BACKGROUND AND AIMS Polyploidy is an important contributor to sympatric speciation and assortative mating is a key mechanism driving cytotype interactions at contact zones. While strong reproductive barriers can mediate the coexistence of different cytotypes in sympatry, positive frequency-dependent mating disadvantage ultimately drives the transition to single-ploidy populations. However, comprehensive estimates of reproductive isolation among cytotypes and across multiple barriers are rare. We quantify the strength of isolation across multiple reproductive stages in a tetraploid-octoploid contact zone to understand the potential for coexistence. METHODS Assortative mating due to flowering asynchrony, pollinator behaviour, morphological overlap, self-fertilization and gametic competition between tetraploid and octoploid Gladiolus communis in a contact zone in Western Iberian Peninsula were assessed in natural and experimental populations to quantify reproductive isolation (RI) between cytotypes. KEY RESULTS Tetraploids and octoploids have a high degree of overlap in flowering time, similar floral morphology, and are visited by generalist insects without cytotype foraging preferences, resulting in weak pre-pollination reproductive isolation (RI from 0.00 to 0.21). In contrast, post-pollination isolation resulting from gametic selection was a strong barrier to inter-cytotype mating, with ploidy composition in stigmatic pollen loads determining the levels of RI (RI from 0.54 to 1.00). Between-cytotype cross-incompatibility was relatively high (RI from 0.54 to 0.63) as was isolation acquired through self-pollination (RI of 0.59 in tetraploids and 0.39 in octoploids). CONCLUSIONS Total RI was high for both tetraploids (RI from 0.90 to 1.00) and octoploids (RI from 0.78 to 0.98). Such high rates of assortative mating will enable cytotype coexistence in mixed-ploidy populations by weakening the impacts of minority cytotype exclusion. This study reveals the key role of gametic selection in cytotype siring success and highlights the importance of comprehensive estimates across multiple reproductive barriers to understand cytotype interactions at contact zones.

中文翻译：

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多重生殖屏障的作用：强大的授粉后相互作用控制四倍体-八倍体接触区中的细胞型分离

背景和目的多倍体是同域物种形成的重要贡献者，而分类交配是驱动接触区细胞型相互作用的关键机制。虽然强大的生殖障碍可以调节同域中不同细胞类型的共存，但积极的频率依赖性交配劣势最终会推动向单倍体种群的过渡。然而，对细胞型之间和跨多个障碍的生殖隔离的综合估计很少见。我们量化了四倍体-八倍体接触区跨多个生殖阶段的隔离强度，以了解共存的潜力。方法 由于开花不同步、传粉行为、形态重叠、在自然和实验种群中评估了伊比利亚半岛西部接触区中四倍体和八倍体唐菖蒲之间的自体受精和配子竞争，以量化细胞型之间的生殖隔离 (RI)。主要结果四倍体和八倍体在开花时间上有高度重叠，花的形态相似，并且被没有细胞型觅食偏好的通才昆虫访问，导致授粉前生殖隔离较弱（RI 从 0.00 到 0.21）。相比之下，配子选择导致的授粉后隔离是细胞间交配的强大障碍，柱头花粉负荷中的倍性组成决定了 RI 的水平（RI 从 0.54 到 1.00）。细胞型间的交叉不相容性相对较高（RI 从 0.54 到 0. 63）通过自花授粉获得的分离（四倍体的 RI 为 0.59，八倍体的 RI 为 0.39）。结论 四倍体（RI 从 0.90 到 1.00）和八倍体（RI 从 0.78 到 0.98）的总 RI 都很高。如此高的分类交配率将通过削弱少数细胞型排斥的影响来实现混合倍性种群中的细胞型共存。这项研究揭示了配子选择在细胞型产生成功中的关键作用，并强调了跨多个生殖障碍进行综合估计以了解接触区细胞型相互作用的重要性。如此高的分类交配率将通过削弱少数细胞型排斥的影响来实现混合倍性种群中的细胞型共存。这项研究揭示了配子选择在细胞型产生成功中的关键作用，并强调了跨多个生殖障碍进行综合估计以了解接触区细胞型相互作用的重要性。如此高的分类交配率将通过削弱少数细胞型排斥的影响来实现混合倍性种群中的细胞型共存。这项研究揭示了配子选择在细胞型产生成功中的关键作用，并强调了跨多个生殖障碍进行综合估计以了解接触区细胞型相互作用的重要性。