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体所处的环境，而且还取决于它们的遗传和发育程序的特征，这些特征限制了它们变化的能力。这种“发育约束”的一种模式是不可逆的进化，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。本项目采用了一个不可逆进化的例子，即鲤形鱼类牙齿生长位置的减少，来描述发育限制的遗传特征。包括小鱼和吸盘鱼在内的这一类动物的牙齿在5000万年前就从口腔和上喉咙处消失了，只保留在喉咙的下表面。尽管这个多样化群体的多个谱系采用了祖先的进食方式，但失去的牙齿再也没有回来。该项目将确定与鲤形动物牙齿脱落相关的遗传变化，并验证不可逆转的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形，斑马丹尼奥，试图恢复失去的牙齿。该项目预期将增进对发展限制的理解，这与物种是否能够适应人为的环境变化或最终灭绝的实际问题有关。除了为本科生、研究生和研究生提供研究培训外，该项目还将生产改良鱼类品种，以加强科罗拉多大学鱼类生物学和遗传学课程，并在其自然历史博物馆展出。

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.