Timing of invasive pollen deposition influences pollen tube growth and seed set in a native plant

Invasive plants may threaten the reproductive success of native sympatric plants by modifying the pollination process. One potential mechanism takes place through the deposition of invasive pollen onto native stigmas when pollinators are shared among species. We explore how pollen from the invasive plant Brassica nigra influences pre- and post-fertilization stages in the native plant Phacelia parryi, through a series of hand pollination experiments. These two species share pollinators to a high degree. P. parryi flowers were hand-pollinated with either pure conspecific pollen (the control) or with B. nigra pollen applied prior to, simultaneously with, or following conspecific pollen. Application of B. nigra pollen lowered seed set, with the simultaneous application resulting in the highest reduction. Pollen tube growth was also influenced by the presence of invasive pollen, with fewer conspecific pollen tubes reaching the base of P. parryi styles in treatments where B. nigra pollen was applied prior to or simultaneously with conspecific pollen. The deleterious effects of invasive pollen on native seed set in this study are likely not due to loss of stigmatic receptivity since seed set was less affected when heterospecific pollen was applied prior to conspecific pollen, but may instead involve interactions between interspecific pollen grains on the stigma or within the style. Our study highlights the importance of timing of foreign pollen deposition on native stigmas and suggests that interspecific pollen transfer between native and exotic plants may be an important mechanism of competition for pollination in invaded plant communities.     

Nectar thieves or invited pollinators? A case study of tansy flowers and common house mosquitoes

Mosquitoes are generally considered nectar thieves that do not contribute to the pollination of the flowers they visit. Here we tested the hypothesis that the common house mosquito, Culex pipiens, contributes to the pollination of tansies, Tanacetum vulgare, and possibly the pollination of other members of the Asteraceae (Achillea millefolium, Leucanthemum vulgare, Solidago canadensis). To test this hypothesis, we (1) field-collected mosquitoes probing inflorescences of T. vulgare, A. millefolium, and L. vulgare, and recorded the number and distribution of pollen grains on their bodies, (2) exposed laboratory-reared Cx. pipiens to inflorescences of T. vulgare, A. millefolium, and S. canadensis, and (3) ran pollination experiments with Cx. pipiens and T. vulgare in a greenhouse. We found (1) that 41 of 164 field-collected Cx. pipiens carried pollen, (2) that 48, 34, and 34 % of Cx. pipiens accumulated pollen from T. vulgare, A. millefolium, and S. canadensis, respectively, during floral visits of greenhouse-grown specimens, and (3) that cross-pollination by Cx. pipiens resulted in significant seed set of T. vulgare in pollination experiments. Based on our observations that Cx. pipiens are frequent floral visitors and are able to carry pollen and to induce seed set in T. vulgare, it is clear that Cx. pipiens plays a role in the pollination of T. vulgare, and possibly other members of the Asteraceae.     

Floral divergence and temporal pollinator partitioning in two synchronopatric species of <Emphasis Type="Italic">Vigna</Emphasis> (Leguminosae-Papilionoideae)

Exclusivity of pollinators, temporal partitioning of shared pollinators and divergence in pollen placement on the shared pollinators’ bodies are mechanisms that prevent interspecific pollen flow and minimize competitive interactions in synchronopatric plant species. We investigated the floral biology, flower visitors, pollinator effectiveness and seasonal flower availability of two syntopic legume species of the genus Vigna, V. longifolia and V. luteola, in ‘restinga’ vegetation of an island in southern Brazil. Our goal was to identify the strategies that might mitigate negative consequences of their synchronous flowering. Vigna longifolia and V. luteola were self-compatible, but depended on pollinators to set seeds. Only medium to large bees were able to trigger the ‘brush type’ pollination mechanism. Vigna longifolia, with its asymmetrical corolla and hugging mechanism, showed a more restrictive pollination system, with precise sites of pollen deposition/removal on the bee’s body, compared to V. luteola, with its zygomorphic corolla and cymbiform keel. There was a daily temporal substitution in flower visitation by the main pollinators. Vigna longifolia and V. luteola had overlapping flowering phenology but the densities of their flowers fluctuated, resulting in a seasonal partitioning of flower visitation. The differences in corolla symmetry and mainly the temporal partitioning among pollinators throughout the day and the flowering season proved to be important factors in maintaining the synchronopatry of V. longifolia and V. luteola.     

<Emphasis Type="Italic">Mycoceros antennatissimus</Emphasis> gen. et sp. nov.: a mitosporic fungus capturing pollen grains

Mycoceros antennatissimus gen. et sp. nov. is described and illustrated from pollen grains deposited on the bark of Elaeagnus angustifolia and Platanus?×?acerifolia in Hungary. This fungus is shown to capture pollen grains by its three-dimensional shape. It clearly shows seasonality and appears to be rare. The following factors determine its ecological niche: (1) the availability of fresh Pinaceae pollen grains deposited from the air on the bark of a nearby standing angiosperm tree with (2) water-retaining spongious bark, and (3) rainy weather. Conidia are mainly dispersed by stemflow rainwater, while they hardly become airborne. Direct polymerase chain reaction (PCR) from single conidia made it possible to perform molecular phylogenetic investigation in order to clarify its taxonomic relationship within the Ascomycota.     

Influence of environmental variation on the pollination of the ambophilous sedge <Emphasis Type="Italic">Rhynchospora ciliata</Emphasis> (Cyperaceae)

In typically anemophilous families, there are species, such as Rhynchospora ciliata (Cyperaceae), in which both wind and insects have been registered as pollen vectors (ambophily). However, the contribution of each vector to pollination of ambophilous species can change under different environmental conditions. Therefore, this study aimed to determine the primary pollination system, abiotic or biotic, of R. ciliata, comparing wet and dry seasons. We tested the following hypotheses: (1) in dry months, wind is the main pollen vector of R. ciliata; (2) in wet months, insects will contribute more to the reproductive success of R. ciliata and compensate for low fruit formation by the abiotic vector. Our hypothesis was not confirmed. We found that higher wind speed can favor pollination by wind in R. ciliata even in wetter months. Because insects were less susceptible to environmental variation, they contributed more in dry months when wind speed was low, thus compensating for lower fruit set by wind. High rainfall and humidity can result in faster settling of pollen grains suspended in the air; however, rainfall does not prevent pollination by wind. Since individuals of R. ciliata are located near the edge of the forest, grouped quite close together, and as the inflorescence is located at the apex of the floral scape, wind can act as pollen vector and the inhibiting effects of rainfall can be minimized. The contribution of each pollen vector is important to the reproductive success of R. ciliata and the effectiveness of wind varies with local environmental conditions.     

Pollen morphology of selected crop plants from southern China and testing pollen morphological data in an archaeobotanical study

Identification of pollen grains of cultivated plants is essential in archaeobotanical studies. In this study, we investigated the pollen morphology of 30 species which are representatives of most of the crop plants in southern China, using a light microscope. Our results show that the pollen grains of these species or genera can generally be identified by their size, aperture(s) and exine sculpture. We found that: (1) some cultivated cereals can be distinguished from wild species of Poaceae according to their size frequency combined with their morphological features; (2) the lengths of the equatorial diameter (E), polar axis (P) and the greatest dimension of the lumina (the size of the network sculpturing) of the exine reticulum may be diagnostic features to distinguish some brassicaceous vegetables. There are significant differences between the E and P values among Brassica campestris (B. rapa, oilseed rape, Chinese cabbage), B. alboglabra (B. oleracea var. alboglabra, gai lan, Chinese kale), B. parachinensis (B. rapa var. parachinensis, choy sum, Chinese flowering cabbage) and B. chinensis (B. rapa ssp. chinensis, pak choi), but moderate differences in the longer axis length of the reticulum lumina, which provide potential for identifying species on the basis of pollen grains. We compared the P values and the longer axis length of the lumina of modern specimens of Brassicaceae pollen grains with those of fossil pollen extracted from the Ming-Qing cultural layer in the Fuqikou site at Chongqing, China, and found that the fossil pollen grains of Brassicaceae probably represent vegetable plants related to B. parachinensis. Moreover, we measured the diameters of rice pollen grains from modern paddy fields to assess the pollen size frequency and found that the size range from ~?34 to 38 µm is closely associated with rice pollen in southern China, which can be used to detect pollen signals of human activities in archaeobotanical investigations.     

Pollen ultrastructure in <Emphasis Type="Italic">Aristolochia manshuriensis</Emphasis> and <Emphasis Type="Italic">A. contorta</Emphasis> (Aristolochiaceae)

Pollen ultrastructure has been studied in two relict and rare species of the genus Aristolochia, A. contorta Bunge and A. manshuriensis Kom. (Aristolochiaceae). Both species have inaperturate, spheroidal, sometimes distally monocolpate or distally bicolpate pollen grains. The equatorial and polar axes of pollen grain in A. manshuriensis are 48.5 and 44.0 μm, respectively. The percentage of defective pollen grains in A. manshuriensis is 3.4%. The fossulate, perforated exine is up to 2.3 μm in thickness; the sexine and the nexine are almost equal in thickness. In A. contorta, the equatorial axis of pollen grain is 36.6 μm: the defectiveness percentage, 24.5%. The exine is verrucate, up to 0.3 μm in thickness, while the sexine is two to three times thicker than the nexine. The pollen germination experiments have shown that pollen of A. manshuriensis, in contrast to A. contorta, can germinate in 10–20% sucrose at 22°С. These data and the high percentage of pollen defectiveness in A. contorta indicate that the androecium function in this species is reduced. The reduction of the androecium function is evidenced by a small amount of pollen grains in anthers or empty anthers and a high percentage of defective pollen grains.     

Bee visitors of <Emphasis Type="Italic">Centaurea solstitialis</Emphasis> L. (Asteraceae) in an urban environment in northwestern Turkey

Information on the pollination ecology and floral visitors of the noxious weed Centaurea solstitialis is available for several populations in its invasive range, but limited information is available in its native range, with most studies conducted on the Greek island of Lesvos. Herein, we document the visitation pattern of bees and explore the relationship of bee body size and nectar availability in weedy populations of C. solstitialis from an urban environment within its native range in northwestern Turkey. Studies were conducted at patches of C. solstitialis in abandoned lots at the Uluda? University near the city of Bursa. A total of 41 species, including honey bees, belonging to five families and 19 genera were recorded. Small megachilid and halictid bee species were the most common visitors. Average nectar standing crop volume per floret was low (0.003–0.117 μL) and did not significantly vary throughout the day. Average bee head width significantly correlated with average nectar standing crop volume but did not significantly change throughout the day. Analyses of pollen loads as well as direct observations of bee foraging behavior indicate that a large number of bees visit C. solstitialis, primarily in search of nectar while carrying a large percentage of pollen grains of this plant species on their bodies. These results are similar to previous observations on a non-weedy population of C. solstitialis from the island of Lesvos.     

Specialized pollination by fungus gnats in the introduced population of <Emphasis Type="Italic">Aspidistra elatior</Emphasis>

The monocot genus Aspidistra comprises rhizomatous perennials that are distributed in tropical to warm temperate regions of Asia. Little is known about the pollinators of almost all the species, probably due to the inconspicuous nature of Aspidistra flowers. Nevertheless, the unusual floral morphology suggests biotic pollination, since pollen grains are hidden under each flower’s stigma. Aspidistra elatior has been suspected to have a very peculiar pollination ecology. So far, pollination by mollusks, crustaceans, or collembolans has been suspected. However, a recent study showed that A. elatior is mainly pollinated by species of fungus gnats in Kuroshima Island, southern Japan, which is its natural habitat. Here, we investigated the pollination ecology of A. elatior in Shiga Prefecture, central Japan, which is the introduced population, to reveal whether fungus gnats are also the main pollinator in the introduced population. Our study confirmed fungus gnats pollination in the investigated pollination. Furthermore, the main pollinators (i.e., Cordyla sixi and Bradysia sp.) are the same in both Kuroshima and Shiga Prefecture. Therefore, A. elatior mainly depends on a narrow taxonomic group of fungus gnats for pollination. In contrast, we failed to document any terrestrial amphipods visiting the A. elatior flowers, in spite of a relatively high fruit set in natural conditions. This fact will refute the amphipod pollination hypothesis proposed by previous studies. We consider that A. elatior is pollinated by fungus gnats through fungal mimicry, due to its superficial similarity to mushroom fruiting bodies and strong, musky floral scent.     

Bamboo flowers visited by insects: do insects play a role in the pollination of bamboo flowers?

Relatively little is known about pollination and other aspects of the reproductive biology of bamboos, but wind pollination is assumed to be the rule, at least in woody bamboos. Documenting the reproductive biology of woody bamboos is a complex task due to the long periods of time between flowering cycles, which range from 3 to 120 years. Insects visiting Guadua paniculata and G. inermis flowers were collected in the field. Scanning electron micrographs were taken of the visiting insects. Four species of bees, three from tribe Meliponini (Geotrigona acapulconis, Plebeia frontalis and Trigona fulviventris) and one from tribe Apini (Apis mellifera), along with a syrphid fly (Toxomerus teligera) were found visiting bamboo flowers. Some species of Hemiptera were also found feeding on the flowers, such as Neortholomus jamaicensis (Lygaeidae), or preying on the flower visitors (Apiomerus pictipes (Reduviidae)). Insects visiting bamboo inflorescences may facilitate the release of pollen grains into the air, promoting outcrossing and genetic flow among the individuals of the flowering bamboo populations.     

More than protein? Bee–flower interactions and effects of disturbance regimes revealed by rare pollen in bee nests

Bees and their host flower populations were studied by identifying pollen to species or genus, from trap nests where bees were reared. Rare plant species in bee diets, and disturbance regimes, have not previously been researched and are emphasized here. Two focal bee groups with one species each (Megachilidae and Apidae) were studied in a 500,000-ha tropical reserve in the Yucatán Peninsula nine complete years. The number of rare or major pollen species in nests had no statistical correlation; thus, rare pollen analysis complements study of major brood provisions. We found most nests (87 % Megachile zaptlana, 93 % Centris analis) contained rare pollen; only 12 % of the 438 nests contained major pollen alone. Rare pollen sometimes indicated an energy source rather than a scarce protein resource. Trichome nectar of Cydista, along with Ipomoea and Caesalpinia, were nectar sources. Malpighiaceae, despite lacking nectar, often provided the complete Centris diet. Considering rare pollen, only Centris responded to drought, or competition from immigrant honeybees. Neither bee responded to hurricanes. Drought years coincided with low bee populations; Centris nests contained more rare species then. After feral Africanized honeybees colonized, Centris had more major species and fewer rare. Some herbarium vouchers from the study area contained exotic pollen, demonstrating in situ floral contamination and ecological generalization by bees, but this rarely occurred in plants found among the bee diets. Megachile and Centris responded differently to competition and resource scarcity, and plausibly evolved under different disturbance regimes, yet appeared well adapted to hurricane disturbance.     

Differentiation of the pollen size in five representatives of <Emphasis Type="Italic">Taraxacum</Emphasis> sect. <Emphasis Type="Italic">Palustria</Emphasis>

Measurements of the pollen size in 5 species of Taraxacum sect. Palustria at three levels of ploidy: 2n = 3x = 24 (T. paucilobum), 2n = 4x = 32 (T. vindobonense, T. trilobifolium), 2n = 5x = 40 (T. mendax) and one taxon of unknown number of chromosomes 2n = ? (T. portentosum) are presented in this paper. Obtained results indicate a lack of distinct positive correlation between the pollen size and ploidy in the studied group of plants. Distinct relationship was, however, found between ploidy and the range of pollen size and shape variability. Most variable were the pollen grains of triploid T. paucilobum and the least — those in pentaploid T. mendax. Ranges of pollen variability in tetraploid T. trilobifolium and T. vindobonense and in T. portentosum of unknown number of chromosomes showed intermediate values.     

<Emphasis Type="Italic">Cannabis</Emphasis> is indigenous to Europe and cultivation began during the Copper or Bronze age: a probabilistic synthesis of fossil pollen studies

Conventional wisdom states Cannabis sativa originated in Asia and its dispersal to Europe depended upon human transport. Various Neolithic or Bronze age groups have been named as pioneer cultivators. These theses were tested by examining fossil pollen studies (FPSs), obtained from the European Pollen Database. Many FPSs report Cannabis or Humulus (C/H) with collective names (e.g. Cannabis/Humulus or Cannabaceae). To dissect these aggregate data, we used ecological proxies to differentiate C/H pollen, as follows: unknown C/H pollen that appeared in a pollen assemblage suggestive of steppe (Poaceae, Artemisia, Chenopodiaceae) we interpreted as wild-type Cannabis. C/H pollen in a mesophytic forest assemblage (Alnus, Salix, Populus) we interpreted as Humulus. C/H pollen curves that upsurged and appeared de novo alongside crop pollen grains we interpreted as cultivated hemp. FPSs were mapped and compared to the territories of archaeological cultures. We analysed 479 FPSs from the Holocene/Late Glacial, plus 36 FPSs from older strata. The results showed C/H pollen consistent with wild-type C. sativa in steppe and dry tundra landscapes throughout Europe during the early Holocene, Late Glacial, and previous glaciations. During the warm and wet Holocene Climactic Optimum, forests replaced steppe, and Humulus dominated. Cannabis retreated to steppe refugia. C/H pollen consistent with cultivated hemp first appeared in the Pontic-Caspian steppe refugium. GIS mapping linked cultivation with the Copper age Varna/Gumelni?a culture, and the Bronze age Yamnaya and Terramara cultures. An Iron age steppe culture, the Scythians, likely introduced hemp cultivation to Celtic and Proto-Slavic cultures.     

Morphological variation in pollen grains of <Emphasis Type="Italic">Mucuna</Emphasis> (Leguminosae): new biogeographic and evolutionary patterns

Mucuna comprises 105 species with an overall pantropical distribution and is divided into three subgenera: M. subg. Mucuna, M. subg. Stizolobium and M. subg. Macrocarpa. Although phylogenetic studies have supported the occurrence of three main clades, evolutionary relationships among them are not fully resolved. The objective of this study was to examine pollen grain morphology from representatives of all three subgenera and map these onto the phylogenetic trees generated by analysis of other characters. Pollen grain surface, form, size, and aperture number were compared. A Bayesian inference tree using matK sequences was constructed. The results indicate that the representatives of M. subg. Macrocarpa have the smallest pollen grains in the genus (a synapomorphic character here identified for this subgenus) and that species of subgenus Mucuna (those with umbelliform inflorescences) have the largest pollen grains. Additional morphological diversity of the pollen grain surface was noted: reticulate and/or micro-reticulate (in all three subgenera), perforate, gemmate or verrucose (only in M. subg. Mucuna). For all studied taxa, the pollen grains are triaperturate, except for two species of M. subg. Mucuna, which have tetraperturate pollen. The phylogenetic tree obtained using the matK marker resolved M. subg. Stizolobium as the earliest diverging lineage in Mucuna. Based on this phylogeny, a reticulate ornamentation pattern of the pollen surface may represent the ancestral state for the genus, while the larger pollen size and the foraminate, gemmate, and verrucose ornamentations are derived characteristics within the genus. These putative derived ornamentations have been observed only in neotropical species.     

Pollen morphology of selected species of the genera <Emphasis Type="Italic">Chrysodracon</Emphasis> and <Emphasis Type="Italic">Dracaena</Emphasis> (Asparagaceae,subfamily Nolinoideae) and its systematic implications

Pollen grains of 3 species from the genus Chrysodracon and 20 species from the genus Dracaena were examined by light, scanning electron and fluorescence microscopy. The basic shape of the pollen grains is subprolate and prolate, but prolate-spheroidal pollen grains may also be found. Pollen of Chrysodracon and Dracaeana is dispersed as monads, rarely as dyads. In terms of size, the pollen grains studied were classified as medium-sized and large. There are two different types of apertures: monosulcate and monoulcerate in Dracaena and monoulcerate in Chrysodracon. The surface of the non-apertural areas is psilate-perforate, irregularly folded, microreticulate and fossulate. Ornamentation of the apertural region is microreticulate, microreticulate-baculate, baculate, psilate-perforate, psilate-perforate-verrucate, granulate and irregularly folded. Irregular perforations are present, and the wall structure is tectate-columellate. Our results suggest that some species of Chrysodracon and Dracaena may be separated based on their pollen grain micromorphology on the distal region.     

Changes in the Mediterranean pine forest: pollination patterns and annual trends of airborne pollen

In some areas, forests are being affected in diverse aspects such as structure, composition and biodiversity showing an increase or a decrease in the growth rates. Pinus is one of the most dominant genera in the forests of the Northern Hemisphere. This study analyzes the pine pollination patterns in 30 locations of Spain with an average of 21-year dataset. The aim is to evaluate possible changes in flowering intensity as well as in annual pollen production trends, according to the airborne pollen patterns. Annual Pollen Indices show three threshold values: (1) over 4000 grains per year in Catalonia, the Central System Mountains and Ourense (Galicia), (2) between 4000 and 1000 grains in central-south Spain and in the Balearic Islands, and (3) under 1000 in eastern Spain, Cartagena and the Canary Islands. Airborne pollen patterns were also influenced by Pinus species: The species located in the littoral and low land areas pollinated in the first pollination phase, from February to April, and the mountain pine species did in the second one, from April to June. The statistical analyses reveal increasing significant trends in 12 sites and significant decreasing trends in two. The Pinus flowering intensity is showing an earlier start and a delay in the end of the pollination period, thus a longer period of pollen in the air. This study suggests that the aerobiological monitoring is an interesting bio-indicator of changes happening in Pinus landscapes, and therefore explains the vulnerability of this genus in Spain.     

Embryological peculiarities of interspecific hybridization in <Emphasis Type="Italic">Pinus sibirica</Emphasis>

Cytoembryological research of the ovules in experiments with interspecific hybridization of Pinus sibirica (pollination be the pollen of P. koraiensis, P. armandii, P. parviflora, P. strobus, P. hokkaidensis, P. wallichiana, P. monticola, and P. сembra) revealed that the development of megagametophytes occurred in them by the usual scenario and resulted in the formation of mature archegonia. Pollen successfully germinated on the nucellus of ovules. However, disturbances were observed in the process of male gametophyte development, and pollen tubes on the nucellus were not visible by the period of archegonia maturation. Fertilization was usually absent. The development of embryonic channel is determined by egg cell maturity. The only exception was the variant of the controlled pollination of Pinus sibirica × P. сembra, in which the embryo has been formed.     

First aerobiological study in Mediterranean part of Croatia (Dalmatia): pollen spectrum and seasonal dynamics in the air of Split

The aim of this study was to investigate aerobiological dynamics of pollen in the Mediterranean part of Croatia in the air of the city of Split. Pollen monitoring during the period from 2005 to 2013 was performed using a Hirst volumetric trap. Among the identified pollen of 50 taxa, 21 were allergenic. The average annual pollen index was 33,513. Three pollination seasons were established: early winter season dominated by tree pollen, spring–summer season dominated by herbaceous plants and summer–autumn season with lower amounts of Parietaria and Cupressaceae pollen. According to the abundance, the main taxa were: Cupressaceae, Parietaria/Urtica, Pinus, Quercus, Olea, Carpinus/Ostrya, Poaceae, Platanus and Ambrosia. The annual pollen index together with the daily maximum concentrations showed an upward trend for selected taxa during the study period. The highest monthly pollen index and the highest biodiversity were recorded in April and the lowest during the late autumn and winter months. The pollen calendar created for the city of Split confirmed Mediterranean features of the pollen spectrum. The longest pollen seasons were recorded for Cupressaceae, Parietaria/Urtica and Poaceae pollen types. The correlations between pollen concentrations and meteorological parameters were analyzed. The correlations between pollen concentrations and temperature were positive, while the humidity and the precipitation mostly showed negative influence.     

Morphology and variability of pollen of the genus <Emphasis Type="Italic">Spiraea</Emphasis> L. (Rosaceae) in Siberia and the Far East

Pollen of 12 species of the genus Spirea L. growing in different regions of Siberia and the Far East was investigated. The ultrasculpture of pollen grains is described. On the basis of aperture morphology and exine sculpture, pollen grains are typified, with key indices given for their identification. The species of the Spiraria section are distinguished by large grains. Pollen grains of S. media and S. alpina considerably vary in size. The level of natural polymorphism of palynological indices has been established.