Low Pollination Success Research Articles

Reproductive character displacement allows two sexually deceptive orchids to coexist and attract the same specific pollinator

An increased divergence in characters between species in secondary contact can be shaped by selection against competition for a common resource (ecological character displacement, ECD) or against maladapted hybridization (reproductive character displacement, RCD). These selective pressures can act between incipient species (reinforcement) or well-separated species that already completed the speciation process, but that can still hybridize and produce maladapted hybrids. Here, we investigated two well-separated sexually deceptive orchid species that, unusually, share their specific pollinator. Sympatric individuals of these species are more divergent than allopatric ones in floral characters involved in a mechanical isolating barrier, a pattern suggestive of RCD. To experimentally test this scenario, we built an artificial sympatric population with allopatric individuals. We measured flower characters, genotyped the offspring in natural and artificial sympatry and estimated fertility of hybrids. Different from naturally sympatric individuals, allopatric individuals in artificial sympatry hybridized widely. Hybrids showed lower pollination success and seed viability than parentals. Character displacement did not affect plant pollination success. These findings suggest that RCD evolved between these species to avoid hybridization and that selection on reinforcement may be very strong even in plants with highly specialized pollination.

Pollination success in three tropical dry forest orchid species from Mexico: insights from floral display, visitation rates, and flower micromorphology

Background: Despite long-lasting efforts to disentangle the drivers of orchid pollination, pollination success in tropical dry forest orchids remains largely unknown.
 Questions and hypothesis: How successful are pollination in three tropical dry forest orchids? How is pollination influenced by floral display and floral rewards (as suggested by floral micromorphology)? We hypothesized a positive effect of floral display on pollinia removal and deposition rates.
 Studied species: Barkeria whartoniana (C. Schweinf.) Soto Arenas, Clowesia dodsoniana E. Aguirre, and Cyrtopodium macrobulbon (La Llave & Lex.) G.A. Romero & Carnevali.
 Study site and dates: Nizanda (Oaxaca), Mexico; flowering periods of 2013 and 2014.
 Methods: We calculated pollinia removal and deposition rates, identified floral visitors and analyzed flower microstructure to search for structures potentially producing rewards. Floral display was measured through number of open flowers, and number and length of inflorescences, and its effect on pollination success was assessed through linear modeling.
 Results: Pollinia removal rates were higher than deposition rates, and floral display was related to pollination success in C. dodsoniana only. Visitation rates were low for the three species and most visitors were not true pollinators. The three species possess potentially secreting structures, but for B. whartoniana and C. macrobulbon these rewards are likely part of the pollinator deception mechanism.
 Conclusions: The generalized low pollination success implies the need for high population densities of both interacting parts. We emphasize the need for integrated evaluations of different aspects of the plant-pollinator interaction.

Pola kunjungan serangga liar dan efek penambahan koloni Trigona (Tetragonula) laeviceps Smith pada penyerbukan kabocha (Cucurbita maxima)

Insects hold important role in pollination of many crops. However, studies on pollination in Indonesia could be considered rare. This study focussed on obtaining the basic information of wild pollinators and the effect Trigona ( Tetragonula ) laeviceps Smith innundation release to the production and quality of pumpkin ( C. maxima ) in traditional farming system. Observations were carried out from 07:00 to 15:00 during flowering period for 3 weeks. Sampling area was divided into three plots : open pollination + T. laeviceps (OPT), open pollination (OP), and hand pollination (HP). Pollination was assessed by three main parameters, which were visitation pattern, plant reproductive success, and fruit quality. Visitation pattern was assessed by measuring frequency and duration of pollinator visits, the plant reproductive success by fruit set and number of seed produced; while fruit quality by diameter, weight, and number of fruit produced/plant. We recorded different visitation pattern in which wild pollinator preferred to visit flowers in the morning while T. laeviceps preferred to visit from noon to afternoon. This pattern could be relate to difference in thermal tolerance among pollinators. There were significant differences among fruit set produced in OPT (80%), OP (65%), and HP (38.3%) (F 2,35 = 19,907, P = 0,000). Number of seeds and fruit quality produced in OPT and OP much higher than HP while number of fruits produced in OPT significantly higher that OP and HP. Low pollination success in HP showed pollination process in pumpkin highly depend on pollination time. Thus, pollination by bees in pumpkin hard to be replace by human and variation of visit provided by T. laeviceps produce positive effect to pumpkin.

Floral scent and species divergence in a pair of sexually deceptive orchids.

Speciation is typically accompanied by the formation of isolation barriers between lineages. Commonly, reproductive barriers are separated into pre‐ and post‐zygotic mechanisms that can evolve with different speed. In this study, we measured the strength of different reproductive barriers in two closely related, sympatric orchids of the Ophrys insectifera group, namely Ophrys insectifera and Ophrys aymoninii to infer possible mechanisms of speciation. We quantified pre‐ and post‐pollination barriers through observation of pollen flow, by performing artificial inter‐ and intraspecific crosses and analyzing scent bouquets. Additionally, we investigated differences in mycorrhizal fungi as a potential extrinsic factor of post‐zygotic isolation. Our results show that floral isolation mediated by the attraction of different pollinators acts apparently as the sole reproductive barrier between the two orchid species, with later‐acting intrinsic barriers seemingly absent. Also, the two orchids share most of their fungal mycorrhizal partners in sympatry, suggesting little or no importance of mycorrhizal symbiosis in reproductive isolation. Key traits underlying floral isolation were two alkenes and wax ester, present predominantly in the floral scent of O. aymoninii. These compounds, when applied to flowers of O. insectifera, triggered attraction and a copulation attempt of the bee pollinator of O. aymoninii and thus led to the (partial) breakdown of floral isolation. Based on our results, we suggest that adaptation to different pollinators, mediated by floral scent, underlies species isolation in this plant group. Pollinator switches may be promoted by low pollination success of individuals in dense patches of plants, an assumption that we also confirmed in our study.

APETALA2 and APETALA3 Genes Expression Profiling on Floral Development of Teak (Tectona grandis Linn f.)

eak (Tectona grandis Linn f.) is one of valuable timber species because of the beauty, strength and durability properties. Main problem in teak improvement program is reproductive biology, a low pollen viability, high embryo abortion, low pollination success and low fruit production. Investigation carried out at the teak improvement that flowering aspects is very important. Teak development program was facing difficulties due to the lack of information about the role of genes regulating flowering. APETALA2 (AP2) and APETALA3 (AP3) genes as member of the floral organ Identity. The role of teak flowering development predicted by up and down regulation of TgAP2 and TgAP3 genes. This study was conducted to determine the gene expression profile of TgAP2 and TgAP3 in the developmental stages of teak flowering. Materials and Methods: In this study, TgAP2 and TgAP3 genes in teak identified from NGS transcriptome data that is annotated with Solanum lycopersicum. The TgAP2 and TgAP3 genes activities on the several developmental stages of teak flowering tissues are done with QRT-PCR analysis using 18S RNA as gene reference. Results: The highest expression level of TgAP2 on the floral development stages of 4th lateral floral buds. The TgAP3 gene expression reached the highest level on the apical floral bud stage development. Vegetative shoot as control stages, TgAP2 gene expression level reached 9 times compared to the control and TgAP3 more than 12 times. The TgAP2 and TgAP3 genes expression profile has non-significant correlation on all floral development stages. Conclusion: The TgAP2 and TgAP3 genes expressed with different level in all stages of the teak flowering development. The TgAP2 and TgAP3 genes have non-significant correlation expression profile in role of teak floral development. These results indicate that the TgAP2 and TgAP3 expression profiles equivalent to the general pattern in the Arabidopsis model plant.

Low pollination success of hybrids between nectar-rewarding and food-deceptive orchids

Natural hybridization is widespread among food-deceptive orchids, whereas hybridization between deceptive and rewarding species is less common among Mediterranean species and its evolutionary consequences remain under-investigated. Here, we examine the morphological variation in floral traits, pollination success and demographic dynamics of natural hybrids between the widespread nectar-rewarding Anacamptis fragrans and the Mallorca endemic, food-deceptive A. robusta. We confirmed the status of hybrids using ribosomal DNA and assessed their maternal contribution using length polymorphism in the plastid tRNALEU intron. Genetic analyses confirmed that hybridization occurred in both directions, but the hybrids were morphologically closer in floral metric characters to A. fragrans and exhibited reduced among-individual variation in floral traits. No obvious secreting papillae were present in the hybrid spur, which more closely resembled the spur of non-rewarding A. robusta, reinforcing field observations that hybrids were probably nectarless. Compared with both rewarding and deceptive parents, the hybrids were less attractive for pollinators, most likely because of the absence of significant reward and of their combination of contrasting parental floral advertisements. In spite of its low pollination success, the hybrid population is presently expanding alongside the endemic A. robusta, suggesting that it follows the demographic dynamics of the parental species.

The pine reproductive process in temperate and tropical regions

Our knowledge of the pine reproductive process is confined to the developmental stages and time relations in a particular species. Lacking in the literature is a comparative analysis from a broader perspective such as pines from temperate versus tropical regions. Also, important information that may have beneficial implications for pine breeding and management purposes may be missed by going with a single generalized reproductive cycle model which is usually derived from well-studied northern temperate species. Detailed developmental analysis of the reproductive process is necessary, particularly for tropical pines where information is limited. Most pines undergo a reproductive cycle that spans three calendar years with two dormant periods. In temperate pines, many of the stages that are initiated by fall generally come to a halt during the winter and development resumes in spring of the following year. In tropical pines, reproductive development appears to be generally a continuous process characterized by a gradual rate of development with indistinct first dormant period. The distinct first dormant period in north temperate pines serves to synchronize pollen release and seed-cone receptivity which results in higher pollination success and seed production. Tropical pines exhibit asynchrony in pollen release and thus has extended pollination period. Relatively less pollen are available which results in lower pollination success and seed set. Interestingly, since asynchrony may enhance cross-pollination, tropical pines might benefit from this through the capture of genetic diversity. The length of the second dormant period is generally the same in temperate and tropical pines which indicates strong genetic control.

The importance of fruit set, fruit abortion, and pollination success in fruit production of teak (Tectona grandis)

Teak ( Tectona grandis L.) is believed to have been introduced from India 400–500 years ago and there appear to be no old-growth natural forests. However, Indonesia has many teak plantation forests and 40%–50% of seeds for reforestation come from seed orchards and the remainder from plantations. In both, flower and fruit abortion results in low fruit set and thus seed production. We investigated flower and fruit development in a clonal seed orchard in East Java in 1999 and 2001 using cross- and open-pollinated trees. The rates of abortion using cross-pollinations showed a similar pattern but were lower than for open-pollinations. The highest rate of abortion in cross- and open-pollinations was during pollination and fertilization, ranging 11%–23% and 31%–32%/day, respectively, less during fruit initiation (5%–6% and 6%–8%/day) and the lowest was during fruit maturation (<0.5%/day). Cross-pollinations increased fruit production by 10-fold compared with open-pollinations. About 30% of flowers were pollinated with an average of five pollen grains per stigma in open-pollinations. Pollen viability varied among clones and time of day but was not affected by position of flowers in an inflorescence. We conclude that low pollination success and low pollen viability are major causes for low fruit production in teak and are related to insect pollinators.

The pollination ecology of durian (Durio zibethinus, Bombacaceae) in southern Thailand

Abstract:The floral biology and pollination ecology of durian, Durio zibethinus, were determined in eight semi-wild trees in mixed-fruit orchards in southern Thailand during April-May 2003 and 2005. Flowers open fully at 16h00–16h30 and most androecia drop around 01h00. Anthers dehisce at 19h30–20h00 when the stigmata are already receptive. In a series of pollination experiments, fruit was set in all treatments within 10 d. The greatest pollination success occurred after hand-crossed (76.6%), open (54.4%) and emasculation pollination (53.3%). Consistently, hand-crossed (12.2%), emasculation (8.7%) and open pollination (5.1%) yielded a substantial fruit set 2 mo after the pollination experiments. Very low pollination success in facilitated autogamy suggests that most durian trees are highly self incompatible. No mature fruit was found after insect pollination and automatic autogamy. Fruit bats, especially Eonycteris spelaea, are the major pollinators of this durian although the giant honey bee (Apis dorsata) was the most frequent visitor to the flowers. Bats visited durian flowers at the rate of 26.1 (SD = 20.7) visits per inflorescence per night. Since this semi-wild durian depends on fruit bats as its pollinator, protecting fruit bat populations and their roosts is vital for the production of the durian fruit crop.

Ecological context of breeding system variation: sex, size and pollination in a (predominantly) gynodioecious shrub.

Species that exhibit among-population variation in breeding system are particularly suitable to study the importance of the ecological context for the stability and evolution of gender polymorphism. Geographical variation in breeding system and sex ratio of Daphne laureola (Thymelaeaceae) was examined and their association with environmental conditions, plant and floral display sizes, and pollination environment in a broad geographic scale was analysed. The proportion of female and hermaphrodite individuals in 38 populations within the Iberian Peninsula was scored. Average local temperature and precipitation from these sites were obtained from interpolation models based on 30 years of data. Pollination success was estimated as stigmatic pollen loads, pollen tubes per ovule and the proportion of unfertilized flowers per individual in a sub-set of hermaphroditic and gynodioecious populations. Daphne laureola is predominantly gynodioecious, but hermaphroditic populations were found in northeastern and southwestern regions, characterized by higher temperatures and lower annual precipitation. In the gynodioecious populations, female plants were larger and bore more flowers than hermaphrodites. However, due to their lower pollination success, females did not consistently produce more seeds than hermaphrodites, which tends to negate a seed production advantage in D. laureola females. In the northeastern hermaphroditic populations, plants were smaller and produced 9-13 times fewer flowers than in the other Iberian regions, and thus presumably had a lower level of geitonogamous self-fertilization. However, in a few southern populations hermaphroditism was not associated with small plant size and low flower production. The findings highlight that different mechanisms, including abiotic conditions and pollinator service, may account for breeding system variation within a species' distribution range and also suggest that geitonogamy may affect plant breeding system evolution.

Microsporogenesis, Pollination, Pollen Germination and Male Gametophyte Development in Taxus brevifolia

Taxus brevifolia(Nutt.), commonly known as Pacific or western yew, is a conifer native to the Pacific northwest of North America. Contrary to other Taxus species, T. brevifolia staminate strobili are usually located on 2-year-old foliage although they may occur on foliage from 1 to 5-years-old. This delayed staminate strobilus development may be an adaptation to the low light environment where T. brevifolia grows. Microsporogenesis occurred in the autumn preceding pollination. Successive divisions produced isobilateral tetrads visible as early as mid-October. Over-wintering staminate strobili usually contained separate microspores. In 1996 to 1999, pollination occurred in March and April in two natural forest sites on southern Vancouver Island, British Columbia, Canada. The low amounts of airborne pollen and prolonged pollination period indicated low pollination success within T. brevifolia. Female receptivity was measured by the presence of a pollination drop. Protandry up to 18d was observed. In vitro pollen germination was moderate to good, ranging from 65 to 88% depending on the tree and year. DAPI fluorescence staining showed successful male gametophyte development in vitro. The microspore divided forming a tube nucleus and generative cell within 3d of culture. The generative cell then divided forming a sterile nucleus and spermatogenous nucleus after 17d. The spermatogenous nucleus acquired a cell wall then divided forming two equal sperm after 24d.

Pollination Biology in a TropicalAcaciaHybrid (A. mangiumWilld. ×A. auriculiformisA. Cunn. ex Benth.)

Floral biology and pollination mechanism of theAcaciahybrid (A. mangiumWilld. ×A. auriculiformisA. Cunn. ex Benth.) growing in Thailand are investigated using light and electron microscopy. The hybrid is andromonoecious. A floral spike consists of about 150 loosely arranged flowers. Flowers are cream coloured, fragrant and have no floral nectaries. The pistil has a solid style with a smooth, wet stigma and amphitropous ovules with immature integuments. The anther consists of eight loculi, each bearing only one 16-grain polyad. The flowers are weakly protogynous. Anthesis is complete at 0500–0600 h but peak female receptivity begins at 0200–0300 h and is completed that day. The stigmatic exudate is of the lipophilic type and is secreted from the stigmatic cells by a holocrine mechanism. Pollen is the main floral reward for the insect pollinators. There are several floral characteristics which facilitate pollen transfer from anthers and deposition on stigmas.Apis melliferaandCeratinasp. are the most effective pollinators because they are the most common visitors and carry a heavy load of hybrid polyads. However, their behaviour in foraging for pollen in the same tree and weak protogynous dichogamy may promote self-pollination in the hybrid. The hybrid has low pollination success due to low pollinator number. An increase in exposure time of flowers to pollinators or pollinator number may increase pollination success but may not affect the rate of pollen deposition on stigmas due to the relatively small size of the stigma in relation to the polyad.

A test of McGinley and Charnov's multiple resource pool hypothesis

McGinley and Charnov (1988) propose that seasonal seed weight decline results from optimization of independently varying resource components: in particular, carbon and nitrogen. Canada thistle (Cirsium arvense) (L.) Scop, does not express seasonal seed weight reduction when the number of seeds competing for the plant's resources is reduced by low pollination success. Seeds sampled from thistles treated to high and low pollination regimes were analyzed here for relative investment of carbon and nitrogen. The ratio of these two elements remained constant over the season in both treatment groups. The seasonal decline in mean seed weight displayed by this plant under high pollination is therefore not explainable by McGinley and Charnov's multiple resource pool hypothesis.