Department of Forest and Conservation Sciences, University of British Columbia, 3041-2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
Department of Botany, University of British Columbia, 3200-6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada.
BMC Genomics. 2017 Dec 15;18(1):970. doi: 10.1186/s12864-017-4344-8.
Mutation load is expected to be reduced in hybrids via complementation of deleterious alleles. While local adaptation of hybrids confounds phenotypic tests for reduced mutation load, it may be possible to assess variation in load by analyzing the distribution of putatively deleterious alleles. Here, we use this approach in the interior spruce (Picea glauca x P. engelmannii) hybrid complex, a group likely to suffer from high mutation load and in which hybrids exhibit local adaptation to intermediate conditions. We used PROVEAN to bioinformatically predict whether non-synonymous alleles are deleterious, based on conservation of the position and abnormality of the amino acid change.
As expected, we found that predicted deleterious alleles were at lower average allele frequencies than alleles not predicted to be deleterious. We were unable to detect a phenotypic effect on juvenile growth rate of the many rare alleles predicted to be deleterious. Both the proportion of alleles predicted to be deleterious and the proportion of loci homozygous for predicted deleterious alleles were higher in P. engelmannii (Engelmann spruce) than in P. glauca (white spruce), due to higher diversity and frequencies of rare alleles in Engelmann. Relative to parental species, the proportion of alleles predicted to be deleterious was intermediate in hybrids, and the proportion of loci homozygous for predicted deleterious alleles was lowest.
Given that most deleterious alleles are recessive, this suggests that mutation load is reduced in hybrids due to complementation of deleterious alleles. This effect may enhance the fitness of hybrids.
通过有害等位基因的互补，杂种中的突变负荷预计会降低。虽然杂种的局部适应会干扰对降低突变负荷的表型测试，但通过分析推定有害等位基因的分布，评估负荷的变化可能是可行的。在这里，我们在内部云杉（Picea glauca x P. engelmannii）杂种复合体中使用这种方法，该复合体可能受到高突变负荷的影响，并且杂种表现出对中间条件的局部适应。我们使用 PROVEAN 根据位置和氨基酸变化的异常性来预测非同义等位基因是否有害，从而进行生物信息学预测。
正如预期的那样，我们发现预测的有害等位基因的平均等位基因频率低于未预测为有害的等位基因。我们无法检测到许多预测为有害的稀有等位基因对幼树生长率的表型效应。由于 Engelmann 中的稀有等位基因多样性和频率更高，因此预测为有害的等位基因比例以及预测为有害的等位基因纯合的基因座比例均高于 P. glauca（白云杉）。与亲本物种相比，杂种中预测为有害的等位基因比例居中，预测为有害的等位基因纯合的基因座比例最低。
鉴于大多数有害等位基因是隐性的，这表明杂种中的突变负荷由于有害等位基因的互补而降低。这种效应可能会增强杂种的适应性。
