雌雄异株物种一把伞南星雌雄株空间分布及性别二态性

Spatial distribution and sexual dimorphism of dioecious Arisaema erubescens

雌雄异株是有花植物雌雄性别功能在个体水平上由结合到分离的重要进化转变之一,发生于被子植物的多个科属。雌雄异株物种的雌雄个体通常在分布、形态等方面存在差异。研究其雌雄个体的空间分布及性别二态性,是理解雌雄异株物种繁殖策略及其适应与进化的重要前提。天南星属(Arisaema)是天南星科内已报道唯一存在雌雄异株且较为进化的类群,一把伞南星(A.erubescens)是该属中不同性别个体存在差异的多年生草本植物。本文以湖南省八大公山国家级自然保护区内分布的一把伞南星为研究对象,通过研究其雌雄个体的空间分布、花期物候、形态结构及访花者类群,以期明确该物种雌雄植株的空间关联性以及花期物候、形态结构的性别二态性。结果表明:一把伞南星群体内性比均呈极显著雄性偏倚,雌雄个体在小尺度范围呈聚集分布,但在较大尺度上呈随机分布;雄性个体比雌性个体更早进入花期,置换多元方差分析显示雌雄植株间形态特征存在显著差异,其中假茎基径、佛焰苞管部直径、花序基径、花序柄直径等特征对性别二态性有重要贡献;主要传粉者为白天活动的菌蚊科菌蚊属(Mycetophila)的蕈蚊,其对雄株的访问频率极显著高于雌株。这些结果表明:雌雄异株物种一把伞南星不同性别植株的空间关联与其传粉者蕈蚊的活动习性相匹配,其开花物候、形态特征及传粉者访问等方面的性别二态性是对繁殖成功的保障。

Aims:The transition to dioecy constitutes a pivotal milestone in the evolution of sexual functions in flowering plants,marking a shift from the integration of male and female reproductive organs within the same individual to their separation.This sexual system occurs across numerous angiosperm families and genera.Both female and male individuals of dioecious species display variations in distribution,morphology,and life history traits.Therefore,it is essential to examine the spatial distribution and sexual dimorphism of dioecious species in order to comprehend their reproductive strategies,adaptability,and evolutionary patterns.The genus Arisaema is the only reported taxon within the Araceae family known to possess a dioecious sexual system.In this study,we explored the differences between the dioecious members of Arisaema erubescens in the Badagongshan National Nature Reserve,Hunan Province,China,with a specific focus on the spatial distribution and sexual dimorphisms.Methods:We surveyed the coordinate positions of male and female individuals across four plots,analyzed both the sex ratio and spatial distribution patterns of these individuals.Sexual dimorphism was assessed based on phenological and morphological traits of A.erubescens.Additionally,a quantitative comparison of the floral visitor assemblages between female and male individuals was conducted.Results:From our observations,the A.erubescens population was significantly dominated by staminate flora.Male and female individuals were found to clusters on small scales and disperse randomly on a large scale.The male individuals flowered 4 days earlier than the females.The permutational multivariate analysis of variance identified significant disparities in morphological traits between male and female individuals,which are pivotal to sexual dimorphism.These traits include the pseudostem basal diameter,the diameter of spathe tube,the inflorescence basal diameter,and the peduncle diameter.The primary pollinators of A.erubescens were the diurnal fungus gnats of the Mycetophila species,with an extremely higher visitation frequency observed on male individuals compared to those on female individuals.Conclusions:Our study suggests that the spatial association of different genders in A.erubescens corresponds to the pollinators’activity habits.The sex dimorphism of A.erubescens in flowering phenology,morphological traits,and pollination activity collectively guaranteed the reproductive success of the species.