Snail Shell Strength and Total Crush Force of a Northern Michigan Snail as a Function of Predation Risk at the University of Michigan Biological Station Stream Research Facility (5/31/23-8/1/23)

Many prey organisms respond to the non-consumptive effects of predators by altering their physiology, morphology, and behavior. These inducible defenses can create refuges for prey by decreasing the likelihood of consumption by predators. Some prey, as in marine mollusks, have been shown to alter their morphology in response to the presence of size-limited predation. To extend this work into the freshwater realm, we presented pointed campeloma snails (Campeloma decisum) to chemical cues from a natural predator, the rusty crayfish (Faxonius rusticus), to better understand how snail morphology changes under the threat of predation. The total force needed to crush shells, total shell length, aperture width, and total weight, along with changes to these three body measurements were recorded for each individual and used to quantify morphological changes as a function of risk. Snails exposed to crayfish chemical cues needed significantly more force to crush their shells than controls (p = 0.002). Total shell length was greater in crayfish exposed snails than control snails (p = 0.002), and snails in the crayfish treatment also showed significantly more change in shell length than control snails (p = 0.003). Similarly, aperture width was significantly greater in exposed snails (p = 0.002). However, exposed snails exhibited significantly less change in aperture width than controls (p = 0.017). Finally, we found that snails exposed to crayfish weighed significantly more than snails in the control (p = 0.0009). Thus, the results of this study show that morphology of gastropods is altered in the presence of predators, and this may be an antipredator tactic directly related to risk.

许多猎物生物会通过改变自身生理学、形态学与行为特征，响应捕食者的非消耗性效应。这类诱导型防御可通过降低被捕食者捕食的概率，为猎物营造避难场所。已有研究证实，海洋软体动物中的部分类群会响应体型限制性捕食的存在而改变自身形态。为将此类研究拓展至淡水生态领域，我们将尖顶螺（Campeloma decisum）暴露于其天然捕食者锈色螯虾（Faxonius rusticus）释放的化学信号中，以更深入地解析螺类形态在捕食威胁下的变化规律。我们记录了每只螺的壳体破碎所需总力、壳体总长度、壳口宽度与总重量，以及这三项体型指标的变化量，以此量化随捕食风险变化的形态改变程度。结果显示，暴露于螯虾化学信号的螺类，其壳体破碎所需力显著高于对照组（p = 0.002）；暴露组螺类的壳体总长度显著大于对照组螺类（p = 0.002），且该处理组螺类的壳体长度变化量也显著高于对照组（p = 0.003）。同样，暴露组螺类的壳口宽度显著更大（p = 0.002），但暴露组螺类的壳口宽度变化量却显著低于对照组（p = 0.017）。最后我们发现，暴露于螯虾信号的螺类总重量显著高于对照组螺类（p = 0.0009）。综上，本研究结果表明，腹足类的形态会在捕食者存在的情况下发生改变，这或许是一种与捕食风险直接相关的反捕食策略。