Data from: Ancient vicariance and climate-driven extinction explain continental-wide disjunctions in Africa: the case of the Rand Flora genus Canarina (Campanulaceae)

Transoceanic distributions have attracted the interest of scientists for centuries. Less attention has been paid to the evolutionary origins of ‘continent-wide’ disjunctions, in which related taxa are distributed across isolated regions within the same continent. A prime example is the ‘Rand Flora’ pattern, which shows sister taxa disjunctly distributed in the continental margins of Africa. Here, we explore the evolutionary origins of this pattern using the genus Canarina, with three species: C. canariensis, associated with the Canarian laurisilva, and C. eminii and C. abyssinica, endemic to the Afromontane region in East Africa, as case study. We infer phylogenetic relationships, divergence times and the history of migration events within Canarina using Bayesian inference on a large sample of chloroplast and nuclear sequences. Ecological niche modelling was employed to infer the climatic niche of Canarina through time. Dating was performed with a novel nested approach to solve the problem of using deep time calibration points within a molecular dataset comprising both above-species and population-level sampling. Results show C. abyssinica as sister to a clade formed by disjunct C. eminii and C. canariensis. Miocene divergences were inferred among species, whereas infraspecific divergences fell within the Pleistocene–Holocene periods. Although C. eminii and C. canariensis showed a strong genetic geographic structure, among-population divergences were older in the former than in the latter. Our results suggest that Canarina originated in East Africa and later migrated across North Africa, with vicariance and aridification-driven extinction explaining the 7000 km/7 million year divergence between the Canarian and East African endemics.

跨洋分布格局数百年来一直备受科学家关注，而同一大陆内相关类群间断分布于孤立区域的‘大陆尺度间断分布’模式的演化起源，却较少得到学界重视。典型案例当属‘兰德植物区系’分布模式：其姊妹类群间断分布于非洲大陆沿岸区域。本研究以卡纳利亚属（Canarina）为研究对象，选取其3个物种作为案例——伴生有加那利群岛月桂林的卡纳利亚风铃草（C. canariensis），以及东非非洲山地植物区系特有种埃明卡纳利亚（C. eminii）与阿比西尼卡纳利亚（C. abyssinica），以此探究该分布模式的演化起源。本研究通过对大量叶绿体（chloroplast）与核（nuclear）序列数据开展贝叶斯推断（Bayesian inference），解析卡纳利亚属内的系统发育关系、分化时间以及迁移事件历史；同时采用生态位模型（Ecological niche modelling），推演该属随时间变化的气候生态位。针对分子数据集同时包含种上与种群水平采样时难以使用深时间校准点（deep time calibration points）的问题，本研究采用一种全新的嵌套式分析方法开展分化时间估算。结果显示，阿比西尼卡纳利亚（C. abyssinica）为间断分布的埃明卡纳利亚（C. eminii）与卡纳利亚风铃草（C. canariensis）所形成演化支的姊妹群。物种水平的分化事件发生于中新世（Miocene），而种内分化则集中于更新世（Pleistocene）至全新世（Holocene）时段。尽管埃明卡纳利亚与卡纳利亚风铃草均呈现显著的遗传地理结构，但前者的种群间分化时间早于后者。本研究结果表明，卡纳利亚属起源于东非，随后经北非扩散；加那利群岛与东非特有类群间7000公里的地理间隔与700万年的分化时间，可通过隔离分化（vicariance）事件与干旱化（aridification）驱动的灭绝事件得到合理解释。