ABSTRACT

Investigating the level of inbreeding depression is essential to understanding population viability and extinction risk. Albino or chlorophyll-deficient mutants are one of the strongest manifestations of inbreeding depression in plant species, although it is rare to encounter them in a tropical forest. However, during January 2014, we observed a high frequency of albino seedlings in a natural population of Shorea laxa in Lambir Hills National Park in Sarawak, Malaysia. We investigated the fate and compared the cross types of these albino seedlings versus green-leaf seedlings by combining a field survey and genetic analysis using microsatellites. Overall, the albino seedlings survived at least a few months after germination, although they exhibited a 10-fold higher mortality rate than green-leaf seedlings within 19 weeks after germination. Microsatellite analysis confirmed that most albino seedlings (98.3%) were derived from self-pollination. The overall estimated selfing rate was high (61.3%), indicating that reproductive isolation occurred in the mother tree. The observed segregation rate of green:albino types was consistent with the complementation models, indicating that a combination of two dominant genes at two loci are responsible for the green-leaf phenotype in S. laxa. We also found that one albino seedling was derived from outcrossing, suggesting that at least one deleterious gene is maintained in the population. The inbreeding depression of selfed seedlings was exposed as lower initial height of seedlings, which resulted in lower seedling survival. These findings indicate that the population of S. laxa carries recessive deleterious genes and suffers inbreeding depression in selfed offspring.

摘要

调查近亲抑郁程度对于了解种群生存力和灭绝风险至关重要。白化病或叶绿素缺陷型突变体是植物近交衰退的最强表现之一，尽管在热带森林中很少遇到。然而，在2014年1月期间，我们发现在天然浓脂树（Shorela laxa）的自然种群中白化病幼苗的发生频率很高在马来西亚砂拉越的兰比尔山国家公园。我们结合了实地调查和使用微卫星的遗传分析，调查了这些白化病幼苗与绿叶幼苗的命运并比较了它们的杂交类型。总体而言，白化病种子在发芽后至少存活了几个月，尽管它们在发芽后19周内的死亡率比绿叶树苗高10倍。微卫星分析证实，大多数白化病幼苗（98.3％）来自自花授粉。总体估计的自交率很高（61.3％），表明在母树中发生了生殖隔离。观察到的绿色：白化蛋白类型的偏析率与互补模型一致，S.laxa。我们还发现一株白化病幼苗来自异种杂交，这表明种群中至少保留了一种有害基因。自交幼苗的近交凹陷因幼苗的初始高度降低而暴露，这导致幼苗存活率降低。这些发现表明，S.laxa的种群携带隐性有害基因，并且在自交后代中遭受近交衰退。