Flowering and Pollination of Philodendron melinonii (Araceae) in French Guiana

Abstract: The pollination ecology of Philodendron melinonii was studied at two locations in French Guiana. Inflorescences of P. melinonii were regularly visited by Cyclocephala colasi, a scarab beetle also found in inflorescences of P. solimoesense in the same area. The flowering cycle lasted two days and the inflorescence exhibited features typical for beetle pollination (e.g., floral chamber, food rewards, flower heating). The flowering process is well synchronized with the night activity of Cyclocephala visitors. The spadix temperature was measured during the entire flowering cycle in the field in French Guiana and in greenhouse conditions at the Montreal Botanical Garden. Both measurements gave a similar temperature pattern with a two hour delay at the Botanical Garden. The spadix warmed up twice during the flowering period and its temperature was not significantly different from that of ambient air between the two peaks. These two temperature peaks are also well synchronized with the arrival and departure of the beetles on two consecutive nights.     

Pattern of respiration by intact inflorescences of the thermogenic arum lily Philodendron selloum

Inflorescences of the neotropical arum lily, Philodendron selloum, are strongly thermogenic for 2 d during anthesis. Continuous measurements of spadix temperature (Ts) and rate of oxygen consumption (VO2) were made outdoors in whole inflorescences attached to the plants. Some inflorescences were exposed to uncontrolled ambient temperature (Ta) while others were enclosed in clear water-jackets that produced nearly constant ambient conditions. A repeatable, diphasic pattern of heat production appeared, most clearly in water-jacketed inflorescences, and it comprised a short peak phase at sunset followed by a plateau phase that lasted until the following sunset. Regulation of Ta occurred in both phases, but at different levels. Peak phase Ta was regulated in the region of 38-42C, but plateau phase Ta was usually in the range of 25-36C. Both VO2 and total heat produced throughout anthesis increased at lower Ta. The data imply that the short peak phase is related to the enhancement of odour production that attracts a single species of large scarabaeid beetle in its native Brazil, and regulation of maximum Ta may prevent overheating. Thermoregulation in the long plateau phase produces equable temperatures inside the inflorescence that may facilitate the resident beetles' activities as a direct energetic reward.     

Thrips pollination of androdioecious Castilla elastica (Moraceae) in a seasonal tropical forest

Androdioecy is a rare sexual system in nature, as predicted theoretically. Among the androecious species reported so far, Castilla elastica (Moraceae) is unique in that flowers are unisexual and staminate and pistillate flowers on cosexual plants are produced on different inflorescences. In addition, inflorescence structure of staminate inflorescences on males and staminate and pistillate inflorescences on cosexes is markedly different. Staminate inflorescences on males are bivalvate, while staminate inflorescences on cosexes are "fig-like" and urceolate. Pistillate inflorescences are discoidal. The difference may reflect different roles and requirements of the three inflorescences in pollination and protection from herbivores. This study reports thrips pollination of C. elastica, demonstrated by a pollinator introduction experiment. Thrips pollination of the species may be an example of mutualism originating from plant-herbivore interactions. In the Moraceae, shifts from simple herbivores on flowers to pollinators might have occurred many times, evolving into diverse pollination systems including the fig-fig wasp mutualism. The family, of which little is known about pollination systems, provides interesting and unique opportunities to study evolution of pollination systems and roles of nonpollinating associates of inflorescences.     

Flowers and Beetles in the South American Tropics

Examples of beetle pollination in the South American tropics are given. The case histories refer to representatives of the families Cyclanthaceae, Annonaceae, and Araceae. In most cases the cantharophilous syndrome does not seem to be the result of coevolution but of a one-sided adaptation of flowers to the behavior, necessities, and sense-capacities of beetle species. It is emphasized that cantharophily may not necessarily be an indication of ancientness of a flower/insect relationship. Besides primitive angiosperms, there are derived and modern groups which, in their pollination, are specialized for beetles. Carludovica palmata (Cyclanthaceae) is pollinated by small curculionids which are attracted by odors in the early morning hours. Annona coriacea (Annonaceae) and Philodendron selloum (Araceae) are pollinated by large dynastid scarab beetles in the evening hours. In all three species thermogenesis occurs. Although belonging to widely separate systematic groups, Annona flowers and Philodendron inflorescences have a similar pollination biology, which indicates that their adaptations to beetles are the result of convergent evolutionary developments.     

Production of food bodies on the reproductive organs of myrmecophytic Macaranga species (Euphorbiaceae): effects on interactions with herbivores and pollinators

In protective ant–plant mutualisms, plants offer ants food (such as extrafloral nectar and/or food bodies) and ants protect plants from herbivores. However, ants often negatively affect plant reproduction by deterring pollinators. The aggressive protection that mutualistic ants provide to some myrmecophytes may enhance this negative effect in comparison to plant species that are facultatively protected by ants. Because little is known about the processes by which myrmecophytes are pollinated in the presence of ant guards, we examined ant interactions with herbivores and pollinators on plant reproductive organs. We examined eight myrmecophytic and three nonmyrmecophytic Macaranga species in Borneo. Most of the species studied are pollinated by thrips breeding in the inflorescences. Seven of eight myrmecophytic species produced food bodies on young inflorescences and/or immature fruits. Food body production was associated with increased ant abundance on inflorescences of the three species observed. The exclusion of ants from inflorescences of one species without food rewards resulted in increased herbivory damage. In contrast, ant exclusion had no effect on the number of pollinator thrips. The absence of thrips pollinator deterrence by ants may be due to the presence of protective bracteoles that limit ants, but not pollinators, from accessing flowers. This unique mechanism may account for simultaneous thrips pollination and ant defense of inflorescences.     

THE POLLINATION REQUIREMENT OF THE FIELD BEAN (VICIA FABA)

Many of the flowers on field bean plants fail to produce pods even when fully pollinated. When insect pollination is prevented pod production on the lowest inflorescences, which normally produce most pods, is reduced but a compensatory increase on the upper ones ensures a moderate yield. This change in the distribution of pods may be a useful indication of insufficient pollination.     

Zonal thermogenetic dynamics of two species of Philodendron from two different subgenera (Araceae)

Spadix temperature was measured in two species of Philodendron : P. melinonii (subgenus Philodendron ) and P. solimoesense (subgenus Meconostigma ). For each species, the temperature of the male zone, the sterile male zone and the female zone of the spadix were recorded. In both species, the temperature of the male zone warmed up at the beginning of each of the two flowering nights. In P. melinonii , the temperature of the male sterile zone increased the first day but remained not significantly different from that of the ambient air during the second day. The temperature of the male zone warmed up slightly on the second day. In P. melinonii , the temperature of the three zones was not significantly different from that of the ambient air between the two peaks. In P. solimoesense , the temperature of the male zone and sterile zone rose to above that of the ambient air during the first night and then progressively cooled down but remained 3–6°C above the ambient air temperature until the second peak. In both species the temperature of the female zones remained more or less constant during the entire flowering cycle, very close to the temperature of the ambient air. We suggest that the heat production and the spadix temperature patterns observed may reflect a general physiological process common to all species of Philodendron . The biphasic pattern present in the subgenus Meconostigma can be seen as a variant of the 'two peaks' pattern, occurring in the subgenus Philodendron , with a 'plateau' phase between them. The comparison of the different thermogenic cycles occurring in Philodendron , Arum and Dracunculus seems to indicate some clear evolutionary trends. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 79–86.     

Pollination of Ipomopsis aggregata (Polemoniaceae): effects of intra- vs. interspecific competition

Although plants may simultaneously experience intra- and interspecific competition for pollination, their relative strength has rarely been experimentally evaluated. Yet because intra- and interspecific competition can be caused by different mechanisms, their effect on the ecology and evolution of plants may differ. To determine the relative strength of intra- and interspecific competition for pollination, I manipulated the presence of heterospecifics and density of conspecifics using Ipomopsis aggregata as the focal species. All plots contained I. aggregata and Castilleja linariaefolia, but C. linariaefolia inflorescences were removed from half of the plots to create the heterospecifics-absent treatment. Within each plot, all I. aggregata inflorescences were removed from a 5-m radius around a focal plant to create a low conspecific density experimental unit, and a group of 12 I. aggregata plants/1 m² was designated as a high conspecific density unit. Conspecific pollen deposition was reduced when C. linariaefolia was present but was not influenced by I. aggregata density. Although seed set per fruit was reduced by 17% when C. linariaefolia was present, it was not significantly influenced by either treatment. Interspecific competition for pollination is stronger than intraspecific competition in the I. aggregata–C. linariaefolia system, but neither process appears to influence plant fitness.     

Dioecy and the evolution of pollination systems inSchiedea and Alsinidendron (Caryophyllaceae:Alsinoideae) in the Hawaiian Islands

The transition from biotic to wind pollination and the consequencesof this transition for the evolution of dioecious breeding systems wereinvestigated in Schiedea and Alsinidendron(Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for wind pollination was studied for five species ofSchiedea using a wind tunnel. Morphological correlates of windpollination for these species were then used to infer the presence orabsence of wind pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species,which occur in mesic to wet forests, or less commonly in dry habitats,show little or no indication of wind pollination. These species had lowpollen:ovule ratios, large relative pollen size, diffuse inflorescences,substantial nectar production in several cases, and appear to bebiotically pollinated or autogamous. Sexually dimorphic species, whichall occur in dry habitats, are wind pollinated, based on wind tunnelresults or morphological adaptations indicating the potential for windpollination. These adaptations include high pollen:ovule ratios, smallpollen size, moderately to highly condensed inflorescences, and reducednectaries and nectar production. Shifts to wind pollination anddimorphism are strongly correlated in Schiedea, suggesting theclose functional relationship of the twophenomena.     

The Bizarre Inflorescence of Norantea brasiliensis (Marcgraviaceae): Visits of Hovering and Perching Birds1

The pollination biology of Norantea brasiliensis (Marcgraviaceae) was studied in the rain forest of southeastern Brazil. This plant presents bizarre, brush-type racemous inflorescences bearing numerous flowers and extrafloral cup-shaped nectaries. Flower anthesis is diurnal, nectar production is continuous and copious, and the sticky pollen is readily removed by visitors during the first morning hours. The ruby-coloured inflorescences were visited by eight species of hummingbirds (Trochilidae), and 10 species of passerine birds (three Coerebidae and seven Thraupidae). Hummingbirds hovered while probing for nectar and touched flowers occasionally, whereas passerine birds perched and made contact with flowers habitually. Due to differences in flower-visiting and general foraging behaviour, perching birds act as better pollen vectors than hovering birds. The inflorescence of Norantea brasiliensis seems well fitted for pollination by passerine birds, and the hexose-dominated nectar supports this idea. Pollination syndrome trends within Marcgraviaceae may stem from insect-pollinated, condensed and spike-like inflorescences which would give rise to bird-pollinated, brush-type inflorescences. From the same basic condensed inflorescence, bat-pollinated umbelliform inflorescence may be derived from bird-pollinated, pendulous and corymb-like inflorescences. These postulated inflorescence types are found among the extant species of Marcgraviaceae.     

The evolution of beetle pollination in a South African orchid

The pollination biology of the orchid Ceratandra grandiflora was investigated in order to determine whether the partial loss of a specialized floral reward (i.e., oil) was the result of an incomplete shift from one specialized pollinator to another. In the three-species clade of section Ceratandra, there has been a progressive loss of the oil-secreting callus. lt is always present in C atrata, sometimes present in C. grandiflora, and never present in C. globosa. Thirty-nine to 67% of individuals in populations of C. grandiflora bear the callus gland, but gland presence has no signifikant effect on the proportion of flowers pollinated. Pollinator observations show that the shift in pollinators is complete and that the oil-secreting callus is a vestige of the ancestral oil-bee pollination system that no longer plays a role in pollination. C grandiflora is pollinated almost exclusively by a single species of hopliine beetle (Scarabaeidae). Experiments with artificial flower traps indicate that color alone can explain the attraction of beetles to C. grandiflora, despite the absence of a floral reward. The proportion of C. grandiflora flowers pollinated (50.2 and 61.1%; N = 524 and 324 flowers, respectively) is unusually high for a plant that relies on generalized food deception and is probably due to the use of inflorescences as mating sites (i.e., rendezvous pollination).     

Neither insects nor wind: ambophily in dioecious Chamaedorea palms (Arecaceae)

Pollination of Neotropical dioecious trees is commonly related to generalist insects. Similar data for non‐tree species with separated genders are inconclusive. Recent studies on pollination of dioecious Chamaedorea palms (Arecaceae) suggest that species are either insect‐ or wind‐pollinated. However, the wide variety of inflorescence and floral attributes within the genus suggests mixed pollination mode involving entomophily and anemophily. To evaluate this hypothesis, we studied the pollination of Chamaedorea costaricana, C. macrospadix, C. pinnatifrons and C. tepejilote in two montane forests in Costa Rica. A complementary morphological analysis of floral traits was carried out to distinguish species groups within the genus according to their most probable pollination mechanism. We conducted pollinator exclusion experiments, field observations on visitors to pistillate and staminate inflorescences, and trapped airborne pollen. A cluster analysis using 18 floral traits selected for their association with wind and insect pollination syndromes was carried out using 52 Chamaedorea species. Exclusion experiments showed that both wind and insects, mostly thrips (Thysanoptera), pollinated the studied species. Thrips used staminate inflorescences as brood sites and pollinated pistillate flowers by deception. Insects caught on pistillate inflorescences transported pollen, while traps proved that pollen is wind‐borne. Our empirical findings clearly suggest that pollination of dioecious Chamaedorea palms is likely to involve both insects and wind. A cluster analysis showed that the majority of studied species have a combination of floral traits that allow for both pollination modes. Our pollination experiments and morphological analysis both suggest that while some species may be completely entomophilous or anemophilous, ambophily might be a common condition within Chamaedorea. Our results propose a higher diversity of pollination mechanisms of Neotropical dioecious species than previously suggested.     

Adaptive plasticity of floral display size in animal-pollinated plants

Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.     

Influence of photosynthetic restriction due to defoliation at flowering on seed abortion in lucerne (Medicago sativa L.)

The seed yield of lucerne is poor, in contrast to its good vegetativegrowth. This is partly due to a lack of pollination under naturalconditions, pod abortion and the production of only a few seedsper pod. In this study, lucerne plants were grown in controlledconditions and about 30% of the inflorescences were pollinatedmanually. There were about 10 ovules per flower, which remainedconstant throughout the flowering period. There were 4.5 seedsper pod, indicating over 50% seed abortion. One group of plantswas defoliated and the lack of recent assimilates at floweringcaused a small but significant decrease in the number of seedsper pod (4.1). The effect of defoliation varied with seed age;the youngest fertile inflorescences were the most affected andthere was no effect at around 400C d^–1 . This stage markedthe end of the lag phase, which was determined separately incontrol plants. Thus, it is assumed that this date is the abortionlimiting stage (ALS) for this species. The long lag phase forlucerne could be a key influence on seed yield. The longer theALS, the greater the risk of vegetative competition, thus reducingreproductive development. Key words: Lucerne, flowering, pollination, abortion limiting stage (ALS), seed production     

Change of Floral Orientation within an Inflorescence Affects Pollinator Behavior and Pollination Efficiency in a Bee-Pollinated Plant,Corydalis sheareri

Vertical raceme or spike inflorescences that are bee-pollinated tend to present their flowers horizontally. Horizontal presentation of flowers is hypothesized to enhance pollinator recognition and pollination precision, and it may also ensure greater consistency of pollinator movement on inflorescences. We tested the hypotheses using bee-pollinated Corydalis sheareri which has erect inflorescences consisting of flowers with horizontal orientation. We altered the orientation of individual flowers and prepared three types of inflorescences: (i) unmanipulated inflorescences with horizontal-facing flowers, (ii) inflorescences with flowers turned upward, and (iii) inflorescences with flowers turned downward. We compared number of inflorescences approached and visited, number of successive probes within an inflorescence, the direction percentage of vertical movement on inflorescences, efficiency of pollen removal and seed production per inflorescence. Deviation from horizontal orientation decreased both approaches and visits by leafcutter bees and bumble bees to inflorescences. Changes in floral orientation increased the proportion of downward movements by leafcutter bees and decreased the consistency of pollinator movement on inflorescences. In addition, pollen removal per visit and seed production per inflorescence also declined with changes of floral orientation. In conclusion, floral orientation seems more or less optimal as regards bee behavior and pollen transfer for Corydalis sheareri. A horizontal orientation may be under selection of pollinators and co-adapt with other aspects of the inflorescence and floral traits.     

Variations of floral traits among different life forms illustrate the evolution of pollination systems in Potamogeton species from China

Four leaf morpha groups (floating-leaved, submerged broad-leaved, submerged linear-leaved and filiform-leaved) and three inflorescences type groups (erect, facultative floating and floating) can be found in the genus Potamogeton. Life forms in the genus correlate with pollination types (anemophily, epihydrophily and hydroautogamy). Floral traits vary greatly among different life forms and pollination types. Both floating and submerged broad-leaved species produce erect inflorescences that are suited for anemophilous pollination. These flowers also have the highest pollen/ovule (P/O) ratio (25,013) and the smallest pollen grain volume (6046 μm³). On the contrary, submerged filiform-leaved species produce only floating inflorescences and their flowers produce the largest pollen grains (17,567 μm³) and have the lowest P/O ratio (6752), which is typical of the syndromes of hydroautogamy and epihydrophily. The relatively prolific seed production (about 70%) and wide dispersal in the floating and submerged broad-leaved species and the submerged filliform-leaved species indicate that these two groups are well adapted to the aquatic environment. This is in contrast with the less well-adapted complex and unstable pollination system found in linear-leaved species. We propose that the pollination systems and life forms in the Potamogeton, have undergone modification in response to the demands imposed by the aquatic environment during the evolutionary process in the genus.     

Flowering dynamics in Arum italicum (Araceae): relative role of inflorescence traits, flowering synchrony, and pollination context on fruit initiation

We studied the relative role of inflorescence traits, flowering synchrony, and pollination context for infructescence and fruit initiation in two Spanish populations of Arum italicum, a species in which inflorescences are the pollination unit. In this species, a specialized inflorescence organ, the appendix, is important for pollinator attraction. However, the short floral longevity and the production of mostly one inflorescence per plant make its pollination potentially dependent on strong flowering synchrony and on external factors not controlled by the plant (the pollination context). The flowering period in both sites lasted >3 mo. Day-to-day variation in simultaneous antheses was high, and 11-50% of antheses occurred on days during which no pollen donor was present. Inflorescence traits, flowering synchrony, and between-plant distance all influenced infructescence and fruit initiation, but their relative importance differed between sites. In one large population, infructescence initiation was positively related to inflorescence traits; in a smaller population infructescence initiation increased with the number of donor inflorescences. In both sites, percentage of fruits initiated per infructescence was dependent on a combination of inflorescence traits, flowering synchrony, and between-plant distance. Plants producing 2-4 inflorescences had higher probability of infructescence initiation and overlapped their antheses with more plants than single-inflorescence ones.     

Philodendron adamantinum (Araceae) lures its single cyclocephaline scarab pollinator with specific dominant floral scent volatiles

Cyclocephline scarabs and their host plants are documented as highly specialized plant–pollinator associations, with various fine‐tuned adaptations. We studied the association between Philodendron adamantinum, a species endemic to the Espinhaço Range in Minas Gerais, South‐East Brazil, and its exclusive pollinators. We focused on the pollination mechanism and reproductive success of P. adamantinum, analysed its floral scent composition, and performed field bioassays to verify the scent‐mediated attraction of pollinators. The reproductive success of P. adamantinum depends on the presence of Erioscelis emarginata (Scarabaeidae, Cyclocephalini), its sole pollinator. At dusk, the inflorescences heat up to 18 °C above the surrounding ambient air temperature and give off a strong sweet odour, from which 32 volatile compounds were isolated. Dihydro‐β‐ionone, the major constituent in the floral scent bouquet, lures individuals of E. emarginata when applied to scented artificial decoys, either alone or blended with methyl jasmonate. We attribute the low fruit set of P. adamantinum at our study sites to pollinator limitation of small and isolated populations and geitonogamic pollen flow of vegetatively generated clonal plant groups. The interaction between P. adamantinum and E. emarginata shows common traits typical of the known plant–pollinator associations involving cyclocephaline scarabs: the asymmetrical dependence of plants on their pollinators, and the scent‐mediated interaction between flowers and beetles. In addition to updating the current catalogue of active compounds of cantharophilous pollination systems, further experimental studies should elucidate the role of the specific chemical compounds that attract pollinators along different time and biogeographic scales. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 679–691.     

A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

Wind pollination, sexual dimorphism, and changes in floral traits of Schiedea (Caryophyllaceae)

Both changes in sex allocation and pollination mode may promote the separation of sexes in plant populations. Simultaneous evolution of wind pollination and dimorphism has occurred in Schiedea, where species with different female frequencies provide an opportunity to observe the effect of wind pollination on sex allocation and floral morphology. Differences among species in the ratio of anther to ovary volume were not the result of sex allocation trade-offs, but instead resulted from production of vestigial stamens in females; there were no changes in ovary volume in males and hermaphrodites (MH) of dimorphic species. Relative to hermaphroditic species, dimorphic species had more condensed inflorescences, a pattern often associated with wind pollination. Within dimorphic species, MH had longer filament lengths than females, and females had longer stigmas than MHs. These traits are characteristic of wind pollination, but there was no relationship between the degree of sexual dimorphism and female frequency. Ovary volume and ovule number and size had positive phenotypic correlations between females and MH of dimorphic species, making sex specialization more difficult. In dimorphic Schiedea species, selection for wind pollination may have a greater effect on floral traits than trade-offs in allocation between male and female function.