摘要
简述了世界鼠尾草属传粉模式多样性,从宏观层面对东亚鼠尾草属分布中心———中国的鼠尾草属传粉模式进行归纳与总结。研究补充了以往所缺乏的东亚鼠尾草属核心类群的雄蕊结构和传粉模式,并提出雄蕊结构的可能进化方向。根据花器官形态、内部结构、雄蕊特征、花粉接触传粉昆虫的部位,将中国分布的鼠尾草属植物划分为3种模式类型:TypeⅠ,短药隔杠杆传粉模式(short-lever type),主要发生在弧隔鼠尾草亚属(subg.Salvia Benth.),其雄蕊药隔短,属原始结构类型;TypeⅡ,长药隔杠杆传粉模式(long-lever type),主要发生在荔枝草亚属(subg.Sclarea Benth.),雄蕊药隔明显伸长,是典型的背部杠杆传粉结构;TypeⅢ,退化杠杆传粉模式(degraded-lever type),主要发生在鼠尾草亚属(subg.Allagospadonopsis Briq.),花冠筒变短变窄,雄蕊下臂明显退化,传粉者无需进入冠筒即可取食花蜜,花粉触碰昆虫头部,进而杠杆作用弱化。研究表明,鼠尾草属传粉模式的进化趋向于提高传粉者的专一性,同时保证传粉过程的有效性、精确性和忠实性,推测具有退化雄蕊下臂的TypeⅢ模式可能更为进化。比较美洲和地中海2个进化分支的雄蕊结构和进化趋势,东亚多样性中心可能是一个独立的进化分支。毫无疑问,雄蕊结构与花器官和传粉功能高度相关,是适应传粉者的进化表型,它的进化对东亚分支的物种辐射与多样性形成可能具有关键作用。
Salvia, comprised of almost 1000 species, is the largest genus in the Lamiaceae family and an ideal model system to investigate biological diversity and adaptive radiation. Plant diversity of this species is manifested by the diversification of flower organs and pollination mechanisms, which may be driving forces of their origins and evolution. Salvia is characterized by a staminal lever mechanism which is key to pollen transfer. In Salvia, the two monothetic stamens are modified into levers with a thin ligament between the connective and the filament, forming a joint, which is then divided into upper and lower arms. This enables the stamen to reversibly transfer pollen. A pollinator searching for nectar must push back the lower lever arms to allow the pollen-sacs at the end of the upper lever arms to be pressed onto the pollinator＇s head or back. Then, the pollinator visits a subsequent flower of the same species to transfer pollen to the plant stigma. In Salvia, parallel evolution occurs in American and Eurasian centers of diversity, which have different pollinators but a similar evolutionary direction for Salvia pollination mechanisms. In China, Salvia are classified by three pollination mechanisms based on floral traits, staminal structure, and pollen deposition on the body of bees. Type Ⅰ （short-lever type） is the original group in the subgenus Salvia Benth. with two fertile upper and lower lever arms. Type Ⅱ（ long-lever type）, which is found in the subgenus Sclarea Benth., involves a staminal lever mechanism that is characterized by two posterior thecae that are not expressed and fused. Type Ⅲ （ degraded-lever type）, which is found in the subgenus Allagospadonopsis Briq.,has a degraded staminal lever structure with two separated and thin sterile posterior thecae. We discovered that these three pollination types contribute to the geographical distribution in China of the three Salvia subgenera. Type I was mainly distributed in southwest China with the Hengduan Mountains as its diversity center. Type Ⅱ was mainly distributed in central China including Guizhou, Chongqing, east Sichuan, west Hubei, the Qinling Mountains and the Dabie Mountains. Type Ⅲ was mainly distributed in eastern and southern China; specifically, the Tianmu, Wuyi and Nanling Mountains are their distribution and diversity centers. Unique pollination mechanisms of each plant are based on two aspects of the staminal structures and their automatic movements. Staminal automatic movement was observed in some Salvia species with small flowers from Type Ⅱ or Type Ⅲ. In the corolla, some plant stamens can automatically and slowly make a downward, involuted movement during stamen ageing. Then, the stigma will finally occupy this position the mature stamens had occupied before to accept the pollen from other flowers of the same Salvia species. The evolution of Salvia pollination mechanisms gives rise to pollinator specialization, validity, accuracy, and fidelity. Type Ⅲ plant species have shorter and narrower flower tubes： pollinators are not required to enter the tube to access nectar. Rather, the pollen can be deposited on the pollinator＇s forehead. Thus, the pollination pattern of Type Ⅲ Salvia plants are more evolved in terms of energy-saving and specialization. Staminal lever mechanisms and floral structures involved in pollen transfer may be critical for adaptive radiation and speciation within Salvia. Future comprehensive species surveys and investigations into the floral structure of Salvia and their pollinators are needed to compare species across continents.
出处
《生态学报》
CAS
CSCD
北大核心
2014年第9期2282-2289,共8页
Acta Ecologica Sinica
基金
上海市绿化和市容管理局资助项目(G102404,F132423)
关键词
鼠尾草属
杠杆传粉模式
花器官多样性
适应辐射
东亚
Salvia
lever pollination mechanism
floral diversity
adaptive radiation
East Asia
