The selection of prey by predators should, theoretically, favour uniformity in the warning signals displayed by unpalatable prey. Nevertheless, some aposematically coloured species are polymorphic. We tested the hypothesis that colour morphs of unpalatable prey differ in the efficacy of their aposematic signal for birds, thereby affecting the selective advantages of these morphs. We used colour morphs (red-and-black light, red-and-black dark and metallic) of the chemically defended leaf beetle Chrysomela lapponica. In laboratory experiments, naïve great tits (Parus major) attacked live beetles of all colour morphs at the same rate. By contrast, wild-caught tits attacked light beetles at first encounter at the same rate as a novel control prey, but significantly avoided both dark and metallic beetles. Beetles of all colour morphs were similarly unpalatable for birds, and about half of the attacked beetles were released unharmed. Avoidance learning was similarly fast for all three leaf beetle morphs. However, in the next-day memory test, the dark beetles were attacked at a greater rate than beetles of two other morphs, indicating their lower memorability. A field experiment suggests that at low C. lapponica population densities, dark beetles have a survival advantage over light beetles, potentially due to the lesser conspicuousness of the dark pattern; however, when the density is high, dark beetles lose this advantage due to the low memorability of their pattern. Thus, the direction of selective bird predation on prey colour morphs may depend on prey density and thereby contribute to temporal shifts in colour morph frequencies following population fluctuations.

中文翻译：

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惯性叶甲虫对颜色形态的不同鸟类反应可能影响多态猎物种群形态频率的变化。

从理论上讲，掠食者选择猎物应该有利于使难吃的猎物显示的警告信号保持一致。尽管如此，一些不带颜色的物种还是多态的。我们测试了这样一种假说：难吃的猎物的颜色形态在针对鸟类的姿态信号功效方面有所不同，从而影响了这些形态的选择性优势。我们使用了化学防御过的叶甲虫Chrysomela lapponica的颜色变体（红色和黑色的浅色，红色和黑色的深色和金属色）。在实验室实验中，幼稚的大山雀（Parus major）以相同的速率攻击所有颜色变体的活甲虫。相比之下，野生山雀在初次见面时以与新型对照猎物相同的速率攻击轻甲虫，但显着避免了深色和金属甲虫。类似地，各种颜色的甲虫对鸟类来说都不好吃，大约有一半的甲虫没有受到伤害。对于所有三个叶甲虫变体，回避学习的速度相似。但是，在第二天的记忆力测试中，黑甲虫的攻击率高于其他两种变体的甲虫，表明它们的记忆力较低。田间试验表明，在低C. lapponica时人口密度方面，深色甲虫比深色甲虫具有生存优势，这可能是由于深色图案的显眼性较弱；但是，当密度很高时，黑甲虫由于其图案的低记忆性而失去了这一优势。因此，对猎物颜色形态的选择性鸟类捕食的方向可能取决于猎物密度，从而导致种群波动后颜色形态频率的时间变化。