Collaborative Research: A Molecular Investigation of Trade-Offs and Evolutionary Stability in a Simple Competitive Ecosystem

9629695 Dean两个相互竞争的物种，每一个都是单一替代资源的赢家，当两种资源都可用时，可能共存。这两个物种是否会出现同域分化，各自专注于自己喜欢的资源，还是一个物种会进化取代另一个物种？由于突变是一个随机过程，许多人认为种群的适应性分化是不可复制的：如果生命的磁带重新播放，进化的结果将会截然不同。Drs。Dean和Dykhuizen建议通过克隆细菌复制群体的实验来区分这些假设。由于这些菌株在遗传上几乎是相同的，同域物种形成的生态问题与通过权衡而特殊化进化的遗传问题是一致的。第1部分将建立两株大肠杆菌，它们携带两种不同的乳糖操纵子，并竞争两种可选的半乳糖苷。这项研究将检验从生物化学知识（一种自下而上的方法）得出的预测，即两种菌株只有在两种可选半乳糖苷的一定比例范围内才能共存。第2部分研究共存的进化动态。长期的化学调节实验（自上而下的方法）将允许适应性突变在每个品系中积累。这些实验旨在解决：1)在分子水平上的权衡是否会导致特定资源的专业化；2)增加专业化（或增加泛化）是否会扰乱初始平衡频率或导致竞争排斥（即只有一种菌株获胜）。

9629695 Dean Two competing species, each a winner on a single substitutable resource, may coexist when both resources are available. Will there be a sympatric divergence of the two species, each specializing on its preferred resource, or will one evolve to replace the other? Because mutation is a stochastic process, many believe that the adaptive divergence of populations is irreproducible: if the tape of life is rerun, the evolutionary outcome will be dramatically different. Drs. Dean and Dykhuizen propose to distinguish these hypotheses experimentally using replicated populations of clonal bacteria. Because the strains are almost genetically identical, the ecological question of sympatric speciation becomes congruent with the genetic question of the evolution of specialization through trade-offs. Part 1 will establish two strains of E. coli harboring two different lactose operons and competing for two alternative galactosides. This study will test the prediction, made from a knowledge of biochemistry (a bottom up approach), that the two strains will coexist only within a certain range of ratios of the two alternative galactosides. Part 2 investigates the evolutionary dynamics of coexistence. Long-term chemostat experiments (a top-down approach) will allow adaptive mutations to accumulate in each strain. These experiments are designed to address: 1) whether trade-offs at the molecular level force specialization on particular resources; and, 2) whether increasing specialization (or increasing generalization) perturbs the initial equilibrium frequencies or leads to competitive exclusion (i.e. only one strain wins).