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.     

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.     

Pollinator‐mediated selection in a specialized pollination system: matches and mismatches across populations

Most studies on pollinator‐mediated selection have been performed in generalized rather than specialized pollination systems. This situation has impeded evaluation of the extent to which selection acts on attraction or specialized key floral traits involved in the plant‐pollinator phenotypic interphase. We studied pollinator‐mediated selection in four populations of Nierembergia linariifolia, a self‐incompatible and oil‐secreting plant pollinated exclusively by oil‐collecting bees. We evaluated whether floral traits experience variable selection among populations and whether attraction and fit traits are heterogeneously selected across populations. Populations differed in every flower trait and selection was consistently observed for corolla size and flower shape, two traits involved in the first steps of the pollination process. However, we found no selection acting on mechanical‐fit traits. The observation that selection occurred upon attraction rather than mechanical‐fit traits, suggests that plants are not currently evolving fine‐tuned morphological adaptations to local pollinators and that phenotypic matching is not necessarily an expected outcome in this specialized pollination system.     

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.     

The search for Pleiades in trait constellations: functional integration and phenotypic selection in the complex flowers of Morrenia brachystephana (Apocynaceae)

Pollinator‐mediated natural selection on single traits, such as corolla tube or spur length, has been well documented. However, flower phenotypes are usually complex, and selection is expected to act on several traits that functionally interact rather than on a single isolated trait. Despite the fact that selection on complex phenotypes is expectedly widespread, multivariate selection modelling on such phenotypes still remains under‐explored in plants. Species of the subfamily Asclepiadoideae (Apocynaceae) provide an opportunity to study such complex flower contrivances integrated by fine‐scaled organs from disparate developmental origin. We studied the correlation structure among linear floral traits (i) by testing a priori morphological, functional or developmental hypotheses among traits and (ii) by exploring the organization of flower covariation, considering alternative expectations of modular organization or whole flower integration through conditional dependence analysis (CDA) and integration matrices. The phenotypic selection approach was applied to determine whether floral traits involved in the functioning of the pollination mechanism were affected by natural selection. Floral integration was low, suggesting that flowers are organized in more than just one correlation pleiad; our hypothetical functional correlation matrix was significantly correlated with the empirical matrix, and the CDA revealed three putative modules. Analyses of phenotypic selection showed significant linear and correlational gradients, lending support to expectations of functional interactions between floral traits. Significant correlational selection gradients found involved traits of different floral whorls, providing evidence for the existence of functional integration across developmental domains.     

Are pollinators the agents of selection on flower colour and size in irises?

Plant–pollinator interactions are believed to play a major role in the evolution of floral traits. Flower colour and flower size are important for attracting pollinators, directly influencing reproduction, and thus expected to be under pollinator‐mediated selection. Pollinator‐mediated selection is also proposed to play a role in maintaining flower colour polymorphism within populations. However, pigment concentrations, and thus flower colour, are also under selective pressures independent of pollinators. We quantified phenotypic pollinator‐mediated selection on flower colour and size in two colour polymorphic Iris species. Using female fitness, we estimated phenotypic selection on flower colour and size, and tested for pollinator‐mediated selection by comparing selection gradients between flowers open to natural pollination and supplementary pollinated flowers. In both species, we found evidence for pollen limitation, which set the base for pollinator‐mediated selection. In the colour dimorphic Iris lutescens, while pigment concentration and flower size were found to be under selection, this was independent of pollinators. For the polymorphic Iris pumila, pigment concentration is under selective pressure by pollinators, but only for one colour morph. Our results suggest that pollinators are not the main agents of selection on floral traits in these irises, as opposed to the accepted paradigm on floral evolution. This study provides an opposing example to the largely‐accepted theory that pollinators are the major agent of selection on floral traits.     

Floral integration,phenotypic covariance structure and pollinator variation in bumblebee‐pollinated Helleborus foetidus

By analysing patterns of phenotypic integration and multivariate covariance structure of five metric floral traits in nine Iberian populations of bumblebee‐pollinated Helleborus foetidus (Ranunculaceae), this paper attempts to test the general hypothesis that pollinators enhance floral integration and selectively modify phenotypic correlations between functionally linked floral traits. The five floral traits examined exhibited significant phenotypic integration at all populations, and both the magnitude and the pattern of integration differed widely among populations. Variation in extent and pattern of integration was neither distance‐dependent nor significantly related to between‐population variation in taxonomical composition and morphological diversity of the pollinator assemblage. Patterns of floral integration were closer to expectations derived from consideration of developmental affinities between floral whorls than to expectations based on a pollinator‐mediated adaptive hypothesis. Taken together, results of this study suggest that between‐population differences in magnitude and pattern of floral integration in H. foetidus are probably best explained as a consequence of random genetic sampling in the characteristically small and ephemeral populations of this species, rather than reflecting the selective action of current pollinators.     

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.     

Phylogenetic analysis of floral integration in Schizanthus (Solanaceae): does pollination truly integrate corolla traits?

To assess whether floral integration patterns result from the action of pollinator selection on functionally related traits, we compared corolla integration patterns in eight Schizanthus species differing in pollination systems and in their degree of pollinator dependence across a molecular phylogeny. Integration patterns differed among species and these differences were not related to their phylogenetic relatedness. When the putative original function of some corolla traits was lost in pollinator-dependent species, the integration among nonfunctional characters and the rest of the corolla traits was disrupted. This pattern was not presented in species adapted for late autonomous selfing, which exhibited higher corolla integration than their pollinator-dependent relatives. These results suggest that corolla integration in pollinator-dependent species was shaped by pollinator-mediated selection. Decoupling of nonfunctional traits in these species may result from a relaxation of correlational selection or from selection acting against a default covariation provided by genetic and developmental connections.     

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.     

INFLUENCE OF POLLINATION SPECIALIZATION AND BREEDING SYSTEM ON FLORAL INTEGRATION AND PHENOTYPIC VARIATION IN IPOMOEA

Natural selection should reduce phenotypic variation and increase integration of floral traits involved in placement of pollen grains on stigmas. In this study, we examine the role of pollinators and breeding system on the evolution of floral traits by comparing the patterns of floral phenotypic variances and covariances in 20 Ipomoea species that differ in their level of pollination specialization and pollinator dependence incorporating phylogenetic relatedness. Plants with specialized pollination (i.e., those pollinated by one functional group or by few morphospecies) displayed less phenotypic variation and greater floral integration than generalist plants. Self‐compatible species also displayed greater floral integration than self‐incompatible species. Floral traits involved in pollen placement and pick up showed less variation and greater integration than floral traits involved in pollinator attraction. Analytical models indicate that both breeding system and the number of morphospecies had significant effects on floral integration patterns although only differences in the former were significant after accounting for phylogeny. These results suggest that specialist/self‐compatible plants experience more consistent selection on floral traits than generalist/self‐incompatible plants. Furthermore, pollinators and breeding system promote integration of floral traits involved in pollen placement and pick up rather than integration of the whole flower.     

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.     

Pollinator‐mediated selection in a specialized hummingbird–Heliconia system in the Eastern Caribbean

Phenotypic matches between plants and their pollinators often are interpreted as examples of reciprocal selection and adaptation. For the two co‐occurring plant species, Heliconia bihai and H. caribaea in the Eastern Caribbean, we evaluated for five populations over 2 years the strength and direction of natural selection on corolla length and number of bracts per inflorescence. These plant traits correspond closely to the bill lengths and body masses of their primary pollinators, female or male purple‐throated carib hummingbirds (Eulampis jugularis). In H. bihai, directional selection for longer corollas was always significant with the exception of one population in 1 year, whereas selection on bract numbers was rare and found only in one population in 1 year. In contrast, significant directional selection for more bracts per inflorescence occurred in all three populations of the yellow morph and in two populations of the red morph of H. caribaea, whereas significant directional selection on corolla length occurred in only one population of the red morph and one population of the yellow morph. Selection for longer corollas in H. bihai may result from better mechanical fit, and hence pollination, by the long bills of female E. jugularis, their sole pollinator. In contrast, competition between males of E. jugularis for territories may drive selection for more bracts in H. caribaea. Competitive exclusion of female E. jugularis by territorial males also implicates pollinator competition as a possible ecological mechanism for trait diversification in these plants.     

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.     

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

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

Competition for pollination influences selection on floral traits of Ipomopsis aggregata

Although rarely tested, it is often assumed that interspecific competition results in the divergence of traits related to resource use. Using a plant-pollinator system as a model, I tested the prediction the presence of a competitor for pollination influences the strength and/or direction of pollinator-mediated selection on floral traits. I measured phenotypic selection via female fitness on five floral traits of Ipomopsis aggregata in seven populations. Four contained only conspecifics (I only) and three also contained the competitor Castilleja linariaefolia (C + I). Directional selection via fruits/plant and conspecific pollen deposited/flower on corolla length was positive and significantly stronger in C + I populations. This difference in selection was apparently driven by interpopulation variation in the degree to which reproduction of I. aggregata was pollen limited. Consistent with expectations of interspecific competition, I. aggregata plants in C + I populations received less conspecific pollen per flower and set fewer seeds per fruit and fruits per plant than those in I only populations. Ipomopsis aggregata's corollas were also significantly longer in C + I populations, suggesting that there had been a response to a similar selective regime in past generations. Phenotypic correlations between corolla length and width, which determine the variation in I. aggregata's flower shape, were significantly weaker in C + I populations. These data suggest that competition for pollination can influence the strength of selection on and patterns of correlations among floral traits of I. aggregata. If I. aggregata populations with and without competitors for pollination are linked by gene flow, then measuring selection in competitive and noncompetitive environments maybe necessary to accurately predict how floral traits will evolve.     

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     

MEASURING POLLINATOR-MEDIATED SELECTION ON MORPHOMETRIC FLORAL TRAITS: BUMBLEBEES AND THE ALPINE SKY PILOT,POLEMONIUM VISCOSUM

Sweet-flowered plants of Polemonium viscosum in Colorado are visited by a fly-dominated pollinator fauna at timberline (krummholz), but almost exclusively by bumblebees in higher-elevation tundra habitats. Significant increases in flower size and height are associated with increasing elevation along this habitat gradient. This paper presents the results of an experiment designed to test whether bumblebees exert sufficient selection on morphometric floral phenotypes to account for the clinal shifts seen in natural populations. Two populations of sweet-flowered plants of krummholz origin were established: one randomly pollinated, the other solely bumblebee-pollinated. I tested the effects of two independent axes of floral variation, obtained by principal-components analysis, on mean seed set per flower of plants in each population. PC1, with strong correlations to corolla diameter, corolla length, and stem height, explained a significant amount of variance in seed set for bumblebee-pollinated plants but had no bearing on that of randomly pollinated plants. PC2, with strong correlation to flower number, did not influence seed set in either population. Bumblebee behavior was correlated with variation in PC1 scores of the selected population, yielding positive directional selection on morphometric floral traits associated with PC1. Selection coefficients for PC1, corolla length, corolla diameter, and inflorescence height were estimated, respectively, as 0.11, 0.09, 0.07, and 0.06 (P < 0.025 in all cases). These results support the hypothesis that pollinator-mediated selection can bring about changes in floral form, and can explain shifts in floral morphology of P. viscosum along natural habitat gradients.     

Pollinator‐mediated selection on floral size and tube color in Linum pubescens: Can differential behavior and preference in different times of the day maintain dimorphism?

Diversity of flower traits is often proposed as the outcome of selection exerted by pollinators. Positive directional pollinator‐mediated selection on floral size has been widely shown to reduce phenotypic variance. However, the underlying mechanism of maintaining within‐population floral color polymorphism is poorly understood. Divergent selection, mediated by different pollinators or by both mutualists and antagonists, may create and maintain such polymorphism, but it has rarely been shown to result from differential behavior of one pollinator. We tested whether different behaviors of the same pollinators in morning and evening are associated with dimorphic floral trait in Linum pubescens, a Mediterranean annual plant that exhibits variable within‐population frequencies of dark‐ and light‐colored flower tubes. Usia bicolor bee‐flies, the major pollinators of L. pubescens, are mostly feeding in the flower in the morning, while in the evening they are mostly visiting the flowers for mating. In 2 years of studying L. pubescens in a single large population in the Carmel, Israel, we found in one year that dark‐centered flowers received significantly higher fraction of visits in the morning. Fitness was positively affected by number of visits, but no fitness differences were found between tube‐color morphs, suggesting that both morphs have similar pollination success. Using mediation analysis, we found that flower size was under positive directional pollinator‐mediated selection in both years, but pollinator behavior did not explain entirely this selection, which was possibly mediated also by other agents, such as florivores or a‐biotic stresses. While most pollinator‐mediated selection studies show that flower size signals food reward, in L. pubescens, it may also signal for mating place, which may drive positive selection. While flower size found to be under pollinator‐mediated selection in L. pubescens, differential behavior of the pollinators in morning and evening did not seem to explain flower color polymorphism.     

Evolutionary transition between bee pollination and hummingbird pollination in Salvia: Comparing means,variances and covariances of corolla traits

Covariation among traits can modify the evolutionary trajectory of complex structures. This process is thought to operate at a microevolutionary scale, but its long‐term effects remain controversial because trait covariation can itself evolve. Flower morphology, and particularly floral trait (co)variation, has been envisioned as the product of pollinator‐mediated selection. Available evidence suggests that major changes in pollinator assemblages may affect the joint expression of floral traits and their phenotypic integration. We expect species within a monophyletic lineage sharing the same pollinator type will show not only similarity in trait means but also similar phenotypic variance‐covariance structures. Here, we tested this expectation using eighteen Salvia species pollinated either by bees or by hummingbirds. Our findings indicated a nonsignificant multivariate phylogenetic signal and a decoupling between means and variance‐covariance phenotypic matrices of floral traits during the evolution to hummingbird pollination. Mean trait value analyses revealed significant differences between bee‐ and hummingbird‐pollinated Salvia species although fewer differences were detected in the covariance structure between groups. Variance‐covariance matrices were much more similar among bee‐ than hummingbird‐pollinated species. This pattern is consistent with the expectation that, unlike hummingbirds, bees physically manipulate the flower, presumably exerting stronger selection pressures favouring morphological convergence among species. Overall, we conclude that the evolution of hummingbird pollination proceeded through different independent transitions. Thus, although the evolution of hummingbird pollination led to a new phenotypic optimum, the process involved the diversification of the covariance structure.