二倍体与单细胞生物有性生殖的选择优势
Diploidy and the selective advantage for sexual reproduction in unicellular organisms
摘要：
本文建立了描述二倍体单细胞生物无性繁殖和有性繁殖种群进化动力学的数学模型。我们考虑两种形式的基因组组织。在一种情况下，我们假设基因组由两个多基因染色体组成，而在第二种情况下，我们假设每个基因定义一个单独的染色体。如果生物体具有缺少给定基因的功能拷贝的$ l $同源对，则生物体的适合度为$ κ_l $。假设$ κ_l $是单调递减的，因此$ κ_0 = 1 > κ_1 > κ_2 > ... > κ_{\infty} = 0 $。对于几乎所有的繁殖策略，我们认为，我们发现，在大$ N $的限制，在突变选择平衡的平均适合度是$ \max\{2 e^{-μ} - 1, 0\} $，其中$ N $是基因组的单倍体集的基因数，$ ε$是一个给定的DNA模板链的一个给定的基因在复制过程中产生一个突变的女儿的概率，和$ μ= N ε$。唯一的例外是多染色体基因组的有性生殖途径。假设一个乘法的适应度景观，其中$ κ_l = α^{l} $为$ α\in (0, 1) $，这个策略被发现有一个平均适应度，超过了所有其他策略的平均适应度。此外，当其他繁殖策略由于一旦$ μ$超过$ \ln 2 $有害突变的稳定积累而经历生存力的完全丧失时，在有性途径中不发生这样的转变。本文的结果表明，有性生殖的选择性优势，更少，更少的限制性假设比以前的工作。
英文摘要：
This paper develops mathematical models describing the evolutionary dynamics of both asexually and sexually reproducing populations of diploid unicellular organisms. We consider two forms of genome organization. In one case, we assume that the genome consists of two multi-gene chromosomes, while in the second case we assume that each gene defines a separate chromosome. If the organism has $ l $ homologous pairs that lack a functional copy of the given gene, then the fitness of the organism is $ κ_l $. The $ κ_l $ are assumed to be monotonically decreasing, so that $ κ_0 = 1 > κ_1 > κ_2 > ... > κ_{\infty} = 0 $. For nearly all of the reproduction strategies we consider, we find, in the limit of large $ N $, that the mean fitness at mutation-selection balance is $ \max\{2 e^{-μ} - 1, 0\} $, where $ N $ is the number of genes in the haploid set of the genome, $ ε$ is the probability that a given DNA template strand of a given gene produces a mutated daughter during replication, and $ μ= N ε$. The only exception is the sexual reproduction pathway for the multi-chromosomed genome. Assuming a multiplicative fitness landscape where $ κ_l = α^{l} $ for $ α\in (0, 1) $, this strategy is found to have a mean fitness that exceeds the mean fitness of all of the other strategies. Furthermore, while the other reproduction strategies experience a total loss of viability due to the steady accumulation of deleterious mutations once $ μ$ exceeds $ \ln 2 $, no such transition occurs in the sexual pathway. The results of this paper demonstrate a selective advantage for sexual reproduction with fewer and much less restrictive assumptions than previous work.
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