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.

暴露于具有差异化捕猎与取食模式的捕食者的猎物，将承受不同的选择压力，因此理论上其应根据当前面临的风险，展现出具备可塑性的适应性反捕食响应。加州寄居蟹（Calcinus californiensis）面临两种截然不同的捕食类群：一类是以主动搜寻方式捕猎的剥壳型捕食者墨西哥砂蟹（Arenaeus mexicanus），另一类是以伏击策略捕猎的碎壳型捕食者鳞哲蟹（Eriphia squamata）。为探明加州寄居蟹是否会依据捕食者类型展现出可塑性反捕食响应，本研究设置了剥壳捕食者、碎壳捕食者的化学信号组与空白对照组，观测了寄居蟹的壳体大小偏好、隐匿时长与逃逸速度。此外，我们还在自然潮间带水坑中探究了壳体贴合度对寄居蟹逃逸速度的影响。实验结果显示，当接触剥壳捕食者墨西哥砂蟹的化学信号时，寄居蟹会选择贴合度较低的壳体（即相对偏大的螺壳）；而当暴露于碎壳捕食者鳞哲蟹的信号时，则会选择贴合度较高的螺壳。相较于墨西哥砂蟹的刺激，寄居蟹在接触鳞哲蟹的信号时，隐匿时长更短，逃逸速度更快。选择高贴合度螺壳可助力寄居蟹更快脱离碎壳捕食者的攻击（属于捕获前防御策略），但会限制其将身体更深地缩进螺壳内，进而增加其被剥壳捕食者捕获后的捕食风险。反之，选择能抵御剥壳捕食者的低贴合度螺壳，则会阻碍寄居蟹实现快速逃逸。本研究证实，加州寄居蟹会针对两类截然不同的捕食者展现出特异性且具可塑性的反捕食响应，且两种策略分别在捕食序列的不同阶段为其带来适应性收益。