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.     

Stabilizing selection on nectar concentration in wild Petunia axillaris,as revealed by genetic analysis of pollen dispersal

Most animal-pollinated plants produce nectar as a pollinator reward. Despite the main role that nectar plays in plant-pollinator interactions, the impact of natural variation in nectar traits on realized male fitness is poorly known. Here, we assessed this relation for a wild Petunia axillaris population using paternity-based direct selection gradient analysis, which allowed us also to infer pollen dispersal patterns. Because male fecundity may depend on other traits which could be associated with nectar characteristics (i.e. volume and concentration), we also considered selection on other key reproductive traits. The analysis revealed that P. axillaris was a strict outcrosser, but that successful pollination occurred mainly among neighbours. Individual plants varied greatly in their male fecundity. Nectar concentration, a key feature of nectar that determines its profitability, was subjected to stabilizing selection. Selection through male function also affected corolla area (positive directional selection), corolla tube length (negative directional selection), and floral display size (stabilizing selection), but none of these traits were phenotypically correlated with nectar characteristics. Because nectar concentration affects the ability and foraging efficiency of different flower visitors to feed on nectar, stabilizing selection may reflect either the preference of the most effective pollinators, or antagonistic selection driven by pollinators and non-pollinating nectar consumers.     

Long corollas as nectar barriers in <Emphasis Type="Italic">Lonicera implexa</Emphasis>: interactions between corolla tube length and nectar volume

Long corollas are a classical example of nectar barriers, because they prevent undesired visitors from consuming the reward intended for more effective pollinators. As the investment in nectar barriers increases, flower attractiveness and nectar rewards may also increase to maintain loyal visitation of most effective pollinators; and flowers may become more prone to nectar robbing. We evaluated the effect of nectar barriers (corolla tube length), two related traits (nectar volume and upper lip size) and the associated risk of nectar robbing, on the fecundity of Lonicera implexa plants from three populations differing in the abundance of its most efficient pollinator, the hummingbird hawkmoth Macroglossum stellatarum. Corolla tube length varied most among individuals within populations (45–46 % of total variance) and inflorescences within individuals (23–32 %), and showed little variation among populations (0.2–11 %). Longer corolla tubes were always associated with larger nectar volumes and larger upper lips, although the strength of the relationships varied across populations and years. Robbing frequency increased with corolla tube length, decreased with nectar volume and upper lip size, and its weak effects on fecundity were predominantly positive. Plant fecundity peaked at two different optima: long corollas with little nectar and short corollas with abundant nectar. However, the exact shape of the interaction between corolla length and nectar volume, as well as the combination of traits showing the highest fecundity, differed between populations and years. This variation could be explained by among-population differences in pollinator assemblages, and inter-annual changes in resources dedicated to reproduction. Our study shows that large nectar volumes can modulate the effect of corolla length as a nectar barrier, and that the combination of these two traits that maximises fecundity may be related to the identity of pollinators within each population.     

同域分布的紫堇属三种植物的繁育系统和传粉差异

为研究近缘物种之间繁育系统分化对传粉环境的适应性意义,本文针对湖北地区的3种紫堇属植物（紫堇Corydalis edulis Maxim.、尖距紫堇C.shearer S.Moore.和小花黄堇C.racemosa（Thunb.） Pers.）进行了传粉生态学研究,对比分析了它们在花部特征、分布模式、花期、交配系统、传粉系统等方面的差异。3种紫堇属植物常见伴生现象,花期有一定重叠;花色、距长、花蜜量等方面均有显著差异;尖距紫堇交配系统为自交不亲和、依靠传粉者异花授粉;而紫堇和小花黄堇交配系统为自交亲和,兼有自交和异交的混合交配系统。3个物种均由蜂类传粉,且花部性器官与传粉者的接触部位一致,但访花频率差异较大。在混合群落中,传粉者访花具有较高的忠实性,花部特征差异可能是传粉者选择性访花的原因。对于紫堇属3个物种,花部特征和交配系统的分化有助于其避免传粉过程的相互干扰,交配系统与传粉环境具有一定相关性,混合交配系统可能有利于提高植物对不同生境和气候的适应性。     

Association between floral traits and rewards in Erysimum mediohispanicum (Brassicaceae)

Background and Aims

Floral rewards may be associated with certain morphological floral traits and thus act as underlying factors promoting selection on these traits. This study investigates whether some traits that are under pollinator-mediated selection (flower number, stalk height, corolla diameter, corolla tube length and corolla tube width) in the Mediterranean herb E. mediohispanicum (Brassicaceae) are associated with rewards (pollen and nectar).

Methods

During 2005 the phenotypic traits and the visitation rate of the main pollinator functional groups were quantified in 720 plants belonging to eight populations in south-east Spain, and during 2006 the same phenotypic traits and the reward production were quantified in 400 additional plants from the same populations.

Key Results

A significant correlation was found between nectar production rate and corolla tube length, and between pollen production and corolla diameter. Visitation rates of large bees and butterflies were significantly higher in plants exhibiting larger flowers with longer corolla tubes.

Conclusions

The association between reward production and floral traits may be a factor underlying the pattern of visitation rate displayed by some pollinators.Key words: Erysimum, floral traits, nectar, pollen, pollinator visitation rate, reward     

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

Nectar spurs have an important role in floral evolution and plant–pollinator coadaptation. The flowers of some species possess spurs curving into a circle. However, it is unclear whether spur circle diameter is under direct selection pressure from different sources, such as pollinators and nectar robbers. In this study, we quantified selection on some floral traits, such as spur circle diameter in Impatiens oxyanthera (Balsaminaceae) using phenotypic selection analysis and compared the relative importance of pollinators and nectar robbers as selective agents using mediation analysis. The study showed that pollinators caused significant selection on corolla length, spur curvature and spur circle diameter while nectar robbers only imposed strong selection on spur circle diameter. Pollinators favored flowers with large corolla, curly spurs and large spur circle while nectar robbers preferred flowers with small spur circle. More pollinator visits resulted in higher female reproductive success, while robbery reduced female fitness. Conflicting selection on spur traits from pollinators and nectar robbers was not found. Mediation analysis showed that selection on floral traits through nectar robbing was stronger than selection through pollination. The results suggested that pollinators and nectar robbers jointly mediated the directional selection for large spur circle, and nectar robbers caused stronger selection than pollinators on floral traits.     

The role of pollinator shifts in the floral diversification of Iochroma (Solanaceae)

Differences in floral traits among plant species have often been attributed to adaptation to pollinators. We explored the importance of pollinator shifts in explaining floral divergence among 15 species of Iochroma. We examined four continuously varying floral traits: corolla length, nectar reward, display size, and flower color. Pollinator associations were characterized with a continuously varying measure of pollinator importance (the product of visitation and pollen deposition) for four groups of pollinators: hummingbirds, Hymenoptera, Lepidoptera, and Diptera. A phylogenetic generalized least squares approach was used to estimate correlations between pollinator groups and floral traits across a sample of Bayesian trees using different models of trait evolution. Multivariate analyses were also employed to identify suites of traits associated with each pollinator group. We found that nonphylogenetic models typically fit the data better than phylogenetic models (Brownian motion, Ornstein-Uhlenbeck), and thus results varied little across trees. Our results indicated that species with high nectar reward and large displays are significantly more likely to be pollinated by hummingbirds and less likely to be pollinated by all groups of insects. Corolla length and flower color did not show any consistently significant associations with pollinator groups. For these two traits, we discuss alternative evolutionary forces, including phylogenetic inertia and community-level factors.     

Floral traits and mating systems in sister species of <Emphasis Type="Italic">Nicotiana</Emphasis>: interpopulational variability and sympatry effects

Mating systems of Angiosperms are important determinants of population genetic structure and evolutionary potential. Nicotiana longiflora and N. plumbaginifolia are self-compatible, sister species, with contrasting floral morphology and can be found in allopatry and sympatry in North Argentina. In two sympatric and 10 nearby allopatric populations we studied their natural interpopulational variability and sympatry effects on corolla length and anther–stigma distance. We also estimated seed set by selfing and via pollinators using pollination treatments. Both corolla length and anther–stigma distance varied significantly among N. longiflora, but not among N. plumbaginifolia populations. We did not detect an effect of sympatry in either species for any of the floral traits studied. Pollination treatments suggest that N. longiflora is mainly an outcrosser, although selfing occurs at some extent. Seed set attributed to pollinators was significantly higher in N. longiflora whereas most seeds in N. plumbaginifolia were sired through self-pollination. In N. plumbaginifolia, selfing seems to assure reproduction in sympatric populations, where floral visitors have a strong preference for N. longiflora. Corolla length was significantly negatively correlated with an increase in the percentage of self-seeds estimated by pollination treatments. Within N. longiflora, anther–stigma distance showed a positive correlation with selfing.     

Bee visitation rates to cultivated sunflowers increase with the amount and accessibility of nectar sugars

Pollinators make foraging decisions based on numerous floral traits, including nectar and pollen rewards, and associated visual and olfactory cues. For insect‐pollinated crops, identifying and breeding for attractive floral traits may increase yields. In this study, we examined floral trait variation within cultivated sunflowers and its effects on bee foraging behaviours. Over 2 years, we planted different sunflower inbred lines, including male‐fertile and male‐sterile lines, and measured nectar volume, nectar sugar concentration and composition, and corolla length. During bloom, we recorded visits by both managed honey bees and wild bees. We then examined consistency in relative nectar production by comparing field results to those from a greenhouse experiment. Sunflower inbred lines varied significantly in all floral traits, including the amount and composition of nectar sugars, and in corolla length. Both wild bee and honey bee visits significantly increased with nectar sugar amount and decreased with corolla length, but appeared unaffected by nectar sugar composition. While wild bees made more visits to sunflowers providing pollen (male‐fertile), honey bees preferred plants without pollen (male‐sterile). Differences in nectar quantity among greenhouse‐grown sunflower lines were similar to those measured in the field, and bumble bees preferentially visited lines with more nectar in greenhouse observations. Our results show that sunflowers with greater quantities of nectar sugar and shorter corollas receive greater pollination services from both managed and wild bees. Selecting for these traits could thus increase sunflower crop yields and provide greater floral resources for bees.     

Geographical variation in floral traits of the tree tobacco in relation to its hummingbird pollinator fauna

Nicotiana glauca , a hummingbird pollinated plant, exhibits geographical variation in several floral traits. We examined whether geographical differentiation occurred for different flower characters and if this differentiation could be explained, at least in part, by the existence or abundance of different hummingbird species in the respective pollinator assemblages. The comparison between five populations showed significant variation in six floral traits and two female fitness measures. The traits that better discriminated between populations were corolla length and corolla width. There were metric correlations between corolla length and style length in all populations studied and, in four of the five populations, both corolla length and width were also correlated. Among plants in each population, seed weight was correlated positively and significantly with style exertion, suggesting that fruit quality is dependent on the degree of cross pollination. Assemblages of hummingbirds differed between populations in species composition, visitation frequencies, and bill length. Linear regression involving bill length of the more frequent hummingbird pollinators and corolla length yielded positive and significant relationships. Thus, there appears to be an adjustment between pollinators and flowers traits that have high incidence in the among population variation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 657–667.     

MACROEVOLUTIONARY TESTS OF POLLINATION SYNDROMES: A REPLY TO FENSTER ET AL.

Studies of floral ecology and evolution are often centered on the idea that particular floral trait combinations, or syndromes, represent adaptations for particular pollinators. Despite the conceptual importance of pollination syndromes, few macroevolutionary studies have statistically examined the relationship between pollinators and floral traits. Using 15 species of Iochroma, Smith et al. applied phylogenetically structured correlation analyses to test the relationship between floral variation and pollination system, quantified in terms of the importance of major pollinator groups. This study revealed that pollinator shifts are tied to changes in nectar reward and floral display but are not significantly correlated with changes in corolla length or color, contrary to what might be predicted from classical pollination syndromes. Fenster et al. question these findings because our pollinator importance estimates included recently introduced honey bees. To address this concern, we recalculated importance values excluding honey bees and repeated the analyses. We found the same patterns as in our original study with significant correlations between pollinators and nectar reward and display. We conclude that phylogenetic approaches provide essential tools for testing macroevolutionary predictions of pollination syndromes and, by applying these approaches to other radiations, we can refine our understanding of the role of pollinators in floral diversification.     

Nectar reward and advertisement in hummingbird-pollinated Silene virginica (Caryophyllaceae)

We tested for an association between nectar and various floral traits and investigated their roles as primary and secondary pollinator attractants in hummingbird-pollinated Silene virginica. Our goal was to gain insight into the mechanisms of pollinator-mediated selection that underlies floral trait divergence within the genus. In a field population of S. virginica, we measured five floral and eight vegetative traits and quantified nectar volume, nectar sugar concentration, and total sugar reward (nectar volume × nectar sugar concentration). All three components of nectar reward were positively correlated to flower size, and nectar volume varied significantly among individuals within the population. To ascertain whether the correlation of specific floral traits with nectar reward influences the behavior of the primary pollinator of S. virginica, the ruby-throated hummingbird, Archilochus colubris, we investigated whether A. colubris preferred the expression of floral traits associated with high nectar volume and total sugar reward. We accomplished this by constructing floral arrays consisting of artificial flowers that had equal nectar quantity and total sugar reward but that differed in petal area and corolla tube diameter, which were positively correlated with nectar quantity and total sugar reward in our field study. In observations of visitation frequencies to the various floral-trait combinations, hummingbirds preferentially visited artificial floral phenotypes with larger petal displays, with the greatest preference for floral phenotypes with both larger petals and wider corolla-tube diameters. This association between primary and secondary floral attractants and hummingbird discrimination of floral features supports the concept that the floral traits of S. virginica reflect pollinator-mediated selection by the principal pollinator.     

贠建全:广东荷包岛维管束植物名录

以分布于秦岭的金花忍冬（Lonicera chrysantha Turcz.）、忍冬（L.japonica Thunb.）、葱皮忍冬（L.ferdinandii Franch.）和金银忍冬（L.maackii（Rupr.）Maxim.）为对象,通过定位观察、人工授粉实验、人为设置实验斑块的方法对忍冬属4种植物的开花生物学特性、繁育系统、花色变化现象、传粉过程进行了研究。结果表明,4种植物的单花花期、花部特征存在差异。人工授粉实验显示,4种植物均存在一定的花粉限制,自交不亲和。除葱皮忍冬外,其余3种植物随着花色由白变黄,花粉和花蜜报酬减少、雌雄生殖能力逐渐降低;葱皮忍冬花变色后花蜜量变化不显著,且仍保留较强的雌性生殖能力。变色花的保留被认为是植物的一种生殖策略,通过增大植物的花展示来扩大自身的吸引力,以吸引更多远距传粉者访花。人为控制白、黄花不同数量比的实验结果表明,大多数传粉者偏向访问白花（变色前的花）,且白花提供的报酬量和黄花（变色后的花）数量显著影响传粉者的访花频率,即当花蜜量减少或黄花数量增多时,传粉者访花频率随之降低。因此,我们认为忍冬属4种植物的花色变化可能除了增大植物对远距传粉者的吸引力外,对近距传粉者的访花行为也可能具有一定的影响。当传粉者接近植株时,变色后的花可能暗示其花蜜（花粉）报酬已经发生变化,并驱使昆虫离开并飞向同株或异株植物新开放的报酬丰富的白花,这既有利于提高传粉者的觅食效率,又能降低植物同株异花授粉的几率,对忍冬属植物及传粉者都具有重要意义,是植物长期与授粉昆虫相互适应的反映。     

Pollination Biology of Distylous Rubiaceae in the Atlantic Rain Forest, SE Brazil

Abstract: Data on pollination biology constitute important clues for the comprehension of pollen flow and genetic differentiation in plant populations. Pollinator type, availability and behaviour may modify morphological and mating patterns in populations of typically distylous species. This study investigates the pollination biology of four distylous species of Rubiaceae in the Atlantic rain forest, SE Brazil. Data on flowering phenology, floral lifespan, stigmatic receptivity, pollen availability, nectar volume and concentration, and pollinator activity were collected. The species studied flower sequentially throughout the wet season, and produce terminal inflorescences which bear small, tubular, diurnal, nectariferous flowers. Despite these similarities, some of the species studied are pollinated by different groups of pollinators, probably due to their distribution, availability of flowers and corolla length. On the other hand, pollinator specificity does not seem to be so important for distylous species. Long mouthparts, like those of most of the recorded pollinators, may reach lower sexual organs and, together with the self- and intramorph-incompatibilities observed, be sufficient to perform legitimate pollination and maintain levels of intermorph mating.     

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.     

Floral traits variation, legitimate pollination, and nectar robbing in Polygala vayredae (Polygalaceae)

The variation of floral morphology and its effect on the flower visitors of Polygala vayredae Costa (Polygalaceae), a narrow endemic species from the Oriental pre-Pyrenees, were examined. First, to account for the main floral reward (i.e., nectar), the relationship between the dimensions of the nectar gland and nectar production was investigated. Second, floral traits variation was assessed within and between the three most representative populations of the species. Finally, the role of several floral traits in the female fitness was evaluated. Furthermore, as nectar robbing was highly frequent, preferences of robbers for specific floral traits and their impact on legitimate pollinations were also evaluated. The flowers of this species are characterized by significant variations in floral characteristics and nectar rewards. A significant and positive correlation between the nectar gland dimensions and nectar production per flower was observed, with the gland dimensions being a good measure to infer the rewards offered by the flowers of P. vayredae. In general, corolla traits were significant and positively correlated with each other. Nectar was revealed to be an important trait in flower–visitor interactions, with legitimate pollinations being primarily influenced by this floral reward. Negative correlations between robbing frequency and legitimate pollinations were observed in two of the studied populations, and positive correlations between flower size and robbing frequency were observed in one population. An indirect negative selection over phenotypic floral traits mediated by nectar robbers is proposed.     

Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees

Background and Aims

Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.

Methods

For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.

Key Results

Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.

Conclusions

Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.     

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。     

Matching floral and pollinator traits through guild convergence and pollinator ecotype formation

Background and Aims

Pollinator landscapes, as determined by pollinator morphology/behaviour, can vary inter- or intraspecifically, imposing divergent selective pressures and leading to geographically divergent floral ecotypes. Assemblages of plants pollinated by the same pollinator (pollinator guilds) should exhibit convergence of floral traits because they are exposed to similar selective pressures. Both convergence and the formation of pollination ecotypes should lead to matching of traits among plants and their pollinators.

Methods

We examined 17 floral guild members pollinated in all or part of their range by Prosoeca longipennis, a long-proboscid fly with geographic variation in tongue length. Attractive floral traits such as colour, and nectar properties were recorded in populations across the range of each species. The length of floral reproductive parts, a mechanical fit trait, was recorded in each population to assess possible correlation with the mouthparts of the local pollinator. A multiple regression analysis was used to determine whether pollinators or abiotic factors provided the best explanation for variation in floral traits, and pollinator shifts were recorded in extralimital guild member populations.

Key Results

Nine of the 17 species were visited by alternative pollinator species in other parts of their ranges, and these displayed differences in mechanical fit and attractive traits, suggesting putative pollination ecotypes. Plants pollinated by P. longipennis were similar in colour throughout the pollinator range. Tube length of floral guild members co-varied with the proboscis length of P. longipennis.

Conclusions

Pollinator shifts have resulted in geographically divergent pollinator ecotypes across the ranges of several guild members. However, within sites, unrelated plants pollinated by P. longipennis are similar in the length of their floral parts, most probably as a result of convergent evolution in response to pollinator morphology. Both of these lines of evidence suggest that pollinators play an important role in selecting for certain floral traits.     

Adaptation of floral traits and mating system to pollinator unpredictibility: the case of Disterigma stereophyllum (Ericaceae) in southwestern Colombia

The Neotropical group of Ericaceae offers a variety of floral displays. Here we present data on floral characteristics and breeding system of Disterigma stereophyllum, a Neotropical epiphyte Ericaceae abundant in semi-disturbed areas with pollinator unpredictability. Floral characteristics are intermediate between those typical of bee- and hummingbird-pollinated plants: the corolla is short, white, and urceolate, but the composition and amount of nectar are similar to those typically observed in hummingbird-pollinated species. Plants are capable of autonomously self-pollination, but manual outcrossing yielded more than twice as many fruits as self hand-pollination did. Moreover, outcross pollen grows more rapidly than self pollen down the style. Our results provide another example of a species with a ``mixed pollination syndrome'' which is cryptically self-incompatible and preferably attracts high-energy pollinators (hummingbirds), but which can also profit from small bee visitors and retains the ability to self-pollinate just in case. We hypothesize that interaction among several factors, including self pollinating possibility, and the capacity to attract a wide pollinator spectrum, may result in a lack of strong selection for a bee vs. a hummingbird floral morphology, thus allowing the persistence of mixed floral traits in these ericads. The maintenance of these traits may enhance the ability of this species to colonize semi-disturbed areas.