Causes and Consequences of Dentition Reduction in the Zebrafish Lineage

人们早就认识到，进化的方向不仅取决于生物所处的环境，而且还取决于限制变异能力的遗传和发育程序的特征。这种“发育限制”的一种模式是不可逆转的进化，或者当生物体回到祖先的环境或行为时，失去的结构无法重新出现。本研究以鲤科鱼类牙齿位置的减少为例，探讨不可逆演化的遗传特征。这一组中的牙齿，包括小鱼和吸盘，在5000万年前从口腔和喉咙上部消失，只保留在喉咙的下表面。失去的牙齿再也没有回来，尽管这个多样化群体的多个血统采用了祖先的进食方式。该项目将确定与鲤形目鱼类牙齿缺失相关的遗传变化，并检验不可逆进化是多个基因和发育途径累积变化的结果这一假设。此外，基因工程方法将应用于一种常见的实验室鲤科动物斑马，试图恢复失去的牙齿。预计该项目将导致对发展制约因素的进一步了解，这与物种是否能够适应人为环境变化或将灭绝的实际问题有关。除了提供本科生、研究生和研究生水平的研究培训外，该项目还将生产改良的鱼种，以加强科罗拉多大学的鱼类生物学和遗传学课程，并在其自然历史博物馆举办展览。

It has long been recognized that the direction of evolution is determined not only by the environments to which organisms are exposed, but also by features of their genetic and developmental programs that constrain the ability to vary. A pattern indicative of such 'developmental constraint' is irreversible evolution, or the failure of lost structures to reappear when organisms return to ancestral environments or behaviors. This project employs an example of irreversible evolution, the reduction of tooth-bearing locations in cypriniform fishes, to characterize the genetic features underlying developmental constraint. Teeth in this group, which includes minnows and suckers, were lost from the mouth and upper throat over 50 million years ago and are retained only on the lower surface of the throat. The lost teeth have never returned, despite the adoption of ancestral feeding modes by multiple lineages of this diverse group. The project will identify genetic changes that occurred in association with loss of teeth in cypriniforms and test the hypothesis that irreversible evolution is the result of accumulated changes in multiple genes and developmental pathways. In addition, genetic engineering approaches will be applied to a common laboratory cypriniform, the Zebra Danio, in an attempt to restore lost teeth. The enhanced understanding of developmental constraint expected to result from the project is relevant to the practical question of whether species will be able to adapt to manmade environmental change or will instead become extinct. In addition to providing research training at the undergraduate, graduate, and post-graduate levels, the project will produce modified fish strains that will enhance courses in Fish Biology and Genetics at the University of Colorado, as well as an exhibit at its Museum of Natural History.