草乌花蜜产量的梯度分布及熊蜂自下而上的访花行为

收益降低假说(declining reward hypothesis)认为熊蜂自下而上的访花顺序是对花蜜产量的直接响应,先访问下部花蜜产量高的花可以获得更多的收益;花开口方向假说认为自下而上访花是因为熊蜂更容易看见其上部的花朵。为了验证上述两个假说,我们于2008年8月在北京小龙门国家森林公园调查了红光熊蜂(Bombus ignitus)访问草乌(Aconitum kusnezoffii)直立和倒立顶生花序的访问顺序,测量了直立花序下部雌性阶段花和上部雄性阶段花花蜜的糖浓度、体积,计算了花蜜中的糖含量。结果表明,红光熊蜂在直立花序和倒立花序内均以向上运动为主,分别占总运动次数的62.77%和68.35%;直立花序下部雌性阶段花花蜜糖浓度比上部雄性阶段花低1.44%,但是花蜜体积和花蜜中的糖含量都显著高于雄性阶段的花。由于熊蜂访问倒立花序时先访问的是下部的低回报雄性阶段的花,然后再访问上部高回报的雌性阶段的花,这与收益降低假说矛盾,表明红光熊蜂自下而上访问草乌直立花序可能不是受到花蜜产量的调节。     

新疆党参的花部综合征与次级花粉呈现

次级花粉呈现是植物提高花粉输出和接受的效率与准确性以及促进异交的一种繁殖策略.新疆党参(Codonopsis clematidea)具有典型的次级花粉呈现特性.本文采用野外观测、授粉实验与室内显微观测等方法,对该物种的花部综合征及其次级花粉呈现过程进行了详细观测,并对这些特征的适应意义进行了探讨.结果表明:新疆党参钟状下垂的蓝色花冠及黑黄色蜜腺,不仅避免了雨水冲刷雌雄蕊、稀释花蜜以及风移出花粉等不利影响,还增加了对传粉者的吸引,延长了花粉活力及柱头可授性持续时间.次级花粉呈现属于亚顶端花柱呈现者,呈现机制为沉积机制.该特性限制了单个传粉者带走的花粉量,延长了花粉呈现时间,使更多传粉者参与传粉过程,增加了雄性适合度.其雄性先熟及雌雄蕊空间位置变化,避免了雌雄功能干扰,为传粉者取食花蜜、输出花粉以及柱头接受异源花粉提供了通道和机会.其泛化传粉系统的主要传粉昆虫为林野熊蜂(Bombus silvarum)、草地熊蜂(B.paradoxus)和树长黄胡蜂(Dolichovespula sylvestris),其较长的单花花期(6 d左右),昆虫访花高峰期与花粉活力最高时期及柱头最佳授粉期相吻合,以及较大的泌蜜量、较高的花蜜糖浓度和较长的泌蜜时间等特征,可提高传粉者的访花频率,增加成功传粉的机会和传粉效率.在气候多变的天山山区,该物种特殊的花部综合征和次级花粉呈现机制对提高其传粉效率并促进异交繁殖成功具有重要意义.     

鸢尾属植物的传粉者吸引及异交策略

已知鸢尾属（Iris）植物约有280种且花部特征多变,具有较高的科研和观赏价值。尽管该属植物具备一定的克隆和自交繁殖能力,但传粉者介导的异交仍在其物种和遗传多样性的维持中发挥重要作用,然而目前仍缺乏对该属植物传粉者吸引及异交策略的系统性总结。本文首先简述了鸢尾属植物的传粉者种类及其适应动物传粉的花部构造,以明确其动物传粉概况。在此基础上,详细论述了该属植物如何通过视觉和嗅觉信号呈现花粉、花蜜和热量报酬供给等策略,实现对传粉者的有效吸引。在传粉者访问前后,鸢尾属植物还可通过合理的花展示、单花内雌雄功能的时空隔离以及传粉后的调控以实现最大程度的异交。此外,影响其传粉者吸引及异交的第三方生物和非生物因素,如食花者和资源配置,也应受到重视。今后随着相关研究的深入和技术手段的革新,研究者应针对鸢尾属植物传粉的热点或有争议的问题,采用花信号定量测定及异交率分子检测等先进技术,通过大范围的对比研究,深入揭示鸢尾属植物与传粉者的互作模式及其繁殖策略。     

鸢尾属植物的传粉者吸引及异交策略

已知鸢尾属(Iris)植物约有280种且花部特征多变,具有较高的科研和观赏价值。尽管该属植物具备一定的克隆和自交繁殖能力,但传粉者介导的异交仍在其物种和遗传多样性的维持中发挥重要作用,然而目前仍缺乏对该属植物传粉者吸引及异交策略的系统性总结。本文首先简述了鸢尾属植物的传粉者种类及其适应动物传粉的花部构造,以明确其动物传粉概况。在此基础上,详细论述了该属植物如何通过视觉和嗅觉信号呈现花粉、花蜜和热量报酬供给等策略,实现对传粉者的有效吸引。在传粉者访问前后,鸢尾属植物还可通过合理的花展示、单花内雌雄功能的时空隔离以及传粉后的调控以实现最大程度的异交。此外,影响其传粉者吸引及异交的第三方生物和非生物因素,如食花者和资源配置,也应受到重视。今后随着相关研究的深入和技术手段的革新,研究者应针对鸢尾属植物传粉的热点或有争议的问题,采用花信号定量测定及异交率分子检测等先进技术,通过大范围的对比研究,深入揭示鸢尾属植物与传粉者的互作模式及其繁殖策略。     

毛翠雀花花序内的性分配和繁殖成功

两性花植物花序内不同位置的性分配和繁殖成功一般存在差异,通常认为资源竞争、结构效应和交配环境是形成这种差异的主要原因。为了研究雄性和雌性繁殖资源在花序内不同位置间的最优分配问题,该文以青藏高原高寒草甸典型高山植物毛翠雀花为材料,通过比较花序内不同位置的花部特征和种子性状,对其花序内的性分配模式和雌性繁殖成功进行研究,并通过观察传粉者运动特点以及人工去花和补授花粉实验,探讨花序内资源竞争和交配环境对繁殖资源分配的影响。结果表明:(1)不同位置间的雄蕊数、雄蕊鲜重/雌蕊鲜重、花粉数及花粉胚珠比从花序基部到上部显著增加,而雌蕊鲜重和胚珠数逐渐减少,表现出上部花偏雄的性分配;上部花的结籽率显著低于基部花和中部花,不同位置间的发育种子数/果实和发育种子重/果实随着花位置的升高而显著降低,说明基部花具有更佳的雌性繁殖成效。(2)去花处理后,剩余果实的单个种子重/果实显著增加,但发育种子数/果实没有显著增加;而给上部花人工补授异花花粉后,位置间结籽率的差异消失,说明传粉限制而非资源竞争导致了花序内位置依赖的种子生产模式。(3)毛翠雀花雄性先熟的开花特征,以及传粉者苏氏熊蜂从花序基部到上部的定向访花行为,导致了花序内交配环境的变化。综上结果表明,毛翠雀花花序内的性分配和繁殖成功差异是对交配环境适应的结果,对其在高山环境中实现雌雄适合度最优化具有重要意义。     

荒漠短命植物异喙菊的小花异形性及繁殖特性

异喙菊(Heteracia szovitsii)是分布于新疆北部荒漠、具短寿命花和多态果实的菊科一年生短命植物。本文对该物种的开花式样和花部特征以及繁育系统与昆虫传粉特性进行了研究,以期明确其头状花序中小花的形态差异及其与多态果实间的关系、揭示其在短的花寿命内的繁殖特性。结果表明:该物种头状花序中发育成多态果实的3类小花在数量、冠毛的有无以及舌片长/宽、子房宽、花柱裂片长和子房喙长之间均存在不同程度的差异,且3类小花冠毛的有无以及子房宽和喙长与多态果实的形态一致,说明多态果实的数量与形态在小花发育过程中就已完成分化。花序中的小花每天集中在上午开放,使花序在功能上犹如一朵花,可快速增大花展示和对传粉者的吸引,以使异交在开花后短时间内完成;3类小花的自花花粉均可在花柱裂片上萌发并长出花粉管,说明该物种自交亲和。3类小花不去雄套袋后均能结实,且自然授粉后的结实率显著高于不去雄套袋的,说明该物种能自主自花授粉,且异花授粉促进了结实。3类小花通过雄性先熟以及次级花粉呈现中的泵/刷机制,将花粉呈现在花柱上部和未展开的柱头裂片外侧刷状毛上以及裂片顶端,延长了花粉呈现(雄性阶段)持续的时间,减少了花内雌雄功能间的干扰,有利于传粉者异花传粉,提高了雄/雌性适合度;同时,柱头裂片展开时可将自花花粉落置到裂片上,以完成自主自花授粉。主要传粉者六显甜花蜂(Halictus sexnotatulus)的访花时间与花序开放时间、花粉活力最高期和柱头最佳授粉期高度吻合,有利于雄性阶段花粉的输出以及雌性阶段柱头接受花粉,保障授粉在开花后短时间内快速有效地完成以及异交成功。在新疆北部荒漠的春季环境中,具短寿命花的异喙菊既可在低温多风导致传粉者不足或活动受限时,通过快速自主自花授粉及自交亲和机制来提供繁殖保障,也可在传粉者活动正常时,通过集中开花、雄性先熟及次级花粉呈现等机制来快速完成异交,提高雌/雄性及后代的适合度。     

宁夏枸杞的花粉呈现式样及交配系统研究北大核心CSCD

被子植物的花回馈、雌雄蕊时空分离特征和花粉呈现式样等花部特征及传粉者效率会影响雄性适合度和有性繁殖过程。宁夏枸杞(Lycium barbarum)是中国宁夏、新疆、内蒙等干旱和半干旱地区分布的特有种。该研究对新疆喀什地区宁夏枸杞自然种群的花部综合征、花粉呈现式样、花回馈、传粉者行为与交配方式的关系进行观察及统计分析,以探讨其花粉逐步呈现的适应性及其在提高雌雄繁殖过程中的意义。结果表明:(1)宁夏枸杞的单花寿命为(4.07±0.15) d,而雄性持续时间(0.07±0.01 d)比雌性持续时间短(4±0.01 d);花寿命内雌蕊长度比雄蕊长,属柱头探出式异位类型;花粉呈现式样为不完全逐步呈现。(2)花寿命不同阶段花回馈间存在显著差异。(3)意大利蜜蜂(Apis mellifera)、熊蜂(Bombus sp.)、食蚜蝇(Syrphidae sp.)是宁夏枸杞在自然居群的主要访花者,其中熊蜂和食蚜蝇是主要传粉者,但传粉者效率低,属于高移出低沉积类型。(4)宁夏枸杞的花粉胚珠比(2 448.11±448.32)及授粉实验结果均表现出兼性异交特征;自发自交及人工自花授粉花的座果率及结籽率很低,属于自交不亲和类型;自然传粉花的座果率及结籽率比人工去雄异花低,存在其较高的花粉限制(40.71%)。研究发现,宁夏枸杞花部综合征表现出雌雄异位和花粉不完全逐步呈现式样,这是避免雌雄功能及雄蕊各花药间的干扰、减少花粉同步移出及保障其雄性适合度的有效途径,但自然居群的传粉者种类限制、传粉效率低以及自交不亲性是导致宁夏枸杞花粉限制及降低雌性繁殖成功的主要原因。     

雄蕊合生植物半边莲的花部综合征与繁育系统

 为了解花内雄蕊合生结构的繁殖适应意义, 初步研究了雄蕊合生植物半边莲(Lobelia chinensis)的花部综合征、传粉特性和繁育系统。半边莲花大且鲜艳, 花瓣中下部弯折并合生成背部有裂缝的不封闭的花冠筒。5雄蕊的花药紧密合生成花药筒, 花丝中上半部也合生在一起, 只有花丝基部分离插生于花冠筒上。柱头被包裹在花药筒内。半边莲单花寿命可达5 d左右。雄性先熟, 柱头在伸出花药筒之后才具活性。花的主要访问者为蚂蚁、食蚜蝇和苍蝇类等小型昆虫。半边莲单花花粉数约为(5 200±130)粒、胚珠数约为(55±6)颗, 花粉胚珠比为94.54, 应属于兼性自交繁育系统, 但异交指数和其它特征都显示其以异交为主, 部分自交亲和。套袋和人工授粉实验发现, 半边莲不存在无融合生殖与自发自交, 但自交亲和性高。雄蕊合生(尤其是花药的合生)能把花药中的花粉聚拢在一起在传粉者的一次访问中就被同时带出, 与同样具有较低花粉胚珠比的花粉聚联(Pollen aggregation)传粉过程近似。半边莲的雄蕊合生结构(花药合生成筒、花丝上部也合生)可能与一些特定的花部特征, 如花被合生成未完全封闭的筒、雌雄异熟以及低花粉胚珠比等联系在一起, 形成了适应小型传粉者的“花部综合征”     

5种地黄花部综合特征与繁育系统的初步研究

生殖隔离是物种分化与延续的基础,地黄属植物是否存在生殖隔离仍不清楚。通过实地观测地黄属5个物种(天目地黄、湖北地黄、裂叶地黄、地黄和茄叶地黄)自然种群的花部形态、开花动态、花蜜体积、花蜜的糖浓度及其日变化、杂交指数、花粉-胚珠比等指标,结合人工授粉套袋,对地黄属植物的花部综合特征和繁育系统进行研究。结果显示:(1)地黄属植物的花为两性花,单花花期5～7 d,种群花期40～60 d;5种地黄在花序类型、花形态、花粉量、花粉-胚珠比等方面都存在差异,其中茄叶地黄的花粉完全败育。(2)5种地黄属植物的繁育系统属于异交,部分自交亲和,需要传粉者,不具有无融合生殖特性,地黄与茄叶地黄存在强烈营养繁殖。(3)5种地黄属植物的花朵基部有蜜腺可以产生糖浓度较高的花蜜,这也支持传粉者的存在,但除地黄确定为蜜蜂传粉外,其它地黄植物在野外并未观测到有效的传粉者,可能与地黄的散生特性、生境相互隔离以及传粉观测期气象条件恶劣有关。研究认为,5种地黄属植物较长的花期能有效弥补传粉者访问频率低的不足;除遗传屏障外,推测地黄属5个物种花展示方式的差异可能吸引不同的传粉者,加之地理、生态因素的作用导致了5种地黄属植物繁育系统的分化。     

基于同质园栽培的21种淫羊藿属植物花部特征的分类学意义

以采自中国多地并同质园栽培于吉首大学种质资源圃的21种淫羊藿为研究材料,通过观测这些物种的花梗长、花直径、内萼片长宽、蜜距长、雌雄蕊长、花药长、花柱长、胚珠数、花粉大小及花粉量等16个花部特征数量性状和花序类型、有无蜜距、花瓣颜色、内萼片颜色、内萼片与花瓣相对长度及花粉颜色6个质量性状,并对其分类学意义进行探讨。结果表明,(1)21种淫羊藿内轮萼片花瓣状,4枚花瓣除无距淫羊藿外均特化成蜜距,但花部形态种间存在显著差异,尤其体现于花直径、内萼片长宽、蜜距长、雌蕊长、胚珠数、花粉量、花粉直径等特征。(2)主成分分析显示花直径、内萼片长、花药长、胚珠数和花粉直径等性状信息负荷量较大,在该属分类中起主要作用。(3)根据花部特征聚类分析,物种间区分良好,21物种可分为4支:第1支花小,花瓣短于内轮萼片,囊状距或兜状距;第2支花较大,花瓣远长于内轮萼片,长距状;第3支花小,花瓣没有特化形成蜜距;第4支花较小,花丝伸长明显,可达10 mm,花蜜距呈钻状。(4)依据所观察到的花部形态特征编写了淫羊藿属21种植物花部特征分种检索表。研究认为,基于同质园栽培下的淫羊藿属物种的花部特征具有分类学意义,可以为该属分类提供一定依据。     

塔落岩黄芪主要传粉蜂的传粉效率研究

塔落岩黄芪 (Hedysarum laeve)是毛乌素沙地重要豆科植物, 在我国西部生态系统恢复与重建中起着重要作用, 但其自交率非常低, 必须依靠传粉昆虫授粉才能结实。野生传粉蜂是其主要传粉者。为了明确塔落岩黄芪的主要传粉蜂组成及优势传粉蜂的传粉效率, 2004–2006年, 我们设置了4个2 m×2 m样方观测访花昆虫的组成并对主要传粉蜂的访花频率、花粉移出率和柱头花粉沉降数目及单花停留时间进行了观测。结果表明白脸条蜂(Anthophora albifronella)、海切叶蜂(Megachile maritima)和散熊蜂(Bombus sporsdicus)是塔落岩黄芪的主要传粉蜂, 其中白脸条蜂在数量和访花频率上占有明显优势, 但其花粉移出率比海切叶蜂和散熊蜂的低, 3种蜂的柱头花粉沉降数目没有显著区别。通过对这3种蜂的花粉移出率、柱头花粉沉降数目和访花频率综合分析后, 我们认为白脸条蜂是塔落岩黄芪最有效的传粉蜂。     

Bumblebee-pollination and temporal change of the calyx tube length in Clematis stans(Ranunculaceae)

Clematis stans is dioecious semi-arboreal, with pale purple–blue, nodding, tubulous flowers in a paniculate inflorescence. Both male and female flowers produce nectar from the base of the calyx tube during a flowering period of 3 or 4 days, and are pollinated by two bumblebee species, Bombus diversus and B. honshuensis, with different proboscis lengths. When the flowers open, four sepals constructing a calyx tube separate at the top and their respective tips gradually curl up, so that a tubular part shortens. Observations at two field sites showed that B. diversus (with a longer proboscis) most often visits the flowers with a longer calyx tube, and B. honshuensis (with a shorter proboscis) the flowers with a shorter calyx tube, i.e., later in the flowering period. By changing the calyx tube length, the flowers of C. stans accept the two bumblebee species with different proboscis length as pollinators and thus increase the chance of pollination for each flower. It was also found that the two bumblebee species prefer the male flowers to the female flowers, although the female flowers secrete more nectar as a reward than male flowers. This is likely because they visit the male flowers to collect pollen grains in addition to nectar. Electronic Publication     

An Examination of the Function of Male Flowers in an Andromonoecious Shrub Capparis spinosa

The pollen donor and pollinator attractor hypotheses are explanations for the functions of the male flowers of andromonoecious plants. We tested these two hypotheses in the andromonoecious shrub Capparis spinosa L. (Capparaceae) and confirmed that pollen production and cumulative volume and sugar concentration of nectar do not differ between male and perfect flowers. However, male flowers produced larger anthers, larger pollen grains and smaller ovaries than perfect flowers. Observations on pollinators indicated that two major pollinators (Xylocopa valga Gerst and Proxylocopa sinensis Wu) did not discriminate between flower morphs and that they transferred pollen grains a similar distance. However, there were more seeds per fruit following hand pollination with pollen from male flowers than from perfect flowers. Individuals of C. spinosa with a larger floral display (i.e. bearing more flowers) received more pollen grains on the stigma of perfect flowers. Female reproductive success probably is not limited by pollen. These results indicate that male flowers of C. spinosa save resources for female function and that they primarily serve to attract pollinators as pollen donors.     

Breeding system and bumblebee drone pollination of an explosively pollen‐releasing plant,Meliosma tenuis (Sabiaceae)

• Explosive pollen release is a mechanism used by some angiosperms that serves to attach pollen to a pollinator's body. It is usually adopted by species with zygomorphic tubular flowers and pollinated by birds and bees. The tree genus Meliosma (Sabiaceae, Proteales) has unique disc‐like flowers that are externally actinomorphic, but internally zygomorphic, and release pollen explosively.
• To elucidate the adaptive significance of explosive pollen release, we observed flowering behaviour, the breeding system and pollinator visits to flowers of the Japanese species Meliosma tenuis in a temperate forest. Flowers bloomed in June and were nectariferous and protandrous. Explosive pollen release was triggered by slight tactile stimuli to anther filaments or staminodes in male‐stage flowers.
• Because pollen cannot come into contact with the pistils enclosed by staminodes, M. tenuis is functionally protandrous. Artificial pollination treatments revealed that M. tenuis is allogamous. The dominant flower visitors were nectar‐seeking drones of the bumblebee species Bombus ardens (Apidae). The drones’ behaviour, pollen attachment on their bodies and fruit set of visit‐restricted flowers suggest that they are the only agent triggering the explosive pollen release mechanism, and are the main pollinator of M. tenuis.
• The finding that bumblebee workers rarely visit these flowers suggests that the explosive pollen release has another function, namely to discourage pollen‐harvesting bumblebee workers.

     

Visitation rate of pollinators and nectar robbers to the flowers and inflorescences of Tabebuia aurea (Bignoniaceae): effects of floral display size and habitat fragmentation

Large floral displays favour pollinator attraction and the import and export of pollen. However, large floral displays also have negative effects, such as increased geitonogamy, pollen discounting and nectar/pollen robber attraction. The size of the floral display can be measured at different scales (e.g. the flower, inflorescence or entire plant) and variations in one of these scales may affect the behaviour of flower visitors in different ways. Moreover, the fragmentation of natural forests may affect flower visitation rates and flower visitor behaviour. In the present study, video recordings of the inflorescences of a tree species (Tabebuia aurea) from the tropical savannah of central Brazil were used to examine the effect of floral display size at the inflorescence and tree scales on the visitation rate of pollinators and nectar robbers to the inflorescence, the number of flowers approached per visit, the number of visits per flower of potential pollinators and nectar robbers, and the interaction of these variables with the degree of landscape disturbance. Nectar production was quantified with respect to flower age. Although large bees are responsible for most of the pollination, a great diversity of flower insects visit the inflorescences of T. aurea. Other bee and hummingbird species are highly active nectar robbers. Increases in inflorescence size increase the visitation rate of pollinators to inflorescences, whereas increases in the number of inflorescences on the tree decrease visitation rates to inflorescences and flowers. This effect has been strongly correlated with urban environments in which trees with the largest floral displays are observed. Pollinating bees (and nectar robbers) visit few flowers per inflorescence and concentrate visits to a fraction of available flowers, generating an overdispersed distribution of the number of visits per inflorescence and per flower. This behaviour reflects preferential visits to young flowers (including flower buds) with a greater nectar supply.     

Changes in Florets’ Vertical Direction within Inflorescence Affects Pollinator Behavior,and Fitness in <i>Trifolium repens</i>

Ecological interactions between flowers and pollinators greatly affect the reproductive success. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission, flower rewards and floral vertical direction, in a rhythmic fashion. However, less is known about how plants regulate the relationship between these flower traits to adapt to pollinator visiting behavior and increase reproduction success. Here we investigated the adaptive significance of the flower bending from erect to downward in Trifolium repens. We observed the flowering dynamic characteristics (changes of vertical direction of florets, flowering number, pollen grain numbers, pollen viability and stigma receptivity over time after blossom) and the factors affecting the rate of flower bending in T. repens. Then we altered the vertical direction of florets in inflorescence of different types (upright and downward), and compared the pollinator behaviors and female reproductive success. Our results showed that florets opened sequentially in inflorescence, and then bend downwards slowly after flowering. The bending speed of florets was mainly influenced by pollination, and bending angle increased with the prolongation of flowering time, while the pollen germination rate, stigma receptivity and nectar secretion has a rhythm of “low-high-low” during the whole period with the time going. The visiting frequency of all the four species of pollinators on upward flowers was significantly higher than that of downward flowers, and they especially prefer to visit flowers with a bending angle of 30°–60°, when the flowers was exactly of the highest flower rewards (nectar secretion and number of pollen grains), stigma receptivity and pollen germination rate. The seed set ratio and fruit set ratio of upward flowers were significantly higher than downward flowers, but significantly lower than unmanipulated flowers. Our results indicated that the T. repens could increase female and male fitness by accurate pollination. The most suitable flower angle saves pollinators’ visiting energy and enables them to obtain the highest nectar rewards. This coordination between plants and pollinators maximizes the interests of them, which is a crucial factor in initiating specialized plant-pollinator relationships.     

THE INTRAFLORAL PHENOLOGY OF STREPTANTHUS TORTUOSUS (BRASSICACEAE)

The sequence of floral events during anthesis was examined in Streptanthus tortuosus to determine the relationship between the male and female floral phases. The flowers are strongly protandrous. In the staminate phase, the anthers mature sequentially over a 3–4-day period. Because pollinators quickly remove pollen from the anthers, sequential anther maturation prolongs the male phase relative to what it would be if anthers did not mature sequentially. Pollen applied to the stigma during the staminate phase does not adhere readily and does not germinate. The length of the pistillate phase depends on pollinator activity, as pollination accelerates the abscission of floral parts. Unpollinated flowers remain pistillate for 3–4 days, during which time stigmatic receptivity declines gradually. In the field, 72% to 80% of flowers are staminate at any time, indicating that the staminate phase is three times longer than the pistillate phase when pollinators have access to the flowers. The consequences of the relative length of the floral phases and the schedule of stigmatic receptivity are discussed in terms of outcrossing mechanism, floral longevity, and sexual selection models.     

Sexual differences in reproductive characters and pollinator attractiveness in gynodioecious Glechoma longituba (Lamiaceae)

We quantified the differences in floral characters and attractiveness to flower visitors under natural conditions between the sexual types in the gynodioecious plant Glechoma longituba. We also manipulated flowers by altering corolla size or nectar volume, or by removing anthers, to examine the effect of these primary and secondary attractants (i.e. rewards and advertisements) on attractiveness. A change in corolla size and shape reduced visiting frequency and pollen load. Removal of anthers did not affect visiting rates, but significantly reduced pollination rates and stigmatic pollen load. A decrease in the nectar volume of a flower was associated with a reduction in handling time and pollen loads on stigmas. These results show that corolla size is an important advertisement to pollinators (particularly at greater distance), which associate hermaphrodite flowers with a larger corolla and a larger volume of nectar than female flowers. We found that artificial changes in population structure affected the behavior of pollinators as well as the pollination rates of flowers. We suggest that the pattern of distribution of hermaphrodite and female clones in a population may serve to avoid pollen limitation in a female clone or patch. This effect may ensure female reproductive success and allow for the maintenance of female individuals in natural populations of this gynodioecious plant.     

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright‐coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand‐, self‐ and cross‐pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.     

The dynamics of pollen removal and deposition,and its effects on sexual phases in a protandrous plant: Glechoma longituba (Lamiaceae)

The duration of sexual phases in dichogamous plants are affected by many factors. Using both experimental and observational studies, we investigated natural patterns of pollen removal and deposition, visiting frequency of pollinators, patterns of nectar secretion, and effects of pollen removal and stigmatic pollen deposition on the duration of sexual phases in a protandrous plant, Glechoma longituba. We found that visiting frequency of pollinators correlated with the nectar secretion pattern. The nectar volume during the male phase was higher than during the female phase. In the morning, the main pollinator, the bee Anthophora plumipes, mainly foraged for nectar and showed no preference for flowers in male or female phase, despite male phase flowers producing higher amounts of nectar. However, in the afternoon, they changed their behavior and foraged mainly for pollen, and then showed a preference for flowers in male phase. Furthermore, the rates of pollen removal and stigmatic pollen deposition can affect the starting time and the duration of the female phase. When pollen removal and pollination rates are low due to scarcity of pollinator services, the sexual phase can be prolonged, leading to an overlap, and thereby enhance the chance for sexual reproduction through pollinator‐facilitated self‐pollination. We consider the variation of sexual phases in Glechoma longituba an adaptive mechanism prepared for both cross‐pollination enhancement and reproductive assurance depending on the available pollination services.