Levels Of Pollination Research Articles

Southern pollen sired more seeds than northern pollen in southern seed orchards established with northern clones of Pinus sylvestris

Contamination by southern pollen is a considerable problem in Scots pine (Pinus sylvestris L.) seed orchards established with northern clones. This study investigated whether the contamination was due to the competitive superiority of southern pollen by carrying out competition trials using mixtures of pollen from northern and southern populations of Scots pine. Trials were performed in a southerly seed orchard established with clones originating from northern populations. Seed paternity (siring) was determined through the analysis of allozyme variation. Southern genotypes sired significantly more seeds (76%) than their northern competitors and across all mixed-pollen crosses. Maternal genotype had no effect on seed siring success. The mean flower abortion rate was lower in southern pure-pollen crosses and mixed-pollen crosses than in northern pure-pollen crosses. The results show that local pollen may induce high levels of background pollination in southern seed orchards composed of northern genotype grafts. These results must be taken into account when aiming to produce suitable reforestation material for northern areas.

Limited mate availability decreases reproductive success of fragmented populations of Linnaea borealis, a rare, clonal self-incompatible plant.

Small populations of rare plant species are increasingly reported to have high levels of reproductive failure. The objective of this study was to understand the principal constraints on sexual reproduction in small fragmented populations of a rare clonal self-incompatible plant. The pollinator spectrum, diversity of flower colour, natural pollination and fruit-set levels of L. borealis were examined in Scotland. Artificially crossed seed production was compared within and between different flower colour types and patches. Linnaea borealis was pollinated by a diverse spectrum of insect species and the principal pollinators were muscid, syrphid and empid flies which mostly moved only small distances (<0.25 m) between flowers when foraging. Natural pollination levels were high, indicating high pollinator effectiveness, but fruit set was very low in most patches. Flower colour diversity was low in most patches and only those with a diversity of flower colour types had high fruiting success. Pollination experiments showed L. borealis to be highly self-incompatible and artificial crosses within and between patches and flower colour types confirmed that low fruit success was the result of a lack of compatible mates and limited pollen movement between them. Evidence of isolation from pollen exchange was apparent at as little as 6 m and severe at 30 m and beyond. Limited mate availability and isolation from pollen exchange compromise the reproductive success of fragmented populations of L. borealis in Scotland. A diversity of compatible mates situated within close proximity (<6 m) is the key requirement to ensure high natural fruiting success. This study emphasizes that an understanding of the breeding system, pollinator spectrum and potential for interconnectivity via pollinator movement are fundamental to identify isolation distances and to establish when conservation intervention is necessary for rare species.

Pollen Dispersal and Its Spatial Distribution in a Seed Orchard of Larix kaempferi (Lamb.) Carr.

Abstract Pollen dispersal and its spatial distribution in a seed orchard of Larix kaempferi in Changlinggang, Jianshi, Hubei Province has been studied for 3 years. The results show that pollen dispersal is directly affected by weather conditions, with wind speed being the main factor controlling pollen dispersal. Pollen dispersal follows a date rhythm of low-high-low during the whole pollen dispersal season with a peak date for 3-5 days, and a time rhythm of low-high-low with the peak time at 10:00-16:00 during the day. For pollen density in the air there are significant differences among dates, and among different day times during dispersing. There are no significant differences between pollen densities in space with regard to horizontal directions, 8 orientations, and different positions in the tree crown in this seed orchard, in all of these cases pollens are evenly distributed. There are significant differences for pollen densities among different vertical heights, showing a cluster distribution type. The pollination level in this seed orchard is very low and needs a supplement mass pollination (SMP).

Natural hybridisation betweenQuercus petraea(Matt.) Liebl. andQuercus pubescensWilld. within an Italian stand as revealed by microsatellite fingerprinting

Interspecific gene flow is frequently reported in the genus Quercus. However, interfertile oak species often seem to remain distinct, even within areas of sympatry. This study employed molecular markers to verify, at a fine scale, the presence of interspecific gene flow in a natural population of Quercus petraea and Quercus pubescens. Within a delimited area of 6 ha, all adult trees belonging to the studied oak complex and seeds from a subsample of such trees were collected and analysed using molecular microsatellite markers. A low interspecific genetic differentiation and a high level of interspecific genetic admixture suggested past hybridisation. Paternity inference of seeds allowed the estimation of pollination frequencies from the three groups of pollen donors (Q. petraea, Q. pubescens, intermediate). We also assayed pollen viability and germinability of each species group. We observed natural hybridisation between Q. petraea and Q. pubescens, with a predominant component in the direction Q. petraea --> Q. pubescens: Q. pubescens displayed a higher level of heterospecific pollination by Q. petraea (25.8%) and intermediate morphotypes (14.7%), compared to Q. petraea acting as pollen receptor (with less than 5% heterospecific pollinations). Intermediate 'mother trees' were pollinated in similar proportions by Q. petraea (23.1%), Q. pubescens (37.8%) and intermediate morphotypes (39.1%). The asymmetrical introgression observed for the studied generation may be caused, among other factors, by the relative abundance of trees from each species group in the studied area.

Reproductive biology of Acrolophia cochlearis (Orchidaceae): estimating rates of cross-pollination in epidendroid orchids

Pollen fates strongly influence mating success in plants but are difficult to quantify. By promoting foraging constancy in pollinators, floral rewards such as nectar may enhance the overall efficiency of pollen transfer. However, this can also lead to high levels of geitonogamy. Pollen fates were studied in Acrolophia cochlearis, a member of a terrestrial epidendroid orchid genus that includes both rewarding and deceptive species. Pollinator observations were conducted. Pollen transfer efficiency (PTE), the proportion of removed pollinia deposited on stigmas, was measured in a large population at regular intervals throughout the 5-month flowering season. The level of cross-pollination in two populations was estimated from the percentage of seeds with embryos in naturally pollinated fruits. Acrolophia cochlearis (and a congener A. micrantha) produce minute but concentrated nectar rewards. Observations showed that A. cochlearis is pollinated exclusively by a solitary bee species, Colletes claripes. Although both sexes visited flowers, only males carried pollinaria. Overall levels of pollination and PTE of the rewarding A. cochlearis were much higher than in a deceptive congener, A. capensis. Seeds resulting from self-fertilization had a significantly lower probability of containing viable embryos than did those from cross-fertilization. This dichotomy in fruit quality was used to estimate that cross-pollination occurred in approx. 66 % of A. cochlearis flowers in a large dense population and approx. 10 % in a small sparse population. Traits of A. cochlearis that limit geitonogamy include pollinarium reconfiguration that exceeds the visit time of pollinators and rapid flower senescence following visitation. Presence of a nectar reward in Acrolophia cochlearis results in high levels of PTE. It is estimated that approx. 33-90 % of fruits in natural populations arise from self-pollination in this species.

A test of simultaneous resource and pollen limitation in Stylidium armeria.

This study tests the Haig-Westoby model, which predicts that seed output will be limited simultaneously by pollen and resources when plants optimally distribute their reproductive investment. The test was conducted over 2 yr using Stylidium armeria in a factorial design that fully crossed three pollination levels (small stigmatic loads, open pollination, and supplementation of natural loads) with three levels of resource availability (reduction through partial defoliation, unmanipulated resource conditions, and supplementation through nitrogen, phosphorus and potassium (NPK) addition). There was no evidence of pollen limitation from supplemental pollination; however, pollen reductions (to about half the normal mean stigmatic loads) sharply reduced seed output. There was no evidence of resource limitation, in that NPK addition did not, by itself, significantly elevate seed output in either year of the study, while resource reduction by defoliation lowered seed output in the second year. Simultaneous addition of both pollen and resources strongly and significantly increased seed production. These results match the direction of effects predicted by the Haig-Westoby model, and suggest that S. armeria plants at our site are at or near an equilibrium of joint limitation of seed production by pollen capture and resource availability.

Pollinator Shifts and the Origin and Loss of Plant Species1

Pollinators have long been implicated in plant speciation. Peter Raven's earlier work was instrumental in integrating foraging energetics of animals into our understanding of how shifts in major pollinators influence the evolutionary diversification of floral traits. More recently, efforts by Raven and others in the area of conservation have inspired pollination biologists to consider the implications of pollinator shifts and losses due to human activities. This paper uses the shift between hummingbird and hawkmoth pollination as a model for exploring impacts of pollinator shifts on plant populations. Recent studies have quantified the degree of reproductive isolation due to such pollinators in several genera. Data from Ipomopsis Michx. further allow us to consider whether recent changes in pollinator regimes have demographic consequences for plant populations. A majority of plant populations may currently suffer from pollen limitations on seed production, but few data exist on the demographic consequences of poor reproduction. In Ipomopsis, reduced seed production due to pollen limitation can impact the number of individuals surviving to reproduce in the next generation. Some populations of I. tenuituba (Rydb.) V. E. Grant are estimated to have finite rates of increase less than unity, which can be explained in part by current low levels of hawkmoth pollination. In the absence of an increase in hawkmoths, selection for wider corolla tubes and other floral traits could, in principle, attract enough hummingbird pollination to result in a growing population, but models show that such evolution by natural selection may leave the population vulnerable to local extinction. We need more studies of the quantitative demographic consequences of changes in pollinator regimes. Such studies should consider how evolutionary changes influence the risk of extinction.

The relative fitness of parental and hybridKunzea(Myrtaceae): The interaction of reproductive traits and ecological selection

Up to 22% of plant species are the result of breeding among species-hybridization-directly conflicting with the prediction that hybrids, compared to parental species, are intermediate in character and of low fitness and little consequence. Few studies, however, have compared the fitness of hybrids and parental species under field conditions. This study evaluates components of fitness in the field for naturally occurring hybrids of the shrub Kunzea, relative to the parental speciesKunzea rupestris. Hybrid plants did not differ from the parental species in the level of effective pollination. Thus, we found no support for Grant's model (Evolution: International Journal of Organic Evolution3: 82-97) of reduced fitness of hybrids via reduced pollination level (the intermediate hypothesis). Hybrids displayed variable fitness across the measured fitness components. Seed set levels for hybrids were structured among populations, suggesting genetic structuring for this fitness component at this scale. The response of hybrids to fire (a major selective force in the study system) was partly consistent with a resource trade-off model. Hybrids were large robust plants but most did not resprout after fire. Hence, the fitness of hybrids was complex. We developed a model for relative fitness to estimate fitness for species and hybrids with complex life histories.

Reproductive trade-offs in a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae)

The reproductive interactions of a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae: Derelomini) were studied at La Selva, Costa Rica. The inflorescences of A. uncinata exhibit a suite of cantharophilous characters including a precisely synchronized anthesis, protogyny, thermogenesis, olfactory attraction of visitors via modified staminodes, and narrow interfloral entrances. The weevil pollinators use the inflorescences for feeding, mating, and oviposition. The larvae are detritivorous and develop either in the detaching staminate flowers or, at a more favorable rate, in the rotting infructescences. The rate of infructescence abortion was high and caused by low levels of pollination. Manual pollination treatments yielded significantly higher seed counts than obtained under natural conditions, and furthermore demonstrated the inflorescences' ability to reproduce via geitonogamy. In the longer term, the reproductive benefits of maintaining low levels of pollination may shift away from the weevils and towards the plants via an increase in the size of the pollinator population.

CAVEATS TO QUANTIFYING ECOSYSTEM SERVICES: FRUIT ABORTION BLURS BENEFITS FROM CROP POLLINATION

The recent trend to place monetary values on ecosystem services has led to studies on the economic importance of pollinators for agricultural crops. Several recent studies indicate regional, long-term pollinator declines, and economic consequences have been derived from declining pollination efficiencies. However, use of pollinator services as economic incentives for conservation must consider environmental factors such as drought, pests, and diseases, which can also limit yields. Moreover, "flower excess" is a well-known reproductive strategy of plants as insurance against unpredictable, external factors that limit reproduction. With three case studies on the importance of pollination levels for amounts of harvested fruits of three tropical crops (passion fruit in Brazil, coffee in Ecuador, and cacao in Indonesia) we illustrate how reproductive strategies and environmental stress can obscure initial benefits from improved pollination. By interpreting these results with findings from evolutionary sciences, agronomy, and studies on wild-plant populations, we argue that studies on economic benefits from pollinators should include the total of ecosystem processes that (1) lead to successful pollination and (2) mobilize nutrients and improve plant quality to the extent that crop yields indeed benefit from enhanced pollinator services. Conservation incentives that use quantifications of nature's services to human welfare will benefit from approaches at the ecosystem level that take into account the broad spectrum of biological processes that limit or deliver the service.

Maternal Plant Responses to High Pollen Loads

Maternal plant responses to different levels of pollination vary and are of importance for the total fitness of the plant. We studied how varying pollen load affects late flowering, reproduction, and growth of maternal plants. Raphanus raphanistrum, Sinapis arvensis, and Brassica napus were used as study species. We conducted hand‐pollination experiments with different pollen loads for early flowers in the inflorescence and measured responses on vegetative traits, floral traits of late flowers, and seed production. There were no effects on vegetative traits, but floral traits were affected by treatments in two of the study species. The high pollen load treatment in S. arvensis resulted in longer petals on late flowers compared with the low pollen load treatment. In R. raphanistrum, the high pollen load treatment resulted in a higher number of flowers, with narrower petals, than the low pollen load treatment. Total seed production was similar in both treatments in all species. Our results suggest that plants that received a high pollen load were able to allocate resources to high seed production of early flowers and to increased pollen dispersal of late flowers, thereby achieving higher total fitness than plants that received a lower pollen load.

Composition of the pollinator community, pollination and the mating system for a shrub in fragments of species rich kwongan in south-west Western Australia

In this study we investigate the composition of the potential honeyeater pollinator community, patterns of honeyeater visitation, pollination and the mating system in a range of population fragments for the bird-pollinated mixed mating system shrub Calothamnus quadrifidus R.Br. Specifically, we aimed to answer the following questions. For smaller and more isolated population fragments are honeyeater species lost from the pollinator community, patterns of visitation different, levels of pollination lower and rates of selfing, biparental inbreeding and correlated paternity higher. The composition of the honeyeater community was similar across population fragments and there was no relationship between the abundance of birds and population fragment size. Honeyeaters were most commonly observed visiting numerous inflorescences within single plants in all populations, but as population fragments became larger movements between plants were more commonly observed. Our observations of honeyeater visitation were generally consistent with our measurements of pollination and patterns in the mating system across population fragments. We found no significant relationship between population fragment size and levels of pollination. Mating system studies showed outcrossing rates (t m) comparable to those found in other bird-pollinated Myrtaceae, and ranged from 0.54 to 0.90 across populations. Outcrossing rates were not significantly correlated with log population size, but correlations of outcrossed paternity indicate a clear trend from low correlated paternity in larger populations to significantly higher correlated paternities in smaller populations. As a consequence mating in small populations will occur between much smaller groups of plants, and this may affect population fitness in subsequent generations.

Breeding system and early stage inbreeding depression in a Nova Scotian population of the global rarity, Sabatia kennedyana (Gentianaceae)

Abstract The survival of populations of rare plant species may be affected both by total levels of seed production and by inbreeding depression expressed upon self-fertilization. We examined natural seed production and rates of self-fertilization in a Nova Scotian lakeshore population of the globally rare Atlantic Coastal Plain plant, Sabatia kennedyana Fernald (Gentianaceae), and determined the effect of self and cross pollinations on fitness at early plant life stages. Seed production was not limited by natural pollination levels. Furthermore, flowers from which pollinators were excluded produced 66% as many seeds as unprotected, naturally pollinated plants, indicating that substantial seed set can occur in the absence of pollinators. The selfing rate of naturally pollinated flowers was estimated as 21% using the inbreeding depression method. Stage-specific inbreeding depression was 19% at germination, and cumulative inbreeding depression from fertilization through germination was 23%. Seed formation (s...

Biologia floral e polinização de Anemopaegma chamberlaynii Bur. &amp; K. Schum. (Bignoniaceae).

The present work deals with the floral biology, reproductive system and phenological events of Anemopaegma chamberlaynii Bur. &amp; K. Schum. (Bignoniaceae), in the coastal strand vegetation (restinga) of Maricá RJ., between 1997 and 2000. The flowers display daytime anthesis, are yellow, very attractive, tubulous, hermaphrodite, odoriferous and produce nectar as the floral reward. The nectar is secreted by a nectariferous disk and accumulated in a chamber. The stigmas are bifid, wet and papillous. The stigmatic lobes are receptive to pollen only on the inner surfaces and are sensitive to disturbance. If the stigma is touched but no pollen is deposited, the lobes close and soon reopen. The same occurs when self-pollen is deposited on the receptive surface. However, after manual pollination with cross-pollen the lobes close permanently, enabling to estimate levels of pollination by monitoring stigma closure. Euglossa cordata L., Epicharis dejeanii Lepeletier and E. semiflava Moure are potential pollinators. Xylocopa ordinaria Smith is the primary nectar robber. The species is self-incompatible and has a low fruit set (Fruit/Flower=4.86%). The flowering pattern is the “multiple bang”, showing five episodes per year, with the same intensity, all of them occurring in the most hot and rainy months.

Pollen load affects fruit set, size, and shape in cherimoya

Abstract Cherimoya (Annona cherimola Mill.) is a subtropical fruit crop that exhibits protogyny dichogamy and for which the original pollinators are not present in the main producing countries. Under such circumstances the achievement of profitable yields depends on hand pollination. The present work explores the effects of the amount of pollen applied on pollen–pistil interaction and on fruit set, size, shape and growth. Pollen dilution with Lycopodium spores reduced fruit set and size and favoured the appearance of misshapen fruits, whereas the application of double amount of pollen did not improve fruit size and increased fruit set only the first year. Pollen load did not affect fruit growth model, which always followed a double sigmoid pattern. Nevertheless, the slopes of the curves during the two rapid growth phases were higher when a larger amount of pollen grains was applied. Seed index (seed number per 100 g of fresh fruit weight) rose slightly as pollination level increased.

Significant effect of accidental pollinations on the progeny of low setting Prunus interspecific crosses

The incidence of fortuitous pollination on interspecific hybridizations of the plum rootstock Myrobalan with the apricot cultivars ‘Moniqui’ and ‘Moniqui Borde’ was assessed in this work. Progeny was originated through hand pollination of emasculated flowers of three Myrobalan clones, without bagging, in 1998 and 1999. Fruit set was low and variable among years (1.8–8.0%), but higher than the level of accidental pollination measured with emasculated and non-pollinated flowers (1.2%). Molecular characterization of the progeny was performed with three SSR markers showing that only 28% of the seedlings, obtained by in vitro germination and culture of immature embryos, were hybrids. This represents a lower percentage than expected, and is explained here by the low viability of hybrid embryos and seedlings. The use of molecular markers is discussed in terms of a convenient method for an early identification of putative hybrids in breeding programs with low setting crosses, where the proportion of non-hybrids is magnified.

Plant-pollinator biodiversity and pollination services in a complex Mediterranean landscape

Mediterranean landscapes comprise a complex mosaic of different habitats that vary in the diversity of their floral communities, pollinator communities and pollination services. Using the Greek Island of Lesvos as a model system, we assess the biodiversity value of six common habitats and measure ecosystemic ‘health’ using pollen grain deposition in three core flowering plants as a measure of pollination services. Three fire-driven habitats were assessed: freshly burnt areas, fully regenerated pine forests and intermediate age scrub; in addition we examined oak woodlands, actively managed olive groves and groves that had been abandoned from agriculture. Oak woodlands, pine forests and managed olive groves had the highest diversity of bees. The habitat characteristics responsible for structuring bee communities were: floral diversity, floral abundance, nectar energy availability and the variety of nectar resources present. Pollination services in two of our plant species, which were pollinated by a limited sub-set of the pollinator community, indicated that pollination levels were highest in the burnt and mature pine habitats. The third species, which was open to all flower visitors, indicated that oak woodlands had the highest levels of pollination from generalist species. Pollination was always more effective in managed olive groves than in abandoned groves. However, the two most common species of bee, the honeybee and a bumblebee, were not the primary pollinators within these habitats. We conclude that the three habitats of greatest overall value for plant-pollinator communities and provision of the healthiest pollination services are pine forests, oak woodland and managed olive groves. We indicate how the highest value habitats may be maintained in a complex landscape to safeguard and enhance pollination function within these habitats and potentially in adjoining agricultural areas.

Senescence of Eustoma Flowers as Affected by Pollinated Area of the Stigmatic Surface

Senescence of Eustoma flowers is accelerated by pollination which is accompanied by an increase in ethylene production by flowers. We investigated the influence of pollinating different areas of the stigmatic surface on senescence in the flowers of 6 Eustoma cultivars. Anthers were removed from the flowers whose stigma had not yet opened. After the stigmas opened, freshly collected pollen from anthers of same cultivar were placed on them. The pollination levels on stigma were all area, 1/8 area or none (control). Senescence of flowers was significantly accelerated by all and 1/8 area pollination compared with the control. All area-pollinated flowers wilted significantly earlier than did 1/8 area-pollinated ones in three cultivars. In the remaining three cultivars, senescence of flowers by all area pollination tended to be earlier than that of 1/8 area pollination. In ‘Asuka-no-nami’ flowers, ethylene production of flowers rapidly increased 1 day after all area pollination. However, in flowers with 1/8 area pollination, ethylene production slowly increased for 3 days after pollination. A large number of pollen tubes reached the base of the style 2 days after pollination in the all area-pollinated flowers, but on 3rd day in the 1/8 area-pollinated flowers. All area-pollinated flowers required silver thiosulfate complex (STS) at high concentration to delay senescence induced by pollination, compared with the 1/8 area-pollinated flowers. These results suggest that in Eustoma flowers, senescence that is induced by pollination, depends on the pollinated area of the stigmatic surface which resulted in ethylene production.

The role of pollination level on the reproduction of females and hermaphrodites in the gynodioecious plant Gypsophila repens (Caryophyllaceae)

In gynodioecious plant species, females are expected to have more resources available for maturing seeds because pistillate flowers are smaller, do not produce pollen, and are thus less costly that perfect flowers. The potential female advantage arising from more abundant resources is, however, likely to vary depending on whether seed production is limited by resource or pollen availability. Here we experimentally investigated the influence of pollen and resource limitation on female advantage in a gynodioecious species using two levels of pollination. Total seed production of females was always greater than that of hermaphrodites: females produced more flowers and more fruits that contained similar numbers of seeds of similar mass. Under low pollination, female and hermaphrodite plants allocated resources to increased flower production rather than to increased seed size or quality. We did not detect any influence of pollen or resource limitation on female advantage, which remained similar under low (= abundant resources) and full pollination. Outcrossed fruits performed better than selfed fruits when the same plant received both selfed and outcrossed pollen on different flowers. These differences were not greater under high pollination, possibly because resources available for each fruit did not differ between our pollen intensity treatments.

Spatio‐temporal variation in the pollination mode of Buxus balearica (Buxaceae), an ambophilous and selfing species: mainland‐island comparison

Mixed‐pollination systems may allow plants to achieve stable seed production when unpredictable conditions cause variation in the relative success of different pollination modes. We studied variation in time (two years) and space (in five populations, three from an island and two from mainland) in the pollination mode of Buxus balearica, an ambophilous (i.e. pollinated by wind and insects) and selfing species distributed in the Mediterranean Basin, by means of direct observations and experimental manipulations (bagging with different material). The relative importance of each pollination mode differed among populations; however, levels of selfing and wind pollination were similar between island and mainland. Flowers of B. balearica were visited only by generalist insects, and species composition and abundance of flower visitors varied both in space and time. Frequency of insect visits to plants were not higher in mainland than island populations, although insects on the mainland were more diverse, visited a proportionally greater number of flowers, and remained longer on the plants than insects on the island. Frequency of insect visits was negatively correlated with flowering synchrony (all populations pooled) and was found to increase seed set in one of the mainland populations (that with highest frequency of insect visits and highest flower visitation rate). Fruit and seed mass were found to be not affected by pollination mode. Scarcity of pollinators in the island seems to have an effect on the pollination mode, although the greatest variation in breeding system was found at a more local scale.