Data from: Lineages of Silene nutans developed rapid, strong, asymmetric postzygotic reproductive isolation in allopatry

Reproductive isolation can rise either as a consequence of genomic divergence in allopatry or as a byproduct of divergent selection in parapatry. To determine whether reproductive isolation in gynodioecious Silene nutans results from allopatric divergence or from ecological adaptation following secondary contact, we investigated the pattern of postzygotic reproductive isolation and hybridization in natural populations using two phylogeographic lineages, western (W1) and eastern (E1). Experimental crosses between the lineages identified strong, asymmetric postzygotic isolation between the W1 and the E1 lineages, independent of geographic overlap. The proportion of ovules fertilized, seeds aborted, and seeds germinated revealed relatively little effect on the fitness of hybrids. In contrast, hybrid mortality was high and asymmetric: while half of the hybrid seedlings with western lineage mothers died, nearly all hybrid seedlings with E1 mothers died. This asymmetric mortality mirrored the proportion of chlorotic seedlings, and is congruent with cytonuclear incompatibility. We found no evidence of hybridization between the lineages in regions of co-occurrence using nuclear and plastid markers. Together, our results are consistent with the hypothesis that strong postzygotic reproductive isolation involving cytonuclear incompatibilities arose in allopatry. We argue that the dynamics of cytonuclear gynodioecy could facilitate the evolution of reproductive isolation.生殖隔离（reproductive isolation）既可作为异域种群基因组分化的产物形成，也可作为邻域种群中歧化选择的副产物产生。为探明雌全异株垂序蝇子草（Silene nutans）的生殖隔离究竟源自异域分化，还是次生接触后的生态适应，本研究选取西部（W1）与东部（E1）两个系统地理支系（phylogeographic lineages），对自然种群中的合子后生殖隔离（postzygotic reproductive isolation）模式与杂交事件展开了调查。通过两支系间的杂交实验，本研究发现W1与E1支系间存在强烈的不对称合子后生殖隔离（asymmetric postzygotic reproductive isolation），且该隔离模式与地理重叠区域无关。对受精胚珠占比、败育种子比例及萌发种子比例的分析显示，其对杂种适合度的影响相对有限。与之形成显著反差的是，杂种死亡率极高且呈现不对称特征：以西部支系为母本的杂种幼苗有半数死亡，而以东部支系为母本的杂种幼苗几乎全部死亡。这种不对称死亡率与失绿幼苗的占比相吻合，且符合质核不相容性（cytonuclear incompatibility）的典型特征。借助核基因标记与质体标记，本研究未在两支系的同域分布区域发现杂交的证据。综上，本研究结果支持“涉及质核不相容性的强合子后生殖隔离起源于异域分化”这一假说。我们提出，质核调控的雌全异株动态过程可推动生殖隔离的演化。