Howard R S
Biology Department, Indiana University, Bloomington 47406.
Theor Popul Biol. 1994 Jun;45(3):313-23. doi: 10.1006/tpbi.1994.1015.
The mutational deterministic hypothesis postulates an advantage to sexual over asexual reproduction when mutation rates are on the order of 1.0 per genome per generation, provided that selection takes the form of a synergistic epistasis. While the efficacy of this mechanism has been investigated for infinite populations, its ability to protect sex in finite populations exhibiting stochastic dynamics remains untested. Stochastic processes have the potential to undermine protection for sex in two ways: (1) asexual lineages derived from sexual ancestors may, by chance, be founded by individuals bearing fewer than the equilibrium mean number of mutations, and (2) once established, such lineages will undergo random perturbations in the rates at which they grow and accumulate mutations. In the present study, I show using computer simulation that sexual populations of as many as 10,000 individuals are susceptible to invasion by asexual lineages for mutation rates higher than predicted under the mutational deterministic hypothesis. My simulations differ from previous investigations in that they model the progress of asexual lineages into sexual populations as both stochastic and deterministic processes for various mutation rates, selection regimes, and population sizes. It is suggested that ecological factors, such as parasitism or release from competition, could interact with selection against deleterious mutations to protect sex. To provide the sole explanation for sex, however, may require that selection against deleterious mutations be accompanied by mutation rates on the order of 2.0 per genome per generation.
突变确定性假说假定，当突变率约为每代每个基因组1.0时，有性生殖相对于无性生殖具有优势，前提是选择采取协同上位性的形式。虽然已经针对无限种群研究了这种机制的效力，但其在表现出随机动态的有限种群中保护性别的能力仍未得到检验。随机过程有可能以两种方式破坏对性别的保护：（1）源自性祖先的无性谱系可能偶然由携带少于平衡平均突变数的个体建立，（2）一旦建立，这些谱系在其生长和积累突变的速率方面将经历随机扰动。在本研究中，我通过计算机模拟表明，对于高于突变确定性假说预测的突变率，多达10000个个体的有性种群易受无性谱系的入侵。我的模拟与先前的研究不同，因为它们将无性谱系进入有性种群的过程建模为各种突变率、选择模式和种群大小下的随机和确定性过程。有人认为，诸如寄生或竞争释放等生态因素可能与针对有害突变的选择相互作用以保护性。然而，要为性别提供唯一的解释，可能需要针对有害突变的选择伴随着每代每个基因组约2.0的突变率。
