Dietary cognition in educated predators: implications for the evolution of prey defence strategies

许多昆虫保护自己免受有毒化学物质的捕食。它们经常向潜在的攻击者(通常是试图吃掉它们的鸟类)宣传它们的化学防御系统，使用明显的警告颜色，如瓢虫、黄蜂和色彩鲜艳的蝴蝶。通常，科学家假设鸟类学会将警告颜色与毒素的影响联系起来，结果是完全避免了将来有类似颜色模式的人。然而，这一假设最近被证明是错误的。鸟类实际上继续以低水平的有毒昆虫为食，即使它们知道自己被防御了。它们小心翼翼地控制自己吃的有毒昆虫的数量，以获得有毒猎物中包含的营养，但又确保它们不会吃到足够的昆虫来给它们带来任何严重的健康问题。拟议中的实验旨在调查影响鸟类选择食用有毒猎物的因素。我们预计，当鸟类能够从其他来源获得所需的营养时，即当环境中有更多可供选择的无毒猎物时，或者当无毒猎物具有更高水平的营养时，鸟类将减少对有毒昆虫的摄取。我们还预计其他有毒物种的存在会影响鸟类的觅食决定。然而，我们目前不知道捕食者对他们的猎物有什么了解，也不知道他们如何决定有毒猎物作为食物来源的价值。我们将通过给饲养在实验室中的野生捕获的八哥提供有毒和无毒昆虫的序列，并测量它们选择吃哪些昆虫来调查这一点。昆虫的毒性将通过注射奎宁溶液(一种温和的毒素)来操纵，它们的营养含量可以通过注射蛋白质溶液来操纵。这些结果将让我们了解鸟类对它们所吃的食物有什么了解，它们在决定吃什么时如何使用这些信息，以及被捕食物种的营养如何影响其有毒的益处。我们还将进行数学模拟，调查捕食者应该使用什么觅食策略来最大限度地增加营养摄入量，同时尽可能保持较低的毒素摄入量。然后，这些模拟将被扩展到调查捕食者的觅食策略如何确定在什么情况下猎物将受益于有毒，以及何时此类猎物将受益于用明亮的警告颜色宣传其毒性。这些模拟还将帮助我们了解向农作物喷洒有毒化学物质(以阻止鸟类吃掉它们)如何影响鸟类捕食瓢虫和蜜蜂等有毒昆虫的决定。这也可能让我们决定如何最好地阻止这些昆虫物种的数量下降。

Many insects defend themselves against predation with toxic chemicals. They often advertise their chemical defences to potential attackers (generally birds attempting to eat them) using conspicuous warning colouration, as seen in ladybirds, wasps and brightly-coloured butterflies. Typically, scientists have assumed that birds learn to associate the warning colouration with the effects of the toxins, and as a result totally avoid individuals with similar colour patterns in the future. However, this assumption has recently been shown to be wrong. Birds actually continue to eat toxic insects at low levels, even when they know that they are defended. They carefully control the number of toxic insects that they eat in order to gain the nutrients contained in the toxic prey, but ensuring they do not eat enough insects to cause them any serious health problems. The proposed experiments aim to investigate what factors influence birds' choices to eat toxic prey. We would expect that birds will eat fewer toxic insects when they can gain the nutrients they need from other sources i.e. when there are more alternative non-toxic prey in the environment, or when non-toxic prey have higher levels of nutrients. We would also expect the presence of other toxic species to influence birds' foraging decisions. However, we do not currently know what predators learn about their prey, or how they decide how 'valuable' toxic prey are as a food source. We will investigate this by giving wild-caught starlings, which are housed in a laboratory, sequences of toxic and non-toxic insects, and measuring which insects they choose to eat. The toxicity of the insects will be manipulated by injecting them with quinine solution (a mild toxin), and their nutrient content can be manipulated by injecting them with a protein solution. The results will allow us to understand what birds learn about the food they eat, how they use this information when deciding what to eat, and how the nutrition of a prey species influences the benefit of it being toxic. We will also produce mathematical simulations that investigate what foraging strategies predators' should use to maximize their nutrient intake whilst keeping their toxin intake as low as possible. These simulations will then be extended to investigate how predators' foraging strategies determine under what circumstances prey will benefit from being toxic, and when such prey will benefit from advertising their toxicity with bright warning colouration. These simulations will also be used to help us to understand how spraying crops with toxic chemicals (to stop birds eating them) influences birds decisions to eat toxic insects like ladybirds and bees. This might also allow us to decide how best to stop these insect species declining in numbers.