Laforsch Christian, Ngwa Wilfred, Grill Wolfgang, Tollrian Ralph
Department of Biological Sciences, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
Proc Natl Acad Sci U S A. 2004 Nov 9;101(45):15911-4. doi: 10.1073/pnas.0404860101. Epub 2004 Nov 1.
Inducible defenses are common strategies for coping with the selective force of predation in heterogeneous environments. In recent years the conspicuous and often dramatic morphological plasticity of several waterflea species of the genus Daphnia have been found to be inducible defenses activated by chemical cues released by predators. However, the exact defensive mechanisms remained mysterious. Because even some minute morphological alterations proved to be protective against predatory invertebrates, it has been suggested that the visible morphological changes are only the tip of the iceberg of the entire protective mechanisms. Here we applied a method of ultrasonic microscopy with vector contrast at 1.2 GHz to probe hidden morphological defenses. We found that induction with predator kairomones increases the stability of the carapace in two Daphnia species up to 350%. This morphological plasticity provides a major advantage for the induced morphs during predation because predatory invertebrates need to crush or puncture the carapace of their prey to consume them. Our ultrastructural analyses revealed that the internal architecture of the carapace ensures maximal rigidity with minimal material investment. Our results uncover hidden morphological plasticity and suggest a reconsideration of former classification systems in defended and undefended genotypes in Daphnia and possibly in other prey organisms as well.
诱导防御是在异质环境中应对捕食选择压力的常见策略。近年来，人们发现水蚤属几种水蚤显著且通常具有戏剧性的形态可塑性是由捕食者释放的化学信号激活的诱导防御。然而，确切的防御机制仍然神秘。因为即使是一些微小的形态改变也被证明对捕食性无脊椎动物具有保护作用，所以有人认为可见的形态变化只是整个保护机制的冰山一角。在这里，我们应用了一种1.2吉赫兹的具有矢量对比度的超声显微镜方法来探测隐藏的形态防御。我们发现，用捕食者信息素诱导可使两种水蚤的头胸甲稳定性提高350%。这种形态可塑性为被捕食时的诱导形态提供了一个主要优势，因为捕食性无脊椎动物需要压碎或刺穿猎物的头胸甲才能将其吃掉。我们的超微结构分析表明，头胸甲的内部结构以最少的物质投入确保了最大的刚性。我们的结果揭示了隐藏的形态可塑性，并建议重新考虑水蚤以及可能其他猎物生物中防御型和未防御型基因型的先前分类系统。
