被子植物隐性雌雄异株性系统的多样性、系统演化及进化意义

Cryptic dioecy in angiosperms:Diversity,phylogeny and evolutionary significance

隐性雌雄异株指植株表型为非雌雄异株,但形态上两性花通常雄性不育或雌性不育,植株个体实际仅行使雌性或雄性功能。两性花植株向雌雄异株的转变在被子植物中广泛存在,隐性雌雄异株作为潜在的中间阶段对于理解植物性系统的演化具有重要意义。据APGIV分类系统,这些物种在被子植物的22目36科65属约221种植物中有过报道,分别约占被子植物总目数的34.4%、总科数的8.7%、总属数的0.5%和总种数的0.1%;多为分布于热带或亚热带地区依靠生物传粉的木本植物,且至少存在花蜜或花粉作为访花报酬。该性系统形态学的性表达类型多样:可分为雄花两性花异株(类型Ⅰ)、两性花植株(类型Ⅱ)、雌花两性花异株(类型Ⅲ)及其他类型(类型Ⅳ)4种,分别约占已报道隐性雌雄异株物种数的48.9%、47.5%、2.7%和0.9%。从系统发育看,该性系统在被子植物木兰分支、单子叶植物分支及真双子叶植物分支均有分布,且主要分布于较为进化的核心真双子叶植物类群中。隐性雌雄异株物种不育性器官的进化意义存在多种假说,包括祖先假说、遗传约束假说、促进风媒花粉落置假说、传粉者吸引假说、拟态与欺骗假说等,但相关实证研究较少。本文对隐性雌雄异株物种不同类群的性表达形式、不育性器官败育类型进行了归纳,并对具该性系统的类群在被子植物中的分布与系统演化进行了分析与总结,同时对有关隐性雌雄异株物种不育性器官进化意义的5个假说进行了介绍与评价,最后对今后的相关研究方向进行了展望。以期为深入研究被子植物隐性雌雄异株性系统的进化式样与机制研究提供理论资料。

Background&Aim:Cryptic dioecy refers to a population that is phenotypically non-dioecious,but individuals actually function as males or females due to the morphologically hermaphroditic flower that typically exhibits female or male sterility.As a widespread transitional from hermaphroditism to dioecy,understandings of adaptive strategy of cryptic dioecy could help of illuminating the evolution of diverse sexual systems within angiosperms.Progress:The morphological sex expressions of cryptic dioecy are diverse and can be classified into four types:androdioecy(type I),hermaphrodite(type II),gynodioecy(type III)and others(type IV),constituting 48.9%,47.5%,2.7%,and 0.9%of reported species,respectively.In the APG IV system,cryptic dioecy occurs across 22 orders,36 families and 65 genera in around 221 species which accounts for approximately 34.4%of orders,8.7%of families,0.5%of genera and merely about 0.1%of angiosperms species.Most cryptic dioecious species are woody,biotic pollinated and distributed in tropics or subtropics.They have nectar or pollen as a floral reward.Phylogenetically,the sexual system appears in magnolia,monocotyledon and eudicots,particularly prevalent among more advanced core eudicots.Several hypotheses have been proposed to explain the evolutionary significance of sterile sex organs in cryptic dioecy,including ancestry hypothesis,genetic constraints hypothesis,promotion of wind-borne pollen dispersal hypothesis,pollinator attraction hypothesis,mimicry and deception hypothesis,but empirical studies remain little known.In this study,we provide a comprehensive summary of the forms of sex expression and types of sterile sex organs of cryptic dioecious in plant lineages.Families with cryptic dioecious species evolved are mapped into an updated phylogeny of angiosperms and systematic evolution of taxa with this sexual system in.Furthermore,five hypotheses regarding evolutionary significance of sterile sex organs in cryptic dioecious are also presented.Prospects:The future trajectory of related research is presented,with the aim of providing insights into the empirical studies of selection underlying the evolution of cryptic dioecy in angiosperms.