Department of Zoology, Institute of Ecology and Earth Sciences, University of Tartu, 46 Vanemuise Street, Tartu 51014, Estonia.
J Insect Sci. 2011;11:4. doi: 10.1673/031.011.0104.
To understand the evolution of warning coloration, it is important to distinguish between different aspects of conspicuous color patterns. As an example, both pattern element size and body size of prey have been shown to enhance the effectiveness of warning signals. However, it is unclear whether the effect of body size is merely a side effect of proportionally increasing pattern elements, or if there is an effect of body size per se. These possibilities were evaluated by offering different sized artificial caterpillars with either fixed or proportionally increasing aposematic color signal elements to wild great tits, Parus major L. (Passeriformes: Paridae). The birds' hesitation time to attack each "caterpillar" was used as a measure of the warning effect. The hesitation time showed a significant, positive size-dependence with the caterpillars whose pattern elements increased proportionally with their body size. In contrast, no size dependence was found in the larvae with fixed-size signal elements. Such a difference in mortality curves is consistent with the idea that pattern element size is a more important aspect than body size in enhancing a warning signal. Since no evidence of an effect of body size per se on signal efficiency was found, this study does not support the hypothesis that aposematic insects gain more from large size than cryptic ones.
要理解警戒色的进化，区分明显颜色图案的不同方面很重要。例如，猎物的图案元素大小和身体大小都被证明可以增强警告信号的有效性。然而，身体大小的影响是仅仅是图案元素成比例增加的副作用，还是身体大小本身有影响，目前还不清楚。通过向野生大山雀（雀形目：山雀科）提供具有固定或成比例增加警戒色信号元素的不同大小的人工毛毛虫，评估了这些可能性。鸟类攻击每个“毛毛虫”的犹豫时间被用作警告效果的衡量标准。犹豫时间与图案元素与身体大小成比例增加的毛毛虫呈显著的正相关。相比之下，在具有固定尺寸信号元素的幼虫中，没有发现尺寸依赖性。这种死亡率曲线的差异与图案元素大小比身体大小更能增强警告信号的观点一致。由于没有发现身体大小本身对信号效率有影响的证据，因此本研究不支持警戒昆虫比隐蔽昆虫从体型较大中获益更多的假设。
