Data from: Is the evolution of inaccurate mimicry a result of selection by a suite of predators? A case study using myrmecomorphic spiders

Several hypotheses have been put forward to explain the evolution of inaccurate mimicry. Here we investigated the novel hypothesis that inaccurate mimicry (in color and shape) is maintained by opposing selective pressures from a suite of different predators: model-aversive visually oriented predators and model- and mimic-specialized predators indifferent to mimetic cues. We hypothesize that spiders resembling ants in color and shape escape predators that typically avoid ants, but fall prey to ant-eating predators. We tested whether inaccurate myrmecomorphic spiders are perceived as their models by two types of predators, and whether they can escape from these predators. We found that model-specialized (ant-eating) predators captured mimics significantly less frequently than their ant models, because mimics changed their behavior by fleeing predatory attacks. The fastest escape was found in less accurate mimics, indicating a negative association between visual resemblance and effectiveness of defenses. In trials with spider-eating predators, mimics were not captured more frequently than their models. The quality of defensive mechanisms appears to result from opposing selection forces exerted by the predator complex: mimics are more accurate (in color and shape) in microhabitats dominated by model-aversive predators, and less accurate in microhabitats with model- and mimic-specialized predators.学界已提出多种假说以解释不准确拟态的演化机制。本研究针对一项全新假说展开探究：不准确拟态（色彩与形态维度）的维持，源于多类捕食者施加的相反选择压力——一类是厌恶拟态原型且依赖视觉的捕食者，另一类是对拟态信号无动于衷、专门以原型和拟态者为食的捕食者。我们提出假说：体色与形态类似蚂蚁的蜘蛛，可避开通常会规避蚂蚁的捕食者，却会成为食蚁捕食者的猎物。我们开展了两项测试：一是两类捕食者是否会将不准确蚁形蜘蛛视作其原型（蚂蚁），二是这类蜘蛛能否逃离两类捕食者的捕食。研究结果显示：专门以原型（蚂蚁）为食的捕食者捕获拟态者的频率显著低于其捕获蚂蚁原型的频率，这是因为拟态蜘蛛会通过逃离捕食攻击来改变自身行为。拟态精准度越低的个体，其逃逸速度越快，这表明视觉相似度与防御有效性之间呈负相关关系。在针对食蛛捕食者的实验中，拟态者的被捕食频率并未显著高于其原型。防御机制的优劣似乎源于捕食者群落施加的相反选择压力：在以厌恶原型的捕食者为主导的微生境中，拟态者的（色彩与形态）拟态精准度更高；而在以专门捕食原型与拟态者的捕食者为主导的微生境中，拟态精准度则更低。