Changes in pollinator fauna affect altitudinal variation of floral size in a bumblebee‐pollinated herb

Geographic trait variations are often caused by locally different selection regimes. As a steep environmental cline along altitude strongly influences adaptive traits, mountain ecosystems are ideal for exploring adaptive differentiation over short distances. We investigated altitudinal floral size variation of Campanula punctata var. hondoensis in 12 populations in three mountain regions of central Japan to test whether the altitudinal floral size variation was correlated with the size of the local bumblebee pollinator and to assess whether floral size was selected for by pollinator size. We found apparent geographic variations in pollinator assemblages along altitude, which consequently produced a geographic change in pollinator size. Similarly, we found altitudinal changes in floral size, which proved to be correlated with the local pollinator size, but not with altitude itself. Furthermore, pollen removal from flower styles onto bees (plant's male fitness) was strongly influenced by the size match between flower style length and pollinator mouthpart length. These results strongly suggest that C. punctata floral size is under pollinator‐mediated selection and that a geographic mosaic of locally adapted C. punctata exists at fine spatial scale.     

Demonstration of pollinator‐mediated competition between two native Impatiens species,Impatiens noli‐tangere and I. textori (Balsaminaceae)

Plant–plant interspecific competition via pollinators occurs when the flowering seasons of two or more plant species overlap and the pollinator fauna is shared. Negative sexual interactions between species (reproductive interference) through improper heterospecific pollen transfer have recently been reported between native and invasive species demonstrating pollination‐driven competition. We focused on two native Impatiens species (I. noli‐tangere and I. textori) found in Japan and examined whether pollinator‐mediated plant competition occurs between them. We demonstrate that I. noli‐tangere and I. textori share the same pollination niche (i.e., flowering season, pollinator fauna, and position of pollen on the pollinator's body). In addition, heterospecific pollen grains were deposited on most stigmas of both I. noli‐tangere and I. textori flowers that were situated within 2 m of flowers of the other species resulting in depressed fruit set. Further, by hand‐pollination experiments, we show that when as few as 10% of the pollen grains are heterospecific, fruit set is decreased to less than half in both species. These results show that intensive pollinator‐mediated competition occurs between I. noli‐tangere and I. textori. This study suggests that intensive pollinator‐mediated competition occurs in the wild even when interacting species are both native and not invasive.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Altitudinal flower size variation correlates with local pollinator size in a bumblebee‐pollinated herb,Prunella vulgaris L. (Lamiaceae)

The influence of locally different species interactions on trait evolution is a focus of recent evolutionary studies. However, few studies have demonstrated that geographically different pollinator‐mediated selection influences geographic variation in floral traits, especially across a narrow geographic range. Here, we hypothesized that floral size variation in the Japanese herb Prunella vulgaris L. (Lamiaceae) is affected by geographically different pollinator sizes reflecting different pollinator assemblages. To evaluate this hypothesis, we posed two questions. (1) Is there a positive correlation between floral length and the proboscis length of pollinators (bumblebees) across altitude in a mountain range? (2) Does the flower–pollinator size match influence female and male plant fitness? We found geographic variation in the assemblage of pollinators of P. vulgaris along an altitudinal gradient, and, as a consequence, the mean pollinator proboscis length also changed altitudinally. The floral corolla length of P. vulgaris also varied along an altitudinal gradient, and this variation strongly correlated with the local pollinator size but did not correlate with altitude itself. Furthermore, we found that the size match between the floral corolla length and bee proboscis length affected female and male plant fitness and the optimal size match (associated with peak fitness) was similar for the female and male fitness. Collectively, these results suggest that pollinator‐mediated selection influences spatial variation in the size of P. vulgaris flowers at a fine spatial scale.     

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

• Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient.
• Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes.
• Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude.
• The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

     

Are there predictable clines in plant–pollinator interactions along altitudinal gradients? The example of Cytisus scoparius (L.) Link in the Sierra de Guadarrama (Central Spain)

Abstract. We analyse the hypothesis that predictable gradients occur in plant–pollinator interactions along altitudinal gradients due to thermal constraints on insect body size and floral traits being selected for by pollinators. Pollinators’ size should follow Bergmann's rule in mountains (larger body size at higher altitudes) and selection should, in turn, lead to larger flower size at higher altitudes. The study focuses on the flower and pollinator size variation in 11 Cytisus scoparius populations located between 680 and 1300 m a.s.l., and on the relationship between flower size and pollination success of plants in each population. Significant differences among populations were found in flower size, pollinator size and fruiting success (anova , P < 0.001 in all cases). Regression models show that (i) pollinator size increases significantly with altitude, (ii) a parallel quadratic increase in flower size and (iii) a quadratic decrease in pollination success with altitude. Moreover, there is a tendency of plants with smaller flowers in each population to have a higher percentage of flowers initiating development into fruits (ancova , P < 0.05). All these observations support the presence of the predicted gradient in the studied species and they suggest the possibility of it to be somewhat common among plants that occupy large altitudinal ranges due to the simple basis on which it could be rooted.     

Refuse attracts? Effect of refuse dumps of leaf‐cutting ants on floral traits

The nutrient‐rich organic waste generated by ants may affect plant reproductive success directly by enhancing fruit production but also indirectly, by affecting floral traits related with pollinator attraction. Understanding how these soil‐nutrient hot spots influence floral phenotype is relevant to plant–pollination interactions. We experimentally evaluated whether the addition of organic waste from refuse dumps of the leaf‐cutting ant Acromyrmex lobicornis (Hymenoptera: Formicidae: Attini) alters floral traits associated with pollinator attraction in Eschscholzia californica (Ranunculales: Papaveraceae), an entomophilous herb. We analysed flower shape and size using geometric morphometric techniques in plants with and without the addition of refuse‐dumps soil, under greenhouse conditions. We also measured the duration of flowering season, days with new flowers, flower production and floral display size. Plants growing in refuse‐dumps soil showed higher flower shape diversity than those in control soil. Moreover, plants in refuse‐dumps soil showed bigger flower and floral display size, longer flowering season, higher number of flowering days and flower production. As all these variables may potentially increase pollinator visits, plants in refuse‐dumps soil might increase their fitness through enhanced attraction. Our work describes how organic waste from ant nests may enhance floral traits involved in floral attraction, illustrating a novel way of how ants may indirectly benefit plants.     

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.     

Plant reproductive strategies vary under low and high pollinator densities

Long‐term variation in the population density of honey bees Apis mellifera across landscapes has been shown to correlate with variation in the floral traits of plant populations in these landscapes, suggesting that variations in pollinator population density and foraging rates can drive floral trait evolution of their host plants. However, it remained to be determined whether this variation in plant traits is associated with adaptive variation in plant reproductive strategies under conditions of high and low pollinator densities. Here we conducted a reciprocal transplant experiment to examine how this variation in floral traits, under conditions of either high and low pollinator density, impacted seed production in the Tibetan lotus Saussurea nigrescens. In 2014 and 2015, we recorded the floral traits, pollinator visitation rates, and seed production of S. nigrescens populations grown in both home sites and foreign sites, where sites varied in honey bee population density. Our results demonstrated that the floral traits reflected those of their original population, regardless of their current location. However, seed production varied with both population origin and transplant site. Seed number was positively correlated with flower abundance in the pollinator‐rich sites, but with nectar production in the pollinator‐poor sites. Pollinator visitation rate was also positively correlated with flower number at pollinator‐rich sites, and with nectar volume at pollinator‐poor sites. Overall, the local genotype had higher seed production than nonlocal genotypes in home sites. However, when pollen is hand‐supplemented, plants from pollinator‐rich populations had higher seed production than plants from pollinator‐poor populations, regardless of whether they were transplanted to pollinator‐rich or ‐poor sites. These results suggest that the plant genotypic differences primarily drive variation in pollinator attraction, and this ultimately drives variation in seed: ovule ratio. Thus, our results suggest that flowering plant species use different reproductive strategies to respond to high or low pollinator densities.     

Functional decoupling between flowers and leaves in the Ameroglossum pernambucense complex can facilitate local adaptation across a pollinator and climatic heterogeneous landscape

Decoupling between floral and leaf traits is expected in plants with specialized pollination systems to assure a precise flower–pollinator fit, irrespective of leaf variation associated with environmental heterogeneity (functional modularity). Nonetheless, developmental interactions among floral traits also decouple flowers from leaves regardless of selection pressures (developmental modularity). We tested functional modularity in the hummingbird‐pollinated flowers of the Ameroglossum pernambucense complex while controlling for developmental modularity. Using two functional traits responsible for flower–pollinator fit [floral tube length (TL) and anther–nectary distance (AN)], one floral trait not linked to pollination [sepal length (SL), control for developmental modularity] and one leaf trait [leaf length (LL)], we found evidence of flower functional modularity. Covariation between TL and AN was ca. two‐fold higher than the covariation of either of these traits with sepal and leaf lengths, and variations in TL and AN, important for a precise flower–pollinator fit, were smaller than SL and LL variations. Furthermore, we show that previously reported among‐population variation of flowers associated with local pollinator phenotypes was independent from SL and LL variations. These results suggest that TL and AN are functionally linked to fit pollinators and sufficiently decoupled from developmentally related floral traits (SL) and vegetative traits (LL). These results support previous evidences of population differentiation due to local adaptation in the A. pernambucense complex and shed light on the role of flower–leaf decoupling for local adaptation in species distributed across biotic and abiotic heterogeneous landscapes.     

Relative impact of mate versus pollinator availability on pollen limitation and outcrossing rates in a mass‐flowering species

Plant mating systems are driven by several pre‐pollination factors, including pollinator availability, mate availability and reproductive traits. We investigated the relative contributions of these factors to pollination and to realized outcrossing rates in the patchily distributed mass‐flowering shrub Rhododendron ferrugineum. We jointly monitored pollen limitation (comparing seed set from intact and pollen‐supplemented flowers), reproductive traits (herkogamy, flower size and autofertility) and mating patterns (progeny array analysis) in 28 natural patches varying in the level of pollinator availability (flower visitation rates) and of mate availability (patch floral display estimated as the total number of inflorescences per patch). Our results showed that patch floral display was the strongest determinant of pollination and of the realized outcrossing rates in this mass‐flowering species. We found an increase in pollen limitation and in outcrossing rates with increasing patch floral display. Reproductive traits were not significantly related to patch floral display, while autofertility was negatively correlated to outcrossing rates. These findings suggest that mate limitation, arising from high flower visitation rates in small plant patches, resulted in low pollen limitation and high selfing rates, while pollinator limitation, arising from low flower visitation rates in large plant patches, resulted in higher pollen limitation and outcrossing rates. Pollinator‐mediated selfing and geitonogamy likely alleviates pollen limitation in the case of reduced mate availability, while reduced pollinator availability (intraspecific competition for pollinator services) may result in the maintenance of high outcrossing rates despite reduced seed production.     

Morphological variation and floral abnormalities in a trigger plant across a narrow altitudinal gradient

Local adaptation in alpine plants has been demonstrated across wide altitudinal gradients, but has rarely been examined across the alpine‐to‐montane transition that often encompasses only a few hundred metres. Here we characterize morphological variation in leaf and floral characteristics of the trigger plant Stylidium armeria along a narrow altitudinal gradient in the Bogong High Plains in Victoria. Across this gradient, which encompasses the high‐elevation limit of this species, linear changes were found for floral scape height, leaf length and flower number. All these traits decreased with increasing altitude, whereas the frequency of abnormal flowers increased. When plants were grown in a common garden environment, an altitudinal pattern for flower abnormalities was no longer detected. However, altitudinal patterns for leaf length and scape height were maintained, albeit weaker than in the field. This indicates heritable variation for these morphological traits; the altitudinal patterns are likely to reflect the effects of selection by environmental factors that vary with altitude. Selection pressures remain to be identified but have generated both cogradient and countergradient patterns of variation.     

Floral plasticity: Herbivore‐species‐specific‐induced changes in flower traits with contrasting effects on pollinator visitation

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant–pollinator interactions. Current knowledge on the full extent of herbivore‐induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore‐induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species‐specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant‐mediated interactions with mutualists.     

Pollinators of the Rocky Mountain columbine: temporal variation, functional groups and associations with floral traits

Background and Aims

Pollinators together with other biotic and some abiotic factors can select for floral traits. However, variation in pollinator abundance over time and space can weaken such selection. In the present study, the variation in pollinator abundance over time and space was examined in populations of the Rocky Mountain columbine. The variation in three floral traits is described and correlations between pollinator type, functional pollinator groups or altitude and floral traits are examined.

Methods

Pollinator observations took place in six Aquilegia coerulea populations over 1–4 years and spur length, flower colour and sepal length were measured in 12 populations. Pollinator abundance, measured as visits per flower per hour, was compared among populations and years. Pollinators were grouped into two functional groups: pollen or nectar collectors. The following associations were examined: annual presence of hawkmoths and whiter flowers with longer spurs; the presence of Sphinx vashti and longer spurs; and higher altitudes and whiter flowers. The study looked at whether an increase in the proportion of hawkmoths in a population was associated with whiter and larger flowers with longer spurs.

Key Results

The abundance of different pollinator groups varied over time and space. Floral traits varied among populations. Higher altitude was correlated with bluer flowers. Whiter flowers were associated with the annual presence of hawkmoths. Populations visited by Sphinx vashti had longer spurs than populations visited only by Hyles lineata. Populations with greater percentage of nectar-collecting pollinators did not have whiter, larger flowers with longer spurs.

Conclusions

Despite the large variation in pollinator abundance over time and space, one species of bumble-bee or hawkmoth tended to predominate in each population each year. Future studies of Aquilegia coerulea should examine the specific influences of pollinators and the environment on flower colour and of hawkmoth species on spur length.Key words: Aquilegia coerulea, columbine, pollinator abundance, bumble-bee, hawkmoth, flower colour, spur length, functional pollinator group, altitude, floral trait     

Seedling traits, plasticity and local differentiation as strategies of invasive species of Impatiens in central Europe

Background and Aims

Invasiveness of some alien plants is associated with their traits, plastic responses to environmental conditions and interpopulation differentiation. To obtain insights into the role of these processes in contributing to variation in performance, we compared congeneric species of Impatiens (Balsaminaceae) with different origin and invasion status that occur in central Europe.

Methods

Native I. noli-tangere and three alien species (highly invasive I. glandulifera, less invasive I. parviflora and potentially invasive I. capensis) were studied and their responses to simulated canopy shading and different nutrient and moisture levels were determined in terms of survival and seedling traits.

Key Results and Conclusions

Impatiens glandulifera produced high biomass in all the treatments and the control, exhibiting the ‘Jack-and-master’ strategy that makes it a strong competitor from germination onwards. The results suggest that plasticity and differentiation occurred in all the species tested and that along the continuum from plasticity to differentiation, the species at the plasticity end is the better invader. The most invasive species I. glandulifera appears to be highly plastic, whereas the other two less invasive species, I. parviflora and I. capensis, exhibited lower plasticity but rather strong population differentiation. The invasive Impatiens species were taller and exhibited higher plasticity and differentiation than native I. noli-tangere. This suggests that even within one genus, the relative importance of the phenomena contributing to invasiveness appears to be species''specific.     

Non-reversion of Impatiens in the absence of meristem commitment

Purple-flowered plants of Impatiens balsamina maintained floral development on transfer from inductive short days (SD) to long days (LD), a treatment in which red-flowered plants of Impatiens are known to revert to leaf production. An investigation into the non-reverting nature of purple-flowered plants was carried out to establish whether these plants achieved meristem commitment or whether their non-reverting state was controlled by the leaves. When the leaves that had unfolded during the inductive SD treatment were removed at the time of transfer to LD, the purple-flowered plant did revert. This result suggests that, as in red-flowered Impatiens, meristem commitment is absent, but that purple-flowered plants maintain flowering in LD conditions because of a more permanent supply of signal from their leaves than occurs in red-flowered plants. A working hypothesis is proposed to explain how a signal from the leaves can retain a controlling role during flower development.Key words: Floral commitment, Impatiens, floral reversion, floricaula.      

Large flowers tend to be short-lived in Mediterranean ecosystems: Insights from three Cistus species

Larger and longer lived flowers receive more pollinators, but may also involve increased water maintenance costs under hot, dry environments. Hence, smaller and/or short-lived flowers may buffer such costs. We surveyed floral longevity in three large-flowered Mediterranean Cistus species. We hypothesize that: (1) in Cistus, floral longevity decreases with increasing air temperature and flower size; (2) in C. ladanifer, flower size and longevity increase along an altitudinal gradient; (3) floral longevity is differentially affected by temperature rather than flower size along the gradient; (4) under similar temperature, floral longevity decreases with flower size. For each species, we evaluated the effects of flower size and air temperature on floral longevity. Specifically, floral longevity was surveyed along an altitudinal gradient in the largest flowered species Cistusladanifer. Floral longevity in Cistus species lasted < 1 d and was affected by air temperature, independently of flower size. In C. ladanifer, flower size increased along the gradient but floral longevity decreased. Still, floral longevity decreased with increasing air temperature and, to a lesser extent, with flower size. Together, our findings show a triangular relationship among air temperature, flower size and floral longevity with margins for plasticity to accommodate pollinator attraction with the costs of large-flowered Mediterranean plants.     

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.     

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 Display in Narcissus: Variation in Flower Size and Number at the Species, Population, and Individual Levels

Floral display (the size, number, and arrangement of open flowers) influences pollinator visitation to animal-pollinated plants and should be an important determinant of reproductive success. We examined variation in the size and number of open flowers in wild daffodils (Narcissus). Our analysis of published data on 45 taxa showed that flower number varied negatively with flower diameter among Narcissus species, which supports the widespread assumption that there is a trade-off between these traits. In contrast, field measurements indicated a positive relation between flower number and diameter within two populations of Narcissus dubius, and no relation was evident after we controlled for variation in bulb size. The discrepancy between inter- and intraspecific patterns may have occurred because variable resource levels obscure trade-offs when variation in flower size is low (e.g., within species). Size-related increases in floral tube length were half as great as corresponding increases in flower diameter, a result that is consistent with stronger stabilizing selection on tube length. Staggered flowering within N. dubius inflorescences limited the mean number of open flowers to <66% of total flower number, and slow expansion by later opening flowers resulted in significant differences in flower size throughout flowering. Although pollinators preferred large flowers, experimental reductions in flower diameter did not affect seed production. Our results illustrate how the relative importance of the factors influencing floral display can vary among levels of biological organization. Interspecific variation in flower size and number appeared to be constrained by allocation trade-offs, but intraspecific variation in both traits was more greatly influenced by plant resource status. Within plants, the size and number of open flowers reflected the relative age of individual flowers and floral longevity.