青藏高原特有植物露蕊乌头从冰期避难所扩张后传粉系统的进化转变

Wind pollination and autonomous selfing can provide reproductive assurance for plant species in new environments under the selective pressure of pollinator scarcity. In recent yrears, evolution of selfing and its role in assuring reproduction during range expansion of populations have been paid more attention, but little attention has been paid to the evolution of wind pollination and its effects on reproduction of plant species during range expansion. Some up-to-date research findings revealed there were different evolutionary histories of alpine plants on the Qinghai-Tibet Plateau (QTP), which provided a perfect opportunity to study the evolutionary transition of pollination systems in alpine plants during their range expansions. Aconitum gymnandrum, an alpine herb endemic to the Qinghai-Tibet Plateau, could produce seeds via bumblebee pollination and wind pollination. Furthermore, there were multiple glacial refugia on the QTP during the last glacial maximum, but range expansion occurred in only one refugium after the last glacial refugium. Therefore, A. gymnandrum could be a good proxy to study the evolutionary transition between wind pollination and insect pollination during population colonization. In this proposal, we are planning to carry out comparisons on floral traits, nectar secretion, pollinator visitation rates and their pollination efficiency, airborne pollen grains and their contribution on seed production, inbreeding depression and the selfing rate of seeds from wind pollination between populations from the glacial refugium and marginal populations after range expansion. Our results will provide evidences of evolutionary transition between wind and insect pollination and its role in range expansion, and elucidate the evolution of wind pollination and its effects on sexual reproduction of this plant species. Our research will be a good example for studying the evolutionary transitions of pollination system and mating system after range expansion from the glacial refugia in plant species on the QTP.

在缺乏传粉者的环境中，风媒传粉与自交均能为植物提供繁殖保障。植物入侵到新生境后，自交的进化与适应意义得到了较多的关注，但长期以来，风媒传粉在植物种群扩张中的作用和角色没有得到足够的重视；青藏高原植物在冰期过后气候变暖时经历了不同的进化历史，这些结果为研究植物种群扩张过程中的传粉系统进化转变提供了一个非常好的机会。本项目在前期研究的基础上，以青藏高原特有且兼具风媒与虫媒传粉特征的露蕊乌头为研究对象，通过比较冰期避难所种群和扩张后分布区边缘种群的花特征、花蜜特征、传粉昆虫的访问频率和传粉效率、空气中的花粉流、风媒传粉对结实的贡献、近交衰退和自交率差异，探讨露蕊乌头风媒和虫媒传粉的进化转变及其在种群扩张过程中的适应意义，阐明风媒传粉的进化在露蕊乌头繁殖过程中的角色和作用。本项目的研究结果将为青藏高原植物在冰期后种群扩张过程中的传粉系统和交配系统进化研究提供一个范例。

青藏高原植物在冰期-间冰期时一般会发生分布区的退缩或者扩张，比如露蕊乌头避难所种群在间冰期时就发生了扩张。植物种群在扩张后的势必会在新种群中面临与避难所种群不同的选择压力，比如缺少有效的传粉者，从而表现出不同的进化反应。自交和风媒传粉都可以为缺少传粉者的新种群提供繁殖保障。然而风媒传粉在植物种群扩张中的作用一直没有很好地阐明，因此通过比较青藏高原植物在冰期避难所和扩张后的分布区边缘种群的花特征以及传粉系统差异，可以很好的解决植物如何转变其传粉系统来适应分布区扩张后的传粉环境变化。本项目在前期的研究基础上，以青藏高原植物露蕊乌头为对象，通过详细比较避难所种群和扩张后的分布区边缘种群的花特征、传粉系统、昆虫访问以及花粉流，探讨露蕊乌头风媒传粉和虫媒传粉的进化转变及适应意义。结果发现，露蕊乌头从冰期避难所种群扩张后的种群的大部分花特征都更有利于风媒传粉，比如更大的花密度、更小的花瓣以及更多的柱头等。同时在边缘种群的昆虫访花频率显著低于避难所种群，且有更显著的年际间变化和不可预测性。风媒传粉的效率虽然低于昆虫传粉，但是发生于所有种群。同时发现两种类型的花粉（圆形和梭形）虽然都能通过虫媒和风媒传播，但是梭形花粉主要通过风媒传播，而圆形花粉主要通过昆虫传播，尤其是在扩张后的边缘种群中这种趋势更为明显。我们的结果表明分布区边缘种群通过花粉二态性增强了风媒传粉能力，以适应不可预测的昆虫传粉环境，为露蕊乌头在分布区边缘种群提供了繁殖保障。