Biogeography and diversification patterns in the Irano-Turanian biodiversity hotspot inferred from a molecular phylogeny of the subendemic <em>Iris</em> subgenus <em>Scorpiris</em> (Iridaceae)

The Irano-Turanian Floristic Region harbors a rich flora, but our understanding of the development of this diversity is limited by a lack of data on phylogenetic relationships and biogeographic patterns of endemic and more widespread plants. Hypotheses of in situ diversification versus allopatric diversification were tested using Iris subgen. Scorpiris, a species-rich group that is widely distributed in this region. Phylogenetic relationships of the subgenus were inferred using a comprehensive sampling strategy that incorporated newly collected accessions that represent previously under-sampled clades and underrepresented geographical regions. Included was I. drepanophylla, the type species for a major clade that had not been included in previous Iris studies. Six markers were used, thus increasing plastid region sampling compared to previous studies. The historical biogeography of resolved clades was explored to determine patterns of origin, dispersal, vicariance, and divergence, while the RelTime method was used to estimate times of divergence. This study confirmed major clades previously identified in the subgenus, suggested monophyly or non-monophyly of several species, and revealed unrecognized diversity in two species. Ages of major clades date from the Miocene to the Pliocene, while diversification continued into the Pleistocene. Our biogeographic inferences indicate that the subgenus and most major clades of I. subgen. Scorpiris originated and diversified in the Pamir-Alay, with subsequent diversification after expansion into the Tian Shan and Irano-Anatolian regions. Species from one clade dispersed to the Mediterranean and Caucasian regions from the Irano-Turanian region with relatively little diversification. We conclude, diversification of I. subgen. Scorpiris mainly followed the model of dispersal, then allopatric diversification,n mostly through founder events and/or ecological speciation facilitated by general aridification across Eurasia and mountain uplifts that created rain shadows. We hypothesize that their multi-scaled bulbs facilitated adaptation to seasonally dry conditions that developed with climatic and geological changes.伊朗-图兰植物区（Irano-Turanian Floristic Region）拥有极为丰富的植物区系，但我们对该区域物种多样性演化过程的认知仍受限于特有植物与广布植物的系统发育关系及生物地理格局数据的匮乏。本研究以鸢尾属蝎尾鸢尾亚属（Iris subgen. Scorpiris）为研究类群，该类群物种丰富且广泛分布于该植物区，以此检验就地分化与异域分化两种演化假说。 研究采用全面取样策略，纳入了此前取样不足的支系与代表性不足的地理区域的新采集种质材料，其中包含镰叶鸢尾（I. drepanophylla）——此前鸢尾属研究未涉及的某主要支系的模式种。本研究使用6个分子标记，相较于既往研究扩大了质体区域的测序覆盖范围。 本研究通过解析支系的历史生物地理学特征，以探究其起源、扩散、地理分异与分化模式，并采用相对时间法（RelTime）估算分化时间。研究证实了该亚属既往已识别的主要支系，明确了数个物种类群的单系性与非单系性，并在两个物种中发现了未被识别的物种多样性。主要支系的分化时间可追溯至中新世至上新世，而物种多样化过程持续至更新世。 生物地理推演结果显示，蝎尾鸢尾亚属及其多数主要支系起源并分化于帕米尔-阿赖区域，随后扩散至天山及伊朗-安纳托利亚区域并进一步分化。某单一支系的物种从伊朗-图兰植物区扩散至地中海与高加索区域，且类群分化程度相对较低。 综上，蝎尾鸢尾亚属的物种多样化主要遵循“先扩散、后异域分化”的模式，该过程多由奠基者事件及/或欧亚大陆普遍干旱化与山地隆升形成雨影效应所驱动的生态物种形成所促成。我们推测，该类群具多鳞片的鳞茎助力其适应了随气候与地质变化出现的季节性干旱环境。