The evolution of integrated defence systems

简介：走进加拿大大多数后院，你很可能会看到许多保护性色彩图案的例子：与它们的背景相似的飞蛾，颜色警示的瓢虫，以及通过模仿被叮咬的黄蜂或蜜蜂而获得保护的无害的飞蝇。捕食为自然选择的力量提供了一些最著名的例子，它塑造了学者和普通公众对进化过程的思考方式。然而，人们越来越认识到，大多数猎物物种并没有进化出一条单一的防线，而是在早期策略失败时按顺序部署的一系列防御措施。例如，许多伪装的蛾子在被发现时试图惊吓潜在的捕食者，许多颜色警示的瓢虫在接触时会反射出血。同样，为了应对多重威胁，许多猎物物种进化出了一把瑞士军刀，针对捕食者特有的防御，某些防御针对特定的捕食者，如鸟类或寄生蜂。如何解释这些后备防御，为什么一些物种有后备防御，而另一些物种没有，为什么一些物种将所有资源投入一条防线，而其他物种投资于一系列威慑措施？目标：我们的广泛目标是了解不同的反捕食者特征是如何结合在一起保护生物不被杀死的，并了解为什么物种进化出不同的系统来保护自己。要做到这一点，我们将调查特定的防御对如何结合。例如，我们会问，是否以及为什么只有令人不快的物种才进化出了被抓住的生存能力，为什么某些物种在飞行时会进行模仿，但在休息时会躲起来，为什么一些模仿动物在外表上看起来像它们的有害模型，但其他模仿动物的行为也与它们相似。方法：为了达到上述目的，我们将使用多种方法，包括评估野外蝴蝶的临界翅膀撕裂力，物理检查博物馆标本，展示野生鸟类的人工猎物，分析蝗虫和蝴蝶在风洞中的飞行特征。为了补充这项工作，我们将收集整个家系中防御系统分布的数据，并测试某些防御特征，如躲避能力和毒素水平，是否与之相关。然后，我们将开发数学模型来帮助理解为什么会出现这些关联。这项工作为加拿大缺乏的技能提供了极好的培训机会，包括昆虫识别和数学建模。意义：尽管军事理论家对多层次防御进行了广泛的研究，但我们对防御系统如何在自然界中整合的理解仍处于初级阶段。这项研究不是为了增加脚注，而是测试旨在理解我们在自然界中看到的防御特征多样性的“大图景”假说。

INTRODUCTION: Go into most Canadian backyards and you are likely to see numerous examples of protective colour patterns: moths that resemble their backgrounds, warningly-coloured ladybugs, and harmless hover flies that gain protection by resembling stinging wasps or bees. Predation has provided some of the most celebrated examples of the power of natural selection, and it has shaped the way both academics and the general public think about evolutionary processes. However, it is increasingly recognized that most prey species have not evolved a single line of defence, but a portfolio of defences that are deployed sequentially when earlier strategies fail. For example, many camouflaged moths attempt to startle potential predators when discovered, and many warningly-coloured ladybugs engage in reflex bleeding on contact. Likewise, to deal with multiple threats, many prey species have evolved a Swiss-army knife of predator-specific defences, with certain defences targeted at particular predators such as birds or parasitic wasps. What explains these back-up defences, why do some species have them and not others, and why do some species put all of their resources into one line of defence when other species invest in a range of deterrents? OBJECTIVES: Our broad goal is to understand how different anti-predator traits combine to protect organisms from being killed, and to understand why species have evolved different systems to protect themselves. To do this we will investigate how specific pairs of defences combine. For example, we will ask if and why only unpalatable species have evolved an ability to survive being grasped, why certain species engage in mimicry while flying but resort to hiding when at rest and why some mimics evolve to look like their noxious models in appearance but other mimics behave like them too. METHODS: To address the above aims we will use a variety of methods including evaluation of the critical wing tear forces of butterflies in the field, physical inspection of museum specimens, presentations of artificial prey to wild birds and an analysis of the flight characteristics of grasshoppers and butterflies in wind tunnels. To complement this work we will gather data on the distribution of defences across whole family trees and test whether certain defensive traits, such as evasive ability and toxin level, are associated. We will then develop mathematical models to help understand why these associations arise. The work provides excellent training opportunities for skills that are in short supply in Canada, including insect identification and mathematical modelling. SIGNIFICANCE: Although multi-level defences are widely investigated by military theorists, our understanding of how defensive systems are integrated in the natural world is still in its infancy. This research is not about adding footnotes, but testing "big picture" hypotheses aimed at understanding the diversity of defensive traits we see in the natural world.