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1.
植物的花部性状在异质环境中表现出不均一的适应性进化,其自然变异可能在时空格局上呈现一定的规律性。选择同一物种的不同地理居群进行花部表型变异分析,能揭示花部性状随地理梯度的变异模式。海仙花报春(Primula poissonii)属于典型的二型花柱植物,依赖昆虫传粉实现严格的型间异交。该物种广布于横断山地区亚高山–高山草甸,其分布海拔跨度大且花部性状在种内具有较高变异,但这些变异在不同地理梯度(海拔梯度和经纬度梯度)的特定选择因子作用下的变化规律尚不清楚。本研究选择海仙花报春16个居群,对8个花部关键性状和二型花柱繁殖器官的互补度与海拔和经纬度的关系进行研究,探究花部性状随地理梯度变异的模式及其潜在的选择因素。研究表明,海仙花报春两种花型的花冠管开口大小、花药高度以及短柱花柱头高度与海拔均呈正相关,但两种花型的花冠大小,长柱花的花瓣长度、柱头到花冠管开口的距离,以及短柱花的花冠管长度与海拔高度间均呈负相关,其余性状与海拔无显著相关性。除短柱花中柱头高度以外的性状均随着纬度升高而逐渐减小。长柱花中除花药和柱头间的距离以及柱头到开口的距离外,其余性状均随着经度的增加而减小;短柱花的花瓣长度、花药高度以及花药和柱头间的距离随着经度的增加而变大,其余性状均随着经度的增加而减小。繁殖器官间的互补度并不随地理环境的变化而变化。花部性状的地理变异可能受访花昆虫组成的地理变化驱动。繁殖器官间互补程度的高度保守表明非选型交配在居群二态性的维持和稳定过程中起关键作用。本研究为进一步深入开展报春花属(Primula)花部性状及其选择压力的地理变异研究奠定了基础。  相似文献   

2.
为了解濒危二型花柱植物安徽羽叶报春(Primula merrilliana)居群的形态变异,对其4个核心居群和3个边缘居群的14个形态性状进行了比较研究。结果表明,核心居群形态性状的变异系数为0.09~0.50,边缘居群为0.05~0.56,变异幅度两者间差异不明显;核心居群有8个性状的均值显著高于边缘居群(P0.05),仅有3个性状(花冠直径、花瓣宽和叶宽)为边缘居群高于核心居群。核心居群两型花间的互惠指数较高也较稳定(0.83~0.90),花型间互惠程度较高,而边缘居群的互惠指数差异较大(0.60~0.93),不同居群的互惠程度变化较大。因此,两型花柱植物安徽羽叶报春的形态性状变异基本支持"中心丰富模型"假说,并对其保护策略进行了探讨。  相似文献   

3.
安徽特有植物安徽羽叶报春的繁殖生物学研究   总被引:1,自引:0,他引:1  
陈明林 《生物多样性》2007,15(6):599-607
本文分别从物候、繁育结构和传粉等方面研究了国家三级保护植物、安徽特有种——安徽羽叶报春(Primula merrilliana)的繁殖生物学特征。研究结果表明:(1)安徽羽叶报春是典型的形态和功能意义上的花柱二型的二年生植物,其始苗期为9月,一直持续到第二年6月底或7月初死亡,各居群长柱花植株比短柱花植株开花略早3-5d;(2)安徽羽叶报春的散孔型花粉显示其在报春花属中有重要的系统意义和进化意义。同时,短柱花花粉量比长柱花少,但其花粉直径是后者的1.78倍左右;(3)长花柱的雌蕊长度是短花柱的1.64倍,而且其柱头上的乳头状突起比短花柱上的长而稀;(4)3个研究居群的P/O比都不相同,我们发现花粉量比胚珠数量有更大的变异,这可能与生境有关;(5)安徽羽叶报春为异花授粉植物,蓟马属(Thrips)昆虫为其重要的传粉者,其同型花授粉可育性远比异型花授粉的高;(6)其长、短柱型种子没有明显的形态差异,多属不等边七面体,少为其他多面体。据研究,在小居群中两种花柱类型植株的比例失衡,生境的破坏和伴生种的消失可能是导致安徽羽叶报春濒危的重要原因。  相似文献   

4.
 被子植物虫媒传粉植物的物种分化通常被认为是花性状响应传粉环境(传粉者)的空间变异而发生适应性分化的结果。通过对鼠尾草属(Salvia) 3个物种(共4个居群)传粉互作系统的比较, 探索了花性状对不同传粉环境的进化响应。结果表明: 各居群的传粉者组成、主要传粉者类型及其大小各不相同, 杠杆状雄蕊及相关花部性状大小在不同居群间具有显著差异; 各居群均表现出腹部传粉和背部传粉2种传粉模式, 但背部传粉仍然是最有效的传粉方式; 居群间杠杆状雄蕊长度与传粉者体长表现出极显著的正相关, 然而花冠长与传粉者体长表现出负相关; 花冠口高度和柱头高度与传粉者胸厚也表现出一定的协同变异。鼠尾草属植物的杠杆状雄蕊及相关花部性状在传粉系统的进化过程中表现出高度的可塑性, 表明雄蕊杠杆传粉机制对传粉环境的变异非常敏感, 在该属植物的物种分化过程中具有关键作用。  相似文献   

5.
异型花柱是一种受遗传因素控制的花型多态性现象,包括二型花柱和三型花柱两种类型.本文以茜草科艳丽耳草(Hedyotis pulcherrima)为实验材料,通过对其野外居群的花型、花部形态及花粉特征等观察,发现艳丽耳草野外居群同时存在长花柱型花和短花柱型花,长/短花柱型花的数量比例为1∶1.两型花具有精确的交互式雌雄异位特征,并且该特征与花冠长度相关性显著.长/短花柱型花的柱头裂片长度、花粉大小及淀粉含量等具有二型性.花粉体外培养时花粉萌发率及花粉管生长速率无显著性差异.人工授粉后,艳丽耳草长/短花柱型花型间异交花粉管生长形态正常,授粉24 h后花粉管均已进入子房.而长/短花柱型花在自交及型内异交下均表现为不亲和,花粉管生长停止于柱头,花粉管顶端累积胼胝质并膨大.艳丽耳草没有无融合生殖现象,型间人工辅助异交授粉结实率为100%,显著高于自然结实率.本研究结果表明,艳丽耳草是典型的二型花柱植物,并具有异型自交不亲和系统.  相似文献   

6.
连翘花的结构与繁育系统研究   总被引:6,自引:2,他引:4  
通过定株观察、解剖和人工套袋交叉授粉试验对连翘花的生长发育和繁殖系统进行研究.结果表明:(1)连翘具有2种避免自交的方式,雌雄异位和雌雄异熟.其雌雄异位表现为长雄蕊短雌蕊花型和短雄蕊长雌蕊花型;雌雄异熟表现为长雄蕊短雌蕊花型为雄蕊先于雌蕊成熟,短雄蕊长雌蕊花型表现为雌蕊先于雄蕊成熟.(2)连翘花P/O值测定和户外套袋交叉授粉试验显示,P/O值为2 000±300;不同类型花的异花授粉结果率在50.64%~80.32%,其中短型花的花粉授到长型花柱头的结果率最高,达80.32%,而长型花和短型花的同型花授粉结果率分别为2.92%和34.15%,表明连翘的异花授粉结果率高于自花授粉,以异交为主,其繁育系统属兼性异交.研究结果认为,连翘雌雄异位和雌雄异熟是其自然结果率低下的主要原因,为进一步探讨连翘在木犀科中的系统进化提供了生殖生态学的依据.  相似文献   

7.
黑果枸杞(Lycium ruthenicum)是中国西北地区极端环境中分布的国家二级保护植物, 该物种在新疆南部的自然种群中出现了同型花柱类型(同位花)和柱头探出式雌雄异位类型(异位花)个体, 并且遭遇沙尘暴频繁的种群中异位花个体出现频率减少。该研究对喀什市自然种群中黑果枸杞两种不同花型植株的花部综合征和传粉特性进行比较研究, 以期探讨该物种不同花型植株在南疆早春极端环境中的花部特征的可塑性及其适应性机制。结果表明: 同位花雌雄蕊高度间无显著差异, 而异位花雌蕊高度显著高于雄蕊; 同位花花冠直径、花冠筒长、胚珠数均高于异位花, 而异位花雌雄蕊空间距离、花粉数及花粉胚珠比均比同位花高。黑果枸杞同位花个体比例(68%)高于异位花个体(32%), 种群水平及个体水平同位花花期((117.00 ± 2.25) d, (101.65 ± 1.98) d)比异位花((26.00 ± 1.00) d, (18.75 ± 1.00) d)长, 而单花水平上异位花单花寿命((4.50 ± 0.14) d)比同位花((3.13 ± 0.11) d)长。两种类型花在花早期(紫色)分泌的花蜜量均高于花后期(白色)。在紫色花阶段(花开放早期), 同位花上的主要传粉者意大利蜜蜂、熊蜂和食蚜蝇的访花频率和停留时间均高于异位花; 而白色花阶段(花开放后期)意大利蜜蜂、熊蜂在异位花上的访花频率比同位花高。在不同花色阶段, 同位花柱头花粉落置数、花粉移出率、花粉传递效率均比异位花高, 并且同位花自然坐果率及结籽率均比异位花高。在新疆南部的沙尘暴极端环境下, 同位花通过较高的自交亲和性保障繁殖, 而异交为主的异位花提高了异交率。异位花与同位花在花部综合征和花报酬上的差异, 是影响其繁殖成功的主要因素。  相似文献   

8.
二型花柱植物通常具有自交不亲和性,在不同植物中所表现的可育性不同。欧报春(Primula vulgaris)是典型的二型花柱植物,为了探究欧报春的繁育特性,通过温室栽培,对欧报春的长花柱和短花柱的花部特征、花粉和花柱形态、花粉活力、柱头可授性、花粉/胚珠比、杂交指数、杂交亲和性、花粉管观察进行研究。结果表明,(1)长花柱和短花柱的花冠直径、花冠筒长度、柱头高度、花药高度和花筒中部直径均表现出两型性;(2)花粉和柱头观察发现花粉极轴长、花粉赤道轴长、花柱直径、柱头乳突细胞和花粉数量均有差异;(3)长花柱的花粉/胚珠比为384.20,短花柱为369.70,属于兼性异交类型;长花柱和短花柱的花粉活力和柱头可授性能在较长时间内维持较高活力;(4)长花柱杂交指数值为5,短花柱为4,表明繁育系统类型为异交,部分自交亲和,需要传粉者;6种授粉组合均能结实,异型花间授粉的结实数明显高于同型自花授粉和异株同型授粉;短花柱为母本的异型花间授粉组合亲和性优于其他组合;欧报春存在自交不亲和性,长花柱的自交不亲和性低于短花柱。  相似文献   

9.
阮成江 《广西植物》2008,28(2):143-147
报道了连翘中的二型花柱(长花柱和短花柱)。长花柱的柱头和雄蕊高度分别为6.12±0.05 mm和2.35±0.04mm,短花柱则为2.23±0.04mm和6.02±0.06mm。短花柱花的花冠大小明显超过长花柱。开放授粉条件下,长短花柱花的座果率分别为9.11 %±0.04%和8.93 %±0.07%。人工异交的座果率在长-短(36.8%±0.04%)与短-长(36.2%±0.07%)组合间无明显差异(F(1,39)=1 .38,P=0.14)。人工异交实验表明,传粉者限制可能发生在生长于中国东北部的人工连翘种群中,这可能是因为该地区早春的低温和多风气候条件影响传粉者的种类和活动。  相似文献   

10.
绣球茜的二型花柱及其传粉生物学初步研究   总被引:1,自引:0,他引:1       下载免费PDF全文
首次对绣球茜(Dunnia sinensis Tutch)的花药和柱头高度、花粉和柱头形态,以及人工辅助授粉的结实情况等进行了研究.结果表明:绣球茜在同一居群中同时具有长花柱(Pin 型)和短花柱(Thrum)两种花型,长花柱植株的柱头和雄蕊高分别为9.61±0.36 mm和6.79±0.38 mm,短花柱则为6.11±0.56 mm和8.96±0.59 mm,表现出互补式雌雄异位的花部特征.通过人工辅助授粉,两种花型植株的自交和同型植株间异交都不结实,仅在型间异交方能正常结实,说明绣球茜中存在极强的自交不亲和和型内不亲和现象.在花粉与柱头形态方面:长柱型花的单花花粉量(38555.6±6258.4)显著地小于短柱型花(52145.45±8924.5)(t=4.009,P<0.01),长柱花和短柱型花的胚珠数分别为38.73±1.85和39.1±2.25(t=-4.13,P>0.01);长柱型花花粉粒的大小(极径21.27±0.70 μm)显著地小于短柱花(21.92±0.79μm)类型(t=3.890,P<0.01),而柱头乳突大小长柱类型要大于短柱类型,表现出明显的二型性.研究结果表明绣球茜是一种典型的二型花柱植物.此外,对其传粉昆虫及昆虫访花行为的观察表明,蝶类(青风蝶属Graphium)和蜂类(熊蜂Bombus sp.和木蜂Xylocopa magnifica Smith)为绣球茜的主要访花昆虫和传粉昆虫,它们能够在两种不同花型植株之间有效地传粉.  相似文献   

11.
Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma-anther separation is bimodally distributed and can be used to identify a long-styled and a short-styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self-compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short-styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long-styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short-styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.  相似文献   

12.
Heterostyly is a genetic polymorphism in which plant populations possess two (distyly) or three (tristyly) morphs with flowers differing reciprocally in stigma and anther height. Sex organ deployment has been described as being highly variable among and within species of several distylous taxa belonging to different taxonomic groups. However, the number of studies considering within‐species disparities is still limited. For a better overview of the existing amount of variation that can occur within and between heterostylous species, we sampled 46 populations of six Melochia spp., a style‐polymorphic genus in Cuba. We characterized the floral morphology in all populations and described a set of ancillary characters per species. All of these Melochia spp. are distylous, except for the monomorphic M. nodiflora. The S‐morph produces fewer, larger pollen than L‐morphs, and has verrucose ornamentation. The L‐morph produces reticulate pollen and has larger stigmatic papillae than the S‐morph. The monomorphic M. nodiflora shows ancillary characteristics that are similar to the L‐morph individuals in the related species. As expected, there are differences in ancillary characters among species and also dissimilarities in reciprocity among and within species of Melochia. Our results highlight the importance of considering intraspecific variation in the morphometric characterization of heterostylous taxa. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 147–158.  相似文献   

13.
Heterostyly is a stylar polymorphism that has been shaped by the evolution of floral characters adapted for efficient pollen transfer. Different types of stylar polymorphism are described in which the discrete characterization of the exact polymorphic type (e.g., distyly vs. stigma-height dimorphism) requires detailed floral measurements (e.g., sex-organ reciprocity). In clonal and aquatic Nymphoides montana, although the presence of two floral morphs that contain styles of two lengths has been previously reported, no studies have quantitatively estimated the level of reciprocity and/or described the stylar condition. Morphological variations and incompatibility relationships were explored between the two morphs in three southeastern Australian populations. In this study, one population is characterized as stigma-height dimorphism (i.e., two morphs with discrete variation in stigma height but little variation in anther height), whereas the other two populations are typical distylous (i.e., two morphs for reciprocal stigma and anther height). Nymphoides montana is dimorphic in a wide range of ancillary characters, including corolla size, stigma size, shape and papillae morphology, and pollen size, number and exine sculpture. Following glasshouse pollinations, full incompatibility systems were observed in the distylous populations, whereas the stigma-height dimorphic population showed between-morph variation in the extent of incompatibility. Despite the variation in sex-organ reciprocity and incompatibility, other lines of evidence appear to assure the maintenance of the stylar polymorphism in the N. montana study populations. All populations are nearly isoplethic (i.e., both morphs in equal frequencies), which is indicative of balanced polymorphisms that appear to be maintained by legitimate pollen transfer between the morphs.  相似文献   

14.
异型花柱是一种受遗传因素控制的花型多态性现象,其适应意义在于提高不同花型间传粉精确性,从而促进异交。为检验二型花柱植物滇丁香(Luculia pinceana)是如何促进异交并确定有效传粉者的类型,实验统计自然种群中长、短柱型的植株数量,测量花部特征,统计自然种群植株柱头上的型间花粉落置的数量和比例,比较型内、型间花粉的萌发率以及花粉管长度,比较不同人工授粉处理结实情况,观察传粉昆虫类型并测量虫体特征。结果表明(1)滇丁香自然居群中长、短柱型植株的数量没有显著性差异。长柱型的筒深、筒直径、开口直径、雄蕊长和柱头长均显著小于短柱型,而长柱型的叶片长和宽、雌蕊长、花药体积、花粉粒体积、柱头厚均显著大于短柱型。(2)自然种群植株柱头上型间花粉所占比例显著低于型内花粉的比例。(3)型间授粉的花粉萌发率以及花粉管长度均大于型内授粉和混合授粉。(4)型间授粉的结实率显著高于型内授粉的结实率,型内授粉具有一定的结实。(5)夜行性长喙条背天蛾(Cechenena lineosa)是滇丁香的有效传粉者,其吻长和滇丁香的花筒深相适应。本研究表明二型花柱植物滇丁香主要是通过与其花部特征相匹配的长喙天蛾实现有效的传粉,通过促进型间花粉的萌发和花粉管的伸长而有利于型间授粉结实,提高传粉精确性。  相似文献   

15.
Background and Aims Distyly is a floral polymorphism characterized by the presence of two discrete morphs with reciprocal positioning of anthers and stigmas in flowers on different plants within the same population. Although reciprocal herkogamy and associated floral traits are generally thought to be discrete and strict polymorphisms, little is known about variation in floral traits related to the distylous syndrome within and among populations of a single species. In this study, variation in floral morphology and reciprocal positioning of the sexual organs in the distylous Primula veris (cowslip) is quantified.Methods Data were collected in ten populations occurring in two contrasting habitat types (grasslands and forests), and for each population the average level of reciprocity was assessed, the strength of the self-incompatibility system was determined, and seed production under natural conditions was quantified.Results In grassland populations, flowers showed clear distyly with low and symmetric reciprocity indices at both the lower and upper level. In forests, P. veris produced larger flowers that showed strong deviations in stigma–anther separation, especially in the L-morph. This deviation was mainly driven by variation in stigma height, resulting in high and asymmetric reciprocity indices and the occurrence of several short-styled homostylous plants. Self-incompatibility was, however, strict in both habitats, and morph ratios did not differ significantly from isoplethy. The observed shift in reciprocity in forest populations was associated with a significant reduction in seed production in the L-morph.Conclusions The results indicate that populations of P. veris show habitat-specific variation in flower morphology. Deviations from perfect reciprocal positioning of stigmas and anthers also translate into reduced seed production, suggesting that small changes in sexual organ reciprocity can have far-reaching ecological and evolutionary implications.  相似文献   

16.
  • Populations of heterostylous plant species are ideally composed of equal frequencies of two (distylous) or three (tristylous) morphologically different floral morphs. Intra-morph incompatibility helps to avoid inbreeding and to maintain genetic diversity, supporting plant fitness and long-term viability. Habitat fragmentation can lead to skewed morph ratios and thereby reduce the abundance of compatible mates. This, in turn, can result in a loss of genetic diversity. We tested whether the genetic diversity of heterostylous plants is affected by morph ratio bias using populations of the distylous grassland plant Primula veris in recently fragmented grasslands.
  • We recorded morph frequencies and population sizes in 30 study populations of P. veris on two Estonian islands characterised by different degrees of habitat fragmentation. Examining variation of thousands of single nucleotide polymorphisms (SNPs) and heterostyly-specific genetic markers, we quantified overall and morph-specific genetic diversity and differentiation in these populations.
  • Morph frequencies deviated more in smaller populations. Skewed morph ratios had a negative effect on the genetic diversity of P. veris in more fragmented grasslands. In the populations of better-connected grassland systems, genetic differentiation among S-morphs was higher than among L-morphs.
  • Our study shows that deviations from morph balance are stronger in small populations and have a negative impact on the genetic diversity of the distylous plant P. veris. Together with the direct negative effects of habitat loss and decreased population size on the genetic diversity of plants, morph ratio bias may intensify the process of genetic erosion, thus exacerbating the local extinction of heterostylous species.
  相似文献   

17.
  • Studies of floral polymorphisms have focused on heterostyly, while stigma‐height dimorphism has received considerably less attention. Few studies have examined the reproductive biology of species with stigma‐height dimorphism to understand how factors influencing mate availability and pollen transfer are related to morph ratios in populations.
  • Floral morphological traits, especially herkogamy and reciprocity, pollinator visitation, breeding system and spatiotemporal mate availability, are known to affect inter‐morph pollination and morph ratios in species with stigma‐height dimorphism. In this study, we investigated the presence of stigma‐height dimorphism and estimated morph ratios in four naturally occurring populations of Jasminum malabaricum. We quantified morph‐ and population‐specific differences in the abovementioned factors in these populations to understand the observed morph ratios.
  • The positions of anthers and stigmas were characteristic of stigma‐height dimorphism, the first report of this polymorphism in the genus. All study populations were isoplethic, implying equal fitness of both morphs. Herkogamy was higher in the short‐styled morph, while reciprocity was higher between the long‐styled stigma and short‐styled anthers. Long‐ and short‐tongued pollinators were common floral visitors, and we observed no differences between morphs in spatiotemporal mate availability or pollinator visitation. Neither morph exhibited self‐ or heteromorphic incompatibility.
  • The short‐styled stigma had lower reciprocity but likely receives sufficient inter‐morph pollen from long‐tongued pollinators, and also by avoiding self‐pollination due to higher herkogamy. These results highlight the importance of sufficient effective pollinators and floral morphological features, particularly herkogamy, in maintaining isoplethy in species with stigma‐height dimorphism.
  相似文献   

18.
BACKGROUND AND AIMS: Because distylous species have two hermaphroditic style-length floral morphs, they face two sex allocation problems: the equilibrium morph ratio and the optimal allocation to pollen and seed production in each floral morph. Gender specialization is expected among distylous species when floral morphs differ in reproductive output. However, spatio-temporal variability in female reproductive output between morphs needs to be investigated to fully understand patterns of sexual expression and gender specialization in distylous plants. Between-year variation in flower and fruit production of hummingbird-pollinated Palicourea padifolia (Rubiaceae) was examined, focusing on functional gender expression of long- and short-styled morphs and comparing their reproductive performance in five consecutive years (1998-2002). METHODS: Between-year variation in inflorescence, floral bud and fruit production was monitored and quantified. These traits were then used as parameters to determine functional gender differences between floral morphs through time. KEY RESULTS: Inflorescence production varied among years but no significant differences were found between floral morphs. Long-styled plants initiated more floral buds per inflorescence every year than short-styled plants, suggesting higher allocation to pollinator attraction and, potentially, an increase in male fitness through pollen donation. Although fruit production was similar between morphs, their functional gender shifted across years. CONCLUSIONS: The gender expression inconsistency across years is surprising because a number of floral characters and attributes that contribute to differently attracting and rewarding effective pollinators in P. padifolia suggest gender specialization. The evidence that morphs of distylous species might specialize in functional gender mostly comes from differences among populations in seed production and non-equilibrium morph ratios based on 1-year field population surveys. The results suggest that more sampling through time is needed to detect gender specialization among distylous species with a perennial habit.  相似文献   

19.
Hedyotis caerulea possesses two distinct floral morphs that are generally found in equal numbers in naturally occurring populations. Flowers either possess a relatively long style and short anthers, called a “pin,” or a short style and long anthers, called a “thrum.” This placement of reproductive organs is considered herkogamous and distylous, as it encourages outcrossing by restricting pollination to individuals of the alternate morph. Numerous species have been described as distylous without quantitative data establishing stigma-anther reciprocity. Here we assess those assumptions in H. caerulea by measuring stigma height, anther height and a suite of additional floral traits across multiple localities. All populations surveyed were isoplethic, although variation among them was present in all floral traits measured as well as for pollen diameter, pollen count, flower dry weight, and seed set. Pins produced smaller pollen than thrums, but made more of them. Thus, the total volume of pollen was similar for pins and thrums, and seed set was similar, suggesting that each morph has equal male and female fitness with no movement towards dioecy. Given a significant degree of variation found in the morphometric analysis, and that two of the three measures used to assess reciprocity were not consistent with predictions of precise symmetry, extensive change is possible where selection is acting on these traits. Even so, the distylous mating system in H. caerulea appears to be stable.  相似文献   

20.
Heteromorphic characters and structural features of the pollen tube pathway are described in tristylous Pontederia sagittata to assess their influence on the pollination process and in mediating self-incompatibility behavior. Heteromorphic characters that distinguish the floral morphs include style length, stigma depth, stigmatic papillae length, stylar parenchyma cell length, area of the stylar canal, stamen height, anther size, and pollen size. Unlike several distylous species that have been investigated, the exine of pollen in P. sagittata was not strongly differentiated among the pollen types, and no differences in stigma cytochemistry were apparent. Features common to the floral morphs were a wet stigma, a hollow trilobed stylar canal separating into two sterile and one fertile canal, and a single anatropous ovule with a highly elaborated integumentary obturator. The similarity in structural features of the pollen tube pathway of P. sagittata to those found in monocotyledonous taxa with gametophytic self-incompatibility suggests that phylogenetic constraints may have influenced the evolution of trimorphic incompatibility in the Pontederiaceae.  相似文献   

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