PHYLOGENY AND ONTOGENY OF AN AUDITORY SYSTEM

本研究旨在发现在无耳和有耳（听力）动物之间的进化过渡过程中，感觉外围和中枢神经系统发生了什么变化。听觉的机械感受外周和中枢神经系统的基础是什么？是否出现了专门针对听觉和声学行为的新的处理电路？还是来自新感觉系统的传入信号与现有回路相连？昆虫系统为研究这些问题提供了一个极好的模型，因为脊椎动物和无脊椎动物的听觉受体和耳朵的基本结构非常相似。此外，昆虫的听觉进化了很多次（超过14次，而脊椎动物的听觉进化不到3次），所以有很多类似的情况可以比较和对比，以寻找新的听觉系统进化的基本规则。螳螂，这个项目的重点动物，是独特的，在身体的腹中线有一个单一的，超声波敏感的耳朵。先前的研究已经确定了螳螂最亲密的姐妹群体蟑螂（没有鼓室听觉）的听觉系统成分的同源物，并详细描述了螳螂耳朵的淋巴发育。目前的项目将定义行为的转变——从非声学（蟑螂；听力发育前的螳螂若虫）到声学（成年螳螂）——这必须伴随着听力的获得。这将伴随着听觉中间神经元及其同系物的生理学检查，作为理解行为变化背后的中枢神经系统回路变化的第一步。该项目将研究导致螳螂不同听觉能力的个体发生路径的进化。本文将重点讨论听觉性二态性物种中有听力的雄性和有听力的雌性的发育差异，并强调幼体激素和外体激素的作用。该项目试图证实一种假设，即许多看似不同的昆虫耳朵实际上是从昆虫身体上完全相同的结构独立进化而来的。因此，身体上适合建造耳朵的进化热点数量非常有限。免疫染色将用于绘制一些鼓膜昆虫腹部和胸部的脊索器官分布图，以准确确定哪些脊索器官已成为鼓膜器官——预计在超过90个的昆虫耳朵中，有3或4个脊索器官占大多数。这条研究路线将导致对神经和非神经特征的更清晰的理解，这些特征定义了听觉系统进化的热点。

This research seeks to discover what changes occur in the sensory periphery and the CNS during the evolutionary transition between earless and eared (hearing) animals. What are the underlying mechanoreceptive peripheral and CNS substrates for hearing? Do new processing circuits arise specifically for hearing and acoustic behaviors? Or do the afferents from the new sensory system link to existing circuits? Insect systems provide an excellent model for studying these questions since the fundamental structures of auditory receptors and ears are remarkably similar in vertebrates and invertebrates. Further, hearing has evolved many times in insects (greater than 14 compared with less than 3 in vertebrates) so there are many parallel cases to compare and contrast in search of fundamental rules for the evolution of a new auditory system. Praying mantises, the focal animal of the project, are unique in possessing a single, ultrasound-sensitive ear in the ventral midline of the body. Previous research has identified the homologs of auditory system components in the mantis closest sister group, cockroaches (without tympanate hearing) and has detailed the nymphal development of the mantis ear. The current project will define the transition in behaviors-from non-acoustic (cockroach; mantis nymphs before hearing develops) to acoustic (adult mantis)-that must accompany the acquisition of hearing. This will be accompanied by an examination of the physiology of auditory internuerons and their homologs as a first step in understanding the CNS circuitry changes underlying the behavioral changes. The project will study the evolution of ontogenetic paths that have led to different auditory capabilities among mantises. It will focus on the developmental contrast between hearing males and deaf females in species with auditory sexual dimorphism, emphasizing the role of juvenile hormone and ecdysteroids. The project seeks to substantiate the hypothesis that many seemingly disparate insect ears have, in fact, evolved independently from exactly the same structures on the insect body. Thus, there are a very limited number of evolutionary hot spots on the body suitable for building an ear. Immunostaining will be used to map chordotonal organ distribution in the abdomen and thorax of a number of tympanate insects to determine exactly which chordotonal organs have become tympanal organs-the expectation is that three or four chordotonal organs out of greater than 90 account for most insect ears. This line of research will lead to a clearer understanding of the neural and non-neural characteristics that define a hot spot for auditory system evolution.