Unidad de Genética, Centro de Investigación Forestal, INIA, Carretera de La Coruña km 7.5, Madrid, Spain.
Heredity (Edinb). 2010 May;104(5):482-92. doi: 10.1038/hdy.2009.159. Epub 2009 Nov 18.
How self-incompatibility systems are maintained in plant populations is still a debated issue. Theoretical models predict that self-incompatibility systems break down according to the intensity of inbreeding depression and number of S-alleles. Other studies have explored the function of asexual reproduction in the maintenance of self-incompatibility. However, the population genetics of partially asexual, self-incompatible populations are poorly understood and previous studies have failed to consider all possible effects of asexual reproduction or could only speculate on those effects. In this study, we investigated how partial asexuality may affect genetic diversity at the S-locus and fitness in small self-incompatible populations. A genetic model including an S-locus and a viability locus was developed to perform forward simulations of the evolution of populations of various sizes. Drift combined with partial asexuality produced a decrease in the number of alleles at the S-locus. In addition, an excess of heterozygotes was present in the population, causing an increase in mutation load. This heterozygote excess was enhanced by the self-incompatibility system in small populations. In addition, in highly asexual populations, individuals produced asexually had some fitness advantages over individuals produced sexually, because sexual reproduction produces homozygotes of the deleterious allele, contrary to asexual reproduction. Our results suggest that future research on the function of asexuality for the maintenance of self-incompatibility will need to (1) account for whole-genome fitness (mutation load generated by asexuality, self-incompatibility and drift) and (2) acknowledge that the maintenance of self-incompatibility may not be independent of the maintenance of sex itself.
自交不亲和系统在植物种群中是如何维持的仍然是一个有争议的问题。理论模型预测，自交不亲和系统会根据自交衰退的强度和 S 等位基因的数量而崩溃。其他研究探索了无性繁殖在自交不亲和中的维持功能。然而，部分无性、自交不亲和种群的群体遗传学理解较差，以前的研究未能考虑无性繁殖的所有可能影响，或者只能推测这些影响。在这项研究中，我们研究了部分无性繁殖如何影响小自交种群中 S 位点的遗传多样性和适合度。建立了一个包含 S 位点和生存力位点的遗传模型，用于对各种大小的种群进化进行正向模拟。与部分无性繁殖相结合的漂变导致 S 位点等位基因数量减少。此外，种群中存在过多的杂合子，导致突变负荷增加。在小种群中，这种杂合子过剩被自交不亲和系统增强了。此外，在高度无性繁殖的种群中，无性繁殖产生的个体比有性繁殖产生的个体具有一些适应优势，因为有性繁殖产生的是有害等位基因的纯合子，与无性繁殖相反。我们的研究结果表明，未来对无性繁殖维持自交不亲和的功能的研究需要考虑（1）全基因组适合度（无性繁殖、自交不亲和和漂变产生的突变负荷），（2）承认自交不亲和的维持可能与性本身的维持不独立。
