瘤蟹蛛鸟粪伪装的适应性意义及其起源与进化

The function of crypsis, mimicry and aposematism has been intensively studied, but one type of deception, masquerade, is poorly understood. Unlike crypsis, masquerading animals bear an uncanny resemblance to inedible and often inanimate objects such as twigs, leaves, stones or bird-droppings to deceive predators or prey. Animals that master these types of disguise are likely to be misclassified as either inedible objects by their predators, or as innocuous objects by their prey and thus stand to gain protection from predation or greater access to prey. While the most common forms of masquerades are sticks and leaves, bird-dropping masquerading has also been established in many groups of animals, including caterpillars and spiders. The crab spider genus Phrynarachne Thorell, 1869 (Araneae: Thomisidae) is a group of sit-and-wait predators. Their shape, size and colour bear striking resemblance to bird droppings, and they are often cited as textbook examples of bird-dropping masquerade. However, to date, no empirical studies have tested the adaptive significance and the evolution of bird-dropping masquerading in Phrynarachne crab spiders. This project is the first integrative, comparative and multidiscipline study to investigate how masquerading functions and evolves using bird-dropping crab spiders as model organisms. Comprehending the adaptive significance and mechanisms of bird-dropping masquerading stands to further our understanding of how local environment influence diversification, leading to extensive spider biodiversity. Furthermore, deciphering the processes that have led to the evolution of bird-dropping masquerading across Phrynarachne will shed light on the repeatability of evolution and continue to heighten our curiosity about the diversity of life. The research will advance basic research by establishing a novel finding that will open up new lines of research in several fields, particularly visual ecology, animal behaviour and evolutionary biology.

动物的捕食与被捕食既是一对进化的矛盾体，也是相互依存，协同进化的。与隐避、拟态及警戒色等保护色一样，伪装也是生物学中最精妙的验证自然选择理论的经典例子。但与隐避不同，伪装动物常将自身伪装成不可食且无生命的物体，如枯枝、树叶、石头或鸟粪等，使其捕食者或猎物无法正确识别，从而减少被捕食或增加捕食的机率。尽管树枝或树叶伪装较常见，但许多鳞翅目幼虫和蜘蛛的鸟粪伪装也广为人知。虽然瘤蟹蛛属蜘蛛作为鸟粪伪装的经典例子一直被广泛引用，但很少有学者研究其鸟粪伪装的功能及其进化。此课题将应用和整合光谱分析、视觉模型、行为学、触角电位气相色谱仪、进化生物学及比较方法学等多学科，从多种捕食者和猎物的角度探索蜘蛛鸟粪伪装是如何行使其伪装功能的，及鸟粪伪装是如何起源和进化的。我们相信研究的结果不仅能加深我们对动物伪装的进一步了解，而且也极有可能为动物伪装提供全新的解释，因此对于动物的协同进化有着重要的理论意义。

与隐避、拟态及警戒色等保护色一样，伪装也是生物学中最精妙的验证自然选择理论的经典例子。但与隐避不同，伪装动物常将自身伪装成不可食且无生命的物体，如枯枝、树叶、石头或鸟粪等，使其捕食者或猎物无法正确识别，从而减少被捕食或增加捕食的机率。虽然瘤蟹蛛属蜘蛛作为鸟粪伪装的经典例子一直被广泛引用，但很少有学者研究其鸟粪伪装的功能及其进化。此课题从多种捕食者和猎物的角度探索蜘蛛鸟粪伪装是如何行使其伪装功能的，及鸟粪伪装是如何起源和进化的。研究结果表明：(1)鸟粪蛛在自然界中不仅能够减少被捕食者捕食，并且还能增加捕获猎物的机会; (2) 捕食者和猎物很难从视觉上辨别出鸟粪蛛与鸟粪的颜色，因此，捕食者和猎物可能将鸟粪蛛错认为鸟粪，以加强鸟粪蛛视觉伪装的效果; (3) 在实验室里，孔蛛捕食者从视觉上和化学上趋避捕食者，而锡兰瘤蟹蛛视觉上和化学上却吸引猎物家蝇。因此，通过行为学实验验证了鸟粪蛛鸟粪视觉伪装和化学伪装的躲避捕食者假说和吸引猎物的假说；(4) 不管雏鸡有没有取食鸟粪的经验，雏鸡很少啄锡兰瘤蟹蛛或鸟粪，但是啄食非鸟粪蛛显著地比啄食锡兰瘤蟹蛛多。由此通过控制捕食者对取食鸟粪经验的学习实验验证了鸟粪蛛躲避捕食者的假说; (5) 鉴定分析了瘤蟹蛛可能用于趋避天敌和/或吸引猎物的挥发性气味的化学成分；(6) 瘤蟹蛛在分子系统进化树上为单系，鸟粪伪装可能是一次起源，起源的大致时间为148万年左右。我们相信研究结果不仅能加深了我们对动物鸟粪伪装的进一步认识，而且为深入探讨动物鸟粪伪装的功能及其进化提供了依据。更重要的是，本研究丰富和完善了动物伪装的理论和研究手段, 也为动物伪装提供全新的解释，对与动物保护色有关的行为进化及动物的协同进化有着重要的理论意义。同时，本课题组有关节肢动物颜色在性选择、隐蔽、拟态及伪装方面的研究结果，也将会让生物学家们意识到在今后的由视觉主导的行为学和进化生物学研究中，不可忽视动物视觉系统的重要性。