Jensen Lora M, Wallis Ian R, Foley William J
Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Canberra 0200, Australia.
PLoS One. 2015 May 4;10(5):e0121584. doi: 10.1371/journal.pone.0121584. eCollection 2015.
Although ecologists believe that vertebrate herbivores must select a diet that allows them to meet their nutritional requirements, while avoiding intoxication by plant secondary metabolites, this is remarkably difficult to show. A long series of field and laboratory experiments means that we have a good understanding of the factors that affect feeding by leaf-eating marsupials. This knowledge and the natural intraspecific variation in Eucalyptus chemistry allowed us to test the hypothesis that the feeding decisions of greater gliders (Petauroides volans) depend on the concentrations of available nitrogen (incorporating total nitrogen, dry matter digestibility and tannins) and of formylated phloroglucinol compounds (FPCs), potent antifeedants unique to Eucalyptus. We offered captive greater gliders foliage from two species of Eucalyptus, E. viminalis and E. melliodora, which vary naturally in their concentrations of available nitrogen and FPCs. We then measured the amount of foliage eaten by each glider and compared this with our laboratory analyses of foliar total nitrogen, available nitrogen and FPCs for each tree offered. The concentration of FPCs was the main factor that determined how much gliders ate of E. viminalis and E. melliodora, but in gliders fed E. viminalis the concentration of available nitrogen was also a significant influence. In other words, greater gliders ate E. viminalis leaves with a particular combination of FPCs and available nitrogen that maximised the nutritional gain but minimised their ingestion of toxins. In contrast, the concentration of total nitrogen was not correlated with feeding. This study is among the first to empirically show that browsing herbivores select a diet that balances the potential gain (available nutrients) and the potential costs (plant secondary chemicals) of eating leaves. The major implication of the study is that it is essential to identify the limiting nutrients and relevant toxins in a system in order to understand feeding behaviour.
尽管生态学家认为，脊椎动物食草动物必须选择一种能满足其营养需求的饮食，同时避免因植物次生代谢产物而中毒，但这很难得到证实。一系列长期的野外和实验室实验让我们很好地了解了影响食叶有袋动物进食的因素。这些知识以及桉树叶化学成分的种内自然变异，使我们能够检验这样一个假设，即大滑翔机（Petauroides volans）的进食决策取决于可利用氮（包括总氮、干物质消化率和单宁）以及甲酰化间苯三酚化合物（FPCs）的浓度，FPCs是桉树特有的强效拒食剂。我们给圈养的大滑翔机提供了两种桉树（细叶桉和蜜味桉）的叶子，这两种桉树的可利用氮和FPCs浓度自然存在差异。然后，我们测量了每只滑翔机吃掉的叶子量，并将其与我们对每棵提供的树木叶子中的总氮、可利用氮和FPCs的实验室分析结果进行比较。FPCs的浓度是决定滑翔机食用细叶桉和蜜味桉叶子量的主要因素，但对于食用细叶桉的滑翔机来说，可利用氮的浓度也有显著影响。换句话说，大滑翔机食用的细叶桉树叶具有特定的FPCs和可利用氮组合，这种组合能使营养获取最大化，同时将毒素摄入量最小化。相比之下，总氮浓度与进食量没有相关性。这项研究是最早通过实证表明食叶食草动物选择的饮食能平衡吃树叶的潜在收益（可利用营养）和潜在成本（植物次生化学物质）的研究之一。该研究的主要意义在于，为了理解进食行为，必须确定一个系统中的限制营养物质和相关毒素。
