Sex-dependent thermogenesis during reproductive organ development in the inflorescence is a characteristic feature of some of the protogynous arum species. One such plant, skunk cabbage (Symplocarpus renifolius), can produce massive heat during the female stage but not during the subsequent male stage in which the stamen completes development, the anthers dehisce, and pollen is released. Unlike other thermogenic species, skunk cabbage belongs to the bisexual flower group. Although recent studies have identified the spadix as the thermogenic organ, it remains unclear how individual tissues or intracellular structures are involved in thermogenesis. In this study, reproductive organ development and organelle biogenesis were examined during the transition from the female to the male stage. During the female stage, the stamens exhibit extensive structural changes including changes in organelle structure and density. They accumulate high levels of mitochondrial proteins, including possible thermogenic factors, alternative oxidase, and uncoupling protein. By contrast, the petals and pistils do not undergo extensive changes during the female stage. However, they contain a larger number of mitochondria than during the male stage in which they develop large cytoplasmic vacuoles. Comparison between female and male spadices suggests that mitochondrial number rather than their level of activity correlates with thermogenesis. Their spadices, even in the male, contain a larger amount of mitochondria that had greater oxygen consumption, compared with non-thermogenic plants. Taken together, our data suggest that the extensive maturation process in stamens produces massive heat through increased metabolic activities. The possible mechanisms by which petal and pistil metabolism may affect thermogenesis are also discussed.
Alternative oxidase; bisexual flower; mitochondrial density; respiration; stamen; thermogenesis; thermoregulation; ultrastructure; uncoupling protein; vacuole
Dracunculus vulgaris is a protogynous arum lily with thermogenic inflorescences consisting of male and female florets on a spadix within a floral chamber. Above the chamber, an odour-producing appendix and a carrion-coloured spathe attract flying insects. The inflorescence shows a triphasic warming pattern. The floral chamber warms weakly on the first night as the spathe opens. Then the appendix produces a large amount of heat and a powerful scent during the first day. As the appendix cools on the second night, scent production ceases and the floral chamber rewarms. Warming ceases when the pollen is shed on the second day. The heating pattern is associated with attraction of pollinating insects by the appendix on the first day, entrapment in the warm chamber at night and release after pollen shedding. The temperature in the floral chamber is regulated at around 18 °C during the second night. The oxygen consumption rate of the florets is inversely related to the ambient temperature as in other thermoregulatory flowers. Conversely, the oxygen consumption rate of the appendix is directly related to the ambient temperature, indicating that it does not thermoregulate. Thus, temperature regulation is not associated with scent production, but with some activity inside the floral chamber.
The dead horse arum, Helicodiceros muscivorus, is a conspicuous, foul smelling and thermogenic plant of the Araceae family. This Mediterranean arum lily copies several aspects of a carcass in order to attract carrion blowflies, which are subsequently exploited as unrewarded pollinators. We have previously shown that this plant exhibits a highly accurate olfactory carrion mimicry, which serves to attract the blowflies. In this study, we have investigated the role of thermogeny in the arum. We show that the thermogeny has a direct effect on the pollinators, altering their behaviour. By manipulating heat and odour release of the plant, we can show that the heat, produced along the appendix, is important to lure the flies to this structure, which is vital as the flies from the appendix are more prone to enter the trap chamber that houses the female and male florets. This study provides rare evidence for a direct functional role of thermogeny.
As olfactory perceptions vary from person to person, it is difficult to describe smells objectively. In contrast, electronic noses also detect smells with their sensors, but in addition describe those using electronic signals. Here we showed a virtual connection method between a human nose perceptions and electronic nose responses with the smell of standard gases. In this method, Amorphophallus titanum flowers, which emit a strong carrion smell, could objectively be described using an electronic nose, in a way resembling the skill of sommeliers. We could describe the flower smell to be close to that of a mixture of methyl mercaptan and propionic acid, by calculation of the dilution index from electronic resistances. In other words, the smell resembled that of “decayed cabbage, garlic and pungent sour” with possible descriptors. Additionally, we compared the smells of flowers which bloomed on different dates and at different locations and showed the similarity of odor intensities visually, in standard gas categories. We anticipate our assay to be a starting point for a perceptive connection between our noses and electronic noses.
electronic nose; FF-2A; semiconductor; Amorphophallus titanum; titan arum; smell; objective display; smell description
Symplocarpus renifolius and Arum maculatum are known to produce significant heat during the course of their floral development, but they use different regulatory mechanisms, i.e. homoeothermic compared with transient thermogenesis. To further clarify the molecular basis of species-specific thermogenesis in plants, in the present study we have analysed the native structures and expression patterns of the mitochondrial respiratory components in S. renifolius and A. maculatum. Our comparative analysis using Blue native PAGE combined with nano LC (liquid chromatography)-MS/MS (tandem MS) has revealed that the constituents of the respiratory complexes in both plants were basically similar, but that several mitochondrial components appeared to be differently expressed in their thermogenic organs. Namely, complex II in S. renifolius was detected as a 340 kDa product, suggesting an oligomeric or supramolecular structure in vivo. Moreover, the expression of an external NAD(P)H dehydrogenase was found to be higher in A. maculatum than in S. renifolius, whereas an internal NAD(P)H dehydrogenase was expressed at a similar level in both species. Alternative oxidase was detected as smear-like signals that were elongated on the first dimension with a peak at around 200 kDa in both species. The significance and implication of these data are discussed in terms of thermoregulation in plants.
alternative oxidase (AOX); Blue native PAGE; mitochondrial respiratory chain; thermogenic plants; type II NAD(P)H dehydrogenase; 1D, one-dimensional; 2D, two-dimensional; AOX, alternative oxidase; BCA, bicinchoninic acid; BN-PAGE, Blue native PAGE; COX, cytochrome c oxidase; Fp, flavoprotein; MS/MS, tandem MS; RACE, rapid amplification of cDNA ends; RT, reverse transcription; TCA, tricarboxylic acid; UTR, untranslated region
• Background and Aims Several families of tropical plants have thermogenic flowers that show a 2-d protogynous sequence. Most are pollinated by large beetles that remain for the entire period in the flowers, where they compete for mates and feed. Active beetles require high body temperatures that they can achieve endogenously at great energy expense or attain passively and cheaply in a warm environment. Floral heating is therefore hypothesized to be a direct energy reward to endothermic beetles, in addition to its accepted role in enhancing scent production.
• Methods This study measures the pattern of floral heat production (as temperature in 20 flowers and respiration rates in five flowers) in Victoria amazonica at field sites in Guyana and correlates floral temperatures with body temperatures necessary for activity in visiting Cyclocephala hardyi beetles.
• Key Results Thermogenesis occurred in a bimodal pattern, with peaks associated with the arrival and departure of beetles near sunset. Peak CO2 production rates averaged 2·9 µmol s−1, equivalent to a heat production of 1·4 W. Heat was generated mainly in the floral chamber on the first evening and by the stamen complex on the second. Mean chamber temperature remained between 29·3 and 34·7 °C during the first night, when ambient temperature was 23·5–25·2 °C. Beetles actively competed for mates and consumed stylar processes in the floral chamber, where their mean thoracic temperature was 33·2 °C. At the lower ambient temperatures outside of the flower, beetles capable of sustained flight had a similar mean temperature of 32·0 °C.
• Conclusions Floral heating is not only associated with attraction, but continues throughout the night when beetles are active inside the flower and increases again when they leave. Floral chamber temperatures similar to activity temperatures of actively endothermic beetles imply that thermogenesis is an energy reward.
Pollination biology; thermogenesis; respiration; beetle; endothermy; Nymphaeaceae; Guyana; Victoria amazonica; Cyclocephala hardyi
Flowers of the sacred lotus, Nelumbo nucifera Gaertn. (Nelumbonaceae) are thermogenic and physiologically thermoregulatory. The 42 g flowers remain between 30-36°C during a 2 to 4-day period despite fluctuations in environmental temperatures between about 10-45°C. As the ambient temperature drops, the flowers increase heat production in proportion. Temperature regulation apparently occurs at a cellular level, by a steep, reversible thermal inhibition of respiration at flower temperatures above 30°C. There was a marked time lag between change in flower temperature and compensatory response, suggesting regulation through a biochemical feedback mechanism rather than structural changes in enzymes or membranes. By oxidizing carbohydrate, the flowers produce up to 1 W, with about half of the heat coming from the 8.5 g carpellary receptacle. The period of temperature regulation begins before petal opening and continues through the period of stigma receptivity. Temperature regulation may reward insect pollinators with a warm, equable environment, or it possibly enhances and coordinates flower development.
Flowering synchrony and floral sex ratio have the potential to influence the mating opportunities and reproductive success through female function. Here, we examine the variances in synchronous display of female and male function, ratio of male to female flowers per day and subsequently reproductive output in small populations of two monoecious plants, Sagittaria trifolia and Sagittaria graminea.
We created plant populations of size 2, 4, 10 and 20 and recorded the daily number of blooming male and female flowers per plant to determine daily floral display, flowering synchrony index and ratio of male to female flowers per day. We also harvested the fruits, counted the seeds and calculated the number of fruits and seeds per flower to measure reproductive success through female function. There is less overlap in flowering time of female and male function in smaller populations than in larger populations. Most importantly, we found that male-biased floral sex ratio and imbalanced display period of female and male function for individual plant can lead to a population-size-dependent ratio of male to female flowers per day. Increasing ratio of male to female flowers per day was generally associated with a greater percentage of fruit production.
Our results highlight the importance of flowering synchrony of female and male function and population-size-dependent ratio of male to female flowers per day for female reproductive success. This finding improves our understanding of a mechanism that reduces reproductive success in small populations.
Background and Aims
Why are sterile anthers and carpels retained in some flowering plants, given their likely costs? To address this question, a cryptically dioecious species, Petasites tricholobus, in which male and female plants each have two floret types that appear pistillate and hermaphroditic, was studied. The aim was to understand the function of sterile hermaphroditic florets in females. In addition, the first examination of functions of sterile female structures in male plants was conducted in the hermaphroditic florets on males of this species. These female structures are exceptionally large in this species despite being sterile.
Differences in floret morphology between the sex morphs were documented and the possible functions of sterile sex organs investigated using manipulative experiments. Tests were carried out to find out if sterile female structures in male florets attract pollinators and if they aid in pollen dispersal, also to find out if the presence and quantity of sterile hermaphroditic florets in females increase pollinator attraction and reproductive success. To investigate what floret types provide nectar, all types of florets were examined under a scanning electron microscope to search for nectaries.
The sterile female structures in male florets did not increase pollinator visits but were essential to secondary pollen presentation, which significantly enhanced pollen dispersal. Sterile pistillate florets on male plants did not contribute to floral display and disappeared in nearly half of the male plants. The sterile hermaphroditic florets on female plants attracted pollinators by producing nectar and enhanced seed production.
The presence of female structures in male florets and hermaphroditic florets on female plants is adaptive despite being sterile, and may be evolutionarily stable. However, the pistillate florets on male plants appear non-adaptive and are presumably in decline. Differential fates of the sterile sex organs in the species are determined by both the historical constraints and the ecological functions.
Cryptic dioecy; sterile sex organ; secondary pollen presentation; pollinator attraction; breeding system evolution; ecological function; Petasites tricholobus
Background and Aims
The mutualistic interaction between insects and flowers is considered to be a major factor in the early evolution of flowering plants. The Schisandraceae were, until now, the only family in the ANITA group lacking information on pollination biology in natural ecosystems. Thus, the objective of this research was to document the pollination biology and breeding system of Schisandra henryi.
Field observations were conducted in three populations of S. henryi and the floral phenology, floral characters and insect activities were recorded. Floral fragrances were sampled in the field and analysed using TCT-GC-MS. Floral thermogenesis was measured with a TR-71U Thermo Recorder. Pollen loads and location of pollen grains on insect bodies (including the gut) were checked with a scanning electron microscope and under a light microscope.
Schisandra henryi is strictly dioecious. Male flowers are similar to female flowers in colour, shape, and size, but more abundant than female flowers. The distance between tepals and the androecium or gynoecium is narrow. Neither male nor female flowers are fragrant or thermogenic. Schisandra henryi is pollinated only by adult female Megommata sp. (Cecidomyiidae, Diptera) that eat the pollen grains as extra nutrition for ovary maturation and ovipositing. Both male and female flowers attract the pollinators using similar visual cues and thus the female flowers use deceit as they offer no food.
Schisandra henryi exhibits a specialized pollination system, which differs from the generalized pollination system documented in other ANITA members. Pollen is the sole food resource for Megommata sp. and the female flowers of S. henryi attract pollinators by deceit. This is the first report of predacious gall midges utilizing pollen grains as a food source. The lack of floral thermogenesis and floral odours further enforces the visual cues by reducing attractants for other potential pollinators.
Schisandra henryi; Schisandraceae; ANITA group; Megommata sp.; Cecidomyiidae; specialized pollination system; pollination by deceit
•Background and Aims In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species.
•Methods Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles.
•Key Results Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3–4 months) in dry-season and winter-flowering species, 6–9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized.
•Conclusions The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.
Tropical tree phenology; flowering types; fruiting; asynchrony; leafless period; semi-evergreen species; summer flowering; summer leaf flushing
We analyzed VOC composition of complete inflorescences and single flowers of lavender during the flowering period. Our analyses, focused on the 20 most abundant terpenes, showed that three groups of components could be separated according to their patterns of variation during inflorescence ontogeny. These three groups were associated with three developmental stages: flower in bud, flower in bloom and faded flower. The expression of two terpene synthases (TPS) was followed using qPCR during inflorescence ontogeny. A comparison of these chemical and molecular analyses suggested that VOC production in lavender spike is mainly regulated at the transcriptional level. These results highlighted that lavender could be a model plant for future investigations on terpene biosynthesis and regulation, and could be used to explore the functions of terpene metabolites.
chemical ecology; floral scent; flower ontogeny; lavender; terpenes; terpene synthase; volatile organic compound
The role of gibberellins (GAs) during floral induction has been widely studied in the annual plant Arabidopsis thaliana. Less is known about this control in perennials. It is thought that GA is a major regulator of flowering in rose. In spring, low GA content may be necessary for floral initiation. GA inhibited flowering in once-flowering roses, whereas GA did not block blooming in continuous-flowering roses. Recently, RoKSN, a homologue of TFL1, was shown to control continuous flowering. The loss of RoKSN function led to continuous flowering behaviour. The objective of this study was to understand the molecular control of flowering by GA and the involvement of RoKSN in this inhibition. In once-flowering rose, the exogenous application of GA3 in spring inhibited floral initiation. Application of GA3 during a short period of 1 month, corresponding to the floral transition, was sufficient to inhibit flowering. At the molecular level, RoKSN transcripts were accumulated after GA3 treatment. In spring, this accumulation is correlated with floral inhibition. Other floral genes such as RoFT, RoSOC1, and RoAP1 were repressed in a RoKSN-dependent pathway, whereas RoLFY and RoFD repression was RoKSN independent. The RoKSN promoter contained GA-responsive cis-elements, whose deletion suppressed the response to GA in a heterologous system. In summer, once-flowering roses did not flower even after exogenous application of a GA synthesis inhibitor that failed to repress RoKSN. A model is presented for the GA inhibition of flowering in spring mediated by the induction of RoKSN. In summer, factors other than GA may control RoKSN.
Floral initiation; floral repressor; gibberellins; PEBP family; polycarpic plants; rose.
Background and Aims
Self-pollination dominates in wheat, with a small level of out-crossing due to flowering asynchrony and male sterility. However, the timing and synchrony of male and female flowering in wheat is a crucial determinant of seed set and may be an important factor affecting gene flow and resilience to climate change. Here, a methodology is presented for assessing the timing and synchrony of flowering in wheat, Triticum aestivum.
From the onset of flowering until the end of anthesis, the anther and stigma activity of each floret was assessed on the first five developing ears in potted plants grown under ambient conditions and originating from ‘Paragon’ or ‘Spark-Rialto’ backgrounds. At harvest maturity, seed presence, size and weight was recorded for each floret scored.
Key Results and Conclusions
The synchrony between pollen dehiscence and stigma collapse within a flower was dependent on its relative position in a spike and within a floret. Determined on the basis of synchrony within each flower, the level of pollination by pollen originating from other flowers reached approx. 30 % and did not change throughout the duration of flowering. A modelling exercise parameterized by flowering observations indicated that the temporal and spatial variability of anther activity within and between spikes may influence the relative resilience of wheat to sudden, extreme climatic events which has direct relevance to predicted future climate scenarios in the UK.
Wheat; Triticum aestivum; flowering synchrony; pollination; climate change; heat resistance
Background and Aims
The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.
To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.
Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.
Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.
Bumble-bee; floral display size; functional gender; geitonogamy; male selfing rate; mating system; Mimulus ringens; paternity analysis; pollen discounting; pollination; self-fertilization; siring success
Two taxonomically undescribed Colocasiomyia species were discovered from inflorescences of Alocasia macrorrhizos in Kota Kinabalu City, Sabah, Borneo, Malaysia. The aims of this study were to investigate the reproductive ecology of the flies and the plant, ascertain the importance of the flies as pollinators and examine the intimate association between flowering events and life history of the flies. We conducted sampling, observations and field pollination experiments. The flies were attracted by the odour of female-phase inflorescences in the early morning on the first day of anthesis. They fed, mated and oviposited in the inflorescences for 1 day. On the second day, the flies, covered with pollen grains, left the male-phase inflorescences for the next female-phase inflorescences. The immature forms of both fly species hatched, developed and pupated within the infructescences without damaging the fruits, and developed adults emerged when the mature infructescences dehisced. The flowering events and fly behaviours were well synchronized. In field pollination experiments, inflorescences bagged with a fine mesh (insect exclusion) produced almost no fruits, whereas those bagged with a coarse mesh (bee exclusion) produced as many fruits as the open-pollinated controls. These results indicate that these flies are the most efficient and specialised pollinators for their host, A. macrorrhizos. These flies, in return, depend on A. macrorrhizos for food and habitat through most of their life cycle. This study provides a deeper insight into the less recognised, highly intimate pollination mutualism between Araceae plants and Colocasiomyia flies.
Colocasiomyia sp.1 aff. sulawesiana; Colocasiomyia sp.2 aff. sulawesiana; Kota Kinabalu; life history; pistilicolous species; pollination experiment
Volatiles from flowers at three blooming stages of nine citrus cultivars were analyzed by headspace-solid phase microextraction (HS-SPME)-GC-MS. Up to 110 volatiles were detected, with 42 tentatively identified from citrus flowers for the first time. Highest amounts of volatiles were present in fully opened flowers of most citrus, except for pomelos. All cultivars were characterized by a high percentage of either oxygenated monoterpenes or monoterpene hydrocarbons, and the presence of a high percentage of nitrogen containing compounds was also observed. Flower volatiles varied qualitatively and quantitatively among citrus types during blooming. Limonene was the most abundant flower volatile only in citrons; α-citral and β-citral ranked 2nd and 3rd only for Bergamot, and unopened flowers of Ponkan had a higher amount of linalool and β-pinene while much lower amount of γ-terpinene and p-cymene than Satsuma. Taking the average of all cultivars, linalool and limonene were the top two volatiles for all blooming stages; β-pinene ranked 3rd in unopened flowers, while indole ranked 3rd for half opened and fully opened flower volatiles. As flowers bloomed, methyl anthranilate increased while 2-hexenal and p-cymene decreased. In some cases, a volatile could be high in both unopened and fully opened flowers but low in half opened ones. Through multivariate analysis, the nine citrus cultivars were clustered into three groups, consistent with the three true citrus types. Furthermore, an influence of blooming stages on clustering was observed, especially with hybrids Satsuma and Huyou. Altogether, it was suggested that flower volatiles can be suitable markers for revealing the genetic relationships between citrus cultivars but the same blooming stage needs to be strictly controlled.
citrus types; volatiles; unopened flower; half opened flower; fully opened flower; HS-SPME; GC-MS
Background and Aims
Intermediate individuals (perfect flowers with very high degree of pollen abortion) in a gynodioecious plant species are very rare. A study is made of male–female relationships in each flower type and how floral characters can enhance the avoidance of ‘pollen discounting’ and ‘self-pollination’ in two gynodioecious species, Teucrium capitatum and Origanum syriacum.
The relationship between stigma receptivity and pollen viability was studied in two gynodioecious protandrous species of Lamiaceae, in addition to measuring some floral morphological characters over the life span of the flowers.
Three plant types in each species were found: plants bearing hermaphrodite (or male fertile) flowers (MF), female (or male sterile) flowers (MS) and intermediate flowers (INT). Plant types differed in flower size, with MS types being shorter than the other two types. There was no difference in style length among plant types in T. capitatum. Stigma receptivity decayed with floral age and was negative and significantly correlated with pollen viability in the two species, and positive and significantly correlated with style length in O. syriacum but only in MS flowers of T. capitatum.
Reduction in size of floral characters is associated with male sterility, except style length in T. capitatum. MF flowers have two successive reproductive impediments: self-pollination and pollen–stigma interference. In both species, self-pollination is avoided by dichogamy (negative correlation between stigma receptivity and pollen viability), and pollen–stigma interference shows two different patterns: (1) style elongation in O. syriacum is characterized by a significant length increase, final MF dimensions are greater than those of MS dimensions, and style length is positively and significantly correlated with stigma receptivity; and (2) style movement in T. capitatum is characterized by a non-significant increase in style length, final MF floral dimensions are similar to those of MS dimensions, and there is no correlation between style length and stigma receptivity.
Dichogamy; gynodioecy; Lamiaceae; Origanum syriacum; pollen discounting; pollen–stigma interference; pollen viability; protandry; stigma receptivity; style movement; style elongation; Teucrium capitatum
CYCLOIDEA (CYC)-like genes have been implicated in the development of capitulum inflorescences (i.e. flowering heads) in Asteraceae, where many small flowers (florets) are packed tightly into an inflorescence that resembles a single flower. Several rounds of duplication of CYC-like genes have occurred in Asteraceae, and this is hypothesized to be correlated with the evolution of the capitulum, which in turn has been implicated in the evolutionary success of the group. We investigated the evolution of CYC-like genes in Dipsacaceae (Dipsacales), a plant clade in which capitulum inflorescences originated independently of Asteraceae. Two main inflorescence types are present in Dipsacaceae: (1) radiate species contain two kinds of floret within the flowering head (disk and ray), and (2) discoid species contain only disk florets. To test whether a dynamic pattern of gene duplication, similar to that documented in Asteraceae, is present in Dipsacaceae, and whether these patterns are correlated with different inflorescence types, we inferred a CYC-like gene phylogeny for Dipsacaceae based on representative species from the major lineages.
We recovered within Dipsacaceae the three major forms of CYC-like genes that have been found in most core eudicots, and identified several additional duplications within each of these clades. We found that the number of CYC-like genes in Dipsacaceae is similar to that reported for members of Asteraceae and that the same gene lineages (CYC1-like and CYC2B-like genes) have duplicated in a similar fashion independently in both groups. The number of CYC-like genes recovered for radiate versus discoid species differed, with discoid species having fewer copies of CYC1-like and CYC2B-like genes.
CYC-like genes have undergone extensive duplication in Dipsacaceae, with radiate species having more copies than discoid species, suggesting a potential role for these genes in the evolution of disk and ray florets. The similarity in CYC-like gene diversification seen in Dipsacaceae and some members of the Asteraceae sets the stage to investigate whether the convergent evolution of capitulum inflorescences in both groups may have been underlain by convergent evolution in the same gene family.
Pollinators mediate the evolution of secondary floral traits through both natural and sexual selection. Gender-biased nectar, for example, could be maintained by one or both, depending on the interactions between plants and pollinators. Here, I investigate pollinator responses to gender-biased nectar using the dichogamous herb Chrysothemis friedrichsthaliana (Gesneriaceae) which produces more nectar during the male floral phase. Previous research showed that the hummingbird pollinator Phaethornis striigularis visited male-phase flowers more often than female-phase flowers, and multiple visits benefited male more than female fecundity. If sexual selection maintains male-biased rewards, hummingbirds should prefer more-rewarding flowers independent of floral gender. If, however, differential rewards are partially maintained through natural selection, hummingbirds should respond to asymmetry with visits that reduce geitonogamy, i.e. selfing and pollen discounting. In plants with male biases, these visit types include single-flower visits and movements from low to high rewards. To test these predictions, I manipulated nectar asymmetry between pairs of real or artificial flowers on plants and recorded foraging behaviour. I also assessed maternal costs of selfing using hand pollinations. For plants with real flowers, hummingbirds preferred more-rewarding flowers and male-phase morphology, the latter possibly owing to previous experience. At artificial arrays, hummingbirds responded to extreme reward asymmetry with increased single-flower visits; however, they moved from high to low rewards more often than low to high. Finally, selfed flowers did not produce inferior seeds. In summary, sexual selection, more so than geitonogamy avoidance, maintains nectar biases in C. friedrichsthaliana, in one of the clearest examples of sexual selection in plants, to date.
hummingbird pollination; nectar; Phaethornis striigularis; Chrysothemis friedrichsthaliana; floral evolution; sexual selection
• Background and Aims Heterodichogamy differs from normal dichogamy, in that it involves two mating types (protogyny and protandry) that occur at a 1 : 1 ratio in a population. Flowering phases of the two mating types are synchronized and reciprocal, which was considered to ensure between-type outcrossing. This study aims to quantify the flowering pattern and pollination efficacy in Juglans mandshurica, a wind-pollinated heterodichogamous tree.
• Methods The pattern of flowering phenology was monitored within individual trees and pollen traps were used to measure air-borne pollen loads during the spring in 2003 and 2004. Pollen longevity was determined by staining technique. Also a pollen supplementation experiment was performed in 2004 to assess pollen limitation of fruit production.
• Key Results There was no overlap between sexual functions within individual trees. Flowering periods of the two mating types were reciprocal and synchronous in both 2003 and 2004. Air-borne pollen loads were large, and protogynous and protandrous individuals each produced a high pollination peak, consistent with the two blooming periods. Maximum pollen longevity was about 4 h for protandrous individuals, and 3 h for protogynous individuals. Pollen supplementation did not increase fruit production in either protogynous or protandrous individuals.
• Conclusions Heterodichogamous flowering in Juglans mandshurica effectively avoids selfing, promotes between-type outcrossing, and leads to efficient pollination in a natural population.
Heterodichogamy; Juglans mandshurica; protandry; protogyny; pollination efficacy
Background and Aims
Outcrossing animal-pollinated plants, particularly non-rewarding species, often experience pollinator limitation to reproduction. Pollinator visitation is affected by various factors, and it is hypothesized that reproduction in non-rewarding plants would benefit from low spatial flower abundance and asynchronous flowering. In order to test this hypothesis, the influence of spatial pattern and flowering phenology on male and female reproductive success (RS) was investigated in a non-rewarding orchid, Cypripedium japonicum, in central China over two flowering seasons.
The probabilities of intrafloral self-pollination and geitonogamy caused by pollinator behaviours were estimated from field observations. Pollinator limitation was evaluated by hand-pollination experiments. RS was surveyed in different spatial flower dispersal patterns and local flower densities. The effects of flowering phenological traits on RS were assessed by univariate and multivariate regression analyses.
Hand-pollination experiments revealed that fruit production was strongly pollen limited throughout the entire reproductive season – over two seasons, 74·3 % of individuals set fruit following hand pollination, but only 5·2–7·7 % did so under natural conditions. Intrafloral self-pollination and geitonogamy within the potential clones might be rare. Both male and female fitness were substantially lower in clustered plants than in those growing singly. An increase in local conspecific flower density significantly and negatively influenced male RS, but had no effect on female RS. Phenotypic selection analysis indicated that individuals flowering earlier have the greatest probability of RS. Over 85 % of sampled flowering individuals had a flowering synchrony value >0·7; however, highly synchronous flowering was not advantageous for RS, as indicated by the negative directional selection differentials and gradients, and by the positive quadratic selection gradients.
These results support the hypothesis that, as a consequence of density-dependent selection, low spatio-temporal flower abundance is advantageous for attracting pollinators and for reproduction in natural populations of non-rewarding C. japonicum.
Cypripedium japonicum; pollen limitation; spatial dispersal pattern; flowering synchrony; reproductive success; selection differential; selection gradient; deceptive flower
Kiwifruit vines rely on bees for pollen transfer between spatially separated male and female individuals and require synchronized flowering to ensure pollination. Volatile terpene compounds, which are important cues for insect pollinator attraction, were studied by dynamic headspace sampling in the major green-fleshed kiwifruit (Actinidia deliciosa) cultivar ‘Hayward’ and its male pollinator ‘Chieftain’. Terpene volatile levels showed a profile dominated by the sesquiterpenes α-farnesene and germacrene D. These two compounds were emitted by all floral tissues and could be observed throughout the day, with lower levels at night. The monoterpene (E)-β-ocimene was also detected in flowers but was emitted predominantly during the day and only from petal tissue. Using a functional genomics approach, two terpene synthase (TPS) genes were isolated from a ‘Hayward’ petal EST library. Bacterial expression and transient in planta data combined with analysis by enantioselective gas chromatography revealed that one TPS produced primarily (E,E)-α-farnesene and small amounts of (E)-β-ocimene, whereas the second TPS produced primarily (+)-germacrene D. Subcellular localization using GFP fusions showed that both enzymes were localized in the cytoplasm, the site for sesquiterpene production. Real-time PCR analysis revealed that both TPS genes were expressed in the same tissues and at the same times as the corresponding floral volatiles. The results indicate that two genes can account for the major floral sesquiterpene volatiles observed in both male and female A. deliciosa flowers.
Actinidia; α-farnesene; floral volatiles; germacrene D; kiwifruit; ocimene; terpene; terpene synthases
In angiosperm evolution, autogamously selfing lineages have been derived from outbreeding ancestors multiple times, and this transition is regarded as one of the most common evolutionary tendencies in flowering plants. In most cases, it is accompanied by a characteristic set of morphological and functional changes to the flowers, together termed the selfing syndrome. Two major areas that have changed during evolution of the selfing syndrome are sex allocation to male vs. female function and flower morphology, in particular flower (mainly petal) size and the distance between anthers and stigma.
A rich body of theoretical, taxonomic, ecological and genetic studies have addressed the evolutionary modification of these two trait complexes during or after the transition to selfing. Here, we review our current knowledge about the genetics and evolution of the selfing syndrome.
We argue that because of its frequent parallel evolution, the selfing syndrome represents an ideal model for addressing basic questions about morphological evolution and adaptation in flowering plants, but that realizing this potential will require the molecular identification of more of the causal genes underlying relevant trait variation.
Evolution; selfing syndrome; autogamy; pollen-to-ovule ratio; flower size; herkogamy; quantitative trait loci; self-incompatibility
Yeasts are ubiquitous in terrestrial and aquatic microbiota, yet their ecological functionality remains relatively unexplored in comparison with other micro-organisms. This paper formulates and tests the novel hypothesis that heat produced by the sugar catabolism of yeast populations inhabiting floral nectar can increase the temperature of floral nectar and, more generally, modify the within-flower thermal microenvironment. Two field experiments were designed to test this hypothesis for the winter-blooming herb Helleborus foetidus (Ranunculaceae). In experiment 1, the effect of yeasts on the within-flower thermal environment was tested by excluding them from flowers, while in experiment 2 the test involved artificial inoculation of virgin flowers with yeasts. Nectary temperature (Tnect), within-flower air temperature (Tflow) and external air temperature (Tair) were measured on experimental and control flowers in both experiments. Experimental exclusion of yeasts from the nectaries significantly reduced, and experimental addition of yeasts significantly increased, the temperature excess of nectaries (ΔTnect = Tnect − Tair) and the air space inside flowers in relation to the air just outside the flowers. In non-experimental flowers exposed to natural pollinator visitation, ΔTnect was linearly related to log yeast cell density in nectar, and reached +6°C in nectaries with the densest yeast populations. The warming effect of nectar-dwelling yeasts documented in this study suggests novel ecological mechanisms potentially linking nectarivorous microbes with winter-blooming plants and their insect pollinators.
floral microbiology; floral microclimate; Helleborus foetidus; Metschnikowia reukaufii; nectar yeasts; yeast communities