Bohannan Brendan J M, Travisano Michael, Lenski Richard E
Department of Biological Sciences, Stanford University, Stanford, California, 94305.
Department of Biology and Biochemistry, University of Houston, Houston, Texas, 77204.
Evolution. 1999 Feb;53(1):292-295. doi: 10.1111/j.1558-5646.1999.tb05355.x.
It is widely assumed that resistance to consumers (e.g., predators or pathogens) comes at a "cost," that is, when the consumer is absent the resistant organisms are less fit than their susceptible counterparts. It is unclear what factors determine this cost. We demonstrate that epistasis between genes that confer resistance to two different consumers can alter the cost of resistance. We used as a model system the bacterium Escherichia coli and two different viruses (bacteriophages), T4 and Λ, that prey upon E. coli. Epistasis tended to reduce the costs of multiple resistance in this system. However, the extent of cost savings and its statistical significance depended on the environment in which fitness was measured, whether the null hypothesis for gene interaction was additive or multiplicative, and subtle differences among mutations that conferred the same resistance phenotype.
人们普遍认为，对消费者（如捕食者或病原体）的抗性是有“代价”的，也就是说，当没有消费者时，具有抗性的生物体比其易感同类适应性更差。目前尚不清楚哪些因素决定了这种代价。我们证明，赋予对两种不同消费者抗性的基因之间的上位性可以改变抗性的代价。我们使用大肠杆菌和两种以大肠杆菌为食的不同病毒（噬菌体）T4和Λ作为模型系统。在这个系统中，上位性倾向于降低多重抗性的代价。然而，成本节省的程度及其统计学意义取决于测量适应性的环境、基因相互作用的零假设是加性还是乘性，以及赋予相同抗性表型的突变之间的细微差异。
