露蕊乌头花性状的表型选择

为解释植物的花性状的进化机制,分析选择作用的强度和方向是必须的方法之一。采取表型操控实验和表型选择分析,通过人为增加露蕊乌头侧萼片开度,本文揭示了露蕊乌头花性状与适合度的关系,探究了花性状的表型选择作用。结果发现,增加侧萼片开度后,传粉者首访的频率及访花的总次数降低,但对单花种子产量没有影响;露蕊乌头的株高、花数目、盔高及侧萼片宽度均受到总选择作用,而花数目和株高的选择梯度显著,受到了直接选择作用;而花数目则受到稳定选择,即中等开花数目具有更高的种子产量。以上结果表明,侧萼片宽度是露蕊乌头吸引传粉者的主要特征,而花序越高、花数目适中的植株,种子产量也越多。     

Pollinator-dependent evolution of floral trait combinations in an orchid herb

作为驱动花性状进化的重要媒介之一,传粉者塑造了被子植物多样的花部特征。目前,大部分研究集中于传粉者驱动被子植物单个性状的进化,而较少涉及对传粉者驱动被子植物组合性状进化的研究。本研究以兰科植物绶草(Spiranthes sinensis)为材料,分别鉴别和估算了传粉者对植物单个性状和组合性状施加的定向选择和关联选择压力。研究结果表明,传粉者对开花时间和花大小施加定向选择压力,传粉者选择早开花、花更大的个体。传粉者对绶草花展示的组合性状(花大小与花数目)施加正向的关联选择压力,而对开花时间与花展示的组合性状(开花时间与株高、开花时间与花数目)施加负向的关联选择压力。同时,传粉者的选择强度在年际间存在差异。该研究证实了传粉者在驱动植物组合性状进化过程中的作用,同时强调在认识和理解被子植物表型性状进化轨迹时,需要考虑植物组合性状的影响。     

海拔对全缘叶绿绒蒿植株性状和花特征的表型选择分析

为了研究海拔差异对植株性状、花特征表型选择的影响,以青藏高原高寒草甸的全缘叶绿绒蒿（Meconopsis integrifolia）为研究材料,于盛花期内,测定不同海拔（4 452、4 081和3 681 m）种群中个体植株性状、花特征、单果结实数并进行统计分析,采用线性回归模型估计不同海拔种群间植株性状、花特征所受的表型选择（选择差与选择梯度）。结果表明：（1）随着海拔升高,全缘叶绿绒蒿植株性状、花特征及单果结实数显著降低,海拔越高的种群中株高越矮、叶面积越小、花数越少、花越小、单果结实数越低。（2）不同海拔种群中各性状的表型选择存在差异,较低海拔（3 681 m）种群中花数、花大小具有显著的选择差和选择梯度,表现为花越多、花越大的个体雌性适合度越高;海拔较高（4 081 m）的种群中株高、叶面积及花数更容易受到选择,表现为植株越高、叶面积越大、花越多的个体雌性适合度越高;海拔最高（4 452 m）的种群中叶面积与花数的选择梯度接近显著。（3）植物性状分化伴随着海拔的变化而呈现出差异,较低海拔种群中花特征容易受到选择,而较高海拔种群中可能由于传粉者稀少、资源限制等因素使得株高、叶面积更容易受到选择。     

展毛翠雀花期繁殖特征和生物量分配对放牧的响应

生物量分配影响植物生长和繁殖,是植物生活史研究的重要内容。为了了解植物生活史性状对放牧的响应,该研究以青藏高原高寒草甸毒杂草展毛翠雀为对象,分析了放牧干扰对展毛翠雀的花期繁殖分配和性分配的影响。结果表明:放牧显著降低了展毛翠雀的总生物量、个体大小和繁殖投入; 放牧未改变展毛翠雀的营养部分与繁殖部分的等速生长关系,但显著增加了繁殖部分的生物量分配和总花数; 展毛翠雀的个体大小与总花数呈显著的正相关关系,但与性分配呈显著的负相关关系; 展毛翠雀的总花数与单花大小、单花的花瓣比例均表现出负相关关系,表明总花数与单花大小之间、总花数与单花的花瓣比例之间均存在权衡。因此,在放牧条件下,展毛翠雀的繁殖分配和性分配均表现出显著的可塑性。     

毛茛状金莲花不同花期的花特征和访花昆虫的变化及表型选择

为了研究植物生长季内开花时间对花特征表型选择的影响,我们以青藏高原东缘高寒草地的毛茛状金莲花Trollius ranunculoides)为实验材料,在生长季内不同开花时间(花前期、花末期)测定花特征,观察访花昆虫的类群和访花频率,生长季结束后收集种子.根据昆虫访花的喜好和季节内类群与访花频率的变化,分析了不同开花时间毛茛状金莲花的花特征与昆虫的选择;并用种子产量表示雌性适合度,估计了毛茛状金莲花的花特征在不同开花时间所受的表型选择.结果表明:不同花期植物的花特征有显著差异,相应的访花昆虫的类群和频率也存在差异,不同类群昆虫访花喜好也不一样.蜂喜好花瓣和花萼较宽、花茎短和花茎数少的个体,这正符合花前期的特征,因而蜂的访花频率在花前期较高;蝇对花特征没有明显的偏好.而通过雌性适合度估计毛茛状金莲花花特征所受的表型选择则是:花前期,花茎较长和花茎数多的植株适合度大;花末期,花茎数多的植株适合度大.我们的研究表明:在植物生长季,花期的分化伴随着传粉昆虫活动的变化.不同花期,访花昆虫的变化可能对植物花特征的分化起了至关重要的作用.但是访花昆虫对花特征的选择与通过雌性适合度估计植物受到的选择不尽相同,这可能是由于其他因素造成的.     

Vegetation context modifies selection on flowering start and plant height in an orchid perennial herb

背景环境影响兰科植物绶草开花时间和株高性状获得的表型选择 摘要：厘清背景环境因素(本研究定义为目标植株周围物种的数量、密度以及植株高度)对植物花性状获得表型选择压力的影响，是认识和预测同域开花物种-种间竞争环境下植物花性状进化模式和进化轨迹的关键环节；同时，对认识和理解传粉者施加的表型选择在时空上的变化具有重要作用。本研究以兰科多年生草本植物绶草(Spiranthes sinensis)为材料，通过人为降低绶草周围植株高度，连续两年定量衡量背 景环境因素分别通过结实数和花粉输出途径对绶草4个花性状(开花时间、株高、花冠大小和花数目)获得表型选择的影响。研究结果表明，降低周围植株高度导致的背景环境改变对开花时间和株高等表型性状具有选择作用：改变了的背景环境选择开花时间更早、株高更矮的绶草植株个体，且两类性状获得的表型选择强度于年际间存在差异。进一步研究表明，这种背景环境的改变通过雌性适合度产生的影响强于通过雄性适合度。本研究证实了背景环境因素在驱动被子植物花性状分化和塑造花多样性过程中的潜在作用。     

毛姜花原变种花寿命对两性适合度的影响

植物的花寿命被认为是由雌、雄适合度的增长和维持花开放的花费之间的平衡来决定的。姜花属(Hedychium)是姜科唯一一个从热带到高海拔地区分布的大属, 属内不同种类植物的花寿命差异很大。毛姜花原变种(H. villosum var. villosum)的花寿命为5 d, 显著长于其它同域分布的姜科植物。通过人工剪除毛姜花原变种的柱头来使花朵具雌性功能的时间缩短, 结果显示: 在不同的处理中, 结实率随花朵具雌性功能时间的延长而增加, 开花1 d后剪除柱头的结实率为1.85% ± 1.59%, 极显著低于对照的结实率20.96% ± 4.13%, 说明其较长的花寿命能显著地增加传粉的成功率和结实率, 长达5 d的花寿命有利于雌性适合度的提高。同时, 毛姜花原变种开花1 d后, 剩余的平均花粉数和总平均花粉数没有显著差异, 而开花后2、3和4 d后剩余的平均花粉数则极显著少于总平均花粉数, 说明随着花寿命的延长, 花粉输出量也显著增加, 其长达5 d的花寿命也有利于其雄性适合度的提高。较长的花寿命在毛姜花原变种拓展新的生境、向更高海拔地区的扩散中也许起着重要的作用。姜科植物有着极其多样性的传粉和繁育系统, 花寿命在姜科植物传粉和繁育系统的多样性形成及其进化中起着重要作用, 同时, 较长的花寿命有效地提高了雌性适合度和雄性适合度, 从而使姜科植物能脱离热带生境, 向更高海拔的地区扩散, 花寿命在姜科植物从热带地区到高海拔地区的分布过程中也起着重要作用。     

蓝翠雀花退化雄蕊上的黄色髯毛对其繁殖成功的影响

蜜导是一类对传粉者具有特殊吸引和指示作用的花图案或花结构,在被子植物尤其是虫媒花中普遍存在,但目前有关蜜导对植物繁殖成功影响的研究相对较少.在野外条件下,我们以毛茛科翠雀属的蓝翠雀花(Delphinium caeruleum)为研究对象,通过人工授粉和去除髯毛实验对其交配系统和退化雄蕊上黄色髯毛的作用进行了初步研究,以探讨蜜导对于蓝翠雀花雌雄繁殖适合度的影响.结果发现,蓝翠雀花自交亲和,但其雌雄异熟和雌雄异位相结合的花特征完全避免了自动自交,因此该物种是专性异交植物,其传粉过程需要传粉者协助才能完成.与对照相比,去除髯毛处理显著降低了花粉的输出总量,但坐果率和结籽数并没有显著降低.我们的研究结果表明,蓝翠雀花退化雄蕊上的髯毛确实起到了蜜导的作用,但蜜导的存在主要提高了该植物的雄性繁殖适合度,表明雄性适合度的繁殖成功在蓝翠雀花的花进化过程中具有重要的作用,但这一结果仍有待在更多的居群中做进一步的验证.     

Phenotypic variations in cones and seeds of natural Pinus kesiya var. langbianensis populations in Yunnan Province,China

以云南省思茅松(Pinus kesiya var. langbianensis)天然分布区的11个种群的16个种实性状为研究对象, 采用巢式方差分析、变异系数、相关分析和非加权配对算术平均法(UPGMA)等多种分析方法, 探讨思茅松种群间和种群内的表型变异。结果表明: 思茅松种实表型性状在种群间和种群内均存在着较丰富的差异, 种群内的变异(54.76%)大于种群间的变异(10.44%), 种群间平均分化系数为11.95%, 分化程度相对较小。球果总种子数的平均变异系数最高(35.51%), 其次是球果质量(35.1%), 种子大小的平均变异系数最小(8.86%), 成为最稳定的种实性状; 景谷县的表型多样性最丰富, 景洪市则最小。球果和种子大部分表型性状之间存在显著或极显著相关, 其中球果长和球果质量越大, 种鳞长、种子长、种翅长、千粒重、球果总种鳞数和球果总种子数就越大。生态因子中, 年平均气温对表型性状影响最大, 其次是1月平均气温和>5 ℃积温。利用种群间聚类分析可以把思茅松的11个种群分为2类4个亚类, 表型性状依据地理距离进行聚类, 聚类结果与年降水量和>5 ℃积温相关性显著。     

灌木铁线莲繁育系统特征及其花下垂现象的适应性意义

该研究对兰州市北山地区自然居群下的灌木铁线莲(Clematis fruticosa Turcz.)的繁育系统特征进行了实验分析,并通过对其花朵进行人工上举处理,研究了花朝向改变(花朵上举)后访花昆虫、花粉数量和质量变化以及结籽率和种子特征的变化,以此反证花朵下垂的适应性意义。结果表明:(1)自然状态下,灌木铁线莲的P/O值为9579.5,属于专性异花授粉;套袋实验结果显示,灌木铁线莲自交亲和,兼具异交和自交的混合交配系统,但不存在无融合生殖现象。(2)灌木铁线莲的主要传粉者为东亚无垫蜂(Amegill aparhypate)和中华蜜蜂(Apis cerana);人工上举处理改变花朝向后,两种传粉昆虫的访花频率和单花停留时间与自然条件下没有发生变化,但因雨水冲刷造成其花粉数量显著下降,且阳光直射使花粉活力显著下降,说明花朝向改变会降低其雄性适合度。(3)花朝向改变后,灌木铁线莲结籽率显著下降,种子宿存花柱长度降低,但并没有影响种子大小和千粒重,说明花朝向改变降低了雌性适合度,并影响到灌木铁线莲种子传播。研究结果证实,灌木铁线莲花期花朵下垂现象对有效传粉昆虫影响不大,但可以显著提高植物雄性适合度和雌性适合度,并作为一种有效的适应策略保障了其繁殖成功。     

Selection by Pollinators on Floral Traits in Generalized Trollius ranunculoides (Ranunculaceae) along Altitudinal Gradients

Abundance and visitation of pollinator assemblages tend to decrease with altitude, leading to an increase in pollen limitation. Thus increased competition for pollinators may generate stronger selection on attractive traits of flowers at high elevations and cause floral adaptive evolution. Few studies have related geographically variable selection from pollinators and intraspecific floral differentiation. We investigated the variation of Trollius ranunculoides flowers and its pollinators along an altitudinal gradient on the eastern Qinghai-Tibet Plateau, and measured phenotypic selection by pollinators on floral traits across populations. The results showed significant decline of visitation rate of bees along altitudinal gradients, while flies was unchanged. When fitness is estimated by the visitation rate rather than the seed number per plant, phenotypic selection on the sepal length and width shows a significant correlation between the selection strength and the altitude, with stronger selection at higher altitudes. However, significant decreases in the sepal length and width of T. ranunculoides along the altitudinal gradient did not correspond to stronger selection of pollinators. In contrast to the pollinator visitation, mean annual precipitation negatively affected the sepal length and width, and contributed more to geographical variation in measured floral traits than the visitation rate of pollinators. Therefore, the sepal size may have been influenced by conflicting selection pressures from biotic and abiotic selective agents. This study supports the hypothesis that lower pollinator availability at high altitude can intensify selection on flower attractive traits, but abiotic selection is preventing a response to selection from pollinators.     

MEASUREMENTS OF NATURAL SELECTION ON FLORAL TRAITS IN WILD RADISH (RAPHANUS RAPHANISTRUM). I. SELECTION THROUGH LIFETIME FEMALE FITNESS

Although the role of natural selection in the evolution of floral traits has been of great interest to biologists since Darwin, studies of selection on floral traits through differences in lifetime fitness have been rare. We measured selection acting on flower number, flower size, stigma exsertion, and ovule number per flower using field data on lifetime female fitness (seed production) in wild radish, Raphanus raphanistrum. The patterns of selection were reasonably consistent across three field seasons, with strong directional selection for increased flower production in all three years, weaker selection for increased ovule number per flower in two years, and selection for increased flower size in one year. The causes of the selection were investigated using path analysis combined with multiplicative fitness components. Increased flower production increased fruit production directly, and increased numbers of ovules per flower increased the number of seeds per fruit in all three years; pollinator visitation did not influence either of these fitness components. Increased flower size was associated with increases in both the number of fruit and the number of seeds per fruit in one year, with the latter relationship being stronger. Total lifetime seed production was affected more strongly by differences in fruit production than by differences in either the number of seeds per fruit or the proportion of fertilized seeds that were viable, but all three fitness components were positively correlated with total seed production.     

Variations of flower size and reproductive traits in self-incompatible <Emphasis Type="Italic">Trollius ranunculoides</Emphasis> (Ranunculaceae) among local habitats at Alpine Meadow

For plants that rely on animals for pollination, the ability to attract the animals to their flowers can be a crucial component of fitness. A large number of studies have documented pollinators to be important selective agents driving the evolution of flower size and correlated traits on a large scale. In this paper, we studied variations of reproductive traits in self-incompatible Trollius ranunculoides (Ranunculaceae) among local habitats at Alpine Meadow. The results showed significant variations of floral size, seed mass per fruit and sex allocation (male/female mass ratio) between different habitats, where floral size and seed mass was not explained fully by variation of plant size among habitats. It suggested that other factors unrelated to plant size might also influence floral variation. However, in our manipulated experiment, it showed no effects of manipulated floral size not only on visit rate of effective pollinators (bees and flies) but also on female success (seed set, seed mass per fruit), irrespective of flower density. Consequently, we could not conclude that the variation of floral size in T. ranunculoides was due to phenotypic plasticity, or natural selection. But if selection occurred, it should not be mediated by pollinators. It was likely that variation of sex allocation between habitats lead to changes of flower or corolla size, because plant invested much less to male function (female-biased sex allocation and larger single seed mass) in shade habitat (bottom of bush) than other exposed habitats, to gain higher fitness. In addition, high-floral density in T. ranunculoides had a negative effect on service of main pollinator (bees) and female success. This situation would influence the strength of selection on floral size.     

青藏高原高寒草甸植物花寿命与花吸引特征的关系及其对雌性繁殖成功的影响

花寿命指花保持开放且具有功能的时间长度, 是开花植物繁殖成功的一个重要功能性状。可塑性延长花寿命是植物在不利的传粉环境中保障繁殖的一种策略, 但延长花寿命也会增加繁殖成本。花寿命的可塑性变异不仅受传粉环境的影响, 而且还受资源分配权衡的影响。花寿命的理论模型指出, 植物的花寿命与花吸引特征之间存在资源分配权衡。为了研究在花粉限制环境中, 植物花寿命与花吸引特征之间的资源权衡及其对雌性适合度的相对重要性。该研究以青藏高原高寒草甸不同海拔(2 900和3 600 m)的11种开花植物为研究对象, 分析了不同植物群落中, 物种水平上: (1)花寿命与花吸引特征(花大小以及开花数目)之间的相关关系; (2)花寿命与花吸引特征对植物雌性适合度的相对贡献。结果表明, 无论是低海拔还是高海拔植物群落, 植物的花寿命与开花数目之间均存在权衡关系, 且长的花寿命增加了植物的雌性适合度。但在高海拔环境中, 植物的雌性适合度只与花寿命有关。这说明相对于低海拔植物, 花寿命对高海拔植物的雌性繁殖成功更为重要。     

Pollen limitation and natural selection on floral characters in the yellow monkeyflower, Mimulus guttatus

In flowering plants, pollen limitation has been proposed to intensify selection on floral characters important in pollinator attraction, but may also select for traits that increase seed set through autonomous selfing. Here, a factorial design (+/- pollen addition, +/- pollinator removal) was used to investigate how the pollination environment affects selection on floral morphology via female fitness in a mixed-mating population of the yellow monkeyflower, Mimulus guttatus (Phrymaceae). Female fitness was strongly pollen-limited, with supplementally pollinated plants setting 37% more seeds than open-pollinated individuals. Strong positive selection was found on flower length, weak positive selection on flower width : length ratio and no selection on stigma-anther distance in both open-pollinated and supplementally pollinated treatments. By contrast, flowers with relatively narrow corollas and low stigma-anther distances were favored in the pollinator exclusion treatment. These results provide mixed support for the idea that pollen limitation intensifies selection on floral characters. Despite strong phenotypic selection, natural pollen limitation did not mediate selection on characters associated with either pollinator attraction or self-fertilization. However, the novel pattern of selection on severely pollen-limited plants suggests that reproductive assurance against pollinator loss may have been directly involved in the floral evolution of closely related selfing taxa.     

Earlier snow melt and reduced summer precipitation alter floral traits important to pollination

Climate change can cause changes in expression of organismal traits that influence fitness. In flowering plants, floral traits can respond to drought, and that phenotypic plasticity has the potential to affect pollination and plant reproductive success. Global climate change is leading to earlier snow melt in snow-dominated ecosystems as well as affecting precipitation during the growing season, but the effects of snow melt timing on floral morphology and rewards remain unknown. We conducted crossed manipulations of spring snow melt timing (early vs. control) and summer monsoon precipitation (addition, control, and reduction) that mimicked recent natural variation, and examined plastic responses in floral traits of Ipomopsis aggregata over 3 years in the Rocky Mountains. We tested whether increased summer precipitation compensated for earlier snow melt, and if plasticity was associated with changes in soil moisture and/or leaf gas exchange. Lower summer precipitation decreased corolla length, style length, corolla width, sepal width, and nectar production, and increased nectar concentration. Earlier snow melt (taking into account natural and experimental variation) had the same effects on those traits and decreased inflorescence height. The effect of reduced summer precipitation was stronger in earlier snow melt years for corolla length and sepal width. Trait reductions were explained by drier soil during the flowering period, but this effect was only partially explained by how drier soils affected plant water stress, as measured by leaf gas exchange. We predicted the effects of plastic trait changes on pollinator visitation rates, pollination success, and seed production using prior studies on I. aggregata. The largest predicted effect of drier soil on relative fitness components via plasticity was a decrease in male fitness caused by reduced pollinator rewards (nectar production). Early snow melt and reduced precipitation are strong drivers of phenotypic plasticity, and both should be considered when predicting effects of climate change on plant traits in snow-dominated ecosystems.     

Collinsia sparsiflora in serpentine and nonserpentine habitats: using F2 hybrids to detect the potential role of selection in ecotypic differentiation

Here we document phenotypic differences between serpentine and nonserpentine ecotypes of Collinsia sparsiflora, as well as patterns of selection in these contrasting soil habitats. We transplanted the two parental ecotypes and experimental F2 hybrids into six field sites, and collected morphological, phenological and fitness data on emergent plants. To focus on edaphically mediated selection, rather than on pollinator-mediated selection, we used pollinator-exclusion cages. Transplanted parentals of the two ecotypes showed genetic differentiation for floral traits, but not for phenological traits or cotyledon size. For the F2 hybrids growing on serpentine soils, there was significant directional selection on cotyledon size, flower size and flower shape. However, the pattern of selection did not differ significantly between serpentine and nonserpentine sites. Overall, we did not see evidence for divergent selection on the two soil types. We conclude that differences in floral traits between the ecotypes do not reflect adaptation to physical conditions associated with soil type, and that there are unmeasured traits that must be contributing to ecotypic differentiation.     

Pollinator‐mediated phenotypic selection does not always modulate flower size and number in the large‐flowered Mediterranean shrub Cistus ladanifer (Cistaceae)

Flower size and number usually evolve under pollinator‐mediated selection. However, hot, dry environments can also modulate display, counteracting pollinator attraction. Increased pollen deposition on larger flower displays may not involve higher female fitness. Consequently, stressful conditions may constrain flower size, favouring smaller‐sized flowers. The large‐flowered, self‐incompatible Mediterranean shrub Cistus ladanifer was used to test that: (1) this species suffers pollen limitation; (2) pollinators are spatially–temporally variable and differentially visit plants with more/larger flowers; (3) increased visits enhance reproduction under pollen limitation; (4) stressful conditions reduce female fitness of larger displays; and (5) phenotypic selection on floral display is not just pollinator‐mediated. We evaluated pollen limitation, related floral display to pollinator visits and fruit and seed production and estimated phenotypic selection. Flower size was 7.2–10.5 cm and varied spatially–temporally. Visitation rates (total visits/50 min) ranged from 0.26 to 0.43 and increased with flower size. Fruit set averaged 80% and seed number averaged 855, but only fruit set varied between populations and years. Selection towards larger flowers was detected under conditions of pollen limitation. Otherwise, we detected stabilizing selection on flower size and negative selection on flower number. Our results suggest that selection on floral display is not only pollinator‐dependent through female fitness in C. ladanifer. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 540–555.