The effect of floral morphology on seed set in <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> Linnaeus (Asteraceae) clones of Sichuan province in China

The relationships among the floral morphologies, breeding system and pollination insects in nine Carthamus tinctorius L. clones were investigated in Ya’an, Sichuan province, China. No significant differences in seed setting rate were observed among the clones following unbagged treatment, but significant differences in seed setting rate were observed among the clones following bagged treatment. Breeding experiments indicated that both reproductive systems (selfing and outcrossing) coexisted in each tested C. tinctorius clone. It exhibited reproductive assurance through automatic self-pollination, which might be an important factor in enhancing the amount of seeds. Among 17 species of visitors, the main effective pollinators were Apis cerana Fabricius, Apis mellifera Linnaeus and Eristalis tenax Linnaeus. All floral morphology traits (corolla length, corolla diameter, pistil length, anther length, stigma length, and stigma–anther separation) showed significant variations among the clones. However, only corolla diameter showed a significant negative correlation with the frequency of pollinator visits and a positive correlation with seed set following unbagged treatment. There was a negative correlation between stigma–anther separation and seed set, and although this was not significant, it could be argued that if a pistil developed that was too long, seed set would decline under natural conditions. Corolla length was significantly positively correlated with stamen and anther length, and corolla diameter was significantly negatively correlated with pistil length. Stigma length was also significantly positively correlated with stamen length. These findings indicate that corolla diameter could significantly affect seed set in C. tinctorius under the conditions in Ya’an, China, and corolla diameter affects seed set by the combined effect of multiple traits.     

Effects of herkogamy and inbreeding on the mating system of <Emphasis Type="Italic">Mimulus luteus</Emphasis> in the absence of pollinators

Self-pollination mechanisms are often invoked to explain plant reproduction in environments devoid of pollinators. However, populations may evolve a diverse variety of strategies depending on the ecological context of pollination. In this study we examined the pollination environment, inbreeding depression, and herkogamy of Mimulus luteus (Phrymaceae) in two consecutive years in an attempt to evaluate the extent to which these factors determine the current level of autogamy in this population. Results indicate that pollinators were almost absent in the study site in 2005 and 2006. Likewise, no evidence of significant inbreeding depression for seed production and seed germination was detected in the 2 years. Because M. luteus presents hermaphrodite flowers with ‘movement herkogamy’ (touch-sensitive stigmata that close upon contact), and anther–stigma separation, we evaluated the role of these traits in self-fertilization. First, we assessed the effects of pollen source (self- and xenogamous pollen, and control solution) on stigmata dynamics after pollen deposition, and seed production. We observed that stigmata that received pollen (self- and xenogamous hand-pollinated) remained closed for a longer time than flowers that received no pollen (control flowers). Seed production, however, was unaffected by pollen source, indicating that movement herkogamy does not prevent self-fertilization in this population. Second, a phenotypic selection analysis revealed that seed production increased with a reduction of anther–stigma separation in absence of pollinators (bagged flowers), suggesting that low herkogamy levels are promoted in this population. Our results indicate that lack of inbreeding depression, ineffective movement herkogamy, and selection against anther–stigma separation are factors that may contribute to the prevalence of autogamous reproductive mechanisms when M. luteus faces environments with scarce mating opportunity.     

Floral ecology of Oreocharis pumila (Gesneriaceae): a novel case of sigmoid corolla

Attraction of pollinators and successful pollen transfer represent the primary targets of selection during flower evolution, leading to repeated evolutionary shifts between pollinators and consequently to the diversification of floral forms. However, most studies in floral evolution focus on the characteristics of flowers with straight corolla tube. Here, we report on an unusual form of sigmoid corolla combined with protandry and herkogamy in a Chinese species of Gesneriaceae, Oreocharis pumila (formerly Opithandra pumila). Contrary to species with sigmoid corollas studied previously, the base of the corolla tube of this species is inclined at an oblique angle downwards before the tube bends forward, and the stigma and anthers are included in the upper part of the corolla tube. The plants were found to be self‐compatible but incapable of autonomous selfing. Successful pollination was found to depend fully on the presence of insect pollinators (Nomia sp.) and pollen grains are the greatest reward for the visitors. Different from the other sigmoid flowers, the sigmoid corolla of O. pumila was not found to favor insect pollinators with long flexible proboscises. A mechanical fit between floral morphology and pollinator was found, in which only small insect visitors with specialized visiting behavior are legitimate pollinators. The protandry combined with herkogamy in the sigmoid corolla tube strongly ensures pollination efficiencies. Oreocharis pumila is the only species with sigmoid corolla in the genus Oreocharis. We hypothesize that such a corolla has arisen through selection due to inadequate pollination in early spring in the mountainous habitat that O. pumila occupies.     

The relative strength of different floral visitors driving floral evolution within a <Emphasis Type="Italic">Primula secundiflora</Emphasis> population

Floral visitor assemblages within plant populations are usually composed of different visitors, and the relative abundance of these visitors also varies. Therefore, identifying the relative strength of these floral visitors driving floral evolution within the population is an important step in predicting the evolutionary trajectory of floral traits. Using supplemental hand pollination and nectar-robbing exclusion treatments, we experimentally identified the relative strengths of legitimate pollinators (that visit flowers through the corolla tube entrance) and nectar robbers (that visit flowers by biting a hole in the corolla tube or using an existing hole) driving floral evolution within the Primula secundiflora population. We also estimated legitimate pollinator- and nectar robber-mediated selection separately for pin and thrum flowers. Both legitimate pollinators and nectar robbers mediated selection on pollination efficiency traits in P. secundiflora population. Legitimate pollinators mediated selection for wider corolla tubes, whereas nectar robbers mediated selection for longer corolla tubes. In addition, nectar robber-mediated selection on corolla tube length marginally varied between the pin and thrum flowers. Nectar robber mediated selection for longer corolla tube length in the pin flowers not in the thrum flowers. These results indicate that legitimate pollinators and nectar robbers within a population can drive differential evolutionary trajectories of floral traits.     

Divergence on floral traits and vertebrate pollinators of two endemic Encholirium bromeliads

Shifts in pollen vectors favour diversification of floral traits, and differences in pollination strategies between congeneric sympatric species can contribute to reproductive isolation. Divergence in flowering phenology and selfing could also reduce interspecific crossing between self‐compatible species. We investigated floral traits and visitation rates of pollinators of two sympatric Encholirium species on rocky outcrops to evaluate whether prior knowledge of floral characters could indicate actual pollinators. Data on flowering phenology, visitation rates and breeding system were used to evaluate reproductive isolation. Flowering phenology overlapped between species, but there were differences in floral characters, nectar volume and concentration. Several hummingbird species visited flowers of both Encholirium spp., but the endemic bat Lonchophylla bokermanni and an unidentified sphingid only visited E. vogelii. Pollination treatments demonstrated that E. heloisae and E. vogelii were partially self‐compatible, with weak pollen limitation to seed set. Herbivores feeding on inflorescences decreased reproductive output of both species, but for E. vogelii the damage was higher. Our results indicate that actual pollinators can be known beforehand through floral traits, in agreement with pollination syndromes stating that a set of floral traits can be associated with the attraction of specific groups of pollinators. Divergence on floral traits and pollinator assemblage indicate that shifts in pollination strategies contribute to reproductive isolation between these Encholirium species, not divergence on flowering phenology or selfing. We suggest that hummingbird pollination might be the ancestral condition in Encholirium and that evolution of bat pollination made a substantial contribution to the diversification of this clade.     

Island–mainland difference in <Emphasis Type="Italic">Nicotiana glauca</Emphasis> (Solanaceae) corolla length: a product of pollinator-mediated selection?

A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist. I first determined differences in floral morphology and pollinator composition between island and mainland populations of N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites. I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift.     

MULTIPLE PATERNITY AND SELF-FERTILIZATION IN RELATION TO FLORAL AGE IN MIMULUS GUTTATUS (SCROPHULARIACEAE)

To gain some understanding of the mechanisms responsible for the intermediate levels of both multiple paternity and selfing observed previously in the common monkeyflower, Mimulus guttatus, we performed a field experiment to assess the role of 1) multiple paternity through sequential pollinator visits and 2) selfing through corolla abscission. In M. guttatus, flowers remain open for several days; then, in the process of corolla abscission anthers drag past the stigma. We predicted that multiple visitation by pollinators over this period should increase the degree of multiple paternity of sibling arrays, and that corolla dragging may be the primary cause of the observed selfing. In three northern California populations corollas were removed after being open for 1 day (preventing further mating), and the type of matings resulting was compared to matings from adjacent flowers with undisturbed corollas. On average, seed set was twice as great in flowers with unmanipulated corollas, indicating that about half of all matings in the lifespan of a M. guttatus flower occur after 1 day. Pollen supplementation revealed that pollen was limiting in one population. Electrophoretic assay of progeny showed multiple paternity was greater in unmanipulated flowers in the two populations that were not pollen limited, suggesting that sequential pollination may be an important source of multiple paternity. However, no difference was detected in the selfing rate between the two treatments, suggesting that corolla dragging was not a source of selfing even under pollen-limited conditions.     

Post-pollination mechanisms in Nicotiana longiflora and N. plumbaginifolia: pollen tube growth rate, offspring paternity and hybridization

In natural populations where interfertile species coexist, conspecific and heterospecific pollen can be delivered to the stigmas. Post-pollination mechanisms might determine the seed siring success of different pollen donors within species as well as the chances for hybridization between species. Nicotiana longiflora and N. plumbaginifolia occur in sympatry in Northwest Argentina, where they have overlapping flowering seasons and share floral visitors. We explored (1) pollen tube growth rates for outcross versus self pollen in single-donor pollinations; (2) siring success of self versus outcross pollen donors in competitive pollinations, and (3) possibilities for hybridization by performing two- (outcross conspecific vs. heterospecific) and three-pollen donor (self vs. outcross vs. heterospecific) crosses. In N. longiflora, both pollen tube growth rate and siring success favored outcross pollen over self pollen and strong rejection of heterospecific pollen. In N. plumbaginifolia, pollen tube growth rate was similar for self and outcross pollen, self pollen sired similar numbers of offspring than outcross pollen and heterospecific pollen sired roughly the same number of progeny than self pollen. Results suggest that in natural sympatric populations, interspecific crosses would likely lead to unidirectional hybridization with N. plumbaginifolia as the seed parent.     

Floral biology and mechanisms of spontaneous self‐pollination in five neotropical species of Gentianaceae

Cross‐ and self‐fertilization in angiosperms are regulated by several factors, and a knowledge of the mechanism and time of spontaneous self‐pollination offers opportunities for a better understanding of the evolution of mating systems and floral traits. The floral biology of five species of Gentianaceae found in high‐altitude neotropical grassland is presented, with emphasis on the mechanisms that promote spontaneous self‐pollination. A presumed floral Batesian mimicry system is suggested between the rare and rewardless Zygostigma australe and Calydorea campestris, a species of Iridaceae with pollen‐flowers, pollinated by syrphids and bees. The floral morphology of the other four gentian species points to three different pollination syndromes: melittophily, phalaenophily and ornithophily. However, with the exception of the nocturnal Helia oblongifolia, flowers are nectarless and appear to exhibit non‐model deceptive mechanisms, providing similar floral cues to some sympatric rewarding species with the same syndrome. The similar mechanism of spontaneous self‐pollination in Calolisianthus pedunculatus, Calolisianthus pendulus and H. oblongifolia (Helieae) is based on the stigmatic movements towards the anthers. Selfing is promoted by movements of the style/stigma and of the corolla in Deianira nervosa and Z. australe (Chironieae), respectively. The movements of stamens, style and stigma during anthesis seem to be the most common method of spontaneous self‐pollination in angiosperms. It is suggested that the evolution of delayed spontaneous self‐pollination would be more expected in those taxa with dichogamous flowers associated with herkogamy. Such a characteristic is frequent in long‐lived flowers of certain groups of Asteridae, which comprise most documented cases of autonomous selfing. Thus, the presence of dichogamy associated with herkogamy (which supposedly evolved as a result of selection to promote both separation of male and female functions and the efficient transfer of cross pollen) may be the first step in the adaptive evolution of delayed selfing to provide reproductive assurance. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 357–368.     

Morph-specific variation of floral traits associated with reciprocal herkogamy in natural populations of Primula vulgaris and Primula veris

Documenting the morph-specific variation of floral traits associated with reciprocal herkogamy is of special importance for revealing the functional significance of traits in the evolution and maintenance of the heterostylous syndrome. In order to describe the extent and specificity of variation, stigma height, anther height, stigma-anther separation and corolla tube length were measured on 800 flowers collected in two natural populations of Primula vulgaris and P. veris. Beside the almost complete separation of stigma heights between the two morphs, we found appreciable intermorph overlap in anther height and relatively broad range of stigma-anther separation so far reported for heterostylous species. The corolla tube length–stigma-anther separation relationship showed striking difference between the two floral morphs, which supports the hypothesis that length of the corolla tube plays a more important role in positioning the sex-organs in the appropriate distance in the short-styled than in the long-styled morph.     

Phenotypic selection on the staminal lever mechanism in Salvia digitaloides (Labiaceae)

The staminal lever mechanism of pollination in Salvia has been considered as a key innovation, which was proposed to contribute to adaptive radiation of the genus. Considering its sophisticated interaction with pollinators, we hypothesized that relevant floral traits in the lever mechanism might be subject to intense selection in natural populations. In the present study, Salvia digitaloides was employed to investigate phenotypic selection on the floral traits. The results indicated that there were large variations in the floral structural traits and spatial position of the stigma. No significant selection was detected on the plausible key trait, i.e. the stamen lever length. Strong stabilizing selection acted consistently on the size of corolla entrance; that is, the intermediate corolla entrance was at a selective advantage. Both corolla length and style exsertion were subject to opposite directional selection in both years; and corolla entrance height was subject to disruptive selection, which was attributed to divergent adaptation of the trait to different body-sized pollinators. Furthermore, correlational selection acted on a few pairs of traits which described corolla entrance size and stigma position. Flower production was consistently subject to significantly positive directional selection in both years. In conclusion, it was most likely that floral traits involved in the staminal lever mechanism evolved in a functionally integrated manner for the enhancement of pollination efficiency in the natural population of S. digitaloides.     

Evolutionary consequences of ecological factors: pollinator reliability predicts mating‐system traits of a perennial plant

The reproductive‐assurance hypothesis predicts that mating‐system traits will evolve towards increased autonomous self‐pollination in plant populations experiencing unreliable pollinator service. We tested this long‐standing hypothesis by assessing geographic covariation among pollinator reliability, outcrossing rates, heterozygosity and relevant floral traits across populations of Dalechampia scandens in Costa Rica. Mean outcrossing rates ranged from 0.16 to 0.49 across four populations, and covaried with the average rates of pollen arrival on stigmas, a measure of pollinator reliability. Across populations, genetically based differences in herkogamy (anther–stigma distance) were associated with variation in stigmatic pollen loads, outcrossing rates and heterozygosity. These observations are consistent with the hypothesis that, when pollinators are unreliable, floral traits promoting autonomous selfing evolve as a mechanism of reproductive assurance. Extensive covariation between floral traits and mating system among closely related populations further suggests that floral traits influencing mating systems track variation in adaptive optima generated by variation in pollinator reliability.     

鼠尾草属不同物种的雄蕊杠杆机制对传粉者空间变异的进化响应

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。     

Comparative floral morphometrics in day-flowering, night-flowering and self-pollinated Caryophylloideae (Agrostemma, Dianthus, Saponaria, Silene, and Vaccaria)

Morphological variation of flowers with different pollination modes was studied in 53 species representing five genera (Agrostemma, Dianthus, Saponaria, Silene s.l., Vaccaria) of the subfamily Caryophylloideae. All species were classified a priori as either diurnal, nocturnal, or selfing. Canonical discriminant analysis (CDA) of 13 floral characters revealed significant correlations between floral morphometry and pollination modes. A CDA of taxonomical groups represented with more than three species (Dianthus, and subgroups of Silene s.l.: Lychnis, Silene s.str., and Viscaria), revealed that the discrimination between these four taxa, based on the same floral characters, is also well supported. Main factors for the discrimination of the species with different pollination modes were characters that (a) define nectar accessibility (calyx length, calyx tooth length), (b) are related to the positioning of anthers and stigmatic areas in relation to pollinators and (c) are important for the visual attractiveness of flowers (plate width). The functional distance between the nectar source (anthophore base) and contact zone with pollinators (style tips), given as the sum of anthophore length, ovary length, and style length (hence called AOS-complex) is better correlated with the calyx length than the single characters. Further, the total AOS-complex length differs significantly between pollination modes suggesting that these characters form a functionally linked complex that is related to the pollen placement on, and stigma contact with, the pollinator's body. However, the contribution of anthophore and style length to the total AOS-complex differed significantly between Silene s.l. and other taxa indicating that the taxonomic groups follow different evolutionary ways for the construction of the functionally linked AOS-complex.     

山莨菪(茄科)的传粉生物学

茄科的多数种类具有自交不亲和的特点, 主要通过异花传粉结实; 但是, 一些物种或者物种内的部分种群或者个体却高度自交亲合, 转变为自交的繁育系统。该科植物山莨菪(Anisodus tanguticus)主要分布在青藏高原, 开花较早, 比其他晚开花的植物种类更加缺少有效的异花传粉昆虫。我们选择了位于不同海拔高度的2个种群进行比较研究, 主要目的是检验该物种的繁育系统是否在极端环境下由于传粉者的缺乏而发生了部分改变。研究发现,山莨菪的花不完全雌性先熟, 柱头和花药间的平均距离随着花开放时间的延长而不断缩小, 但两者在多数花的单花花期结束时并没有发生接触。因此, 山莨菪花主要表现为适应异花传粉的雌雄异位特征。然而, 少数花 (4.9％)的柱头和花药发生接触, 为“自动自交”的传粉解除了空间隔离。2个种群的多数个体存在自交不亲和机制, 应具有异花传粉的繁育系统; 但是部分个体具有明显的自交亲和能力, 为自交提供了生理基础。高海拔种群的传粉昆虫主要是厕蝇(Fannia sp.), 它们在不同植株间的活动能够保证异花传粉结实; 同时该种群的部分个体存在“自动自交”。低海拔种群的主要访花昆虫是蚂蚁, 它们在花内的活动导致花粉在同一朵花内传递, 而引起“协助自交”; 而异花传粉昆虫厕蝇的访花频率则较高海拔种群低。两个种群的结实均由于异花传粉者不足而受到传粉限制。因此两种不同类型的自交机制为该早期开花植物异花访花昆虫的不足提供了一定程度上的繁殖补偿。     

Floral colour variation of Nicotiana glauca in native and non-native ranges: Testing the role of pollinators' perception and abiotic factors

• Invasive plants displaying disparate pollination environments and abiotic conditions in native and non-native ranges provide ideal systems to test the role of different ecological factors driving flower colour variation.
• We quantified corolla reflectance of the ornithophilous South American Nicotiana glauca in native populations, where plants are pollinated by hummingbirds, and in populations from two invaded regions: South Africa, where plants are pollinated by sunbirds, and the Balearic island of Mallorca, where plants reproduce by selfing. Using visual modelling we examined how corolla reflectance could be perceived by floral visitors present in each region. Through Mantel tests we assessed a possible association between flower colour and different abiotic factors.
• Corolla reflectance variation (mainly along medium to long wavelengths, i.e. human green-yellow to red colours) was greater among studied regions than within them. Flower colour was more similar between South America and South Africa, which share birds as pollinators. Within invaded regions, corolla reflectance variation was lower in South Africa, where populations could not be distinguished from each other by sunbirds, than in Spain, where populations could be distinguished from each other by their occasional visitors. Differences in corolla colour among populations were partially associated with differences in temperature.
• Our findings suggest that shifts in flower colour of N. glauca across native and invaded ranges could be shaped by changes in both pollination environment and climatic factors. This is the first study on plant invasions considering visual perception of different pollinators and abiotic drivers of flower colour variation.

     

Sex‐specific phenotypic selection and geographic variation in gender divergence in a gynodioecious shrub

In sexually polymorphic plant species the extent of gender divergence in floral morphology and phenology may be influenced by gender‐specific selection patterns imposed by pollinators, which may change geographically. Distribution margins are areas where changes in the pollinator fauna, and thus variation in gender divergence of floral traits, are expected. We tested for pollination‐driven geographic variation in the gender divergence in floral and phenological traits in the gynodioecious shrub Daphne laureola, in core and marginal areas differing in the identity of the main pollinator. Pollinators selected for longer corolla tubes in hermaphrodite individuals only in core populations, which in turn recorded higher fruit set. Consistent with these phenotypic selection patterns, gender divergence in flower corolla length was higher in core populations. Moreover, pollinators selected towards delayed flowering on hermaphrodite individuals only in marginal populations, where the two sexes differed more in flowering time. Our results support that a shift in main pollinators is able to contribute to geographic variation in the gender divergence of sexually polymorphic plant species.     

Floral morph composition and pollen limitation in the seed set of <Emphasis Type="Italic">Nymphoides indica</Emphasis> populations

We investigated the floral morph composition and seed set of the populations in a heterostylous aquatic plant, Nymphoides indica O. Kuntze (Menyanthaceae). The bias of floral morph ratio in the populations was negatively correlated with the seed set. In the populations with biased floral morph ratio, the pollen on the stigma of the common morphs were dominated by pollen of the same morph, resulting in reduced seed set. The addition of pollen of the opposite morph on the stigmas of the common morph resulted in an increase of fruit and seed set rates. The intermorph pollination rate and the fruit and seed set rates of Nymphoides indica were highest when two floral morphs were close in the populations. Various insect species including Lepidoptera, Diptera and Hymenoptera visited the flowers. However, geitonogamous pollination was common because of the short flying distance of the pollinators. These results indicate that the seed set of Nymphoides indica is limited by the shortage of compatible pollens and that the success of intermorph pollination is influenced by spatial distribution of the two floral morphs. As Nymphoides indica is endangered, conservation of the populations with high fecundity is proposed by us.     

Growth discrepancy between filament and style facilitates self‐fertilization in Brandisia hancei (Paulowniaceae)

Self‐pollination has been hypothesized to be beneficial in environments where pollinators are rare as it can provide reproductive assurance. This study presents evidence for an autonomous self‐fertilization mechanism in the winter flowering plant, Brandisia hancei. To determine changes in the spatial separation of stigma and anthers, the length of style and stamens was recorded. Additionally, pollination treatments were carried out to test fruit‐set and seed production. Brandisia hancei is herkogamic in the early flowering stages. However, different growth rates of the filament and style lead to contact of stigma and anthers in the later stages, thereby facilitating self‐pollination. The highest seeds number is produced under an out‐crossing scenario but plants produce a considerable number of seeds even when purely selfed. Although pollinators are scarce, autonomous selfing alleviates the pollen limitation in B. hancei. Self‐fertilization in B. hancei seems to be an adaptive strategy to ensure reproduction when pollinators are scarce.     

Phenotypic selection on flowering phenology and pollination efficiency traits between Primula populations with different pollinator assemblages

Floral traits have largely been attributed to phenotypic selection in plant–pollinator interactions. However, the strength of this link has rarely been ascertained with real pollinators. We conducted pollinator observations and estimated selection through female fitness on flowering phenology and floral traits between two Primula secundiflora populations. We quantified pollinator‐mediated selection by subtracting estimates of selection gradients of plants receiving supplemental hand pollination from those of plants receiving open pollination. There was net directional selection for an earlier flowering start date at populations where the dominant pollinators were syrphid flies, and flowering phenology was also subjected to stabilized quadratic selection. However, a later flowering start date was significantly selected at populations where the dominant pollinators were legitimate (normal pollination through the corolla tube entrance) and illegitimate bumblebees (abnormal pollination through nectar robbing hole which located at the corolla tube), and flowering phenology was subjected to disruptive quadratic selection. Wider corolla tube entrance diameter was selected at both populations. Furthermore, the strength of net directional selection on flowering start date and corolla tube entrance diameter was stronger at the population where the dominant pollinators were syrphid flies. Pollinator‐mediated selection explained most of the between‐population variations in the net directional selection on flowering phenology and corolla tube entrance diameter. Our results suggested the important influence of pollinator‐mediated selection on floral evolution. Variations in pollinator assemblages not only resulted in variation in the direction of selection but also the strength of selection on floral traits.