虎榛子属响应第四纪气候变化的分布迁移和新物种形成

It is well acknowledged that climatic oscillations of the Quaternary had caused the distribution changes of most plant species in China. However, it remains unclear whether such distribution changes of the closely related species might have leaded to the interspecific introgression and production of the new hybrid species. Ostryopsis comprises three species, O. davidiana in northern China, and O. nobilis and O. intermedia in eastern Qinghai-Tibetan Plateau. The available data hypothesized that O. intermedia originated from the interspecific hybridizations of the other two species when O. davidiana migrated southward and overlapped with O. nobilis. In this project, we aim to test these hypotheses by combining genomic data and niche modelling results. We will examine the statistic modelling of hybrid speciation versus other two possible speciation hypotheses and speciation time based on the available genomic data. We will use individual genome and population genomic data to infer changes of the effective population sizes and the corresponding distribution changes in response to the past climate changes. We will check whether distribution changes inferred from genetic data are consistent with those from niche modelling whether O. davidiana had migrated southward and contacted with O. nobilis during the Quaternary glaciation stages. All these results will deepen our understanding of the biodiversity changes and protections under the global climate changes in the future.

第四纪气候变化导致我国植物物种分布变迁，已成为共识；但近缘物种是否由于分布变迁导致杂交、进而产生新物种的可能性还未得到验证。虎榛子属仅3种：滇虎榛子和居中虎榛子分布在青藏高原东部，而虎榛子分布在中国北方。已有的研究提出假设：青藏高原东部分布的居中虎榛子可能是由于第四纪冰期时，虎榛子南迁与滇虎榛子杂交产生的新物种。本项目拟利用个体和群体基因组数据，采用多种方法验证杂交物种形成假设或其它物种形成模型的可能性，同时检测每个物种有效群体大小变化所反映的响应气候变化导致的分布变迁和物种形成时间；然后，基于现有物种地理分布数据，利用生态位模型模拟检验第四纪冰期温度下降情况下虎榛子南迁与滇虎榛子接触和杂交的可能性。通过上述研究，验证和阐明虎榛子属响应气候变化的物种分布变化和新物种形成历史。研究结果对于深入理解气候变化背景下物种多样性的变化和保护这些重要生态资源具有重要意义。

第四纪气候变冷导致北半球物种分布向低海拔、低纬度和向南迁移，同时导致地理隔离的近缘物种再次接触，发生杂交。本项目以中国特有属桦木科的虎榛子属为材料体系，采用群体基因组学方法研究气候变化导致的物种分布变迁和杂交物种形成。完成了三个物种的全基因重测序工作；根据群体基因组研究结果，发现第四纪温度变冷过程时，中国北方分布的虎榛子物种南迁，与分布于中国西南部的滇虎榛子物种杂交，形成二倍体杂交物种；该杂交物种结合了以前两个物种不同的生殖隔离等位基因组合，为该杂交物种的起源，特别与两个亲本物种的生殖隔离提供了遗传基础。本研究证实，气候变化不仅导致已有物种的灭迹，也更可能导致新物种的起源；对于理解气候变化背景下的物种多样性变化提供了新的研究案列。