Lindström L, Alatalo R V, Lyytinen A, Mappes J
Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, P. O. Box 35, FIN-40 351 Jyväskylä, Finland.
Proc Natl Acad Sci U S A. 2001 Jul 31;98(16):9181-4. doi: 10.1073/pnas.161071598. Epub 2001 Jul 17.
The evolution of aposematism, a phenomenon where prey species conspicuously advertise their unprofitability to predators, is puzzling. How did conspicuousness evolve, if it simultaneously increased the likelihood of an inexperienced predator to detect the prey and presumably kill it? Antiapostatic selection, where rare prey is predated relatively more often, is considered as another major difficulty for aposematism to evolve. However, the risk of being conspicuous in low frequencies has not been experimentally tested. We designed an experiment to test how frequency (4%, 12%, 32%) of conspicuous aposematic prey and its dispersion type (solitary vs. aggregated) affect an initial predation risk of the prey and in avoidance learning of predators. Wild great tits (Parus major) were predators on artificial prey in a "novel world." The relative mortality of aposematic prey was antiapostatic, thus the frequency-dependent predation was most severe at low frequencies. In all frequencies, aggregated aposematic prey survived better than solitary prey. Surprisingly, learning was not determined by a fixed number of unpalatable prey eaten, but at low frequencies fewer aposematic individuals eaten generated predators' avoidance learning. However, per-capita risk for the prey remained highest at low frequencies. Our results underscore the problems of initial evolution of rare conspicuous morphs. Aggregated prey suffered less from predation, indicating selective advantage of aggregation over solitary living for a conspicuous individual.
警戒色是一种猎物向捕食者显著表明自身不可食性的现象，其进化过程令人费解。如果显眼性同时增加了无经验捕食者发现猎物并可能将其捕杀的可能性，那么显眼性是如何进化的呢？反 apostatic 选择（即稀有猎物被捕食的频率相对更高）被认为是警戒色进化的另一个主要难题。然而，在低频情况下显眼所带来的风险尚未经过实验验证。我们设计了一项实验，以测试显眼的警戒色猎物的频率（4%、12%、32%）及其分布类型（单独 vs. 聚集）如何影响猎物的初始被捕食风险以及捕食者的回避学习。野生大山雀（Parus major）在一个“新奇世界”中以人工猎物为食。警戒色猎物的相对死亡率呈现反 apostatic 现象，因此频率依赖性捕食在低频时最为严重。在所有频率下，聚集的警戒色猎物比单独的猎物存活得更好。令人惊讶的是，学习并非由所食用的不可口猎物的固定数量决定，而是在低频时，被吃掉的警戒色个体越少，越能促使捕食者产生回避学习。然而，猎物在低频时的人均风险仍然最高。我们的结果强调了稀有显眼形态初始进化的问题。聚集的猎物遭受的捕食较少，这表明对于显眼个体而言，聚集生活相对于单独生活具有选择优势。
