Shifts in flowering time have the potential to act as strong prezygotic reproductive barriers in plants. We investigate the role of flowering time divergence in two species of mountain rose (Metrosideros) endemic to Lord Howe Island, Australia, a minute and isolated island in the Tasman Sea. Metrosideros nervulosa and M. sclerocarpa are sister species and have divergent ecological niches on the island but grow sympatrically for much of their range, and likely speciated in situ on the island. We used flowering time and population genomic analyses of population structure and selection, to investigate their evolution, with a particular focus on the role of flowering time in their speciation. Population structure analyses showed the species are highly differentiated and appear to be in the very late stages of speciation. We found flowering times of the species to be significantly displaced, with M. sclerocarpa flowering 53 days later than M. nervulosa. Furthermore, the analyses of selection showed that flowering time genes are under selection between the species. Thus, prezygotic reproductive isolation is mediated by flowering time shifts in the species, and likely evolved under selection, to drive the completion of speciation within a small geographical area.

This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

开花时间的变化有可能在植物中成为强大的合子前生殖障碍。我们调查了澳大利亚豪勋爵岛（位于塔斯曼海的一个孤岛）特有的两种山玫瑰（Metrosideros）开花时间差异的作用。Metrosideros nervulosa和M. sclerocarpa是姐妹物种，在岛上有不同的生态位，但在它们的大部分范围内同域生长，并且很可能是原位物种在岛上。我们使用开花时间和种群结构和选择的种群基因组分析来研究它们的进化，特别关注开花时间在它们的物种形成中的作用。种群结构分析表明，该物种高度分化，似乎处于物种形成的晚期阶段。我们发现该物种的开花时间发生了显着变化，M. sclerocarpa开花比M. nervulosa晚 53 天。此外，选择分析表明开花时间基因在物种之间处于选择状态。因此，合子前生殖隔离是由物种开花时间的变化介导的，并且可能是在选择下进化的，以推动小地理区域内物种形成的完成。

这篇文章是主题问题“走向物种形成的完成：超越第一道障碍的生殖隔离的进化”的一部分。