Chao L, Tran T T, Tran T T
Department of Zoology, University of Maryland, College Park 20742, USA.
Genetics. 1997 Nov;147(3):953-9. doi: 10.1093/genetics/147.3.953.
When laboratory populations of the RNA bacteriophage phi6 are subjected to intensified genetic drift, they experience a decline in fitness. These experiments demonstrate that the average effect of mutations is deleterious, and they are used to suggest that Muller's ratchet can operate in these viruses. However, the operation of Muller's ratchet does not alone guarantee an advantage of sex. When phi6 populations were subjected to a series of bottlenecks of one individual and then crossed, the measured advantage of sex was not significant. To determine whether a small sample size, as opposed to allelism or another explanation, can account for the negative result, we repeated the phi6 experiments by crossing a larger set of populations. We found that bottlenecked populations of phi6 could recover fitness through mutations. However, hybrids produced by crossing the populations recovered an additional amount over the contribution of mutations. This additional amount, which represents an advantage of sex to phi6, was determined to be significantly greater than zero. These results provide indirect support for an advantage of sex through Muller's ratchet. However, we also use our experimental design and results to propose an alternative to Muller's ratchet as a model for the evolution of sex.
当RNA噬菌体phi6的实验室群体经历强化的遗传漂变时，它们的适应性会下降。这些实验表明，突变的平均效应是有害的，并且这些实验被用来表明穆勒棘轮可以在这些病毒中起作用。然而，穆勒棘轮的运作本身并不能保证有性生殖具有优势。当phi6群体经历一系列单一个体的瓶颈效应然后进行杂交时，所测得的有性生殖优势并不显著。为了确定是小样本量而非等位基因或其他解释能够说明这个负面结果，我们通过让更多群体杂交重复了phi6实验。我们发现，经历瓶颈效应的phi6群体能够通过突变恢复适应性。然而，群体杂交产生的杂种在突变贡献之外还额外恢复了一定的适应性。这一额外的量代表了有性生殖对phi6的优势，经测定显著大于零。这些结果为通过穆勒棘轮体现的有性生殖优势提供了间接支持。然而，我们也利用我们的实验设计和结果提出了一个替代穆勒棘轮的模型，作为有性生殖进化的模型。
