Chemical defense acquired via pharmacophagy can lead to protection from predation for conspecifics in a sawfly

Predation is an important selection pressure acting on organisms, with organisms evolving diverse anti-predator strategies to combat it. One such strategy is chemical defense in which organisms either synthesize or extrinsically acquire defensive chemicals. Little is known about the intraspecific transfer of such chemicals and if such chemicals acquired from conspecifics can also serve as defense against predation. Here, we used adults of the turnip sawfly, Athalia rosae, which can acquire the plant chemicals ‘clerodanoids’ via pharmacophagy after exposure to the plant, Ajuga reptans. We show that clerodanoid access mediates protection against predation by mantids for the sawflies. Moreover, even indirect access to clerodanoids, via nibbling on conspecifics that had access to the plant, resulted in protection against predation albeit to a lower degree than direct access. Furthermore, sawflies that had no direct access to clerodanoids were less consumed by mantids when they were grouped ..., ,

捕食作用是作用于生物体的重要选择压力，生物体由此演化出多样的反捕食策略以应对此类压力。其中一类核心策略为化学防御，即生物体可自主合成或通过外源途径获取防御性化学物质。目前学界对这类化学物质的种内传递机制，以及从同种个体处获取的此类化学物质是否同样可用于反捕食防御，仍知之甚少。本研究以芜菁叶蜂（Athalia rosae）成虫为实验对象，该昆虫在接触筋骨草（Ajuga reptans）后，可通过药理摄食（pharmacophagy）获取该植物中的克罗烷二萜类化合物（clerodanoids）。我们证实，获取克罗烷二萜类化合物可使芜菁叶蜂免受螳螂的捕食。此外，即便通过啃食已接触该植物的同种个体来间接获取克罗烷二萜类化合物，芜菁叶蜂同样能获得反捕食保护，只是保护效果弱于直接获取的情况。进一步研究发现，未直接获取克罗烷二萜类化合物的芜菁叶蜂，当它们成群聚集时，被螳螂捕食的概率也会降低……