Data from: Too hard to swallow: a secret secondary defence of an aposematic insect

Anti-predator strategies are significant components of adaptation in prey species. Aposematic prey are expected to possess effective defences that have evolved simultaneously with their warning colours. This study tested the hypothesis of the defensive function and ecological significance of the hard body in aposematic Pachyrhynchus weevils pioneered by Alfred Russel Wallace nearly 150 years ago. We used predation trials with Japalura tree lizards to assess the survivorship of ‘hard’ (mature) vs. ‘soft’ (teneral) and ‘clawed’ (intact) vs. ‘clawless’ (surgically removed) weevils. The ecological significance of the weevil's hard body was evaluated by assessing the hardness of the weevils, the local prey insects, and the bite forces of the lizard populations. The existence of toxins or deterrents in the weevil was examined by gas chromatography-mass spectrometry (GC-MS). All ‘hard’ weevils were instantly spat out after being bitten once and survived attacks by the lizards. In contrast, the ‘soft’ weevils were chewed and subsequently swallowed. The results were the same regardless of the presence or absence of the weevil's tarsal claws. The hardness of ‘hard’ Pachyrhynchus weevils was significantly higher than the average hardness of other prey insects in the same habitat and the mean bite forces of the local lizards. The four candidate compounds of the weevil identified by GC-MS had no known toxic or repellent functions against vertebrates. These results reveal that the hardness of aposematic prey functions as an effective secondary defence, and they provide a framework for understanding the spatio-temporal interactions between vertebrate predators and aposematic insect prey.反捕食策略是猎物物种适应性演化的重要组成部分。具有警戒色（aposematic）的猎物应具备与其警戒色协同演化的有效防御手段。本研究针对近150年前由阿尔弗雷德·拉塞尔·华莱士提出的假说展开验证，该假说认为警戒象鼻虫属（Pachyrhynchus）的硬壳体具备防御功能并具有生态学意义。我们利用攀蜥属（Japalura）树蜥开展捕食试验，以评估‘硬壳’（成熟个体）与‘软壳’（初羽化个体）、‘具爪’（完整个体）与‘无爪’（经手术移除爪部）象鼻虫的存活率。通过测定象鼻虫、本地猎物昆虫的体硬度以及当地攀蜥种群的咬合力，我们评估了象鼻虫硬壳体的生态学意义。我们借助气相色谱-质谱联用仪（GC-MS）检测了象鼻虫体内是否存在毒素或驱避物质。所有‘硬壳’象鼻虫在被蜥蜴咬噬一次后即被立即吐出，并成功抵御了蜥蜴的攻击。与之相反，‘软壳’象鼻虫则被咀嚼并最终被吞食。无论象鼻虫的跗爪是否存在，实验结果均保持一致。‘硬壳’象鼻虫的体硬度显著高于同栖息地内其他猎物昆虫的平均硬度，同时也高于当地攀蜥的平均咬合力。经GC-MS鉴定出的四种候选化合物，目前未发现其对脊椎动物具有毒性或驱避作用。本研究结果表明，警戒色猎物的体硬度可作为一种有效的次级防御手段，同时为阐明脊椎动物捕食者与警戒色昆虫猎物之间的时空互作关系提供了研究框架。