The observable diversity of antipredator defences across organisms demonstrates predation's impact on trait evolution. The functions of many traits that are presumed to have an antipredator function have never been directly tested. The spiny orb-weaving spider, Micrathena gracilis, for example, stridulates when grasped. While stridulation was first hypothesized to be an antipredator defence nearly 50 years ago, no data exist to support this hypothesis. To explore the form and function of M. gracilis stridulation, we first quantified the behavioural and acoustical properties of sound production. Next, using laboratory assays, we directly tested the effect of stridulation on survival with an avian predator – blue jays, Cyanocitta cristata. Finally, we conducted a large mark–recapture field study in which we compared the natural survival of experimentally manipulated adult female M. gracilis that could not stridulate (silenced) versus could stridulate (control). Stridulatory pulses produced broadband frequency spectra, consistent with acoustic antipredator defences in other taxa. We also observed stridulation by male M. gracilis for the first time. In staged laboratory interactions with captive blue jays, we found no differences in survival between silenced and control M. gracilis. Similarly, in our mark–recapture field study, we found no differences in survival estimates between silenced and control groups, nor an effect of stridulation rate. While M. gracilis stridulation closely resembles antipredator stridulation in other arthropods, our behavioural data do not yet provide solid support for an antipredator function in M. gracilis.

中文翻译：

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测试在多刺的圆织蜘蛛 Micrathena gracilis 中假设的抗捕食者防御功能

生物体中抗捕食者防御的可观察多样性表明捕食对性状进化的影响。许多被假定具有抗捕食者功能的特征的功能从未被直接测试过。例如，多刺的织球蜘蛛，Micrathena gracilis，在被抓住时会发出叫声。虽然在近 50 年前，人们首次假设鸣叫是一种反捕食者防御，但没有数据支持这一假设。为了探索 M. gracilis stridulation 的形式和功能，我们首先量化了声音产生的行为和声学特性。接下来，我们使用实验室检测直接测试了鸣叫对鸟类捕食者——蓝鸟 Cyanocitta cristata 生存的影响。最后，我们进行了一项大型标记-重新捕获实地研究，在该研究中，我们比较了不能鸣叫（沉默）和可以鸣叫（对照）的实验操作的成年雌性纤细纤毛虫的自然存活率。 . . ． ．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．颤动脉冲产生宽带频谱，与其他分类群中的声学反捕食者防御一致。我们还首次观察到雄性纤细纤毛虫的鸣叫。在与圈养蓝鸟的分阶段实验室互动中，我们发现沉默的和控制的 M. gracilis 之间的存活率没有差异。同样，在我们的标记-重新捕获现场研究中，我们发现沉默组和对照组之间的生存估计值没有差异，也没有出现鸣叫率的影响。虽然 M. gracilis stridulation 非常类似于其他节肢动物中的 antipredator stridulation，