸟和食果鸟取食的威慑作用更容易理解。诸如通过时间和糖分同化等消化参数在评估营养利用方面很重要，而威慑作用可能与涉及这些参数的摄食后效应有关。花蜜和许多果实主要含有糖分和水分，鸟类消费者通过增加食物摄入量来弥补其饮食中糖分含量低的问题：这也可能增加它们对次生代谢产物的摄入量。我们研究了烟草属植物花蜜中天然存在的生物碱尼古丁如何影响食蜜鸟的补偿性摄食和消化性能。高浓度尼古丁对白腹太阳鸟（Cinnyris talatala）和海角绣眼鸟（Zosterops virens）的补偿性摄食和表观同化效率产生了负面影响；但尼古丁仅使后者的肠道通过时间减慢。相比之下，高达50μM浓度的尼古丁对黑头短脚鹎（Pycnonotus tricolor）的食物摄入量和消化性能没有影响。短脚鹎主要以果实为食；因此，它们比太阳鸟以及可能比绣眼鸟更容易接触到次生代谢产物。由于它们的食物中毒素含量更高，食果鸟可能已经进化出比专门食蜜的鸟类更有效的解毒策略。
