Data from: Body size affects the evolution of hidden colour signals in moths

Many cryptic prey have also evolved hidden contrasting colour signals which are displayed to would-be predators. Given that these hidden contrasting signals may confer additional survival benefits to the prey by startling/intimidating predators, it is unclear why they have evolved in some species, but not in others. Here, we have conducted a comparative phylogenetic analysis of the evolution of colour traits in the family Erebidae (Lepidoptera), and found that the hidden contrasting colour signals are more likely to be found in larger species. To understand why this relationship occurs, we present a general mathematical model, demonstrating that selection for a secondary defence such as deimatic display will be stronger in large species when (i) the primary defence (crypsis) is likely to fail as its body size increases and/or (ii) the secondary defence is more effective in large prey. To test the model assumptions, we conducted behavioural experiments using a robotic moth which revealed that survivorship advantages were higher against wild birds when the moth has contrasting hindwings and large size. Collectively, our results suggest that the evolutionary association between large size and hidden contrasting signals has been driven by a combination of the need for a back-up defence and its efficacy.

诸多隐蔽猎物亦演化出了隐蔽对比色信号，并向潜在捕食者展示该信号。鉴于此类隐蔽对比色信号可通过惊吓或威慑捕食者，为猎物带来额外生存优势，但目前尚不明确为何此类信号仅在部分物种中演化出现，而非其他物种。本研究针对鳞翅目（Lepidoptera）夜蛾科（Erebidae）的色彩性状演化开展比较系统发育分析，结果发现，体型更大的物种更易演化出隐蔽对比色信号。为阐明该关联的成因，本研究构建了通用数学模型，结果表明：当（i）初级防御（隐蔽防御（crypsis））随体型增大而失效风险升高，且/或（ii）次级防御（如吓阻展示（deimatic display））对大型猎物的防御效果更强时，大型物种对次级防御的选择压力会更强。为验证模型假设，本研究使用机器蛾开展行为实验，结果显示：当蛾类拥有对比色后翅且体型较大时，其对抗野生鸟类的生存优势更为显著。综合来看，本研究结果表明，体型大小与隐蔽对比色信号之间的演化关联，是后备防御需求及其防御效能共同作用的结果。