For many species, the highest predation rates are on the earliest life stages, favoring the early development of predator detection mechanisms. Aquatic larvae of Spotted salamanders, Ambystoma maculatum, suffer very high mortality rates and juveniles are vulnerable to a new suite of terrestrial predators after metamorphosis. In some species, adult salamanders assess predation risk via chemical cues released by damaged conspecifics and some heterospecifics (“alarm cues”), but responses of larvae and metamorphs have not been tested. Our first experiment confirmed that field-caught, experienced larvae responded with fright to chemical cues of damaged conspecifics, but not to control cues or alarm cues from toad tadpoles. Responses of sedentary hatchlings in the next experiment indicated that the alarm cue was not present in damaged tissues of hatchlings (1-day-old), but was present by the time the larvae reached the age of 1 month. The third experiment tested responses of naïve lab-reared, free-swimming larvae to alarm cue. In contrast to the other two experiments, these larvae without experience did not distinguish between conspecific alarm cues and control stimuli, suggesting that either embryonic learning or reinforcement learning as larvae may be required to develop or maintain the alarm response. In the fourth experiment, post-metamorphic juveniles raised from field-experienced larvae significantly avoided alarm cues from conspecifics but not control stimuli, indicating that the production and recognition of alarm cues can be retained after metamorphosis. Our study provides the first evidence of chemical alarm cues produced by both larval and juvenile salamanders and indicates that alarm responses may vary according to experience.

中文翻译：

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幼虫和幼年斑点蝾螈（Ambystoma maculatum）对同种警报线索的反应

对于许多物种来说，最高的捕食率发生在生命最早的阶段，有利于捕食者检测机制的早期发展。斑点蝾螈的水生幼虫，Ambystoma maculatum，死亡率非常高，幼体在变态后很容易受到一组新的陆地捕食者的攻击。在某些物种中，成年蝾螈通过受损的同种动物和一些异种动物释放的化学线索（“警报线索”）评估捕食风险，但尚未测试幼虫和变种动物的反应。我们的第一个实验证实，野外捕获的、有经验的幼虫对受损同种的化学线索有惊吓反应，但对蟾蜍蝌蚪的控制线索或警报线索没有反应。在下一个实验中久坐的幼龟的反应表明，在幼虫（1 日龄）的受损组织中不存在警报提示，但在幼虫达到 1 个月大时出现。第三个实验测试了幼稚的实验室饲养、自由游动的幼虫对警报信号的反应。与其他两个实验相比，这些没有经验的幼虫没有区分同种警报提示和控制刺激，这表明可能需要胚胎学习或强化学习作为幼虫来发展或维持警报反应。在第四个实验中，从野外经历的幼虫中饲养的变态后幼虫显着避免了来自同种的警报提示，但没有控制刺激，表明在变态后可以保留警报提示的产生和识别。