Data from: Sexual signals for the colour-blind: cryptic female mantids signal quality through brightness

1. Cryptic coloration may evolve in response to selective pressure imposed by predators, yet effective intraspecific communication may require some level of detectability. This creates a tension between the benefits of sexually selected visual traits and the predatory costs imposed by greater conspicuousness, and little is known about how this tension may be ameliorated in highly cryptic species. 2. We explore these competing demands in the false garden mantid Pseudomantis albofimbriata, a colour-blind and seemingly cryptic insect. We use reflectance spectrometry and receptor-noise modelling to characterize the conspicuousness of mantid body regions in the visual systems of mates (mantids), as well as potential predators (birds) and prey (bees). We then use condition manipulation and conspecific choice tests to further explore the colour traits of interest. 3. Based on visual modelling, we find that male mantids are inconspicuous to conspecifics, prey and predators – that is, they are chromatically and achromatically cryptic. In contrast, female mantids are chromatically cryptic to all potential receivers, but their abdomens are achromatically conspicuous. Our food manipulation experiment shows that females in good condition (and therefore with more eggs) have brighter abdomens than females in poor condition. Choice assays show male mantids are consistently attracted to females bearing brighter abdomens. 4. Our results reveal brightness-mediated sexual signalling in a colour-blind and classically cryptic insect. By communicating in the only visual channel available to them, female mantids are conspicuously signalling their quality to mates, while potentially minimizing their conspicuousness to predators and prey. Furthermore, by signalling with only a single body region, female mantids are apparently using coincident disruptive coloration to further decrease detectability to potential eavesdroppers. 5. Our data reveal a novel example of the way in which the trade-off between sexual selection for conspicuousness and natural selection for crypsis may be mediated in a visual signalling system. Such signals may be common in apparently cryptic species, and this study once again demonstrates the importance of analysing visual signals beyond the capacity of human vision.

1. 隐蔽色（cryptic coloration）的演化通常是为了应对捕食者施加的选择压力，但有效的种内交流往往需要一定程度的可检测性。这便在性选择所青睐的视觉性状收益，与更高显眼度带来的捕食风险代价之间形成了权衡，而目前学界对高度隐蔽物种如何缓解这一权衡知之甚少。
2. 我们以假花园螳螂（Pseudomantis albofimbriata）——一种色盲且外观高度隐蔽的昆虫——为研究对象，探究其面临的这类竞争性需求。我们采用反射光谱法（reflectance spectrometry）与受体噪声模型（receptor-noise modelling），分别在配偶（同种螳螂）、潜在捕食者（鸟类）与猎物（蜜蜂）的视觉系统中，表征螳螂各身体区域的显眼度。随后我们通过条件操控实验与同种选择试验，进一步探究目标颜色性状。
3. 视觉建模结果显示，雄性螳螂对同种个体、猎物与捕食者而言均不显眼——即其在色彩与明度维度上均具有隐蔽性。与之相对，雌性螳螂在色彩维度上对所有潜在接收者均呈隐蔽状态，但其腹部在明度维度上却较为显眼。我们的食物操控实验表明，身体状况良好（且因此携带更多卵粒）的雌性个体，其腹部亮度高于身体状况较差的雌性。选择试验结果显示，雄性螳螂会持续偏好腹部更亮的雌性个体。
4. 我们的研究结果揭示了在色盲且典型隐蔽的昆虫中，存在以亮度介导的性信号传递现象。雌性螳螂通过自身仅有的视觉通道传递信号，既向配偶显眼地展示了自身的适合度，又尽可能降低了自身对捕食者与猎物的显眼程度。此外，雌性螳螂仅通过单一身体区域传递信号，显然借助了协同破坏性体色（coincident disruptive coloration）进一步降低了被潜在窃听者检测到的概率。
5. 我们的研究揭示了视觉信号系统中，性选择对显眼度的需求与自然选择对隐蔽性的需求之间的权衡得以缓解的一种全新机制。这类信号可能在外观隐蔽的物种中广泛存在，而本研究也再次证明，超越人类视觉能力的范畴分析视觉信号的重要性。