Skelhorn John, Rowe Candy
School of Biology, University of Newcastle, Henry Wellcome Building for Neuroecology, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
Biol Lett. 2005 Dec 22;1(4):500-3. doi: 10.1098/rsbl.2005.0359.
Chemically defended insects advertise their unpalatability to avian predators using conspicuous aposematic coloration that predators learn to avoid. Insects utilize a wide variety of different compounds in their defences, and intraspecific variation in defence chemistry is common. We propose that polymorphisms in insect defence chemicals may be beneficial to insects by increasing survival from avian predators. Birds learn to avoid a colour signal faster when individual prey possesses one of two unpalatable chemicals rather than all prey having the same defence chemical. However, for chemical polymorphisms to evolve within a species, there must be benefits that allow rare chemical morphs to increase in frequency. Using domestic chicks as predators and coloured crumbs for prey, we provide evidence that birds taste and reject proportionally more of the individuals with rare defence chemicals than those with common defence chemicals. This indicates that the way in which birds attack and reject prey could enhance the survival of rare chemical morphs and select for chemical polymorphism in aposematic species. This is the first experiment to demonstrate that predators can directly influence the form taken by prey's chemical defences.
具有化学防御能力的昆虫会利用醒目的警戒色向鸟类捕食者表明自己不可口，捕食者会学会避开它们。昆虫在防御中会利用各种各样不同的化合物，而且防御化学物质的种内变异很常见。我们提出，昆虫防御化学物质的多态性可能通过提高躲避鸟类捕食者的存活率而对昆虫有益。当个体猎物拥有两种不可口化学物质之一，而不是所有猎物都具有相同的防御化学物质时，鸟类会更快地学会避开一种颜色信号。然而，要使化学多态性在一个物种内进化，必须存在能让稀有的化学形态增加频率的益处。我们以家鸡作为捕食者，彩色面包屑作为猎物，提供了证据表明，与具有常见防御化学物质的个体相比，鸟类品尝并拒绝具有稀有防御化学物质的个体的比例更高。这表明鸟类攻击和拒绝猎物的方式可能会提高稀有化学形态的存活率，并促使警戒色物种形成化学多态性。这是第一个证明捕食者能够直接影响猎物化学防御形式的实验。
