Schneider Derek J, Levin Rachel A, Miller Jill S
Department of Biology, Amherst College, Amherst, Massachusetts, 01002, USA.
Am J Bot. 2023 Feb;110(2):e16133. doi: 10.1002/ajb2.16133. Epub 2023 Feb 16.
Whole-genome duplication is considered a major mechanism of sympatric speciation due to the creation of strong and instantaneous reproductive barriers. Although postzygotic reproductive isolation between diploids and polyploids is often expected, the extent of reproductive incompatibility must be empirically determined and compared to patterns of genetic isolation to fully characterize the reproductive dynamics between cytotypes.
We investigated reproductive compatibility between diploid and tetraploid Lycium australe in two mixed-cytotype populations using (1) controlled crossing experiments to evaluate fruit and seed production and (2) germination trials to test seed viability following homoploid and heteroploid crosses. We contrast these experiments with a single-nucleotide polymorphism (SNP) data set to measure genetic isolation between cytotypes and explore whether cytotype or population origin better explains patterns of genetic variation. Finally, we explore mating patterns using the observed germination rates of naturally produced seeds in each population.
Although homoploid and heteroploid crosses resulted in similar fruit and seed production, reproductive isolation between co-occurring diploids and tetraploids was nearly complete, due to low seed viability following heteroploid crosses. Of 191,182 total SNPs, 21,679 were present in ≥90% of individuals and replicate runs using unlinked SNPs revealed strong clustering by cytotype and differentiation of tetraploids based on population origin.
As often reported, diploid and tetraploid L. australe experience strong postzygotic isolation via hybrid seed inviability. Consistent with this result, cytotype explained a greater amount of variation in the SNP data set than population origin, despite some evidence of historical introgression.
全基因组复制被认为是同域物种形成的一种主要机制，因为它会产生强大且即时的生殖隔离。虽然通常认为二倍体和多倍体之间存在合子后生殖隔离，但生殖不相容的程度必须通过实证来确定，并与基因隔离模式进行比较，以全面描述不同细胞型之间的生殖动态。
我们在两个混合细胞型种群中研究了二倍体和四倍体南方枸杞之间的生殖相容性，采用了（1）控制杂交实验来评估果实和种子产量，以及（2）发芽试验来测试同倍体和异倍体杂交后种子的活力。我们将这些实验与一个单核苷酸多态性（SNP）数据集进行对比，以测量不同细胞型之间的基因隔离，并探讨细胞型或种群来源能否更好地解释基因变异模式。最后，我们利用每个种群中自然产生种子的观察发芽率来探究交配模式。
虽然同倍体和异倍体杂交产生的果实和种子产量相似，但由于异倍体杂交后种子活力较低，共存的二倍体和四倍体之间的生殖隔离几乎是完全的。在总共191,182个SNP中，21,679个在≥90%的个体中存在，使用不连锁SNP的重复分析显示，基于细胞型有强烈的聚类，并且四倍体基于种群来源存在分化。
正如经常报道的那样，二倍体和四倍体南方枸杞通过杂种种子无活力经历了强烈的合子后隔离。与这一结果一致的是，尽管有一些历史渐渗的证据，但细胞型在SNP数据集中解释的变异量比种群来源更多。
