Smith Karen E, Halpin Christina G, Rowe Candy
Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University, Henry Wellcome Building, Framlington Place , Newcastle upon Tyne NE2 4HH , UK.
Behav Ecol. 2016 Nov-Dec;27(6):1650-1655. doi: 10.1093/beheco/arw086. Epub 2016 Jun 21.
Many prey have evolved toxins as a defense against predation. Those species that advertise their toxicity to would-be predators with conspicuous warning signals are known as "aposematic." Investment in toxicity by aposematically signaling prey is thought to underpin how aversive prey are to predators; increasing toxicity means that predators learn to avoid prey faster and attack them at lower rates. However, predators' foraging decisions on aposematic prey are determined not only by their toxicity, but also by their nutrient content: predators can trade-off the costs of ingesting toxin with the benefits of acquiring nutrients. Prey body size is a cue that positively correlates with nutrient content, and that varies within and between aposematic species. We predicted that a dose of quinine (known to be toxic to birds) would be a more effective deterrent to avian predators when prey were small compared with when they were large, and that the benefits of possessing toxin would be greater for small-bodied prey. Using an established laboratory protocol of European starlings () foraging on mealworms (), we found evidence for increased protection from a dose of quinine for small-bodied compared with large-bodied prey. This shows that larger prey need more toxin to attain the same level of defense as smaller prey, which has implications for the evolution of aposematism and mimicry.
许多猎物进化出毒素作为抵御捕食的一种防御手段。那些通过显眼的警告信号向潜在捕食者表明自身毒性的物种被称为“警戒色的”。具有警戒色的猎物在毒性方面的投入被认为是其令捕食者厌恶程度的基础；毒性增加意味着捕食者能更快学会避开猎物，且攻击它们的频率更低。然而，捕食者对具有警戒色猎物的觅食决策不仅取决于其毒性，还取决于其营养成分：捕食者可以在摄入毒素的成本与获取营养的益处之间进行权衡。猎物体型是一个与营养成分呈正相关的线索，并且在具有警戒色的物种内部和之间都会有所变化。我们预测，与大型猎物相比，当猎物体型较小时，一剂奎宁（已知对鸟类有毒）对鸟类捕食者的威慑作用会更有效，而且对于体型较小的猎物来说，拥有毒素的益处会更大。通过使用已建立的欧洲椋鸟在黄粉虫上觅食的实验室方案，我们发现有证据表明，与大型猎物相比，一剂奎宁对小型猎物的保护作用增强。这表明，大型猎物需要更多毒素才能达到与小型猎物相同的防御水平，这对警戒色和拟态的进化具有启示意义。
