Department of Biology, McGill University, 1205 Avenue Docteur Penfield, Montreal, QC, H3A 1B1, Canada.
New Phytol. 2019 Nov;224(3):1330-1338. doi: 10.1111/nph.15963. Epub 2019 Jul 1.
The extent to which inbreeding depression can be purged is a major determinant of mating system evolution and is important to conservation and crop improvement. Studies of inbreeding depression purging have not been conducted in self-incompatible plants before. An experimental ('ancestral') treatment was first created from self-incompatible plants of Leavenworthia alabamica. Lines derived from this population were maintained by self-pollination for three generations in the attempt to create a 'purged' population with fewer recessive, deleterious mutations of large effect. Fitness components and the frequency of malformed phenotypes were monitored in progeny derived from selfing and outcrossing in the ancestral and purged treatments. Fitness component means and inbreeding depression were largely unchanged by three generations of forced self-pollination, and there was no reduction in the frequency of plants exhibiting malformed phenotypes. Our findings indicate that inbreeding depression in this species is largely a result of mutations of mild effect, consistent with the observation that self-incompatibility is maintained in most populations of L. alabamica, despite the presence of genetic variants with weaker self-incompatibility. Moreover, although population theory suggests that deleterious mutations of large effect should be sheltered from selection in the region of self-incompatibility locus, our results do not support this prediction.
近亲衰退的程度是交配系统进化的主要决定因素，对保护和作物改良都很重要。以前从未在自交不亲和植物中进行过近亲衰退净化的研究。首先从 Leavenworthia alabamica 的自交不亲和植物中创建了一个实验（“祖先”）处理。从该种群中衍生的系通过自交连续三代进行维持，试图创建一个具有较少隐性、有害大效应突变的“净化”种群。在祖先和净化处理的自交和异交后代中，监测了适合度成分和畸形表型的频率。经过三代强制自交，适合度成分平均值和近亲衰退基本没有变化，也没有减少表现出畸形表型的植物的频率。我们的研究结果表明，该物种的近亲衰退主要是由轻度效应的突变引起的，这与自交不亲和性在 L. alabamica 的大多数种群中得到维持的观察结果一致，尽管存在自不亲和性较弱的遗传变异。此外，尽管种群理论表明，大效应的有害突变应该在自不亲和基因座区域受到选择的庇护，但我们的结果并不支持这一预测。
