HERITABILITY AND GENETIC CORRELATION OF COROLLA SHAPE AND SIZE IN ERYSIMUM MEDIOHISPANICUM

Flower shape has evolved in most plants as a consequence of pollinator-mediated selection. Unfortunately, no study has explored the genetic variation of flower shape, despite that this information is crucial to understand its adaptive evolution. Our main goal here is to determine heritability of corolla shape in Erysimum mediohispanicum (Brassicaceae). Also, we explore heritability of other pollinator-selected traits in this plant species, such as plant size, flower display, and corolla size. In addition, we investigate genetic correlations between all these traits. We found significant heritability for one plant-size trait (stalk height), for number of flowers, for all corolla-size traits (corolla diameter, corolla tube length and corolla tube width), and for corolla shape. Consequently, this species retains a high ability to respond to the selection exerted by its pollinators. Genetic correlation was strong between all functionally related traits and between flower number and plant size, weak between corolla size and plant size and no correlation between corolla shape and any other trait. Thus, selection affecting some E. mediohispanicum traits would also indirectly affect other functionally related and unrelated traits. More importantly, the observed genetic correlation seems to be at least partially adaptive because positive correlational selection currently acts on the covariance between some of these traits ( Gómez 2003 ; Gómez et al. 2006 ).     

THE QUANTITATIVE GENETICS OF SEXUAL DIMORPHISM IN SILENE LATIFOLIA (CARYOPHYLLACEAE). II. RESPONSE TO SEX-SPECIFIC SELECTION

A well-established theoretical relationship exists between genetic correlations between the sexes and the dynamics of response to sex-specific selection. The present study investigates the response to sex-specific selection for two sexually dimorphic traits that have been documented to be genetically variable, calyx diameter and flower number, in Silene latifolia. Following the establishment of a base generation with a known genetic background, selection lines were established and two generations of sex-specific selection were imposed. Calyx diameter responded directly to sex-specific selection, and the positive genetic correlation between the sexes was reflected in correlated responses in the sex that was not the basis for selection within a particular line. Flower number showed a more erratic response to sex-specific selection in that selection in some lines was initially in the wrong direction, that is, selection for a decrease in flower number resulted in an increase. These erratic responses were attributable to genotype-environment interaction as reflected in significant heteroscedasticity in variance among families. Correlated responses to selection in the sex that was not the immediate basis for selection indicated the possible existence of a negative genetic correlation between the sexes for this trait. These results test for the first time the impact of genetic correlations between the sexes on the evolutionary dynamics of sexually dimorphic traits in a plant species.     

Genetics of sex allocation in Mimulus (Scrophulariaceae)

Theoretical models of the evolution of resource allocation patterns to male and female function make the assumption that there are inherent trade-offs between the two. Here we use a quantitative genetic approach to quantify trade-offs between male and female function and to determine whether plant populations could readily respond to natural selection by quantifying the amount of genetic variation for pollen and ovule production. Both intra- and interspecific crossing designs were applied to two populations of the predominantly outcrossing Mimulus guttatus and two populations of the highly selfing congener, M. micranthus. The only significant correlations observed among pollen number, pollen size and ovule number were positive. Positive genetic correlations among the traits were sometimes reduced after removing the effect of flower size but still no significant negative correlations were detected. These results suggest that positive correlations between pollen and ovule production may be due to the joint positive correlation of these characters with the resource pool available for pollen and ovule production, as reflected by flower size. Heritabilities were moderate to high for ovule production but low for pollen number and pollen size and suggest that responses to selection would differ between the two traits. Crosses between the species revealed that there are additional genetic factors contributing to differences between the two species for corolla width, vs. pollen:ovule ratio. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the overall lack of a negative correlation between pollen and ovule production and provides a genetic explanation for little evidence of trade-offs between sexual functions in Mimulus.     

Patterns of contemporary phenotypic selection and flower integration in the hummingbird‐pollinated Nicotiana glauca between populations with different flower–pollinator combinations

We studied six populations of the hummingbird‐pollinated Nicotiana glauca to determine if the marked differences in the degree of floral‐pollinator mismatch between populations promote divergences in the pattern of pollinator‐mediated phenotypic selection on single traits and on the evolution of complexes of many interacting floral traits. We found evidence that flower phenotype is being shaped by pollinator‐mediated phenotypic selection, since corolla length was consistently under contemporary directional or stabilizing selection. Weak directional selection for longer corollas was found in two populations with low flower–pollinator mismatch; much stronger directional selection was detected for shorter corollas in two populations with high flower–pollinator mismatch; finally, the remaining two populations with intermediate flower–pollinator mismatch showed stabilizing selection for corolla length. N. glauca populations differed in every flower character measured but variations in pollinator‐mediated selection among populations were only observed for corolla length. Multiple covariation among traits was favoured, as suggested by the predominately functional patterns of integration and selection of complexes of many interacting floral traits. This was consistent with the patterns of correlational selection exhibited by four of the six populations, where corolla length was under significant selection in combination with corolla width, style length or stamen length. Overall floral integration was relatively high in all populations but phenotypic integration patterns were not clearly accounted by the degree of flower–pollinator mismatch or type of phenotypic selection, suggesting that trait covariation at the entire flower level is not explained by the current scenario of pollinator‐mediated selection.     

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.     

Direct and indirect responses to selection on pollen size in Brassica rapa L.

Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (–), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic‐phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles.     

VARIATION AND COVARIATION AMONG FLORAL TRAITS WITHIN AND AMONG FOUR SPECIES OF NORTHERN EUROPEAN PRIMULA (PRIMULACEAE)

Phenotypic and genetic variation and correlations among floral traits within and among four Primula species were measured to seek evidence for potential constraints on the independent evolution of floral characters, to examine the relationship between mating system, ploidy level, and sex allocation, and to determine whether some traits are more conservative than others within and across these congeners. We measured mean flower diameter, corolla depth, pollen production, modal pollen grain volume, ovule number per flower, and pollen: ovule ratios for 64 field-collected genotypes from northern Europe. These represented one heterostylous (P. farinosa: 2n = 18) and three homostylous (P. scotica: 2n = 54, P. scahdinavica: 2n = 74, and P. stricta: 2n ~ 126) species. All traits differed significantly among species and among the six taxon/morph categories identified (including three morphs of P. farinosa: pin, thrum, and homostylous). Pollen production per flower was significantly higher (and individual pollen grain volume lower) in the outcrossing P. farinosa than in any of the homostylous species; also, pin morphs produced significantly more pollen per flower than thrums in P. farinosa. Among the homostylous species, there were significant differences in all traits except modal pollen grain volume. Ovule number per flower and flower size were less variable among taxa than pollen production and pollen volume. Within species, there were several strong negative correlations among genets between pairs of traits, but each species exhibited a unique set of inverse relationships. We detected only one significant positive genetic correlation; in P. stricta, ovule number and pollen production per flower were positively correlated among genets. Among species means, two pairs of traits were negatively correlated: mean ovule number per flower vs. flower diameter (but P = 0.0587), and mean pollen production per flower vs. modal pollen grain volume. These negative correlations within and among taxa suggest that there may be intrinsic genetic constraints on the independent evolution of these floral characters, but that these constraints differ among species.     

Elimination of a genetic correlation between the sexes via artificial correlational selection

Genetic correlations between the sexes can constrain the evolution of sexual dimorphism and be difficult to alter, because traits common to both sexes share the same genetic underpinnings. We tested whether artificial correlational selection favoring specific combinations of male and female traits within families could change the strength of a very high between-sex genetic correlation for flower size in the dioecious plant Silene latifolia. This novel selection dramatically reduced the correlation in two of three selection lines in fewer than five generations. Subsequent selection only on females in a line characterized by a lower between-sex genetic correlation led to a significantly lower correlated response in males, confirming the potential evolutionary impact of the reduced correlation. Although between-sex genetic correlations can potentially constrain the evolution of sexual dimorphism, our findings reveal that these constraints come not from a simple conflict between an inflexible genetic architecture and a pattern of selection working in opposition to it, but rather a complex relationship between a changeable correlation and a form of selection that promotes it. In other words, the form of selection on males and females that leads to sexual dimorphism may also promote the genetic phenomenon that limits sexual dimorphism.     

黄瓜雄花性状的遗传分析

为了解黄瓜雄花花器的遗传特性,该研究以雄花器官较小的华南型黄瓜二早子为母本,花器较大的加工型黄瓜NC-76为父本,构建4世代遗传群体,并采用多世代联合分离分析方法,分析黄瓜雄花花器性状的遗传特性。结果表明:分离群体的雄花花梗和花冠长2个性状均表现为单峰分布,表明两性状为数量性状且有主基因控制;花梗长性状符合2对完全显性主基因+加性-显性多基因(E-5)模型,花冠长性状符合2对加性-显性-上位性主基因+加性-显性-上位性多基因(E-1)模型;控制花梗长性状的两对主基因的加性效应相等,为0.573,多基因的加性效应和显性效应值相差不大,且均为负向;控制花冠长度性状的2对主基因的加性效应均为0,显性效应分别为-0.226和-0.472,在上位性作用中以加性×加性和显性×显性互作为主,多基因以显性效应为主,正向显性效应值为0.613,大于负向的加性效应值。花梗和花冠长度两个性状在F2群体中主基因遗传率分别为61.04%和69.60%,多基因遗传率均为0。由此看出黄瓜雄花花器性状为数量遗传,遗传率相对较高。该研究结果显示在黄瓜杂交育种中对花器大小选择可以在较早世代选择。     

Quantitative trait loci mapping of floral and leaf morphology traits in Arabidopsis thaliana: evidence for modular genetic architecture

Summary Morphological variation within organisms is integrated and often modular in nature. That is to say, the size and shape of traits tend to vary in a coordinated and structured manner across sets of organs or parts of an organism. The genetic basis of this morphological integration is largely unknown. Here, we report on quantitative trait loci (QTL) analysis of leaf and floral organ size in Arabidopsis thaliana. We evaluate patterns of genetic correlations among traits and perform whole-genome scans using QTL mapping methods. We detected significant genetic variation for the size and shape of each floral and leaf trait in our study. Moreover, we found large positive genetic correlations among sets of either flower or leaf traits, but low and generally nonsignificant genetic correlations between flower and leaf traits. These results support the hypothesis of independent floral and vegetative modules. We consider co-localization of QTL for different traits as support for a pleiotropic basis of morphological integration and modularity. A total of eight QTL affecting flower and three QTL affecting leaf traits were identified. Most QTL affected either floral or leaf traits, providing a general explanation for high correlations within and low correlations between modules. Only two genomic locations affected both flower and leaf growth. These results are discussed in the context of the evolution of modules, pleiotropy, and the putative homologous relationship between leaves and flowers.     

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.     

Rapid independent trait evolution despite a strong pleiotropic genetic correlation

Genetic correlations are the most commonly studied of all potential constraints on adaptive evolution. We present a comprehensive test of constraints caused by genetic correlation, comparing empirical results to predictions from theory. The additive genetic correlation between the filament and the corolla tube in wild radish flowers is very high in magnitude, is estimated with good precision (0.85 ± 0.06), and is caused by pleiotropy. Thus, evolutionary changes in the relative lengths of these two traits should be constrained. Still, artificial selection produced rapid evolution of these traits in opposite directions, so that in one replicate relative to controls, the difference between them increased by six standard deviations in only nine generations. This would result in a 54% increase in relative fitness on the basis of a previous estimate of natural selection in this population, and it would produce the phenotypes found in the most extreme species in the family Brassicaceae in less than 100 generations. These responses were within theoretical expectations and were much slower than if the genetic correlation was zero; thus, there was evidence for constraint. These results, coupled with comparable results from other species, show that evolution can be rapid despite the constraints caused by genetic correlations.     

GENETIC CONSTRAINTS ON THE INDEPENDENT EVOLUTION OF MALE AND FEMALE REPRODUCTIVE CHARACTERS IN THE TRISTYLOUS PLANT LYTHRUM SALICARIA

Here we test whether the potential exists for the independent evolution of allocation to male, female, and attractive functions within a flower. We employed half-sib and parent-offspring regression methods in the tristylous plant Lythrum salicaria to determine whether there is additive genetic variation for characters important to male and female reproductive success and whether genetic correlations could constrain the independent evolution of male and female function. Although significance levels were not consistent among morph types or between populations, there were significant narrow-sense heritabilities for several traits including stamen mass, pistil mass, perianth mass, petal length, and calyx length. Traits that might be under strong stabilizing selection to promote specific pollen transfer, such as stamen and style lengths, had little heritable variation. In the majority of cases in which heritable variation was present, there were positive genetic correlations among floral traits. A strong positive genetic correlation appeared between stamen and pistil mass in the short-styled morph from one of the populations studied. This suggests that selection might not be able to act independently on biomass allocation to male and female flower parts. No evidence of negative genetic correlations appeared that would suggest trade-offs and that could augment a selection response towards sexual specialization. The observed positive correlations could be explained if we consider the “functional architecture” that underlies the covariance structure. If there is more covariance generated by pleiotropic loci controlling overall flower size than at loci controlling male versus female allocation, it could result in the observed positive covariance. At the phenotypic level, we did find significant negative partial correlations between male and female traits when flower size was controlled, but these trade-offs were among rather than within morphs.     

Phenotypic selection to increase floral scent emission, but not flower size or colour in bee-pollinated Penstemon digitalis

Fragrance is a putatively important character in the evolution of flowering plants, but natural selection on scent is rarely studied and thus poorly understood. We characterized floral scent composition and emission in a common garden of Penstemon digitalis from three nearby source populations. We measured phenotypic selection on scent as well as floral traits more frequently examined, such as floral phenology, display size, corolla pigment, and inflorescence height. Scent differed among populations in a common garden, underscoring the potential for scent to be shaped by differential selection pressures. Phenotypic selection on flower number and display size was strong. However, selection favoured scent rather than flower size or colour, suggesting that smelling stronger benefits reproductive success in P. digitalis. Linalool was a direct target of selection and its high frequency in floral-scent bouquets suggests that further studies of both pollinator- and antagonist-mediated selection on this compound would further our understanding of scent evolution. Our results indicate that chemical dimensions of floral display are just as likely as other components to experience selective pressure in a nonspecialized flowering herb. Therefore, studies that integrate visual and chemical floral traits should better reflect the true nature of floral evolutionary ecology.     

Population genetic structure and trait associations in forest savory using molecular,morphological and phytochemical markers

In this investigation, morphological, phytochemical and ISSR markers were used to estimate the relationships among and within seven populations of white savory (Satureja mutica), belonging to four provinces in Iran. The individuals were phenotypically diverse, which stamen length, corolla length, corolla diameter, calyx length, bract length, inflorescence length, calyx length and bracteole width were characteristics with the highest variation. Leaf dimensions were in significant correlation with flower and inflorescence characteristics. Chemical compounds of essential oils were found variable in various individuals and all samples were principally composed of phenolic constituents (carvacrol and/or thymol). As a consequence, the plants were classified into two major chemotypes including carvacrol and thymol. A total of 197 band positions were produced by 14 ISSR primers, of which 176 were found polymorphic with 88.91% polymorphism. ISSR genetic similarity values among individuals ranged between 0.45 and 0.94 which was indicative of a high level of genetic variation. Multiple regression analysis (MRA) revealed that phytochemical compositions as dependent variable, showed statistically significant correlation and in association with leaf and flower traits as independent variable, indicating a main role of leaf and flower on production of these compounds. Also, several ISSR fragments were found associated with some morphological traits and phytochemical compositions. The high diversity within and among populations of S. mutica according to different data systems could provide useful information for conservation and selection of cross-parents in breeding programs.     

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.     

菊花花部特征及花冠精油组分与访花昆虫的相关性

 菊花(Dendranthema morifolium)是异花授粉植物, 具有自交不亲和特性。其自然授粉的主要媒介为蜂类和蝶类。我们对19个菊花品种的花色、花朵繁密度、花冠直径、管状花花盘直径、株高以及花冠精油组分与访花蜂数和访花蝶数的相关性进行了研究。结果表明, 黄花色系较吸引西方蜜蜂(Apis mellifera)访花; 菊花的花朵繁密度、花冠直径、管状花花盘直径均与访花蜂数有显著相关性, 而株高与访花蜂数无相关性。大红蛱蝶(Vanessa indica)青睐红色花, 其访花蝶数与花朵繁密度、管状花花盘直径均有显著相关性, 而花冠直径和株高与访花蝶数无相关性。经气相色谱-质谱(GC-MS)分析得知, 不同菊花品种花冠精油的组分不同, 其主要成分均为单萜和倍半萜类及其含氧衍生物; 并且不同品种含有某些特定的花冠精油组分, 其中樟脑萜(r = –0.909, p<0.05)和6,10,14-三甲基-2-十五酮(r=0.882, p<0.05)与访花蜂数呈一定的相关性, α萜品醇(r=0.979, p<0.01)、顺柠檬烯氧化物(r=0.979, p<0.01)、金合欢烯氧化物(r=0.979, p<0.01)、p-mentha-6,8-dien-2-ol,cis- (r=0.973, p<0.01)、p-menth-1-en-8-ol (r=0.962, p<0.01)和4-萜品烯醇(r=0.957, p<0.05)与访花蝶数呈一定相关性。     

The influence of insects and hummingbirds on the geographical variation of the flower phenotype in Mimulus luteus

We describe the geographical variation of corolla and nectar guide size in seven populations of Mimulus luteus (Phrymaceae) in central Chile, and examine whether flower phenotypes associate with taxonomic composition and flower visit patterns of pollinators across populations. Flowers showed higher variation in nectar guide size than corolla size. Mean corolla size increased with the proportion of bees and decreased with the proportion of lepidopterans in the pollinator assemblages. Nectar guide size increased with the proportion of hummingbirds in the pollinator assemblages. When the frequency of flower visits rather than taxonomic composition was considered, the results revealed similar patterns. Because these traits previously have been described as targets of bee- and hummingbird-mediated selection in M. luteus , our results have implications for understanding the processes that determine flower diversification in Chilean Mimulus . Although we cannot rule out ecological sorting as an explanation for the geographical association between pollinators and flower phenotypes, changes in the prevalence and importance of bees and hummingbirds across populations appear to account, at least in part, for the flower phenotypic variation across populations. The extent to which insect and hummingbird pollination in M. luteus produces pollinator-mediated divergence among populations needs to be examined in future studies.     

Floral stability,pollination efficiency,and experimental manipulation of the corolla phenotype in Nemophila menziesii (Hydrophyllaceae)

The present study examines the degree of phenotypic stability in vegetative and floral traits in a population of the annual, self-compatible, and protandrous Nemophila menziesii (Hydrophyllaceae) and examines whether local pollinators select for a uniform floral phenotype in this population. I found a strong positive association between flower number, leaf size, shoot length, and pedicel length, implying a general effect of overall plant vigor on this suite of traits, while characters reflecting corolla shape were phenotypically stable across a broad range of plant sizes. However, results of a manipulative experiment indicate that individual flowers maintain high pollination success despite drastic changes in the size and shape of the corolla. This suggests that pollinator-mediated selection does not directly favor floral stability in N. menziesii or that selection was weak during the course of this study. Seed number per flower was positively correlated with plant size, which varied greatly from one patch to another.     

EVOLUTION OF FLORAL TRAITS IN A HERMAPHRODITIC PLANT: FIELD MEASUREMENTS OF HERITABILITIES AND GENETIC CORRELATIONS

Genetic variances, heritabilities, and genetic correlations of floral traits were measured in the monocarpic perennial Ipomopsis aggregata (Polemoniaceae). A paternal half-sib design was employed to generate seeds in each of four years, and seeds were planted back in the field near the parental site. The progeny were followed for up to eight years to estimate quantitative genetic parameters subject to natural levels of environmental variation over the entire life cycle. Narrow-sense heritabilities of 0.2–0.8 were detected for the morphometric traits of corolla length, corolla width, stigma position, and anther position. The proportion of time spent by the protandrous flowers in the pistillate phase (“proportion pistillate”) also exhibited detectable heritability of near 0.3. In contrast, heritability estimates for nectar reward traits were low and not significantly different from zero, due to high environmental variance between and within flowering years. The estimates of genetic parameters were combined with phenotypic selection gradients to predict evolutionary responses to selection mediated by the hummingbird pollinators. One trait, corolla width, showed the potential for a rapid response to ongoing selection through male function, as it experienced both direct selection, by influencing pollen export, and relatively high heritability. Predicted responses were lower for proportion pistillate and corolla length, even though these traits also experienced direct selection. Stigma position was expected to respond positively to indirect selection of proportion pistillate but negatively to selection of corolla length, with the net effect sensitive to variation in the selection estimates. Anther position also was not directly selected but could respond to indirect selection of genetically correlated traits.