Cease Arianne J, Fay Michelle, Elser James J, Harrison Jon F
School of Sustainability, Arizona State University, Tempe, AZ 85287, USA
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA Orange Coast College, Costa Mesa, CA 92626, USA.
J Exp Biol. 2016 Jan;219(Pt 1):64-72. doi: 10.1242/jeb.126847. Epub 2015 Nov 13.
Comparisons of the carbon, nitrogen and phosphorus (P) content of plants and insect herbivores suggests that P limitation and herbivore foraging to balance P intake could be common. However, the lack of synthetic diets for testing the effects of lower ranges of dietary P has been a major impediment to experimental assessment of the ecological importance of, and physiological responses to, P limitation for terrestrial herbivores. We manipulated dietary P content (%P) over its observed range in terrestrial foliage using artificial diets containing near-optimal content of other nutrients for the grasshopper Schistocerca americana. Over much of the ecologically relevant range, when consuming single diets over a lifetime, higher P stimulated growth rates and increased survival, with an optimal dietary %P of 0.25-0.50% when measured throughout development. Excessive dietary P (1%) reduced growth and survival. However, with only short-term (3 day) confinement to single diets, dietary P had no effect on food consumption or growth rates. During these short exposures, fifth (but not third) instar hoppers increased the proportion of P excreted relative to P assimilated as dietary P increased. Target experiments demonstrated that, when given a choice, grasshoppers select among foods to attain a P intake target of 0.6%. These data suggest that P limitation could be common for terrestrial insect herbivores and that they can exhibit ingestive and post-ingestive mechanisms to attain sufficient but not excessive P.
对植物和食草昆虫的碳、氮和磷（P）含量进行比较表明，磷限制以及食草动物为平衡磷摄入而进行觅食可能较为普遍。然而，缺乏用于测试较低膳食磷含量影响的合成饲料，一直是对陆地食草动物磷限制的生态重要性及生理反应进行实验评估的主要障碍。我们使用对美洲沙漠蝗（Schistocerca americana）而言其他营养成分含量接近最佳的人工饲料，在陆地植物叶片中观察到的磷含量范围内对膳食磷含量（%P）进行了调控。在生态相关范围的大部分情况下，当蝗虫一生都食用单一饲料时，较高的磷刺激了生长速率并提高了存活率，在整个发育过程中测量时，最佳膳食%P为0.25 - 0.50%。过量的膳食磷（1%）则降低了生长和存活率。然而，仅短期（3天）限制在单一饲料中时，膳食磷对食物消耗或生长速率没有影响。在这些短期暴露期间，五龄（而非三龄）蝗虫随着膳食磷增加，相对于吸收的磷，排泄的磷比例增加。目标实验表明，当可以选择时，蝗虫会在食物中进行挑选，以达到0.6%的磷摄入目标。这些数据表明磷限制对陆地食草昆虫可能较为普遍，并且它们可以表现出摄食和摄食后机制来获取足够但不过量的磷。
