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

9616190当两种资源都可用时，两个相互竞争的物种可以共存，每个物种都是单一可替代资源的赢家。这两个物种是否会出现共域分化，各自专注于自己喜欢的资源，还是会有一个物种进化来取代另一个物种？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，进化结果将截然不同。Dean博士和Dykhuizen博士建议通过实验使用克隆细菌的复制种群来区分这些假说。由于菌株在遗传上几乎完全相同，同域物种形成的生态学问题与通过权衡而进行的专业化进化的遗传学问题变得一致。第一部分将建立两个含有两个不同乳糖操纵子的大肠杆菌菌株，并竞争两个替代的半乳糖苷。这项研究将检验根据生物化学知识(自下而上的方法)做出的预测，即这两种菌株将仅在两种替代半乳糖苷的特定比例范围内共存。第二部分考察了共存的进化动力学。长期的恒化实验(自上而下的方法)将允许适应性突变在每个菌株中积累。这些实验旨在解决：1)分子水平上的权衡是否会迫使特定资源的专门化；以及2)日益专门化(或日益通用化)是否会扰乱初始平衡频率或导致竞争性排斥(即只有一个菌株获胜)。

9616190 Dykhuizen 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).