Successful coexistence with predators depends on the ability of prey to strike a balance between the costs of predator avoidance and the benefits of foraging and reproducing as there is a trade-off between these activities. Prey animals can balance this trade-off by responding to predation risk in a manner that matches the intensity of risk posed by the predator, which is known as the threat-sensitive predator avoidance hypothesis. To test this hypothesis, we exposed larval Indian skipper frogs (Euphlyctis cyanophlyctis) to different intensities of predation risk by increasing the number of predators and the amount of biomass consumed and recorded their behaviour, morphology, and metamorphic traits. We also quantified the whole-body corticosterone to assess the physiological basis of alterations in morphology, behaviour, and life-history traits. The results indicate that behavioural responses of larval skipper frogs increased with the intensity of risk conforming to the predictions of the threat-sensitivity hypothesis. However, the morphological responses did not vary with the intensity of risk and hence did not support the predictions of the hypothesis. Interestingly, tadpoles facing a higher level of predation risk metamorphosed at the largest size, but with increased larval duration. At the physiological level, corticosterone levels increased with increases in the intensity of risk. Thus, our results suggest that certain antipredator responses may vary with the intensity of risk while others may not. Further, the results of our study also show an association between physiological and behavioural responses of larval E. cyanophlyctis to predation risk. More importantly, we show that larval skipper frogs can assess the intensity of predation risk through threat-sensitive learning by associating conspecific alarm cues with odours of dragonfly nymphs.

中文翻译：

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蓝藻Eu的反捕食者反应是否取决于捕食风险的强度？

与捕食者的成功共存取决于捕食者能否在避免捕食者的成本与觅食和繁殖的利益之间取得平衡，因为这些活动之间需要权衡取舍。捕食动物可以通过以与捕食者构成的风险强度相匹配的方式响应捕食风险来平衡这种权衡，这被称为威胁敏感的捕食者回避假设。为了验证这一假设，我们暴露了幼虫印度蛙（Euphlyctis cyanophlyctis），以增加捕食者的数量和消耗的生物量并记录其行为，形态和变质性状，从而应对不同强度的捕食风险。我们还量化了全身皮质酮，以评估形态，行为和生活史特征改变的生理基础。结果表明，幼虫蛙的行为反应随着危险强度的增加而增加，符合威胁敏感性假说的预测。但是，形态反应并没有随风险强度而变化，因此不支持该假说的预测。有趣的是，面临更高捕食风险的t已变大，但幼体持续时间却增加了。在生理层面上 皮质酮水平随风险强度的增加而增加。因此，我们的结果表明，某些抗捕食者的反应可能会随风险强度而变化，而另一些则不会。此外，我们的研究结果还表明，幼虫的生理反应和行为反应之间存在关联蓝藻有捕食的危险。更重要的是，我们表明，幼虫蛙可以通过将威胁警报提示与蜻蜓若虫的气味相关联，通过威胁敏感型学习来评估捕食风险的强度。