Differences in floral traits and flower visitation rates in mating systems in Prunella vulgaris(Lamiaceae)

夏枯草交配系统对花特征和访花频率差异的影响

Floral traits and the number of visitors are expected to change with different mating systems.We tested this hypothesis by comparing flowers of Prunella vulgaris(Lamiaceae)with inserted and exserted styles across a strongly exserted style biased,an exserted style biased,and a strongly inserted style biased subalpine population.We examined flowering phenology,floral morphology,flower visitation rate,capacity for autonomous selfpollination and visitor contribution to seed production for each style type and in each population.We also examined inbreeding depression(ID)by comparing the relative performance of progeny from self-and crosspollination.Exserted style plants had larger and more open flowers,increased pollen production,higher amounts of nectar rewards and higher visitation and outcrossing rates than inserted style plants.Similarly on the population level,the visitation rates were higher in the exserted style-biased populations than in the inserted style-biased population.Inserted style plants provided a stronger reproductive assurance(RA)through autonomous selfing than exserted style plants.RA and outcrossing rates did not differ among populations,showing low visitation rates may be sufficient for adequate seed production in P.vulgaris.Although inserted style plants had a lower ID level than exserted style plants,the ID of both was less than 0.5,suggesting that an ID should not counteract the evolution of selfing in this species.Inserted style plants provide RA through autonomous selfing,and exserted style plants ensure outcrossing through pollinator services,supporting a stable mixed mating system in this subalpine plant.

植物花特征和传粉者的访问次数与交配系统类型密切相关。唇形科植物夏枯草(Prunella vulgaris)存在两种植株类型,分别为柱头伸出花冠和柱头在花冠内部的植株,而且两种植株的比例在不同种群中存在差异。本研究选择柱头伸出花冠外植株占绝大多数、柱头伸出花冠外植株占多数和柱头在花冠内部植株占多数的3个种群,通过比较每个种群中两种植株类型的开花物候、花形态特征、昆虫访问频率、自交能力、传粉者对结实的贡献以及近交衰退的水平,以检验花特征和传粉者访问次数与交配系统类型的关系。研究结果表明,与柱头在花冠内部的植株相比,柱头伸出花冠外的植株具有更大和更多的花,产生更多的花粉和花蜜,具有更高的访花频率,并主要通过异交产生种子。在种群水平,柱头伸出花冠外的植株占多数种群的访花频率显著高于柱头在花冠内部植株占多数的访花频率。柱头在花冠内部的植株比柱头伸出花冠外的植株具有更强的自动自交能力,在传粉者缺乏时为其提供了繁殖保障,但繁殖保障和异交率在不同种群中差异不显著,表明较低的昆虫访问能够满足夏枯草的授粉需求以产生种子,这可能与夏枯草较少的胚珠数量(每朵花仅有4个胚珠)有关。柱头在花冠内部植株的近交衰退水平低于柱头伸出花冠外植株的近交衰退水平,但两种植株类型的近交衰退水平均低于0.5,说明近交衰退不足以阻止该物种中自交的进化。综上所述,柱头在花冠内部的植株能够通过自交为夏枯草提供繁殖保障,而柱头伸出花冠外的植株能够利用昆虫传粉确保异交,表明混合交配系统在该物种中是一个稳定的状态。