Johnston Mark O, Schoen Daniel J
Department of Biology, McGill University, 1205 Docteur Penfield Avenue, Montreal, Quebec, H3A 1B1, Canada.
Evolution. 1996 Aug;50(4):1478-1491. doi: 10.1111/j.1558-5646.1996.tb03921.x.
The relation between inbreeding depression and rate of self-fertilization was studied in nine natural populations of the annual genus Amsinckia. The study included two clades (phylogenetic lineages) in which small-flowered, homostylous populations or species are believed to have evolved from large-flowered, heterostylous, self-compatible ones. In one lineage the small-flowered species is tetraploid with disomic inheritance. Rates of self-fertilization were 25% to 55% in the four large-flowered, heterostylous populations; 72% in a large-flowered but homostylous population; and greater than 99.5% in the four small-flowered, homostylous populations, which produce seed autonomously. When present, inbreeding depression occurred in the fertility but not the survival components of fitness. Using a cumulative fitness measure incorporating both survival and fertility (flower number), we found inbreeding depression to be lower in the four very highly self-fertilizing populations than in the five intermediate ones. The Spearman rank correlation between inbreeding depression and selfing rate for the nine populations was -0.50, but was not statistically significant (P = 0.12). Inbreeding depression was greater in the two tetraploid populations than in the very highly self-fertilizing, diploid ones. Phenotypic stability of progeny from self-fertilization tended to be higher in populations with lower inbreeding depression. We conclude that levels of self-fertilization and inbreeding depression in Amsinckia are determined more by other factors than by each other. Estimates of mutation rates and dominance coefficients of deleterious alleles, obtained from a companion study of the four highly self-fertilizing populations, suggest that a strong relationship may not be expected. We discuss the relationship of the present results to current theory of the coevolution of self-fertilization and inbreeding depression.
在一年生的琴颈草属的九个自然种群中，研究了近亲繁殖衰退与自花受精率之间的关系。该研究涵盖了两个进化枝（系统发育谱系），据信小花、同型花柱的种群或物种是从大花、异型花柱、自交亲和的种群或物种进化而来的。在一个进化枝中，小花物种是具有二体遗传的四倍体。四个大花、异型花柱种群的自花受精率为25%至55%；一个大花但同型花柱的种群为72%；四个小花、同型花柱且能自主产生种子的种群则大于99.5%。近亲繁殖衰退在存在时，出现在适合度的繁殖力而非存活部分。使用结合了存活和繁殖力（花的数量）的累积适合度指标，我们发现四个自花受精率极高的种群中的近亲繁殖衰退低于五个中等自花受精率的种群。九个种群的近亲繁殖衰退与自交率之间的斯皮尔曼等级相关性为-0.50，但无统计学显著性（P = 0.12）。两个四倍体种群中的近亲繁殖衰退比自花受精率极高的二倍体种群更大。自花受精后代的表型稳定性在近亲繁殖衰退较低的种群中往往更高。我们得出结论，琴颈草属中的自花受精水平和近亲繁殖衰退更多地由其他因素而非彼此决定。从对四个自花受精率极高的种群的一项配套研究中获得的有害等位基因的突变率和显性系数估计值表明，可能不存在很强的相关性。我们讨论了当前结果与自花受精和近亲繁殖衰退协同进化的现有理论之间的关系。
