高山植物扁蕾的延迟自交机制

扁蕾(Gentianopsis barbata)具有鲜艳的花和显著的腺体,并且花开放的前5 d柱头和花药始终处于不同的位置(雌雄异位),这些花综合征表明该植物应为异花传粉。为检验这一假设,我们对青藏高原植物扁蕾的海北站种群进行了3年的传粉生物学研究实验。与花综合征所表明的繁育系统相反,两年的野外观察发现昆虫的访花频率十分低,不去雄并隔离昆虫处理也能产生大量种子,说明这一种群的繁殖主要是依赖于自花传粉。尽管利用种子结实评价的柱头可授性从花开放4 d后开始下降,但随着花的发育进程,雄蕊的伸长能使得花药与柱头完全接触。实验也证明,柱头可授性和花粉活力都超过5 d,说明花药和柱头的接触能够发生自花授粉。扁蕾的这种自花传粉机制应属于典型的延迟自交类型。自花授粉发生在单花花期快要结束前,自交之前仍然保持异交传粉机制,这种延迟自交避免了自交与异交竞争造成的花粉或者种子折损,并为扁蕾在青藏高原极端环境下由于访花昆虫缺乏造成的异交失败提供了繁殖保障。     

天仙子的花部特征及延迟自交机制

通过实验观察和野外控制授粉等方法,对天仙子的自交亲和能力和自交传粉机制进行了研究。结果显示:(1)天仙子的花不完全雌性先熟,开花进程中雄蕊伸长是维持其混合交配系统的重要花部特征。(2)野外控制授粉实验证明天仙子的自交亲和性高,具有主动自交能力,主动自交发生的时间集中在晚花期,与花药和柱头接触的时间吻合。(3)在花粉活力和柱头可授期内,花药与柱头的接触能够发生自花授粉,这种依赖花药与柱头接触发生的自花授粉机制属于典型的延迟自交类型。研究表明,天仙子不仅在花结构上首先选择了适于异交的特征,而且还利用雄蕊伸长成功实现自花授粉,通过异交与延迟自交混合的交配系统为该物种提供了灵活的遗传与繁殖保障。     

新西兰岩石百合中两种共存的繁育策略：延迟自动自交和欺骗传粉吸引

延迟自动自交和欺骗传粉吸引在被子植物多数类群中有相关报道,但是至今没有发现两种繁育策略在同一物种中共存现象。本研究通过对照试验检测新西兰岩石百合雄蕊附属物和花冠闭合运动是否分别具有欺骗吸引和延迟自交功能。研究结果表明,新西兰岩石百合黄色的雄蕊附属物拟态花粉（或花药）,约93%的昆虫访花行为源自黄色花药附属物的欺骗吸引,雄蕊附属物的报酬拟态功能有效提高昆虫拜访频率并促进异交。同时,研究发现新西兰岩石百合花期结束时花瓣闭合促使雌雄隔离距离的缩小,花瓣自然闭合的花朵平均结籽数（20.62）显著高于闭合前去雄处理花朵（11.79）。我们的结果表明延迟自动自交与欺骗传粉吸引两种繁育策略在新西兰岩石百合中共存。     

新西兰岩石百合中两种共存的繁育策略：延迟自动自交和欺骗传粉吸引

延迟自动自交和欺骗传粉吸引在被子植物多数类群中有相关报道,但是至今没有发现两种繁育策略在同一物种中共存现象。本研究通过对照试验检测新西兰岩石百合雄蕊附属物和花冠闭合运动是否分别具有欺骗吸引和延迟自交功能。研究结果表明,新西兰岩石百合黄色的雄蕊附属物拟态花粉（或花药）,约93%的昆虫访花行为源自黄色花药附属物的欺骗吸引,雄蕊附属物的报酬拟态功能有效提高昆虫拜访频率并促进异交。同时,研究发现新西兰岩石百合花期结束时花瓣闭合促使雌雄隔离距离的缩小,花瓣自然闭合的花朵平均结籽数（20.62）显著高于闭合前去雄处理花朵（11.79）。我们的结果表明延迟自动自交与欺骗传粉吸引两种繁育策略在新西兰岩石百合中共存。     

松江鲈的生态学和繁殖生物学的研究进展

松江鲈(Trachidermus Fasciatus Heckel),别名四鳃鲈、老虎鱼、新娘鱼、媳妇鱼等,隶属于鲉形目(Scorpaeniformes),杜父鱼科(Cottidae),松江鲈鱼属(Trachidermus)。       

中国大鲵繁殖生物学研究进展

中国大鲵（Amndrias davidiamus Blanchard）是我国特有濒危的两栖物种,是研究生物进化、生物多样性、性别决定分子机制等的好材料,对于科学研究具有巨大的潜在贡献。近年来人们对它的研究力度不断加大,本文综述厂大鲵的繁殖生物学的近期研究工作,也简要探讨了大鲵繁殖生物学今后研究的主要工作,以期为大鲵繁殖生物学及繁殖技术的进一步的研究提供有价值的参考。     

鸟类的合作繁殖

简要介绍了鸟类合作繁殖的概念,列举了４种合作繁殖的典型事例,并从进化生态学理论上说明了合作繁殖的优点,成因及机制。     

芸苔属自交不亲和细胞信号转导的研究进展

在芸苔属植物的自交不亲和细胞信号转导过程中,信号分子-SCR配体是由花粉粒产生的,被柱头乳突细胞SRK受体识别后,进行细胞内信号转导.这对受体-配体是两个由S位点编码的且高度多态的蛋白质,它们决定着自交不亲和反应.配体是位于花粉粒表面的一个小的胞被蛋白,由SCR基因编码;受体是位于柱头乳突细胞原生质膜上的跨膜的蛋白质激酶,由SRK基因编码.在自交授粉过程中,配体SCR和受体SRK的相互作用激活了受体SRK,被激活的SRK通过其下游组分ARC1介导底物的泛肽化,然后泛肽化的底物在蛋白酶体/CSN中被降解,从而导致了自交不亲和性反应.这些降解的底物可能是促进花粉水合、萌发和花粉管生长的雌蕊亲和因子.主要针对芸苔属自交不亲和细胞信号转导作一综述.     

延迟交配对橘小实蝇繁殖适度的影响

橘小实蝇Bactrocera dorsalis Hendel是一种世界性的入侵害虫,严重为害多种经济果蔬。本文通过响应面分析方法,研究了延迟交配对橘小实蝇交配率、产卵量、孵化率和寿命的影响。结果表明,交配率随雌虫交配日龄的延迟先增后减,雌、雄成虫均为35日龄处理组中的交配率最高,为81.00%±2.00%;而雄虫交配日龄的延迟则对其卵孵化率有明显的负面作用,在56日龄雄虫与35日龄雌虫处理组中,其卵孵化率最低,仅为27.56%±4.55%。雌成虫产卵量和寿命受到雌、雄虫双方交配日龄的的影响,产卵量（y）与雄虫日龄（x1）和雌虫日龄（x2）的回归方程为y=514.36+3.08x1-11.05x2,雌成虫寿命（y）与雄虫日龄（x1）和雌虫日龄（x2）的回归方程为y=35.85+0.23x1+0.40x2。研究结果为田间使用性信息素迷向法防治橘小实蝇提供了理论依据。     

高山植物繁殖策略的研究进展

高山地区通常被认为是陆地上最为极端的生境之一,但却拥有许多形态特化的植物和较高的物种多样性。高山植物如何在严酷的环境中实现成功繁殖,这一问题倍受研究者们的关注。本文综合了国内外高山植物在资源分配、花形态对非生物环境因子的响应、动物传粉及其适应机制、果实和种子及克隆繁殖等繁殖策略方面的文献。为应对低温多雨雪的恶劣环境,一些高山植物采取花向日性、花冠闭合及花序保温结构等繁殖策略。高山植物的传粉者类群也发生了改变,主要为蜂类和蝇类。熊蜂(Bombusspp.)传粉的高效性,减少了高山环境对植物传粉造成的不利影响。当传粉者不可得时,植物不仅通过延迟自交和自助自交等机制来提供繁殖保障,还借助克隆繁殖及其他传粉机制(风媒或风虫媒)来维持种群的繁衍。依赖动物传粉的高山植物,可以采取增加繁殖构件的资源分配、加大"广告"投入以及较大的花展示或较长的花寿命来提高传粉者的拜访几率,以及借助泛化的花结构和选择合适的开花时间等策略来提高繁殖成功率。此外,大部分高山植物产生干果且具有持久的种子库,有利于种子的传播以及种子寻找萌发及幼苗生长的最佳外界环境。在今后的研究中,可着重探讨以下几个问题:(1)非生物环境因子对花形态的选择;(2)季节变化与繁殖策略;(3)群落水平上植物与传粉者的关系;(4)高山生态系统对全球变暖的响应。     

Diplostigmaty in plants: a novel mechanism that provides reproductive assurance

Differentiation of female sexual organs in flowering plants is rare and contrasts with the wide range of male reproductive strategies. An unusual example involves diplostigmaty, the possession of spatially and temporally distinct stigmas in Sebaea (Gentianaceae). Here, the single pistil within a flower has an apical stigma, as occurs in most flowering plants, but also a secondary stigma that occurs midway down the style, which is physically discrete and receptive several days after the apical stigma. We examined the function of diplostigmaty in Sebaea aurea, an insect-pollinated species of the Western Cape of South Africa. Floral manipulations and measurements of fertility and mating patterns provided evidence that basal stigmas function to enable autonomous delayed self-pollination, without limiting opportunities for outcrossing and thus avoiding the costs of seed discounting. We suggest that delayed selfing serves as a mechanism of reproductive assurance in populations with low plant density. The possession of dimorphic stigma function provides a novel example of a flexible mixed-mating strategy in plants that is responsive to changing demographic conditions.     

The mechanism of delayed selfing in Collinsia verna (Scrophulariaceae)

Collinsia verna, blue-eyed Mary, has floral attributes of an outcrossing species, yet most flowers readily self-pollinate under greenhouse conditions. Here we describe the mechanism of self-pollination in C. verna via changes in relative positions of the stigma and anthers and late timing of receptivity, resulting in delayed selfing. Each flower contains four anthers that dehisce sequentially over ∼1 wk. Pollen that is not collected by pollinators accumulates in the keel petal and retains high viability (>80% pollen germination) up to the time of corolla abscission. The stigmatic surface does not become receptive until after the third anther dehisces. This overlap in the sexual phases is concurrent with a change in herkogamy during floral development. In most flowers (70%), the stigma has moved to the front of the keel and is positioned near the anthers when the third anther dehisces. Under field conditions, fruiting success of plants within pollinator exclosures was ∼75% of the fruiting success in open-pollinated plants (33% fruiting success via autogamy vs. 44% fruiting success, respectively). Collinsia verna plants in pollinator exclosures exhibit variation in autogamy rates within natural populations (range 0–80%). In addition, only half of naturally pollinated, receptive flowers examined had pollen tubes growing in their styles. In contrast, shortly after corolla abscission, nearly all flowers examined (96%) had pollen tubes in their styles. Thus we find that in C. verna, autogamy occurs late in floral development, which has the potential to provide substantial reproductive assurance, and that individuals vary in their ability to set fruit through this mechanism. We suggest that delayed selfing mechanisms may be overlooked in other species and that variable pollinator availability may play a significant role in the maintenance of mixed mating in species with delayed selfing, such as C. verna.     

The reproductive assurance benefit of selfing: importance of flower size and population size

Autonomous selfing can provide reproductive assurance (RA) for flowering plants that are unattractive to pollinators or in environments that are pollen limited. Pollen limitation may result from the breakdown of once-continuous habitat into smaller, more isolated patches (habitat fragmentation) if fragmentation negatively impacts pollinator populations. Here we quantify the levels of pollen limitation and RA among large and small populations of Collinsia parviflora, a wildflower with inter-population variation in flower size. We found that none of the populations were pollen limited, as pollen-supplemented and intact flowers did not differ in seed production. There was a significant effect of flower size on RA; intact flowers (can self) produced significantly more seeds than emasculated flowers (require pollen delivery) in small-flowered plants but not large-flowered plants. Population size nested within flower size did not significantly affect RA, but there was a large difference between our two replicate populations for large-flowered, small populations and small-flowered, large populations that appears related to a more variable pollination environment under these conditions. In fact, levels of RA were strongly negatively correlated with rates of pollinator visitation, whereby infrequent visitation by pollinators yielded high levels of RA via autonomous selfing, but there was no benefit of autonomous selfing when visitation rates were high. These results suggest that autonomous selfing may be adaptive in fragmented habitats or other ecological circumstances that affect pollinator visitation rates.     

Allee effect and self-fertilization in hermaphrodites: reproductive assurance in demographically stable populations

The fact that selfing increases seed set (reproductive assurance) has often been put forward as an important selective force for the evolution of selfing. However, the role of reproductive assurance in hermaphroditic populations is far from being clear because of a lack of theoretical work. Here, I propose a theoretical model that analyzes self-fertilization in the presence of reproductive assurance. Because reproductive assurance directly influences the per capita growth rate, I developed an explicit demographic model for partial selfers in the presence of reproductive assurance, specifically when outcrossing is limited by the possibility of pollen transfer (Allee effect). Mating system parameters are derived as a function of the underlying demographical parameters. The functional link between population demography and mating system parameters (reproductive assurance, selfing rate) can be characterized. The demographic model permits the analysis of the evolution of self-fertilization in stable populations when reproductive assurance occurs. The model reveals some counterintuitive results such as the fact that increasing the fraction of selfed ovules can, in certain circumstances, increase the fraction of outcrossed ovules. Moreover, I demonstrate that reproductive assurance per se cannot account for the evolution of stable mixed selfing rates. Also, the model reveals that the extinction of outcrossing populations depends on small changes in population density (ecological perturbations), while the transition from outcrossing to selfing can, in certain cases, lead the population to extinction (evolutionary suicide). More generally, this paper highlights the fact that self-fertilization affects both the dynamics of individuals and the dynamics of selfing genes in hermaphroditic populations.     

Wind pollination and reproductive assurance in Linanthus parviflorus (Polemoniaceae), a self-incompatible annual

Wind pollination was experimentally demonstrated in Linanthus parviflorus (Polemoniaceae), a predominantly beefly-pollinated, self-incompatible annual. Seed set in plants enclosed in mesh tents that excluded pollinators but allowed airborne pollen flow provided evidence for wind pollination, and the extent of seed set due to wind pollination was compared to that in open-pollinated controls and pollen-supplemented treatments. Additional controls were included to test for possible confounding effects of the mesh tent. Mean seed number in open-pollinated plants was 72.8–81.1% of that in pollen-supplemented plants, while wind pollination alone produced 49.5–52.2%, a smaller but substantial proportion of seed set with pollen supplementation. Further evidence for wind pollination was found in a comparison of sites differing in the extent of wind exposure in two populations of L. parviflorus. Airborne pollen counts were higher in exposed sites than in protected sites, and the difference was marginally significant. Seed set was significantly pollen limited in protected sites, but not in exposed sites. Taken together, the data suggest that wind pollination provides some reproductive assurance in this obligately outcrossing species. Wind pollination is hypothesized to represent an alternative to selfing as an evolutionary solution to the problem of temporal or spatial variation in pollination visitation.     

Allee effect and self-fertilization in hermaphrodites: reproductive assurance in a structured metapopulation

Reproductive assurance through selfing during colonization events or when population densities are low has often been put forward as a mechanism selecting for the evolution of self-fertilization. Such arguments emphasize on the role of both local demography and metapopulation processes. We developed a model for the evolution of self-fertilization in a structured metapopulation in which local densities are not steady because of population growth. Reproduction by selfing is density-independent (reproductive assurance) but selfed seeds endure inbreeding depression, whereas reproduction by outcrossing is density-dependent (Allee effect). First, we derived an analytical criterion for metapopulation viability as a function of the selfing rate and metapopulation parameters. We show that outcrossers can develop a viable metapopulation when they produce a high amount of dispersal seeds that counterbalances their incapacity to found new populations from low densities. Second, the model shows there is a positive feedback between demography and outcrossing rates, leading to either complete outcrossing or selfing. Specifically, we illustrate that inbreeding depression can paradoxically favor the evolution of selfing because of its negative effect on density. Also, complete outcrossing can be selected despite pollen limitation, although it does not provide a full seed set. This model underlines the influence of the mating system both on demography and gene dynamics in a metapopulation context.     

Stigmatic fluid aids self-pollination in Roscoea debilis (Zingiberaceae): a new delayed selfing mechanism

Background and Aims

Delayed selfing is the predominant mode of autonomous self-pollination in flowering plants. However, few delayed selfing mechanisms have been documented. This research aims to explore a new delayed selfing mechanism induced by stigmatic fluid in Roscoea debilis, a small perennial ginger.

Methods

Floral biology and flower visitors were surveyed. The capacity of autonomous selfing was evaluated by pollinator exclusion. The timing of autonomous selfing was estimated by emasculation at different flowering stages. The number of seeds produced from insect-pollination was assessed by emasculation and exposure to pollinators in the natural population. The breeding system was also tested by pollination manipulations.

Key Results

Autonomous self-pollination occurred after flowers wilted. The stigmatic fluid formed a globule on the stigma on the third day of flowering. The enlarged globule seeped into the nearby pollen grains on the fourth flowering day, thus inducing pollen germination. Pollen tubes then elongated and penetrated the stigma. Hand-selfed flowers produced as many seeds as hand-crossed flowers. There was no significant difference in seed production between pollinator-excluded flowers and hand-selfed flowers. When emasculated flowers were exposed to pollinators, they produced significantly fewer seeds than intact flowers. Visits by effective pollinators were rare.

Conclusions

This study describes a new form of delayed autonomous self-pollination. As the predominant mechanism of sexual reproduction in R. debilis, delayed self-pollination ensures reproduction when pollinators are scarce.     

Staggered arrangement and sequential dehiscence of anthers in didynamous stamens facilitate reproductive fitness of Brandisia hancei

Didynamous stamens are separated into two pairs of different length, and the implication of this arrangement has not been well understood. The functional advantages of didynamous stamens were investigated in Brandisia hancei. Change of stamens during floral aging was recorded; the quantity, viability, and siring ability of pollen grains were tested; the anther arrangement was manipulated into four types based on stamen category and number, and fruit set and number of seeds per fruit were measured. Didynamous stamens exhibited staggered anther arrangement, and pollen sacs dehisced gradually. There was no difference for quantity, viability, and siring ability of pollen grains between the two pairs of anthers. Seed production after the removal of one long and one short stamen was higher than that of two long or two short stamens. Through prolonging pollen presentation and promoting delayed self-pollination, staggered arrangement and sequential dehiscence of anthers in didynamous stamens facilitate reproductive fitness of B. hancei.