Dissertation Research: Heterochrony in Insects: Phylogeny and Evolution of Acoustic Characters in the True Crickets (Orthoptera: Grylloidea)

萧氏蟋蟀和乔斯特蟋蟀一直对生物学家感兴趣，因为它们在求爱时会发出叫声。在大多数物种中，雄性蟋蟀会发出一种被潜在雌性配偶听到并识别的歌声。世界上有成千上万种板球，每一种都有独特的歌曲类型。之前的研究已经找到了板球叫声如此多样化的生态或适应性原因。然而，很少有进化研究从形态的角度来研究板球歌曲，通过检查产生和接收声音的结构。在蟋蟀中，这些声学结构是雄性的专门的前翼，以及两性前腿上的听力器官。这些结构在蟋蟀中极其多样化(世界上约有3500个已描述的物种)，但在许多物种中完全不存在。发育研究发现，发声的身体部位严格来说是成人的结构，直到生命的最后阶段才会出现。此外，许多其他结构--如后飞翼、眼睛、触角和生殖器--在非发声的蟋蟀物种中经常减少或缺失。在一个物种中，许多成年特征可能会减少或消失，最简单的方法是改变总体生长的时间。换句话说，许多非发声的蟋蟀物种可能只是形态上不成熟的密切相关的发声物种。这个项目将检验这样一个假设，即声学结构中的形态多样性可以通过生长和变态时间的变化来解释，这一过程被称为异时性。研究生Manda Jost在教师顾问Kerry Shaw博士的指导下，正在研究蟋蟀样本物种的系统发育关系及其声学进化。检验异时性假说的第一步将是对数百个物种的板球形态进行广泛而详细的调查。然后将从世界各地选择不同的物种样本，并将使用线粒体基因CO-I的DNA序列生成系统发育图。然后，统计和比较测试将确定声学结构的形态“成熟度”是否与其他功能无关的形态结构的“成熟度”显著相关。证明许多功能无关的性状显示同时变化将支持这样的假设，即这些性状都受基本生长时间表的控制。这个想法不是生态或适应性假说的替代，而是提供了一种物理机制，可以产生我们观察到的多样性。这项研究将得出迄今为止最详细的蟋蟀系统发育史，同时使用新的思路和方法来研究蟋蟀声学特征的多样性。

0073187Shaw and Jost Crickets have always interested biologists for their calling songs used incourtship. In most species, male crickets produce a song which is heard and recognized by potential female mates. There are thousands of cricket species worldwide, each of which has a unique type of song. Previous studies have looked for ecological or adaptive reasons that cricket calling songs are so diverse. However, few evolutionary studies have looked at cricket song from a morphological perspective, by examining the structures which produce and receive the sounds. In crickets, these acoustic structures are specialized front wings in males, and hearing organs on the front legs of both sexes. These structures are extremely diverse in crickets (there are ca. 3,500 described species in the world), but in many species are completely absent. Developmental studies have found that acoustic body parts are strictly adult structures which do not appear until the final life stage. In addition, many other structures -- such as hind flight wings, eyes, antennae, and genitalia -- are often reduced or absent in non-acoustic cricket species. The simplest way that many adult traits could be reduced or absent in a species is by changing the timing of overall growth. In other words, many non-acoustic cricket species may simply be morphologically immature forms of closely related acoustic species. This project will test the hypothesis that morphological diversity in acoustic structures can be explained by changes in the timing of growth and metamorphosis, a process known as heterochrony. Graduate student Manda Jost, with guidance from faculty adviser Dr. Kerry Shaw, is studying the phylogenetic relationships of exemplar species of crickets and their acoustic evolution. The first step to testing the heterochrony hypothesis will be a broad, detailed survey of cricket morphology for hundreds of species. A diverse sample of species will then be selected from regions around the world, and a phylogeny will be produced using DNA sequence from the mitochondrial gene CO-I. Statistical and comparative tests will then determine whether morphological "maturity" of acoustic structures is significantly correlated with the "maturity" of other morphological structures which are functionally unrelated. Demonstrating that many functionally unrelated traits show simultaneous change would support the hypothesis that these traits are all under control of a basic growth schedule. This idea is not an alternative to ecological or adaptive hypotheses, but provides a physical mechanism which could produce the diversity we observe. This study will result in the most detailed phylogeny to date of the crickets, while using new ideas and methods to study the diversity of cricket acoustic characters.