Sources of variation in floral nectar production rate in Epilobium canum (Onagraceae): implications for natural selection

Sources of variation in floral nectar production were investigated in a natural population of Epilobium canum (Onagraceae), a hummingbird-pollinated herbaceous shrub. Field measurements showed significant phenotypic variation among plants in floral nectar production rates. Average variance among flowers within plants was approximately one-third to one-half as great as variance among plants, with coefficients of variation among flowers ranging from 6.5% to 116.7%. A greenhouse experiment using clonally propagated ramets from field plants showed significant genetic variation for nectar production rates; broad sense heritability was estimated to have a maximum value of 0.64. In the greenhouse, plants grown under low water or low light conditions produced approximately 25% less nectar on average than those grown under control conditions. However, significant genotype-environment interactions indicated that genets differed in their responses to the changes in conditions. Rank correlations for genet mean nectar production rates across environmental conditions were low, and in two out of three comparisons were not different from zero. It is concluded that although the opportunity for natural selection on nectar production rates exits in this population, the response to selection will likely be slow, and the opportunity for selection of a narrow-optimum nectar production phenotype may be limited. Received: 9 January 1996 / Accepted: 18 December 1996     

The inheritance of vegetative growth traits in strawberries (Fragaria x ananassa) grown at low temperatures and their relationship to field productivity

The genetic relationship between vegetative growth at low temperatures and productivity was investigated for strawberries grown in controlled and field environments. Genotypes from 20 biparental crosses were grown in controlled environments with 11°, 14°, and 17 °C days, 11 °C nights, and 11-h daylength to simulate a range of winter growing conditions expected in mediterranean environments. Individual plants were scored for two initial runner traits and eight vegetative growth traits. Significant main effects of temperature and cross were detected for all growth chamber traits, and conservative estimates of the broad sense heritability (h²) for these traits were 0.10–0.28. None of the temperature x cross interaction effects were significant, suggesting that genetic potential for vegetative growth and vigor is expressed similarly at low and optimal growing temperatures. Highly significant genetic correlations were detected between many growth chamber trait pairs, indicating pleiotropic effects for the genes that condition these traits. Complementary field trials were established, and individual plants were scored for traits that describe yield, production pattern, and plant size. Significant negative genetic correlations were detected between traits that describe growth in the chambers and early production in the field trials, but genetic correlations between chamber growth traits and mid-season or total production were significantly positive and occasionally large. Several of the yield and field growth variables were genetically correlated to initial runner plant traits, suggesting that indirect selection using traits scored in the nursery can be used to improve yield and modify production pattern in the field.     

Testing population differentiation in plant species – how important are environmental maternal effects

The maternal environment may contribute to population differentiation in offspring traits if growing conditions of mother plants are different. However, the magnitude of such environmental maternal effects compared with genetic differentiation is often not clear. We tested the importance of environmental maternal effects by comparing population differentiation in parental seed directly collected in the field and in F₁ seed grown under homogeneous conditions. The F₁ seeds were obtained by random crosses within populations. We used five populations in each of four plant species to analyse seed mass and growth chamber germination of both generations at the same time. In two species, we additionally tested offspring performance in the field. We found a significant population differentiation in all species and for nearly all measured traits. Population‐by‐generation interactions indicating environmental maternal effects were significant for germination (three species) and for seed mass (two species) but not for growth and reproduction. The significant interaction was partly due to a reduction of among‐population differentiation from the parental to the F₁ generation that can be explained by a decrease of maternal provisioning effects. However, in some species by trait combinations a change in population ranking and not a decrease of variation was responsible for significant population‐by‐generation interactions indicating environmental maternal effects beyond maternal provisioning. Fitting of seed mass as covariate was not successful in reducing environmental maternal effects on population differentiation in germination. We discuss alternative methods to account for environmental maternal effects in studies on genetic differentiation among populations.     

Heritability and correlation structure of nectar and floral morphology traits in Nicotiana alata

The heritability and genetic basis of nectar traits have been rarely studied in the field, where plants are exposed to environmental factors that could mask underlying genetic effects. Heritabilities and variance components were estimated for nectar and morphological traits of Nicotiana alata , using a partial diallel design. The main experiment was conducted in a Missouri experimental garden using a randomized block design with three plant density treatments, whereas a smaller experiment was conducted near native Brazil habitat to compare the environmental variance in traits between Missouri and Brazil. Significant heritability was detected for nectar volume and energy content, and for corolla tube length. Phenotypic correlations were significant between all traits investigated, whereas significant genetic correlations were only found between nectar volume and energy and between corolla limb width and mouth diameter. There were no significant family-by-density interactions detected in the Missouri field environment. All traits differed significantly between Missouri and Brazil environments, but significant genetic by environment (G × E) interactions between Missouri and Brazil were detected for only one trait. This study shows that nectar traits can be heritable despite considerable environmental variation.     

VARIATION IN NECTAR SUGAR COMPOSITION AT THE INTRAPLANT LEVEL IN IPOMOPSIS LONGIFLORA (POLEMONIACEAE)

The nectar sugar composition of individual flowers from single plants in both greenhouse and field populations was determined by High-Performance Liquid Chromatography (HPLC). Intraplant variability in nectar sugar composition of greenhouse-grown plants was significantly greater than can be attributed to the analytical methodology. Individual greenhouse-grown plants had significantly different sugar compositions, suggesting genetic differences. Under field conditions the situation was complex. Variation among flowers from single plants in field populations was significantly greater than that of plants under greenhouse conditions. Unprotected flowers of some field populations were more variable at the intraplant level than others. Field experiments showed that, in untreated (open-visited) flowers, the percent sucrose relative to other sugars declined significantly and coefficients of variability increased significantly with flower age. However, nectars never exposed to the natural environment did not change significantly with flower age. Further, within single plants it was found that percent sucrose in nectars varied in a small but significant way during the growing season. The data suggest that, in this species, both intrinsic and extrinsic factors affect nectar sugar composition and it is desirable to obtain samples from numerous flowers to accurately characterize the nectar sugar composition of an individual under field conditions.     

Genetic basis of trichome production in Arabidopsis lyrata

Leaf trichomes may protect plants against herbivorous insects, and may increase tolerance to drought and UV-radiation. The perennial herb Arabidopsis lyrata (Brassicaceae) is polymorphic for trichome production and occurs in a glabrous and trichome-producing form. In addition, there is quantitative variation in trichome density among trichome-producing plants. To examine the genetic basis of glabrousness, we conducted controlled crosses with plants originating from two natural populations in Sweden (one polymorphic for trichome-production, and one consisting of glabrous plants only). In addition, we estimated the heritability of trichome number from parent-offspring regressions for plants originating from the polymorphic population. Crosses between glabrous plants resulted in glabrous offspring only, whereas crosses between glabrous and trichome-producing plants, and crosses between trichome-producing individuals, resulted in either all trichome-producing offspring or both phenotypes. In segregating crosses between trichome-producing plants, the ratio of glabrous:trichome-producing offspring did not deviate significantly from 1:3, while in segregating crosses between glabrous and trichome-producing individuals the ratio did in most cases not deviate from 1:1. Within- and between-population crosses gave similar results. The heritability of trichome number estimated from regression of offspring on mid-parent was high (h2 +/- SE, 0.65 +/- 0.15). The results suggest that glabrousness is inherited in a simple Mendelian fashion, with the allele coding for trichome production being dominant over that for glabrousness. They further indicate that glabrousness is due to a mutation at the same locus in both populations.     

Genetic background,and not ontogenetic effects,affects avian seasonal timing of reproduction

Avian seasonal timing is a life‐history trait with important fitness consequences and which is currently under directional selection due to climate change. To predict micro‐evolution in this trait, it is crucial to properly estimate its heritability. Heritabilities are often estimated from pedigreed wild populations. As these are observational data, it leaves the possibility that the resemblance between related individuals is not due to shared genes but to ontogenetic effects; when the environment for the offspring provided by early laying pairs differs from that by late pairs and the laying dates of these offspring when they reproduce themselves is affected by this environment, this may lead to inflated heritability estimates. Using simulation studies, we first tested whether and how much such an early environmental effect can inflate heritability estimates from animal models, and we showed that pedigree structure determines by how much early environmental effects inflate heritability estimates. We then used data from a wild population of great tits (Parus major) to compare laying dates of females born early in the season in first broods and from sisters born much later, in second broods. These birds are raised under very different environmental conditions but have the same genetic background. The laying dates of first and second brood offspring do not differ when they reproduce themselves, clearly showing that ontogenetic effects are very small and hence, family resemblance in timing is due to genes. This finding is essential for the interpretation of the heritabilities reported from wild populations and for predicting micro‐evolution in response to climate change.     

ECOLOGICAL CONSEQUENCES AND PHENOTYPIC CORRELATES OF PETAL SIZE VARIATION IN WILD RADISH,RAPHANUS SATIVUS (BRASSICACEAE)

In this paper we examine some ecological consequences and phenotypic correlates of flower size variation in wild radish, Raphanus sativus. Mean corolla diameter varied significantly among individuals within natural populations of R. sativus in California. On the average, almost 40% of flower biomass was allocated to corolla tissue. In field experiments, pollinator visitation increased significantly with corolla size. Large flowers also accumulated more nectar when pollinators were excluded from plants. In three populations, corolla size was positively correlated with allocation to pollen per flower (either anther weight or pollen grain number), but there was usually no phenotypic relationship between corolla size and several measures of female allocation (ovule number per flower, proportion fruit set, and total seed mass per fruit). Plants growing in the field produced fewer large flowers per unit of stem, and stem biomass was negatively related to corolla size for plants grown under controlled greenhouse conditions. Male and female fitness may covary differently with allocation to attractive floral features in species such as R. sativus, where seed production is often limited by resources rather than by pollen.     

The effects of becoming taller: direct and pleiotropic effects of artificial selection on plant height in Brassica rapa

Plant height is an important trait for plant reproductive success. Plant height is often under pollinator‐mediated selection, and has been shown to be correlated with various other traits. However, few studies have examined the evolutionary trajectory of plant height under selection and the pleiotropic effects of plant height evolution. We conducted a bi‐directional artificial selection experiment on plant height with fast cycling Brassica rapa plants to estimate its heritability and genetic correlations, and to reveal evolutionary responses to artificial selection on height and various correlated traits. With the divergent lines obtained through artificial selection, we subsequently conducted pollinator‐choice assays and investigated resource limitation of fruit production. We found that plant height variation is strongly genetically controlled (with a realized heritability of 41–59%). Thus, plant height can evolve rapidly under phenotypic selection. In addition, we found remarkable pleiotropic effects in phenology, morphology, floral scent, color, nectar and leaf glucosinolates. Most traits were increased in tall‐line plants, but flower size, UV reflection and glucosinolates were decreased, indicating potential trade‐offs. Pollinators preferred plants of the tall selection lines over the short selection lines in both greenhouse experiments with bumblebees and field experiment with natural pollinators. We did not detect any differences in resource limitation between plants of the different selection lines. Overall, our study predicts that increased height should evolve under positive pollinator‐mediated directional selection with potential trade‐offs in floral signals and herbivore defense.     

ADAPTIVE SIGNIFICANCE OF IPOMOPSIS AGGREGATA NECTAR PRODUCTION: OBSERVATION AND EXPERIMENT IN THE FIELD

Production of floral nectar is generally thought to be an adaptation that increases plant fitness by altering pollinator behavior, and therefore pollination success. To test this hypothesis, I investigated the effects of floral nectar production rate on pollination success of the hermaphroditic plant Ipomopsis aggregata (Polemoniaceae). Success through male function (estimated by the export of fluorescent dyes) was significantly greater for plants with naturally high nectar production rates than for nearby plants with low nectar production rates, whereas success through female function (receipt of fluorescent dye) was unrelated to nectar production rate. Experimental addition of artificial nectar also produced a significant increase in male function success and no increase in several estimates of female function success. Observations confirmed that hummingbirds probed a larger proportion of flowers on plants that received supplemental nectar, as they do in response to natural variation in nectar production. The concordance of results across these observational and experimental studies indicates that nectar production acts primarily to increase pollination success through male function for this species.     

Intra-plant variation in nectar sugar composition in two Aquilegia species (Ranunculaceae): contrasting patterns under field and glasshouse conditions

BACKGROUND AND AIMS: Intra-specific variation in nectar chemistry under natural conditions has been only rarely explored, yet it is an essential aspect of our understanding of how pollinator-mediated selection might act on nectar traits. This paper examines intra-specific variation in nectar sugar composition in field and glasshouse plants of the bumblebee-pollinated perennial herbs Aquilegia vulgaris subsp. vulgaris and Aquilegia pyrenaica subsp. cazorlensis (Ranunculaceae). The aims of the study are to assess the generality of extreme intra-plant variation in nectar sugar composition recently reported for other species in the field, and gaining insight on the possible mechanisms involved. METHODS: The proportions of glucose, fructose and sucrose in single-nectary nectar samples collected from field and glasshouse plants were determined using high performance liquid chromatography. A hierarchical variance partition was used to dissect total variance into components due to variation among plants, flowers within plants, and nectaries within flowers. KEY RESULTS: Nectar of the two species was mostly sucrose-dominated, but composition varied widely in the field, ranging from sucrose-only to fructose-dominated. Most intra-specific variance was due to differences among nectaries of the same flower, and flowers of the same plant. The high intra-plant variation in sugar composition exhibited by field plants vanished in the glasshouse, where nectar composition emerged as a remarkably constant feature across plants, flowers and nectaries. CONCLUSIONS: In addition to corroborating the results of previous studies documenting extreme intra-plant variation in nectar sugar composition in the field, this study suggests that such variation may ultimately be caused by biotic factors operating on the nectar in the field but not in the glasshouse. Pollinator visitation and pollinator-borne yeasts are suggested as likely causal agents.     

EXPRESSION OF GENETIC VARIATION IN BODY SIZE OF THE COLLARED FLYCATCHER UNDER DIFFERENT ENVIRONMENTAL CONDITIONS

Heritability of body size in two experimentally created environments, representing good and poor feeding conditions, respectively, was estimated using cross-fostered collared flycatcher Ficedula albicollis nestlings. Young raised under poor feeding conditions attained smaller body size (tarsus length) than their full-sibs raised under good feeding conditions. Parent-offspring regressions revealed lower heritability (h²) of body size under poor than under good feeding conditions. Hence, as the same set of parents were used in the estimation of h² in both environments, this suggests environment-dependent change in additive genetic component of variance (V_A), or that the genetic correlation between parental and poor offspring environment was less than that between parental and good offspring environment. However, full-sib analyses failed to find evidence for genotype-environment interactions, although the power of these tests might have been low. Full-sib heritabilities in both environments tended to be higher than estimates from parent-offspring regressions, indicating that prehatching or early posthatching common environment/maternal effects might have inflated full-sib estimates of V_A. The effect of sibling competition on estimates of V_A was probably small as the nestling size-hierarchy at day 2 posthatch was not generally correlated with size-hierarchy at fledging. Furthermore, there was no correlation between maternal body condition during the incubation and final size of offspring, indicating that direct maternal effects related to nutritional status were small. A review of earlier quantitative genetic studies of body size variation in birds revealed that in eight of nine cases, heritability of body size was lower in poor than in good environmental conditions. The main implication of this relationship will be a decreased evolutionary response to selection under poor environmental conditions. On the other hand, this will retard the loss of genetic variation by reducing the accuracy of selection and might help explain the moderate to high heritabilities of body-size traits under good environmental conditions.     

The role of progeny quality and male size in the nesting success of smallmouth bass: integrating field and laboratory studies

Smallmouth bass display size-specific variation in reproductive success with larger brood-guarding males in a population more likely to rear offspring to independence than smaller individuals. The exact mechanisms responsible for this size-specific increase in reproductive output have yet to be identified. To assist in this process, we investigated the relationship between the size of brood-guarding male smallmouth bass and offspring quality (in this case, egg physiology, egg morphology, egg size, hatching success and lab survival). Further, we examined how factors such as egg physiology, egg morphology and egg size influenced reproductive success in the wild and hatching success in a controlled laboratory environment. Nesting male smallmouth bass that successfully reared their offspring to independence spawned earliest in the nesting period were the largest individuals, and guarded eggs with greater concentrations of cortisol compared to males that abandoned their offspring prematurely. Offspring survival in the laboratory was not correlated with offspring survival in the wild, indicating that caution should be used interpreting studies that attempt to relate laboratory-derived survival metrics to the wild. Together, results demonstrate size-specific differences in offspring quality for nesting smallmouth bass, which are correlated with higher concentrations of cortisol in eggs. However, hatching success under laboratory conditions was dissimilar to nesting success in the field relative to cortisol concentrations.     

Breeding for high production of leaves of baobab (Adansonia digitata L) in an irrigated hedge system

This study presents an evaluation of an irrigated “market garden” trial established with 3-month-old seedlings of baobab. The trial included offspring from 59 open-pollinated family lots from ten provenances and four bulked provenance sample lots. Leaf productivity and seedling growth were evaluated monthly from the third month after establishment. We found lowered leaf productivity during the dry season despite the plants being irrigated. We provide the first estimates of heritability for leaf production and growth of the species. We assumed that the families of seed from open-pollinated single trees consist of true half-sibs but also provided adjusted estimates assuming a high level of selfing. Differences among provenances and families within provenances were highly significant (p?<?0.01) with respect to leaf productivity. Heritability estimates (adjusted and non-adjusted) for leaf productivity were moderate to low, predicting moderate genetic gain from selection. Strong genetic and phenotypic correlations were estimated between diameter and leaf production, indicating that simple selection for diameter can efficiently increase leaf production. The dry weight/fresh weight ratio was not significantly different among provenances or families within provenances. Based on the findings, we discuss how breeding can increase the total leaf production and its seasonal distribution.     

Quantitative genetics of preference and performance on chickpeas in the noctuid moth, Helicoverpa armigera

If a novel, resistant host-plant genotype arises in the environment, insect populations utilising that host must be able to overcome that resistance in order that they can maintain their ability to feed on that host. The ability to evolve resistance to host-plant defences depends upon additive genetic variation in larval performance and adult host-choice preference. To investigate the potential of a generalist herbivore to respond to a novel resistant host, we estimated the heritability of larval performance in the noctuid moth, Helicoverpa armigera, on a resistant and a susceptible variety of the chickpea, Cicer arietinum, at two different life stages. Heritability estimates were higher for neonates than for third-instar larvae, suggesting that their ability to establish on plants could be key to the evolution of resistance in this species; however, further information regarding the nature of selection in the field would be required to confirm this prediction. There was no genetic correlation between larval performance and oviposition preference, indicating that female moths do not choose the most suitable plant for their offspring. We also found significant genotype by environment interactions for neonates (but not third-instar larvae), suggesting that the larval response to different plant genotypes is stage-specific in this species.     

Nectar Sugar Production across Floral Phases in the Gynodioecious Protandrous Plant Geranium sylvaticum

Many zoophilous plants attract their pollinators by offering nectar as a reward. In gynodioecious plants (i.e. populations are composed of female and hermaphrodite individuals) nectar production has been repeatedly reported to be larger in hermaphrodite compared to female flowers even though nectar production across the different floral phases in dichogamous plants (i.e. plants with time separation of pollen dispersal and stigma receptivity) has rarely been examined. In this study, sugar production in nectar standing crop and secretion rate were investigated in Geranium sylvaticum, a gynodioecious plant species with protandry (i.e. with hermaphrodite flowers releasing their pollen before the stigma is receptive). We found that flowers from hermaphrodites produced more nectar than female flowers in terms of total nectar sugar content. In addition, differences in nectar production among floral phases were found in hermaphrodite flowers but not in female flowers. In hermaphrodite flowers, maximum sugar content coincided with pollen presentation and declined slightly towards the female phase, indicating nectar reabsorption, whereas in female flowers sugar content did not differ between the floral phases. These differences in floral reward are discussed in relation to visitation patterns by pollinators and seed production in this species.     

Novel loci control variation in reproductive timing in Arabidopsis thaliana in natural environments

Molecular biologists are rapidly characterizing the genetic basis of flowering in model species such as Arabidopsis thaliana. However, it is not clear how the developmental pathways identified in controlled environments contribute to variation in reproductive timing in natural ecological settings. Here we report the first study of quantitative trait loci (QTL) for date of bolting (the transition from vegetative to reproductive growth) in A. thaliana in natural seasonal field environments and compare the results with those obtained under typical growth-chamber conditions. Two QTL specific to long days in the chamber were expressed only in spring-germinating cohorts in the field, and two loci specific to short days in the chamber were expressed only in fall-germinating cohorts, suggesting differential involvement of the photoperiod pathway in different seasonal environments. However, several other photoperiod-specific QTL with large effects in controlled conditions were undetectable in natural environments, indicating that expression of allelic variation at these loci was overridden by environmental factors specific to the field. Moreover, a substantial number of QTL with major effects on bolting date in one or more field environments were undetectable under controlled environment conditions. These novel loci suggest the involvement of additional genes in the transition to flowering under ecologically relevant conditions.     

Nectar‐providing plants enhance the energetic state of herbivores as well as their parasitoids under field conditions

Abstract 1. The use of flowering vegetation has been widely advocated as a strategy for providing parasitoids and predators with nectar and pollen. However, their herbivorous hosts and prey may exploit floral food sources as well. 2. Previous laboratory studies have shown that not all flower species are equally suitable in providing accessible nectar. Relatively little is known about actual nectar exploitation under field conditions. 3. The present study investigates nectar exploitation by the pest, Plutella xylostella, and its parasitoid, Diadegma semiclausum, under field conditions and examines whether floral nectar exploitation in the field can be predicted based on controlled laboratory studies. 4. Insects were collected from fields bordered by flowering margins containing Fagopyrum esculentum, Lobularia maritima, Anethum graveolens, Centaurea jacea or the grass Lolium perenne (control). Whole insect bodies were individually assayed by HPLC to establish their sugar profile as a measure of the level of energy reserves and the degree of food source use. 5. The average overall sugar content of P. xylostella and D. semiclausum collected in fields bordered by flowering margins was significantly higher than those of individuals collected from grass‐bordered control plots. To the authors’ knowledge, this represents the first demonstration that nectar‐providing plants enhance the energetic state of herbivores under field conditions. 6. In contrast to earlier laboratory studies, the present study did not find elevated sugar contents in P. xylostella and D. semiclausum individuals collected from fields bordered by buckwheat (F. esculentum). 7. The present study shows widespread sugar feeding by both the herbivore and its parasitoid. It also shows that laboratory studies establishing nectar exploitation under controlled conditions can not always be extrapolated to actual exploitation under field conditions. This emphasises the importance of studying field‐collected insects with regard to food source use and nutritional status.     

Density dependence and microevolution interactively determine effects of phenology mismatch on population dynamics

Life cycle events in plants and animals are typically adaptively tuned to anticipate predictable seasonal changes in environmental conditions or resources. Climate change is expected to affect the temporal component of species’ interactions, e.g. by creating a mismatch between a predator's breeding time (when ample food supply is critical) and the time when prey abundance is high. The demographic implications of such a mismatch remain unclear, however. Here we focussed on changes in the phenology of consumers relative to that of their food. We developed a model where reproductive output of the consumer up to offspring independence depended on mismatch and recruitment of the offspring to breeders depended on offspring density according to a Beverton–Holt function. Using a deterministic version of the model, we clarified how the effects of (constant) mismatch on equilibrium population size depended on the emergent strength of negative density dependence (DD). Using a stochastic, individual‐based version, we showed that when the environment changed abruptly, the rate of population recovery was faster when heritability of seasonal timing was higher and DD was stronger. When the environment shifted continuously, the rate of decline in population size was inversely proportional to the rate of microevolution, but stronger DD slowed the rate of decline for a given heritability and thus effectively ‘bought time’ for evolutionary rescue. These results highlight the importance of negative DD, which interacts with the effects of trait heritability and stabilizing selection strength, in influencing the fate of populations experiencing environmental change. We emphasize, however, that outcomes in nature will depend crucially on the exact nature of DD, in particular whether population growth rate differences are greatest at low or high densities, highlighting the need for empirical comparisons of compensatory processes in different populations or species.     

Generous-like flowers: nectar production in two epiphytic bromeliads and a meta-analysis of removal effects

Animal-pollinated angiosperm plants that respond positively to nectar removal by replenishment invest energy that can entail a reproductive cost. We investigated whether or not nectar removal stimulates replenishment in two hummingbird-pollinated bromeliad species. Nectar replenishment rates were also assessed by removing nectar from manually pollinated flowers because pollination events might be used as signals to save energy by preventing allocation to post-pollination nectar production. Then we synthesized the current understanding of nectar removal effects by reviewing existing published studies with a meta-analysis. The magnitude and significance of estimated nectar removal effects and factors associated with variation in size and direction of nectar removal effects were elucidated with the meta-analysis. We found that both Tillandsia species strongly respond to repeated nectar removal by producing >3 times additional nectar. Nectar secretion patterns were not altered by pollination (stigmatic pollen deposition) and we found no evidence of nectar reabsorption. Although the effect size varied widely across systems and/or environmental conditions, the meta-analysis showed that nectar removal had overall a positive effect on nectar replenishment (mainly among species inhabiting wet tropical habitats such as Tillandsia), and a negative effect on the secretion of additional sugar, suggesting that those plants are resource limited and conservative in the secretion of additional sugar.Electronic Supplementary Material Supplementary material is available for this article at