Clumps Of Pollen Research Articles

Cretaceous-Paleocene Patagonian Spore and Pollen Clumps: New Findings, Alternative Explanations, and Opened Questions

Cretaceous-Paleocene Patagonian Spore and Pollen Clumps: New Findings, Alternative Explanations, and Opened Questions

Palaeoecological changes from 580 to 1220 CE from the Indo-Burma region: A biotic assessment from the Barak Valley of Assam, northeast India

The pollen and diatom analyses of soil samples from a 80-cm deep sedimentary core from the Barak valley of Assam provides an explicit understanding of vegetation, climatic and ecological change in the Indo-Burma region from 580 CE (1370 cal. years BP) to 1220 CE (730 cal. years BP). The impact of the Medieval Warm Period (MWP) has been well documented from palynological records. Based on changes in vegetation succession, the Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) during four pollen phases CP (1–4) were calculated using the coexistence approach. Between 580 and 760 CE (pre-MWP), the occurrence of major riparian tree pollen taxa like Barringtonia, Duabanga and Sapotaceae along with scanty diatom occurrence indicates a warm and relatively less humid climate attributable to a weak Southwest monsoon with low seasonality. This changed to a strikingly enhanced seasonality from 760 to 940 CE (beginning of MWP), indicating the establishment of the dense forest around the lake under increased warm and humid climatic conditions. During the interval from 940 to 1220 CE (MWP peak), the average values of maximum MAT and MAP were the highest recorded (≈31 °C and ≈2250 mm, respectively). From 1220 CE onwards (post MWP), the decline in arboreal pollen coincides with an exponential rise in cereal pollen clumps and shrubby pollen like Melastoma, Clerodendrum and Justicia adhatoda along with the presence of anthropogenic indicator diatom taxa like Ulnaria ulna and Gomphonema indicating increased landscape changes due to human impact under a relatively less warm and humid climate. In many parts of the world, regional data coverage pertinent to the MCA warming has now reached a point which allows compiling palaeoclimate maps for well-defined time intervals. In this direction, future studies need to address the major climatic data gaps from the Indian sub-continent especially during the last millennia.

Neanderthals really did bury their dead

Archaeologists in Iraq have discovered a new Neanderthal skeleton that appears to have been deliberately buried between about 60,000 and 70,000 years ago. The find reinforces earlier claims that this extinct type of human used graves for their dead. Excavations of Shanidar cave in northern Iraq in the 1950s and 1960s yielded the remains of 10 Neanderthals, including one dubbed Shanidar 4, which was found with clumps of pollen--suggesting the body had been deliberately placed in a grave and flowers scattered on it. Here, Marshall discusses an analysis by Emma Pomeroy at the University of Cambridge and her team of a new set of remains from the cave: the upper half of a Neanderthal. They found multiple lines of evidence that this Neanderthal was deliberately buried, including that fact that the sediment layer around the body is visibly different to the layer below. What is more, the sediment below the body shows signs of having been disturbed by digging.

Scanning electron microscope and light microscope investigations of pollen from an atypical mid-Eocene coal facies in Stolzenbach mine (PreußenElektra) near Borken (Kassel, Lower Hesse, Germany)

Light microscope (LM) and scanning electron microscope (SEM) investigations of palynomorphs from a mid-Eocene coal lens at the Stolzenbach brown-coal mine (“Borken brown coal field”) yielded a remarkable microflora assemblage, with 76 pollen and spore taxa, dominated by monolete fern spores. Numerous pollen and pollen clumps of Myrtaceae and Salicaceae might represent in-situ growth of these families, which were associated with pollen of Aralia-type, Eotrigonobalanus spp., Flueggea-type, Nyssa-type, three Pentapollenites taxa, and Spinaepollis spinosus, plus many others. Ericaceae such as Erica-type, Kalmia-type, and Rhododendron-type pollen are described from here for the first time; the last represents the earliest known occurrence of the genus. Additionally, five tropical south Asian Sapotaceae taxa (Mimusopeae- and Isonandreae tribes), and one tropical South American bombacoid Eriotheca-type occur. Several previously undescribed pollen taxa for the Eocene have been found; some are amongst the oldest examples of these pollen taxa: the Nuphar-type pollen represents the earliest occurrence in Europe and, whilst the Acalypha-type and Trochodendron-type are the oldest pollen occurrences in general, the Viburnum-type, affiliable to Viburnumclemesiae probably represents a tropical south Asian lineage.

Studies on pollen deposition pattern in relation to modern vegetation of flood prone region in Assam, India

This paper presents a palynological dataset on Pashumara Wetland and Ranga Reserve Forest to differentiate flooded and non–flooded area in relation to existing vegetation in Assam. Study reveals that the palynoassemblage in Pashumara Wetland is an admixture of arboreal local and extra–local taxa and not fully matches with present vegetation. The various pollen distributions were observed in continuation to study sites and confirmed that pollen deposition pattern in wetland depends on parent plant growth, flood activity and surrounding vegetation. Presence of broken pollen is indicative of long distance transportation under a fluvial environment. The palynoassemblage of Ranga Reserve Forest located in non–flooded area to display modern pollen and vegetation relationship and identification of local arboreal taxa in the region. The main forest elements include Syzigium, Lagerstroemia and Emblica in the palynoassemblage are suggestive of presence of tropical deciduous forest under warm and humid climate. Pollen clumps in the palynoassemblage signifies their local origin and entomophily. This generated palynodata could be precisely utilized to distinguish flooded and non–flooded area and to interpret palaeovegetation and past climate changes in relation to palaeoflood episodes by the analysis of wetland core from the region and to correlate other tropical flood prone region of the globe.

Some cytological, ecological and evolutionary aspects of pollination

Different types of pollen dispersing units are described. The pollen of angiosperms may be dispersed in monads, tetrads, polyads, massulae or compact pollinia. The monads and tetrads may form larger clumps of pollen with the aid of the following substances: a) pollenkitt, a product of <em>in situ</em> degeneration of the tapetum; b) tryphine, a product of tapetal extra situm degeneration, found only in <em>Cruciferae</em>; c) elastoviscin, a highly viscous product of the degeneration of a limited number of tapetal cells, found only in certain <em>Orchidaceae</em>; d) viscin threads or sporopollenin filaments arising from the pollen exine. The number of pollen grains composing the clumps depends on pollen diameter and the cohesive forces holding the pollen grains together. The various types of pollen dispersing unit are discussed in relation to the type of pollination and number of ovules per ovary.

Pollen grain sporoderm and types of dispersal units

The pollen of gymnosperms and angiosperms may be dispersed in monads, tetrads, polyads, massulae or compact pollinia. The monads and tetrads may form larger clumps of pollen because filiform pollen is tangled while other kinds of pollen can be glued by means of different devices. Exine and intine modify their structure to adapt to pollen dispersing units, exine in some cases can be absent. An additional layer, a thin callosic wall, can be present in some species beneath the intine; this occurs when pollen grains are slightly dehydrated before dispersal.

Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers

Pollen dispersal is fundamental in a plant's reproductive ecology and as a result of fragmentation of the landscape, questions have been raised on how isolated plant populations can still exchange genetic information. A common mechanism for gene exchange is wind pollination (anemophily). A successful anemophilous species native to North America is ragweed (Ambrosia), a weed that is hard to eradicate after it takes root on crop fields and its pollen causes very strong allergenic effects (hay fever). Despite the extremely clumpy nature of ragweed pollen that should limit its long distance dispersal, ragweed has spread rapidly across the world during the last century while maintaining a high genetic diversity. One of the reasons for its success may be prolific pollen production as well as an efficient pollen clump release and breakup mechanism. Efficient pollen entrainment and dispersal into the atmosphere is highly influenced by flow field characteristics as pollen released into the atmosphere initially encounters flow structures created by the plant's morphology. Here, the flow field in the wake of a mature ragweed spike having multiple staminate flowers as well as pollen release was studied using Particle Image Velocimetry and high-speed, inline holographic cinematography. The latter enabled to track the pollen in a 3D volume. The spike was set up in a wind tunnel and exposed to wind speeds ranging from 1 to 2 m/s. Results indicated that ragweed pollen was released in multiple sized clumps containing tens to several thousand single grains. Clumps were both “pulled apart” at the point of entrainment while exiting the flowers as well as broke up in smaller sized clumps in high shear rate flow regions not far from the spike. In addition, the largest clumps that did not travel far, deposited in the vicinity of the spike, breaking apart into many small clumps upon deposition. Based on our results, initial release and dispersal of ragweed pollen clumps is characterized by three concomitant mechanisms of clump breakup occurring at entrainment, in mid-air and on deposition, which make it perfectly suited to disperse pollen over a wide range of spatial scales.

Pollen clumping and wind dispersal in an invasive angiosperm

Pollen dispersal is a fundamental aspect of plant reproductive biology that maintains connectivity between spatially separated populations. Pollen clumping, a characteristic feature of insect-pollinated plants, is generally assumed to be a detriment to wind pollination because clumps disperse shorter distances than do solitary pollen grains. Yet pollen clumps have been observed in dispersion studies of some widely distributed wind-pollinated species. We used Ambrosia artemisiifolia (common ragweed; Asteraceae), a successful invasive angiosperm, to investigate the effect of clumping on wind dispersal of pollen under natural conditions in a large field. Results of simultaneous measurements of clump size both in pollen shedding from male flowers and airborne pollen being dispersed in the atmosphere are combined with a transport model to show that rather than being detrimental, clumps may actually be advantageous for wind pollination. Initial clumps can pollinate the parent population, while smaller clumps that arise from breakup of larger clumps can cross-pollinate distant populations.

How old is pastoralism in Tibet? An ecological approach to the making of a Tibetan landscape

The Tibetan highlands host one of the world's largest pastoral ecosystems, but the evolutionary impact of the Tibetan nomadic livestock economy on the environment has not yet been investigated. Despite this grazing impact, the vegetation of the Tibetan highlands is widely believed to be natural. Our ecological approach to reconstructing the making of a pastoral environment uses the present composition of the plant cover as a baseline. Today's prevailing plant functional types are grazing weeds highly adapted to grazing. The first pollen record of grazing weeds can thus be assumed to mark the onset of pastoralism, supposedly with goats and sheep introduced from the Middle East and the endemic large bovid of the yak, domesticated in the Tibetan highlands. This study represents the first attempt to determine the age of pastoralism with the help of palynomorphs using the indicator-species approach. This is independently corroborated 1) by the synchronous occurrence of pollen clumps indicating disturbance effects from trampling and 2) the precipitous decline of forest pollen on the eastern declivity of the highland during the mid-Holocene climatic optimum. As all pollen core sites currently have a climatic potential of forest as demonstrated by fruiting and progenitive forest relicts, it is suggested that early livestock holders continued to burn these forests to obtain pastures. The charcoal record supports this conclusion. It is hypothesized that the making of a pastoral environment in the Tibetan highlands started around 8.8 ka cal BP during the mid-Holocene climatic optimum. As the pattern of arboreal pollen decline at these sites contrasts with δ 13C, δ 18O, TOC content, C/N ratio, and ostracod assemblages that are independent of rangeland management decisions of early pastoralists, we may conclude that pastoralists took advantage of the mid-Holocene climatic optimum to convert forests into high-yield pastures. Using pollen clumps as a proxy for herbivore load suggests a tenfold higher amount of livestock than of wildlife before the introduction of pastoralism. In contrast to pastoralism in arid environments of the Old World's desert belt, pastoralists in the eastern Tibetan highlands created their own environment transforming forests and tall grassland into the present golf course-like pastures.

Early steps of angiosperm–pollinator coevolution

The hypothesis that early flowering plants were insect-pollinated could be tested by an examination of the pollination biology of basal angiosperms and the pollination modes of fossil angiosperms. We provide data to show that early fossil angiosperms were insect-pollinated. Eighty-six percent of 29 extant basal angiosperm families have species that are zoophilous (of which 34% are specialized) and 17% of the families have species that are wind-pollinated, whereas basal eudicot families and basal monocot families more commonly have wind and specialized pollination modes (up to 78%). Character reconstruction based on recent molecular trees of angiosperms suggests that the most parsimonious result is that zoophily is the ancestral state. Combining pollen ornamentation, size, and aperture characteristics and the abundance of single-species pollen clumps of Cenomanian angiosperm-dispersed pollen species from the Dakota Formation demonstrates a dominance of zoophilous pollination (76% versus 24% wind pollination). The zoophilous pollen species have adaptations for pollination by generalist insects (39%), specialized pollen-collecting insects (27%), and other specialized pollinators (10%). These data quantify the presences of more specialized pollination modes during the mid-Cretaceous angiosperm diversification.

The Pollination Mechanism of Three Sympatric Prescottia(Orchidaceae: Prescottinae) Species in Southeastern Brazil

The pollination biology of three Prescottia(Orchidaceae: Prescottinae) species was studied in Picinguaba, São Paulo State, south-eastern Brazil. Plants are self-compatible but pollinator-dependent and offer nectar as the only reward for pollinators. Prescottia plantaginea Lindl. and Prescottia stachyodes(Swartz) Lindl. are pollinated by pyralid moths (Lepidoptera: Pyralidae). Moth-pollination is reported for the first time in the genus Prescottia and the subtribe Prescottinae. Pollination by halictid bees (Halictidae) is confirmed for Prescottia densiflora Lindl. The pollination mechanism is the same regardless of pollinator-type: pollinaria are fixed on the ventral surface of the insect's proboscis through the pad-like viscidium and are removed when the insect leaves the flower. A pollinarium-carrying insect visiting another flower will brush the stigmatic surface and leave clumps of pollen, thus effecting pollination. Prescottia stachyodes is protandrous, a feature that increases the chances of cross-pollination. As far as we know, this is the first report of protandry in the genus Prescottia and also the subtribe Prescottinae.

Tobacco mosaic virus Is Transmissible from Tomato to Tomato by Pollinating Bumblebees

(TMV) was detected by ELISA, electron microscopy and/or bioassay from bumblebee (Bumbus terrestris), pollen clumps, nest materials and bee-visited anthers of flowers from greenhouses in which tomatoes had been pollinated by bees and were severely infected with TMV. Experimental bee-mediated transmission of TMV in greenhouse tomatoes demonstrated that the bumblebees transported TMV from plant to plant and that they spread the virus in greenhouses. This is the first report describing TMV transmission by bumblebees.

Vibratory Collection of Actinidia deliciosa (Kiwifruit) Pollen

Dry, powdery pollen grains were expected from 'buzz pollinated' flower species. However, vibration of Actinidia deliciosa (kiwifruit) anthers (a buzz pollinated species) by a mechanical shaker, at similar vibrations to Bombus terrestris caused clumps of pollen joined by small droplets of tapetal fluid to be ejected. Pollen that was largely covered with tapetal fluid could not be removed by vibration, whereas dehydrated pollen was easily removed, even without vibration. The late desiccation of A. deliciosa anthers after anthesis meant that pollen removed by vibration depended on the anther maturity. The presence of the droplets gives insects which vibrate while foraging advantages over insects which do not. A vibration attachment on a commercial pollen harvester increased the weight of pollen collected by 57% over the whole day; 91% in the afternoon.

Pollination of Aristolochia littoralis (Aristolochiales: Aristolochiaceae) by Males of Megaselia spp. (Diptera: Phoridae)

Thirty-two flowers of Aristolochia littoralis Parodi collected in Gainesville, FL, between 29 August and 29 September 1992 contained 349 phorid flies representing seven species of the genus Megaselia: M. scalaris (Loew), M. aurea (Aldrich), M. perdita (Malloch), and four unidentified species. Experimental evidence suggests that flies are attracted to flowers by an olfactory cue, although visual cues might be used at short range. Ninety-six percent of the flies (334) were males. The reason for this male-biased sex ratio is unknown, but it is possible that the attractive olfactory cue produced by the plant is sex-specific. At least some specimens of each Megaselia species carried clumps of pollen, suggesting that they were of an appropriate size to carry out pollination. Germination tests were conducted on seeds from 10 A. littoralis fruits. The mean germination rate for seeds from the 10 fruits was 56% (range, 4–92%).

Vibratory Pollen Collection Dynamics

At specific times in their maturation, anthers from flowers of Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson (kiwifruit) were observed to emit clumps of pollen when vibrated over a range of frequencies at acceleration magnitudes above a certain threshold level. Shed or dried pollen did not behave in this manner, even when placed inside the same anthers. The force required to explode apart pollen grains joined by tryphine droplets was calculated, and found to agree with the experimental data.

The morphology and phylogenetic significance of Vardekloeftia harris (Bennettitales)

The genus Vardekloeftia Harris, a bennettitalean reproductive structure from the Upper Triassic of East Greenland, is reinvestigated from the original material and from more recent collections. The two previously described species are combined as V. sulcata Harris and new generic and specific diagnoses, as well as more detailed descriptions, are provided. In the ovule of Vardekloeftia the nucellus is surrounded by two distinct layers (integument and cupule). Comparisons indicate that this kind of ovule structure also occurs in other Bennettitales and may be general within the group. The probable leaves of the Vardekloeftia plant are Pterophyllum kochii Harris. The pollen organs are unknown, but Bennettistemon amblum Harris and Bennettistemon ovatum Harris are associated with Vardekloeftia and clumps of pollen very similar to that of these species occur in the micropyles of Vardekloeftia seeds. Comparison of Vardekloeftia with other Bennettitales suggests that pollination and dispersal may have been relatively unspecialized in this early member of the group.

Extinct mountain goat ( Oreamnos harringtoni) in Southeastern Utah

The extinct Harrington's mountain goat ( Oreamnos harringtoni Stock) is predominantly known from dry cave localities in the Grand Canyon, Arizona, in addition to two sites in the Great Basin, Nevada, and from San Josecito Cave, Nuevo Leon, Mexico. A dry shelter in Natural Bridges National Monument, on the central Colorado Plateau, southeastern Utah, preserves numerous remains of the extinct mountain goat in addition to pack rat middens. Remains from a 100-cm stratigraphic profile indicate that O. harringtoni lived on the plateau >39,800 yr B.P., the oldest directly dated find of extinct mountain goat. Plant macrofossils indicate that Engelmann's spruce ( Picea engelmannii), limber pine ( Pinus flexilis), rose ( Rosa cf. woodsii), and Douglas fir ( Pseudotsuga menziesii) grew during the late Pleistocene where a riparian and a pinyon-juniper ( Pinus edulis-Juniperus osteosperma) community now predominates; Douglas fir are found only in mesic, protected, north-facing areas. Limber pine, Douglas fir, bark, and grasses were the major dietary components in the dung. A springtime diet of birch ( Betula) is determined from pollen clumps in dung pellets.

On the pollination mechanism of some eurysaline potamogetonaceae

The pollination mechanism in three eurysaline Potamogetonaceae was studied. These species were Zannichellia peltata Bertol., Ruppia megacarpa Mason and Lepilaena cylindrocarpa (Koernicke ex Walp.) Benth. In Zannichellia peltata pollination occurs underwater. When Ruppia megacarpa flowers, the pollen is released at the water surface and floats in clumps and the stigmata come in close contract with the floating clumps. The flowers are situated at the end of a fast-growing peduncle which spiralizes after flowering. As a consequence, the fruits develop underwater. In Lepilaena cylindrocarpa pollination also occurs at the water surface. Here, the stigmata are in close contact with the water surface. The anther is released from its peduncle and rises to the water surface where it dehisces and releases its floating pollen. The clumps of pollen are attracted by the somewhat depressed water surface around the neighbouring stigmata.

Pollen Release in the Common Ragweed (Ambrosia artemisiifolia)

1. A study of staminate flowers of common ragweed (Ambrosia artemisiifolia L.) revealed six more or less defined stages, which are described: (a) maturation of the flower; (b) extension of pollen sacs; (c) opening of pollen sacs and dropping of pollen clumps; (d) flotation of pollen by wind; (e) extension of the pistillodium; and (f) closure of the flower. Stages b and c were examined in relation to environmental factors-temperature, humidity, light, and water availability. 2. Actual pollen release is accomplished mainly by enlargement of the filaments of the stamens which extends the pollen sacs and pushes open the corolla lobes, and by dehiscence of the sacs by pleating and separation of their walls and extension of the anther appendages. The pistillodium may function as a "sweeper" of pollen grains still remaining in the anthers. 3. Field studies showed the occurrence of a definite diurnal periodicity: extension and opening of the anthers occurs between 6:30 and 8:00 A.M. This is correlated with rise in temperature and reduction of relative humidity. 4. Experimental studies on excised flowers and whole plants confirmed that the opening of flowers is controllable by regulating the temperature and relative humidity. The extension of anthers was slowed or prevented by holding the flowers at reduced temperatures. The opening of pollen sacs was retarded or stopped by high humidity. Both types of inhibition were reversible under the conditions of the experiments. Alterations in the amount of light and water failed to induce significant changes.