Institute of Neuroscience, Newcastle University, Newcastle NE2 4HH, UK.
Proc Biol Sci. 2010 Jun 7;277(1688):1729-34. doi: 10.1098/rspb.2009.2092. Epub 2010 Feb 3.
Aposematic prey advertise their toxicity using conspicuous visual signals that predators quickly learn to avoid. However, it is advantageous for predators not to simply avoid toxic prey, but to learn about the amount of toxin that prey contain, and include them in their diets when the nutritional gains are high relative to the costs of ingesting the toxin. Therefore, when foraging on a defended prey population where individuals vary in their toxin concentration, predators should learn to use cues which distinguish prey with different levels of toxicity in order to include less defended individuals in their diets. In this experiment, we found that European starlings (Sturnus vulgaris) could learn to use a bitter taste to predict the amount of toxin that individual prey contained, and use that information to preferentially ingest less toxic prey to maximize their nutrient intake relative to the amount of toxin ingested. Our results suggest that bitter tastes could evolve as reliable signals of toxicity, and can help to explain why many toxins taste bitter. They also highlight the need to develop new mathematical simulations of the evolution of prey defences which incorporate the adaptive decision-making processes underlying nutrient and toxin management.
警戒性猎物会利用明显的视觉信号来警告捕食者其自身的毒性，而捕食者则会迅速学会避开这些信号。然而，对捕食者来说，仅仅避免食用有毒的猎物是没有好处的，相反，捕食者应该了解猎物中所含毒素的数量，并在摄入毒素的成本相对较高，而营养收益相对较高的情况下，将其纳入自己的食谱中。因此，当捕食者在一个有防御能力的猎物群体中觅食时，猎物个体的毒素浓度存在差异，捕食者应该学会使用能够区分不同毒性水平的线索，以便在其食谱中纳入防御能力较低的个体。在这项实验中，我们发现欧洲椋鸟（Sturnus vulgaris）可以学会利用苦味来预测个体猎物所含的毒素量，并利用这些信息优先摄入毒性较低的猎物，从而在摄入毒素的情况下最大程度地增加其营养摄入。我们的研究结果表明，苦味可能是作为一种可靠的毒性信号而进化出来的，这也可以帮助解释为什么许多毒素都有苦味。这些结果还强调了需要开发新的数学模拟来研究猎物防御的进化，这些模拟应该包含营养和毒素管理的适应性决策过程。
