繁殖保障和延迟自交的研究进展

Advancements in reproductive assurance and delayed selfing

尽管植物在进化过程中面临不利自花授粉的选择,但许多植物仍维持混合的授粉机制。繁殖保障假说是解释自交进化的最重要因子之一,一直是植物生殖生态学和进化生物学关注的焦点之一。概述了近年来的主要研究热点及其进展,包括自交进化的遗传和生态机制及理论模型探讨、繁殖保障假说的提出、验证自交能否提供繁殖保障的例证、延迟自交的类型及延迟自交能否提供繁殖保障的例证等方面。介绍了我国在繁殖保障和延迟自交方面研究的现状和不足之处,结合国际上研究繁殖保障假说的发展趋势已由单季节、单种群、单因子的研究阶段过渡到多季节、多种群、多因子(自交方式及其所占比例、花粉折损、种子折损、自交率和近交衰退)的综合研究阶段,及由传统的、经典的研究方法过渡到应用现代实验手段(如SSR、SNP等分子标记)和先进仪器设备的研究阶段,提出今后研究中应注意的问题。有必要借用多学科(植物学、生态学和分子生物学)的方法及手段进行不同物种的对比和综合细致的研究。

The advancements and novel interests in reproductive assurance and delayed selfing, including genetic and ecological mechanisms for the evolution of selling and its theoretical models, reproductive assurance hypothesis, the exemplifications of testing if selfing provides the reproductive assurance, the types of delayed selfing, and the positive or negative exemplifications of delayed selting supporting the reproductive assurance, were introduced in this review.Though in the face of selection against self-pollination, mixed mating systems are maintained in many plants. Many theoretical and empirical efforts have been made to understand the evolution of selfing. Researches on genetic mechanisms havefocused on the avoidance of selfing if inbreeding depression is high. Recently, researches have shifted on the ecological mechanisms, which oppose the evolution of selfing, including pollen discounting and seed discounting. More recently, there are two novel hypotheses on the evolution of self-fertilization＂ reproductive assurance hypothesis and automatic selection hypothesis. However, up to now, there are a few convincing studies showing selfing is adaptive in species with mixed mating. In many species the selfing component of mixed mating may represent a non-adaptive cost which is associated with the large floral displays required to attract animal pollinators; and it is also difficult to determine which selfing is from the automatic selection or the reproductive assurance.Reproductive assurance hypothesis, where self-fertilization ensures seed production when pollinators and/or potential mate are scarce, is the most longstanding and most widely accepted explanation to the evolution of selfing, and it is one of the central concerns of plant reproductive ecology and evolutionary biology. According to this hypothesis, the fitness advantage of selfing comes from increased success with respect to outcrossing. Selection for the reproductive assurance provided by selfing may be especially important in explaining the widespread occurrence of partial selfing in species where the fitness value of producing selfed progeny is greatly reduced by inbreeding depression. However, despite the exemplifications of selfing supporting the reproductive assurance hypothesis had been reported in some plant species, only two of them have combined experimental measures to test if selfing provides the reproductive assurance with estimates of pollen discounting, seed discounting, selfing rates and inbreeding depression in different populations in different years, and few exemplifications in the level of individual or flower test the reproductive assurance hypothesis.For delayed selfing, self-pollination is delayed until the opportunity for outcrossing has missed. This is regarded as areproductive adaptability because it apparently ensures seed production when pollinators are absent or scare, yet, it allows outcrossing to predominate when they are abundant. Delayed selfing in many plant occurs from three suites of floral morphological traits has been shown to modify the degree of self-pollination within flowers, including dichogamy, transient self-incompatibility, and floral parts movement （eg. pollen slide, the late curling of stylar branche, stamens bending upwards late in flowering, stamens progressively elongate towards the exerted stigma, corolla abscission and co^olla closing, etc. ）. Although delayed selfing were reported in many plant species, few studies have quantitatively measured ts impact on reproductive assurance. As an only exemplification, report in Nature by Kalisz showed that delayed selfing of Coli nsia verna supports the reproductive assurance, which combined reproductive assurance coefficient, selfing rate, pollinator faimre rate and inbreeding depression in different populations in different seasons of different years.The study on the reproductive assurance and delayed selfing in China is on the way in recent years. A simple evolutionarilystable strategy model of resource allocation in partially selling plants was developed, and delayed selfing in some plants were reported by Chinese scholars, but the benefits of these delayed selfing were not further clarified.According to the developments and present studies on the reproductive assurance and delayed selfing, we believe that theresearch on the reproductive assurance is shifting from single season, single population and single factor to comprehensive research phase of multi-seasons, multi-populations and multi-factors （selfing modes and its relative proportion, pollen discounting, seed discounting, selfing rate and inbreeding depression）, and from traditional and classical approaches to modem experimental technologies （e. g. the molecular markers of SSR, SNP, etc. ） with advanced apparatus, We also put forward our insights into the study for future.