Data from: Is floral divergence sufficient to maintain species boundaries upon secondary contact in Mediterranean food-deceptive orchids?

Analysing the processes that determine whether species boundaries are maintained upon secondary contact may shed light on the early phase of speciation. In Anacamptis morio and A. longicornu, two Mediterranean orchid sister-species, we used molecular and morphological analyses, together with estimates of pollination success and experimental crosses, to assess whether floral isolation can shelter the species' genomes from genetic admixture upon secondary contact. We found substantial genetic and morphological homogenization in sympatric populations in combination with an apparent lack of postmating isolation. We further detected asymmetric introgression in the sympatric populations and an imbalance in cytotype representation, which may be due either to a difference in flowering phenology or else be a consequence of cytonuclear incompatibilities. Estimates of genetic clines for markers across sympatric zones revealed markers that significantly deviated from neutral expectations. We observed a significant correlation between spur length and reproductive success in sympatric populations, which may suggest that directional selection is the main cause of morphological differentiation in this species pair. Our results suggest that allopatric divergence has not led to the evolution of sufficient reproductive isolation to prevent genomic admixture upon secondary contact in this orchid species pair.

解析次生接触下物种边界维持的决定机制，可阐明物种形成的早期阶段机制。针对地中海兰科姊妹种红门兰（Anacamptis morio）与长角红门兰（A. longicornu），本研究结合分子与形态学分析、传粉成功率评估以及人工杂交实验，探究花部隔离能否在次生接触时阻挡物种基因组发生遗传混杂。研究结果显示，同域种群中存在显著的遗传与形态同质化现象，同时表观上缺乏交配后生殖隔离。此外，我们在同域种群中检测到不对称渐渗现象以及细胞型占比失衡，该现象可能源于开花物候差异，或是核质不相容性导致的结果。对同域分布区的标记开展遗传渐变群（genetic clines）评估后发现，部分标记显著偏离中性预期。我们还观察到同域种群的距长与繁殖成功率间存在显著相关性，这表明定向选择是该物种类群形态分化的主要驱动因素。本研究结果表明，异域分化并未演化出足够强的生殖隔离，无法阻止该兰物种类群在次生接触时发生基因组混杂。