Data from: Predator discrimination in the hermit crab Calcinus californiensis: tight for shell breakers, loose for shell peelers

Prey exposed to predators with different hunting and feeding modes are under different selective pressures, therefore it is expected that they should exhibit plastic and adaptive antipredator responses according to current risks. The hermit crab Calcinus californiensis faces two contrasting predators, the shell peeler Arenaeus mexicanus that hunts by active searching and the shell breaker Eriphia squamata that hunts by ambush. In order to discover whether C. californiensis displays plastic responses depending on the type of predatory challenge, we examined the shell size preference, the hiding time, and the escape velocity of hermit crabs in the presence of chemical cues from a shell peeler, a shell breaker, and a control. We also examined the role of shell fit on the escape velocity of the hermit crabs in natural tidal pools. Crabs chose shells with a loose fit (relatively large shells) in the presence of chemical cues from the shell peeler Arenaeus and shells with a tight fit when exposed to cues from the shell breaker Eriphia. The hermit crabs hid for shorter times and moved away faster from Eriphia than from Arenaeus stimulus. The use of a tight shell favours faster movement away from the shell breaker (pre-capture strategy), but prevents the crab retracting deeper inside the shell, increasing the risk of be eaten by the shell peeler once captured. Hence, the use of loose shells that protect the crab from the shell peeler hinders fast escape. This study shows specific and plastic antipredatory responses to contrasting predators, each bringing adaptive benefits at different levels of the predator sequence.

面对具有不同捕猎与取食模式的捕食者时，猎物会承受各异的选择压力，因此其理应依据当前的风险等级，展现出具备可塑性的适应性反捕食响应（antipredator responses）。加州钙寄蟹（Calcinus californiensis）就面临两类截然不同的捕食者：一类是以主动搜寻方式捕猎的剥壳捕食者（shell peeler）墨西哥矶蟹（Arenaeus mexicanus），另一类是以伏击方式捕猎的碎壳捕食者（shell breaker）皱纹爱洁蟹（Eriphia squamata）。为探究加州钙寄蟹是否会依据捕食者类型展现出可塑性响应，我们设置了剥壳捕食者、碎壳捕食者的化学信号（chemical cues）组与空白对照组，以此检测寄居蟹的螺壳尺寸偏好、隐匿时长与逃逸速度。此外，我们还在自然潮间带水坑（tidal pools）中，探究了壳体贴合度（shell fit）对寄居蟹逃逸速度的影响。当暴露于剥壳捕食者墨西哥矶蟹的化学信号中时，寄居蟹会选择贴合度较松的螺壳（即尺寸相对偏大的壳体）；而当接触碎壳捕食者皱纹爱洁蟹的信号时，则会选择贴合度紧密的螺壳。相较于墨西哥矶蟹的刺激，寄居蟹在面对皱纹爱洁蟹的刺激时，隐匿时长更短、逃逸速度更快。选用贴合紧密的螺壳，虽有助于更快逃离碎壳捕食者（属于捕获前防御策略），但会限制寄居蟹将躯体更深地缩进螺壳内，进而提升其被剥壳捕食者捕获后的捕食风险。因此，选用能抵御剥壳捕食者的松贴合螺壳，则会阻碍寄居蟹实现快速逃逸。本研究证实，寄居蟹会针对两类截然不同的捕食者，展现出特异性且具备可塑性的反捕食响应，且每种响应在捕食序列的不同阶段均能带来适应性收益。