二型花柱植物海仙花报春花部性状随地理梯度的变异

Variation in floral traits of distylous Primula poissonii(Primulaceae) along geographic gradients

植物的花部性状在异质环境中表现出不均一的适应性进化,其自然变异可能在时空格局上呈现一定的规律性。选择同一物种的不同地理居群进行花部表型变异分析,能揭示花部性状随地理梯度的变异模式。海仙花报春(Primula poissonii)属于典型的二型花柱植物,依赖昆虫传粉实现严格的型间异交。该物种广布于横断山地区亚高山–高山草甸,其分布海拔跨度大且花部性状在种内具有较高变异,但这些变异在不同地理梯度(海拔梯度和经纬度梯度)的特定选择因子作用下的变化规律尚不清楚。本研究选择海仙花报春16个居群,对8个花部关键性状和二型花柱繁殖器官的互补度与海拔和经纬度的关系进行研究,探究花部性状随地理梯度变异的模式及其潜在的选择因素。研究表明,海仙花报春两种花型的花冠管开口大小、花药高度以及短柱花柱头高度与海拔均呈正相关,但两种花型的花冠大小,长柱花的花瓣长度、柱头到花冠管开口的距离,以及短柱花的花冠管长度与海拔高度间均呈负相关,其余性状与海拔无显著相关性。除短柱花中柱头高度以外的性状均随着纬度升高而逐渐减小。长柱花中除花药和柱头间的距离以及柱头到开口的距离外,其余性状均随着经度的增加而减小;短柱花的花瓣长度、花药高度以及花药和柱头间的距离随着经度的增加而变大,其余性状均随着经度的增加而减小。繁殖器官间的互补度并不随地理环境的变化而变化。花部性状的地理变异可能受访花昆虫组成的地理变化驱动。繁殖器官间互补程度的高度保守表明非选型交配在居群二态性的维持和稳定过程中起关键作用。本研究为进一步深入开展报春花属(Primula)花部性状及其选择压力的地理变异研究奠定了基础。

Floral traits are predicted to diverge in a species due to different selective forces acting along eco- logical gradients. As elevation and latitude gradients are always indicative of drastic variation in plant com- munities, elevation and latitude models should indicate how natural selection has shaped some floral traits and/or how floral characteristics have adapted to local or regional conditions. The measurement of floral traits among multiple populations can be used to observe floral trait divergence along geographic gradients. Primula poissonii, a distylous species, is widely distributed in the core areas of the Hengduan Mountains in southwest China. Distyly plays an important role in inter-morph cross pollination in P poissonii. In this study, we investigated 16 populations ofP poissonii in Yunnan and Sichuan provinces. We measured eight floral traits （corolla, androecium and gynoecium） in short- and long-styled morphs of each population. Sexual organ reciprocity was estimated by calculating the spatial distribution overlap between the height of sexual organs. The spatial distribution of sexual organs was fitted by using the maximum likelihood method with a normal distribution. Measured character and sexual organ reciprocity were tested to examine the floral trait variation along geographic gradients by using linear regression models. Results showed that floral tube opening width and anther height in both morphs and stigma height in the short-styled morph displayed a positive correlation with increasing elevation; the petal length in long-styled morph flowers, the distance be- tween the stigma and tube opening in long-styled morph, the floral tube length of short style morph, and co- rolla width in both morphs were decreased along elevational gradients. However, petal length of the short-styled morph, the distance between the highest sexual organs and tube opening in short-styled morph, the distance between anther and stigma in both morphs, and the floral tube length and stigma height in long-styled morph did not correlate with elevation. Furthermore, floral traits except for stigma height of short-styled morph were significantly negatively correlated with latitude gradients. In addition, floral traits vary along a longitudinal gradient. Differences in selective forces may contribute to the geographic mosaic of floral trait variation and sexual reciprocity may be maintained while the other traits differential. We prefer to conclude that floral trait divergence in P poissonii is driven by flower visitors.