Amount Of Pollen Grains Research Articles

Taphonomie des plantes et interprétations paléoécologiques. Une synthèse

The taphonomy is a powerful and requisite tool for environmental reconstructions of ancient plant communities. Necrobiotic processes, which lead to the production of plant fragments, inform us on fossil plant physiology. Among the processes that can be drawn from necrobiotic studies is the retention of leaf organs on plants, the relative quantity of pollen grains produced by different fossil species or the significance of wildfire dynamics in ancient plant communities. Biostratinomy examination is a fundamental tool for elucidating fossil plant habitats. Numerous experimental data allow paleobotanists for evaluating the role of transport in the origin of fossil assemblages. Autochthonous plant assemblages, which are characterised by the preservation of fossil rooting structures, are relatively rare in the nature. In consequence, the search for palaeoecological information from parautochthonous to allochthonous assemblages has been a priority in taphonomy. As a result, taphonomic models have been elaborated in well-known sedimentological contexts, such as small lacustrine deltas, which allow for the distinction between riparian or perideltaic plant remains. Lithospheric processes modify plant debris after burial. The differences in the degrees of transformations (or alterations) during the diagenesis provide for information about the original morphology and biochemical composition of the plant tissues, which are also paleoecologically useful. Thus, amber diagenesis modifies resin biochemistry into new molecules that are still informative from the chemotaxonomical point of view.

Effects of forest fragmentation on male and female reproductive success in Cestrum parqui (Solanaceae).

In this paper we evaluate the effects of forest fragmentation on male (pollen removal, pollen load, and pollen tubes) and female reproductive success (fruit- and seed-set) of Cestrum parqui, a self-incompatible, pollination-specialist plant species. We also measure focal individual conspecific density to account for possible density-related effects that could influence the response variables. We calculate an index which incorporates male and female fitness and gives an integrated assessment of overall reproductive success. Forest fragmentation strongly affected the amount of pollen grains on stigmas and number of pollen tubes as well as seed-set, decreasing from continuous forest to small forest fragments, whereas focal individual conspecific density failed to explain any of the variability for the studied variables. Declines in overall reproductive success (i.e. male and female) in small forest fragments are ascribed to decreases in both the quality and quantity of pollination. Self-incompatibility coupled with a specialist pollination system may be particularly important traits determining the negative fragmentation effects observed in C. parqui. Logarithmic regression models described the behaviour of the variables along the fragmentation size gradient, allowing us to detect a threshold below which the effects of fragmentation begin to negatively affect reproductive success in C. parqui. Our results emphasize the importance of evaluating both components of the total plant fitness, as well as including simultaneously several aspects of pollination and reproduction processes when assessing the effects of forest fragmentation on plant reproductive success.

Contribution to the study of fungal spores in honeys of Galicia (NW Spain)

We analysed 30 samples of Galician honey with the aim of quantifying and identifying the fungal spores contained in them. Using an optical microscope, we could identify 40 different types, among them Cladosporium, Penicillium/Aspergillus and the Basidiospores, which were identified in more than 80% of the samples. We calculated the relationship between fungal spores and amount of pollen grains in the samples. The maximum values were obtained in samples 21 (more than 208/100 grains of pollen) and 5 (153 spores/100 grains of pollen).

Long-duration feedings and caste differentiation in Bombus terrestris larvae

The duration of feedings received by Bombus terrestris larvae was studied using video-recordings. In the last days of development all larvae received feedings mainly of long duration. Worker larvae of the third brood received significantly longer feedings than worker larvae reared in the other broods. Throughout the development queen larvae and worker larvae received feedings of similar duration. Male larvae received shorter feedings than both kinds of female larvae. Therefore, the duration of feedings seems to be associated to the sex and stage of development of the larvae.¶The causes of the long-duration feedings seem not to be related to the amount of food provided, workers' age and size, to the workers' abdominal contraction or to the amount of pollen in the larval food. Perhaps the feeding duration is caused by the viscosity of the food, which is a consequence of the presence of pollen grains, sugar and glandular material. Although the precise amount of pollen was not measured, the differences in colour showed clearly that the larval food samples contained variable quantities of pollen grains. Some of the samples did not contain any pollen at all.¶It is suggested that the duration of feedings may be related (among other factors) to the presence of glandular material (proteins and enzymes) which is added to the larval food. This could be especially important for queen larvae in the last phase of their development. Because they have a long development and are fed with a high frequency they might receive large amounts of these substances. This could help them to grow more efficiently using a relatively smaller amount of pollen than expected.

Pollen production of the genus Cupressus

The study of potential pollen emission in the genus Cupressus was carried out in the city of Córdoba (Spain). Pollen production of 227 trees of the represented species of Cupressus in the area (Cupressus sempervirens, C. macrocarpa and C. arizonica) was studied by counting the number of pollen grains per flower, the number of flowers per branch, and the number of branches per m2 of surface area. Total surface area was estimated by considering the shape of the tree as a cone and estimating the average height and radius of each species. Results indicated that there was little variation in the number of pollen grains produced by a flower within each species. Equally, there were few differences in the number of grains per flower among the species, although C. arizonica had slightly fewer than the other species because it possessed fewer stamens per flower. However, there were clear differences in the number of flowers per branch, with C. macrocarpa having the highest floral density, considerably lower in C. arizonica and even lower in C. sempervirens. All of this indicates that the pollen contribution of C. macrocarpa to the atmosphere is far greater than that of C. arizonica and C. sempervirens. The results indicate a different potential emission in each species, and this must be taken into account when determining the quantity of pollen present in the atmosphere. The maximum amount of pollen grains that one individual can spread is provided in this study and would provide useful data in the development of an airborne forecasting system.

Genetic Variability in Flower Attractiveness to Honeybees (Apis mellifera L.) within the Genus Citrullus

Fruit and seed set in insect-pollinated agricultural crops rely primarily on honeybees because of their ease of management and transportation. In many fruit and vegetable crops, the number of bee visitations can be the limiting step in obtaining optimal yield. Increasing the attractiveness of flowers to honeybees could, therefore, provide a useful means of improving fruit yield and seed production. Genetic variability in attractiveness to honeybees was found within the genus Citrullus. The number of daily visits per flower ranged from six to 12 among cultivars. Moreover, most of the visits to the more attractive cultivars occurred in the first hour of bee activity, whereas visits to the less attractive cultivars started later in the morning. A positive relationship was found between the frequency of bee visitations and seed number per fruit. Analyses of floral attributes indicated no genetic variability in flower size, amount of pollen grains, or nectar volume; however, differences were observed in the concentration of sucrose and total sugars in the nectar. A positive relationship was found between attractiveness to bees and nectar sugar concentration, suggesting that this characteristic is one of the parameters responsible for variability in attractiveness to honeybees.

A comparative study of the efficiency of bumble bees and an electric bee in pollinating unheated greenhouse tomatoes

SummaryThe efficiency of an electric bee in pollinating tomatoes grown in an unheated greenhouse was compared with that of bumble bees. Two years of experiments show that under the moderate climatic conditions of autumn and early winter, the two methods had similar effects on fruit set, seed number, fruit size and yield. Under more severe winter conditions, however, bumble bees were more efficient than the common agricultural practice of using the electric bee 2–3 times a week. Even in the presence of relatively low amounts of pollen grains per flower, a high percentage of fruit set was obtained by the bees. Under these adverse climatic conditions, flower vibration with the electric bee and with bumble bees achieved equal degrees of fruit set, only when the electric bee was operated every day. It may be concluded, therefore, that bumble bees are efficient pollinators as long as the flower organs are functional and a minimum number of pollen grains is available. For achieving similar pollination efficacy with an electric bee, one should adjust the frequency of its use according to the circumstances, with daily operation under unfavourable conditions.

Pollination and fruit growth models for studying the management of kiwifruit orchards. I. Models description

Two models simulating pollination and fruit growth in kiwifruit orchards are described. They are part of a global biotechnical model which aims at studying the effects of planting scheme, pruning intensity and thinning patterns on fruit number and size. The pollination model calculates the amount of pollen grains deposited on pistillate flowers, according to the position of the female vine and the date of anthesis. On this basis, the number of ovules that develop into seeds, and the success of fruit set given this number, are simulated in a stochastic manner. In the fruit growth model, we assumed that the effects of seed number and crop load act at any time in a multiplicative manner on a reference relative growth rate. These two models make it possible to simulate the between-fruit variation in fruit size.

Pollen dynamics of bumble‐bee visitation on Echium vulgare

1. We quantified pollen deposition on the stigma, pollen removal from the anthers and pollen losses in Echium vulgare, visited by workers of Bombus terrestris under controlled conditions. We used dye as a pollen analogue. Bumble‐bees were trained to visit a sequence of non‐emasculated flowers to estimate pollen carryover and to visit individual flowers to estimate pollen loss. 2. Carryover of pollen grains and dye particles between flowers was similar, which justifies using dye as a pollen analogue. On average 93·8% of the dye particles on the bee were carried over to the next flower. Only a small fraction of the pollen grains was deposited on the stigma (0·15%). A much larger fraction (6·1%) was lost in another way: passively during flight, through grooming or on floral parts other than the stigma. The bees removed 44% of the pollen grains from a fresh flower and 50·3% of this removed pollen adhered to the bee. 3. We predict that, using the parameters mentioned above, during a single visit to a newly opened flower, a bee collects an amount of pollen grains which will bring about 60% geitonogamous self‐pollination in the next flower visited. The expected percentage of self‐pollination is considerably less if bees visit flowers that have been visited before.

Unifloral Honeys: Chemical Conversion and Pollen Reduction

Abstract Physico-chemical and pollen analyses were made of unifloral samples of nectar, crop content and honey. The samples were obtained by carrying out cage experiments exclusively with one plant species. The investigations of four plant species are presented: Centaurea montana, Coriandrum sativum. Euphorbia lathyris and Rubus idaeus. During the conversion of nectar to honey its chemical composition changes. The changes in carbohydrate composition cannot be explained by those enzymes described as specific for honey. During the period of time when the bees are working on gathered nectar, the chemical components of the honey, whose origin is the secretion from the bees, is increasing, while the amount of pollen is decreasing. There are negative correlations between the quantity of pollen grains and both enzymatic activity and the amount of proline. With respect to the botanical origin it is suggested that the absolute amount of pollen should be determined and compared with the chemical analysis of the honey.

Why Plants can be too Attractive -- A Discussion of Measures to Estimate Male Fitness

A direct measurement of paternity (e.g. with genetic markers; Devlin & Ellstrand 1990) is time consuming and only feasible in small populations. Male fitness is, therefore, nearly always 'measured' indirectly as the number of pollinator visits or as the amount of pollen grains removed from the anthers although in a few cases pollen export to other plants was estimated with pollen analogues (Waser & Price 1982; for a recent discussion on estimating male fitness in plants see Stanton et al. 1992). Pollen grain removal is assumed to be closely related to pollen export to other plants and hence to male fitness. The step from pollen removal to pollen export is, however, problematic. We will show that the assumption that pollen grain removal is closely related to pollen export to other plants may not be true, especially if plants with different attractiveness to pollinators are considered Pyke's (1991) statement in a recent letter to Nature reflects the general view of the relationship between a plant's attractiveness to pollinators and its fitness: 'All else being equal, a plant that produces more nectar will have a higher average nectar-standing crop per flower when visited by a pollinator, and will therefore have on average more flowers probed during each visit by a pollinator, receive and transmit more pollen, and produce more seeds (its own and those of other plants that it has fathered).' Because seed number per plant (female fitness) is often not limited by pollination, this view is particularly relevant to the number of seeds a plant has fathered (male fitness). In contrast to general belief, we shall show that plants that provide a higher reward and have flowers that are most frequently visited are not necessarily the most fit: plants can be too attractive even if no energetic costs are involved in nectar production. Increasing attractiveness to pollinators leads to more visits per flower and consequently to more pollen removal from the anthers (e.g. Pyke 1981; Waddington 1981; Zimmerman 1983) but, because of increased geitonogamy, this increased pollen removal will not always lead to higher pollen export to other plants (Charlesworth & Charlesworth 1987). Modelling the effects of attractiveness to pollinators on pollen export

Forest Fragmentation, Pollination, and Plant Reproduction in a Chaco Dry Forest, Argentina

In a fragmented, dry subtropical forest in northwestern Argentina, we compared pollination levels, fruit set, and seed set among small (<1 ha) forest fragments, large (>2 ha) fragments, and continuous forest in 16 plant species representing a wide range of pollination systems, breeding systems, and growth forms. For three species, Prosopis nigra (Mimosoideae), Cercidium australe (Caesalpinoideae), and Atamisquea emarginata (Capparaceae), the three treatments were replicated across four sites; we achieved less replication for other species. Because comparisons between forest and fragment populations for different species took place in different sites, however, by treating all 6 species as a unit we lessened the potential bias of confounding site effects and could evaluate the overall impact of fragmentation. Significant or marginal (P < .10) fragmentation—related declines in number of pollen tubes per style, fruit set, and seed set occurred in 9 of 16, 5 of 15, and 3 of 14 species, respectively. Overall, significant or nonsignificant declines occurred in 81% (pollen tubes), 73% (fruit set), and 79% (seed set) of the species. In all cases these proportions were greater (P < .06) than the null binomial expectation of a 1:1 ratio of increases to decreases. Breeding system did not explain sensitivity to fragmentation: the magnitudes of declines in pollen tubes, fruit set, and seed set were virtually indistinguishable between self—compatible and self—incompatible species. At least 4 of the 10 self—incompatible species, however, were heavily visited in small fragments by Africanized honey bees, which may have compensated for a decline in visits by native pollinators. The exact nature of responses varied among plant species. In some, the absolute quantity of pollen grains transferred to stigmas decreased with fragmentation, and sometimes this was reflected in reduced fruit or seed set. In Cercidium, Prosopis, and Atamisquea, the quality of the grains transferred apparently changed: number of pollen tubes produced per pollen grain on the stigma declined with increasing fragmentation, and at least in the latter two species seed production declined as well. Overall, levels of pollination and seed production undoubtedly integrated many idiosyncratic effects of fragmentation on particular plant and animal populations, and indicated that “community health” of fragments suffered in comparison with that of continuous forest. Median decreases in pollination levels and seed output from forest to fragments approached 20%. The impact of these declines on plant recruitment is less clear, however, because cattle grazing and trampling of seedlings and saplings in fragments may constitute a much more serious short—term conservation problem.

Outdoor and indoor pollen grains in sofia

Abstract For frequently two years a period of the range and quantity of pollen grains in the most inhabited rooms of each of 4 dwellings in Sofia was studied, together with the outdoors air pollen spectra. Changes in the health status of the inhabitants affected by pollinosis were recorded at the same time. The characteristic pollen taxa, pollen interference periods and the way sensitive patients were affected were evaluated.

Early-onset hay fever in Israeli children.

In order to investigate the influence of climate and vegetation on the age of onset and clinical picture of hay fever (HF), we examined 116 children with typical HF living in a single climatic area: fifty-four were from rural farming settlements and sixty-two from towns and cities. Overall age of onset was low; 72% of rural children developed HF between the ages of 2 years and 4 years compared to only 24% of urban children (P less than 0.005). At the same time, 57% of rural children had positive skin tests to more than three pollen extracts out of nineteen allergens tested, compared to 19% of urban children (P less than 0.005). There were no significant differences between the rural and urban groups with regard to the incidence of asthma as part of their HF, nor were there differences in total IgE levels. The results of this study suggest that Israeli children develop hay fever earlier than generally reported in the literature, and that this is most marked in the rural areas. This can be explained by their specific environment, which consists of a basically dry, desert-like climate where lawns, crops and trees are extensively irrigated, leading to the dissemination into the environment of large amounts of pollen grains, which are not washed away because of the lack of rain.

The effects of water stress and genotype on the dynamics of pollen-shedding and silking in maize

The effects of exposure to water stress at three developments stages (start of tasseling, start of pollen-shedding, and silking) on the viability of pollen and the dynamics of flowering in maize ( Zea mays L.) were examined using a single genotype. Viability was not affected by stress at any stage, but alterations in the dynamics of flowering reduced the number of pollen grains available for pollination of the last ears to silk within the stressed populations. In a second experiment the effects of stress at the start of pollen-shedding on the availability of pollen during the presentation of silks was studied in a set of six cultivars. There was considerable variability between cultivars in the number of pollen grains produced per tassel, and water stress decreased the quantity of pollen grains harvested. There was a strong association between pollen availability and kernel number in the apical ear (as a proportion of control values). Two effects of stress on pollen availability were distinguished: a reduction in the duration of exposure of silks of the apical ear to pollen, and a fall in the rate of pollen production during the period in which receptive silks were present. The relative importance of these effects in determining pollen availability varied with cultivar.

石狩平野南東部に分布するしお見層および下安平層の花粉学的研究

In the present paper, a pollen analytical study was made on 55 samples obtained from the upper member of the Shimoabira Formation, and the lower and the upper member of the Shiomi Formation belonging to the late Pleistocene in SE Ishikari Plain, Hokkaido, and palaeoenvironmental changes were discussed, being based on three pollen zones or divisions recognized, which were comparable to the three geological divisions mentioned already.Successive palaeoenvironmental changes are suggested from the pollen diagrams that the climatic condition have changed from warm to cool temperature condition. This thermal change, however, was considered to be a change within the Fagus crenata=Sasa Class in a phytosociological sense. Thus, the palaeoclimatic environments were possibly corresponding to the present climatic environments of the Kuromatsunai Area which is a significant demarcation area separating the Cool Temperate vegetation with Fagus crenata from the Cold Temperate vegetation with Quercus crispula, P. glehnii and P. jezoensis but lacking F. crenata in natural habitats in Hokkaido. The conclusion mentioned above was abstracted from the following: (1) gradual increasing of the ratio Picea/Abies from older periods to recent periods or from the pollen zone III to the zone I, although more or less irregular fluctuations were recognizable often in pollen diagrams, (2) conspicuous and nearly constant mixture of Picea, Tsuga, Abies, Cryptomeria, Pterocarya, Fagus, Quercus, etc. which was believed to be a proof of long existence of the Mixed forest, not pure boreal coniferous forests like the Taiga nor exclusive Temperate Summergreen forests, and (3) drastic decrease of maritime Chenopodiaceous pollen grains in the sample number just above the lowest sample number of the upper member of the Shimoabira Formation, showing palaeoenvironmental change from the high sea-level condition to low sea-level condition.Two exceptional pollen diagrams were shown: Ka-II' and Ni-I'. The pollen diagram of Ka-II' was considerably different from diagrams of the remaining 4 diagrams and was characterized by a tendency with increased amount of pollen grains of Picea and Cryptomeria, even though a species list of pollen grains was very similar to the remainder. The diagram of the lower part of Ni-I' pollen zone was characterized by complete lack of conifer grains. Elucidation of these exceptional cases was not tried in the present discussion and remained to be solved.Through the Shiomi Formation Period, it was supposed that bog vegetations were constantly developed; one is Picea-Sphagnum bog and the other is Alnus-Cyperaceae bog. As a result of the present study, it was shown that constant and extensive spreading of bog was considered to be the most characteristic palaeoenvironmental feature of the Shiomi Formation. Thus, the authors proposed that the Shiomi Formation Period should be called“Shiomi Bog Period”in pollen diagrams. This Period was contemporary with the Biraotori Bog Period and dated a period from the Riss-Wurm Interglacial to WI Subglacial Period.

The Food of the Drone Larvae1

The drones are the males of the honeybee, produced from unifertilized eggs, and reared in cells larger than those used for rearing workers. The drone larvae grow larger and during their development receive considerably more food than do the worker larvae. According to Stabe (1930) the maximal weight attained by the drone larvae is 384.0 mg. as compared with 159.1 mg. for worker larvae. Planta (1888) weighed the food of larvae from drone cells and found an average of 9.6 mg. of food per cell, while there was only 1.7 mg. of food per worker cell. Values given by Aeppler (1922) correspond quite closely to those of Planta. Planta (1888) also called attention to the fact that the food of drone larvae more than 4 days old contained large amounts of pollen grains (15,000 pollen grains per mg.) while the food of worker larvae of the same age was almost pollen-free. The food of both worker and drone larvae under 4 days old was pollen free.