The evolution of integrated defence systems

简介：走进大多数加拿大人的后院，你可能会看到许多保护性色彩图案的例子：与背景相似的飞蛾，警示色的瓢虫，以及无害的悬停苍蝇，它们像螫人的黄蜂或蜜蜂一样获得保护。捕食为自然选择的力量提供了一些最著名的例子，它塑造了学术界和公众对进化过程的看法。然而，越来越多的人认识到，大多数猎物物种并没有进化出单一的防线，而是在早期策略失败时依次部署的一系列防御措施。例如，许多伪装的飞蛾在被发现时试图惊吓潜在的捕食者，许多具有警告色彩的瓢虫在接触时会反射性出血。同样，为了应对多种威胁，许多猎物物种已经进化出了一种针对捕食者的防御机制——瑞士军刀，它们有特定的防御措施，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，为什么有些物种有而有些物种没有，为什么有些物种把所有的资源都投入到一道防线上，而其他物种则投入到一系列的威慑中？目的：我们的主要目标是了解不同的反捕食者特征是如何结合起来保护生物体不被杀死的，并了解为什么物种进化出不同的系统来保护自己。为了做到这一点，我们将研究特定的防御组合是如何组合的。例如，我们会问，是否以及为什么只有令人讨厌的物种进化出了一种被抓住的生存能力，为什么某些物种在飞行时进行模仿，但在休息时却求助于躲藏，为什么一些模仿者在外表上进化得像它们有害的模型，但其他模仿者的行为也像它们。方法：为了实现上述目标，我们将采用多种方法，包括实地评估蝴蝶的临界翅膀撕裂力，对博物馆标本进行实物检查，向野生鸟类展示人工猎物，以及分析蝗虫和蝴蝶在风洞中的飞行特性。为了补充这项工作，我们将收集整个家谱中防御分布的数据，并测试某些防御特征（如逃避能力和毒素水平）是否相关。然后，我们将开发数学模型来帮助理解这些关联产生的原因。这项工作为加拿大缺乏的技能提供了极好的培训机会，包括昆虫鉴定和数学建模。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起步阶段。这项研究不是要添加脚注，而是要测试“大图景”假设，旨在理解我们在自然世界中看到的防御特征的多样性。

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.