毛翠雀花花序内的性分配和繁殖成功

Floral sex allocation and reproductive success within inflorescences of Delphinium trichophorum (Ranunculaceae)

关键词:  毛翠雀花, 花序内差异, 性分配, 繁殖成功, 交配环境

Key words:  Delphinium trichophorum, intra-inflorescence variation, sex allocation, reproductive success, mating environment

摘要:

两性花植物花序内不同位置的性分配和繁殖成功一般存在差异,通常认为资源竞争、结构效应和交配环境是形成这种差异的主要原因。为了研究雄性和雌性繁殖资源在花序内不同位置间的最优分配问题,该文以青藏高原高寒草甸典型高山植物毛翠雀花为材料,通过比较花序内不同位置的花部特征和种子性状,对其花序内的性分配模式和雌性繁殖成功进行研究,并通过观察传粉者运动特点以及人工去花和补授花粉实验,探讨花序内资源竞争和交配环境对繁殖资源分配的影响。结果表明:(1)不同位置间的雄蕊数、雄蕊鲜重/雌蕊鲜重、花粉数及花粉胚珠比从花序基部到上部显著增加,而雌蕊鲜重和胚珠数逐渐减少,表现出上部花偏雄的性分配; 上部花的结籽率显著低于基部花和中部花,不同位置间的发育种子数/果实和发育种子重/果实随着花位置的升高而显著降低,说明基部花具有更佳的雌性繁殖成效。(2)去花处理后,剩余果实的单个种子重/果实显著增加,但发育种子数/果实没有显著增加; 而给上部花人工补授异花花粉后,位置间结籽率的差异消失,说明传粉限制而非资源竞争导致了花序内位置依赖的种子生产模式。(3)毛翠雀花雄性先熟的开花特征,以及传粉者苏氏熊蜂从花序基部到上部的定向访花行为,导致了花序内交配环境的变化。综上结果表明,毛翠雀花花序内的性分配和繁殖成功差异是对交配环境适应的结果,对其在高山环境中实现雌雄适合度最优化具有重要意义。

Abstract:

Intra-inflorescence variation in floral sex allocation and reproductive success are common in hermaphroditic plants, and several non-exclusive hypotheses, including resource competition, architectural effect and the mating environment, have been formulated to explain this phenomenon. In order to investigate the optimal allocation mode of male and female reproductive resources between different positions in the inflorescence, through comparison of floral and seed traits, the floral sex allocation and female reproductive success within inflorescences of Delphinium trichophorum(Ranunculaceae), a typical alpine plant of Qinghai-Tibet Plateau was investigated. Observation of pollinator movements, artificial flower-removal experiment, and hand-supplemental pollination were also used to investigate the effects of resource competition and mating environment on allocation of reproductive resource in the inflorescence. The results were as follows:(1)From bottom to upper positions of inflorescence, stamen number, stamen fresh mass/pistil fresh mass, pollen number and pollen/ovule ratio all increased significantly, while pistil fresh mass and ovule number declined gradually, which showed upper flowers performed male-biased function. Seed set ratio of upper flowers were significantly lower than those of bottom and intermediate flowers. The number and mass of mature seed per fruit decreased significantly with the increase of flower position, indicating greater female reproductive success of bottom flowers.(2)The flower-removal experiment improved single seed mass of the remaining fruits, but did not increase the number of mature seeds per fruit. There were no differences of seed set ratio among positions after hand-supplemental pollination of upper flowers, which suggested that the position-dependent pattern of seed reproduction within inflorescences was attributed to pollen limitation rather than resource competition.(3)The protandry of D. trichophorum and the directional visiting behaviors(from bottom to upper)of pollinator Bombus sushikini led to variations of mating environment within inflorescences. All the above results indicate that intra-inflorescence variation in floral sex allocation and reproductive success of D. trichophorum are results of adaptation to mating environment, and this strategy is of great importance to optimize the male and female fitness for the species.