Data from: Aposematism: balancing salience and camouflage

Aposematic signals are often characterized by high conspicuousness. Larger and brighter signals reinforce avoidance learning, distinguish defended from palatable prey and are more easily memorized by predators. Conspicuous signalling, however, has costs: encounter rates with naive, specialized or nutritionally stressed predators are likely to increase. It has been suggested that intermediate levels of aposematic conspicuousness can evolve to balance deterrence and detectability, especially for moderately defended species. The effectiveness of such signals, however, has not yet been experimentally tested under field conditions. We used dough caterpillar-like baits to test whether reduced levels of aposematic conspicuousness can have survival benefits when predated by wild birds in natural conditions. Our results suggest that, when controlling for the number and intensity of internal contrast boundaries (stripes), a reduced-conspicuousness aposematic pattern can have a survival advantage over more conspicuous signals, as well as cryptic colours. Furthermore, we find a survival benefit from the addition of internal contrast for both high and low levels of conspicuousness. This adds ecological validity to evolutionary models of aposematic saliency and the evolution of honest signalling.警戒色信号（aposematic signals）通常以高显著性为特征。信号尺寸更大、色彩更鲜亮的信号能够强化捕食者的回避学习行为，区分具有防御能力的猎物与可食用猎物，且更易被捕食者记忆。然而，显著的信号传递存在代价：与未曾接触过该猎物的特化捕食者或营养匮乏的捕食者的相遇概率很可能升高。有研究提出，警戒色显著性的中间水平可以演化而来，以平衡威慑力与可探测性，这一点对于具有中等防御能力的物种而言尤为关键。但这类信号的有效性尚未在野外条件下通过实验得到验证。我们采用面团制成的毛毛虫状诱饵，检验在自然环境中被野生鸟类捕食时，降低显著性的警戒色模式是否能带来生存优势。研究结果表明，在控制内部对比边界（条纹）的数量与强度的前提下，低显著性的警戒色模式相较于高显著性信号以及隐蔽色（cryptic colours），均具备生存优势。此外，我们还发现，无论显著性水平高低，增加内部对比均能带来生存益处。该研究为警戒色显著性的演化模型以及诚实信号的演化研究增添了生态效度。