Patterns of pollen flow in a dense population of the insect-pollinated canopy tree species Castanopsis sieboldii

Insect pollinations of tree species with high-density populations have rarely been studied. Since the density of adults can affect effective pollen dispersal, short-distance pollination, even by insects, may frequently occur in high-density populations. To test this prediction, we investigated pollination patterns in a high-density population of the insect-pollinated canopy tree species Castanopsis sieboldii by paternity analysis using genotypes at 8 microsatellite loci of 145 adult trees and 439 seeds from 11 seed parents in a 4-ha plot. We then explored their genetic effects on the population by calculating other population genetics parameters. Although C. sieboldii has high potential for long-distance dispersal of pollen (as indicated by a fat-tailed dispersal kernel), the cumulative pollination at the local scale was spatially limited and strongly dependent on the distance between parents due to the high density of adults. Genetic diversity estimates for pollen pools accepted by each seed parent converged on a maximum as the effective number of pollen parents increased. The genetic diversity of pollen pool bulked over all the seed parents from inside the plot did not differ from that of the total pollen pools. Therefore, although pollen flow from distant pollen parents may help to maintain the genetic diversity of offspring, pollen parents neighboring seed parents may be the main contributors to the genetic diversity of the offspring at the seed stage.     

Fluorescent dye particles as pollen analogues for measuring pollen dispersal in an insect-pollinated forest herb

In flowering plants, pollen dispersal is often the major contributing component to gene flow, hence a key parameter in conservation genetics and population biology. A cost-effective method to assess pollen dispersal consists of monitoring the dispersal of fluorescent dyes used as pollen analogues. However, few comparisons between dye dispersal and realized pollen dispersal have been performed to validate the method. We investigated pollen dispersal in two small populations of the insect-pollinated herb Primula elatior from urban forest fragments using direct (paternity analyses based on microsatellite DNA markers) and indirect (fluorescent dyes) methods. We compared these methods using two approaches, testing for the difference between the distance distributions of observed dispersal events and estimating parameters of a dispersal model, and related these results to dye dispersal patterns in three large populations. Dye and realized (based on paternity inference) pollen dispersal showed exponential decay distributions, with 74.2?C94.8% of the depositions occurring at <50?m and a few longer distance dispersal events (up to 151?m). No significant difference in curve shape was found between dye and realized pollen dispersal distributions. The best-fitting parameters characterizing the dye dispersal model were consistent with those obtained for realized pollen dispersal. Hence, the fluorescent dye method may be considered as reliable to infer realized pollen dispersal for forest herbs such as P. elatior. However, our simulations reveal that large sample sizes are needed to detect moderate differences between dye and realized pollen dispersal patterns because the estimation of dispersal parameters suffers low precision.     

Reproductive success and pollen dispersal in urban populations of an insect-pollinated hay-meadow herb

Urban development increasingly occupies more landscape and is responsible for habitat alteration and fragmentation of so many ecosystems that urban environments can no longer be excluded from the areas to be considered in conservation strategies. Appropriate management measures ensuring population viability are needed, but due to the usually irreversible feature of the urbanisation process, the measures may differ from non-urbanised areas. Sufficient gene flow levels, leading to successful seed production, appear to be a key element in the sustainable persistence of insect-pollinated plant remnant populations. This study investigated reproductive success and pollen dispersal patterns in Centaurea jacea, an insect-pollinated hay-meadow herb, in the Brussels urban area (Belgium). Reproductive performance of urban park populations was compared with populations occurring in urban semi-natural sites. Pollen dispersal patterns were examined within and among-population patches from two urban parks using fluorescent dye as a pollen analogue. Urban park populations showed a higher reproductive success than those in urban semi-natural sites. Depositions of fluorescent dye particles on recipient individuals were found within populations (<20 m), among populations within parks (over a few hundred meters) and among parks (maximal investigated distance: 2.6 km), indicating pollinator movements and a potential gene flow by pollen over relatively long distances. Dye dispersal showed an exponential decay distribution with respect to spatial distance. The very small populations received more immigrant dye deposition when located at short distances from the source population. These findings demonstrate that urban populations do not perform worse in reproductive success than populations from agricultural landscapes, despite their small size, and can function as a network exchanging pollen. The conversion of urban park lawns into interconnected networks of ecologically managed hay meadows, allowing simultaneous flowering and seed production in many patches of target species, is to be strongly encouraged.     

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

• Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient.
• Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes.
• Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude.
• The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

     

The pollen dispersal kernel and mating system of an insect-pollinated tropical palm,Oenocarpus bataua

Pollen dispersal shapes the local genetic structure of plant populations and determines the opportunity for local selection and genetic drift, but has been well studied in few animal-pollinated plants in tropical rainforests. Here, we characterise pollen movement for an insect-pollinated Neotropical canopy palm, Oenocarpus bataua, and relate these data to adult mating system and population genetic structure. The study covers a 130-ha parcel in which all adult trees (n=185) were mapped and genotyped at 12 microsatellite loci, allowing us to positively identify the source tree for 90% of pollination events (n=287 of 318 events). Mating system analysis showed O. bataua was effectively outcrossed (t_m=1.02) with little biparental inbreeding (t_m−t_s=−0.005) and an average of 5.4 effective pollen donors (N_ep) per female. Dispersal distances were relatively large for an insect-pollinated species (mean=303 m, max=1263 m), and far exceeded nearest-neighbour distances. Dispersal kernel modelling indicated a thin-tailed Weibull distribution offered the best fit to the genetic data, which contrasts with the fat-tailed kernels typically reported for pollen dispersal in trees. Preliminary analyses suggest that our findings may be explained, at least in part, by a relatively diffuse spatial and temporal distribution of flowering trees. Comparison with previously reported estimates of seed movement for O. bataua suggests that pollen and seed dispersal distances may be similar. These findings add to the growing body of information on dispersal in insect-pollinated trees, but underscore the need for continued research on tropical systems in general, and palms in particular.     

Seed set differs in relation to pollen and nectar foraging flower visitors in an insect-pollinated herb

Assessing the relative contributions to seed sets of each of a plant species' floral visitors provides an indication of the relative influence of these visitors on the plants' reproductive success. In this study we compared the seed set of the gynodioecious Knautia arvensis (Dipsacaceae) in 49 local plant populations in two regions of southern Sweden. We measured the seed set for hermaphroditic and female plant individuals. In both plant sexes and both regions, the seed set was positively related to the abundance of Apidae. The seed set was negatively related to the abundance of pollen-foraging solitary bees (Halictidae, Megachilidae) and beetles (Oedemeridae, Malachidae). The seed set was not related to plant population size, plant density or female frequency. Our results confirm that pollination success in generalised plant–pollinator systems varies between pollinator groups. Flower-visitors foraging for pollen might not contribute to increased pollination success in generalised pollination systems.     

Distance-dependent pollen limitation of seed set in some insect-pollinated dioecious plants

By applying hand pollination, we studied pollen limitation of seed set of female plants in four dioecious plant species with insect-pollination. The effect of hand pollination increased with distance to the nearest male plant. Distances at which seed set was 50% of its maximal value (after hand pollination) were: 2.3 m for Valeriana dioica, 5.3 m for Salix repens, 8.5 m for Asparagus officinale and 10.6 m for Bryonia dioica. We discuss to what extent the reduced seed set was caused by either fewer visits or by visits of a lower quality. We argue that quantifying distance-dependent seed set in dioecious plants may be a good way of studying effects of habitat fragmentation on the breakdown of mutualistic pollination systems.     

Interspecific pollen transfer and competition between co-occurring plant species

Summary Computer simulations of a pollinator foraging in a mixture of two species were used to explore how plant reproduction can be influenced by interspecific pollination movements. Interspecific pollen transfer led to strong competitive effects when availabilities of pollen, receptive stigma surfaces, or pollinator movements were limited relative to the total number of fertilizations possible in the mixed population. Results from simulations suggest that competition for pollination through interspecific pollen transfer can result in rapid exclusion of one of two species, and that such competition represents a selective force promoting stable divergence of potential competitors in habitat affinity, flowering time, or other characteristics related to pollinator sharing.     

NADPH oxidase activity in allergenic pollen grains of different plant species

Pollen is an important trigger of allergic diseases. Recent studies have shown that ragweed pollen NAD(P)H oxidase generates reactive oxygen species (ROS) and plays a prominent role in the pathogenesis of allergies in mouse models. Here, we demonstrated that allergenic pollen grains showed NAD(P)H oxidase activity that differed in intensity and localization according to the plant families. The activity occurred at the surface or in the cytoplasm in pollen of grasses, birch, and ragweed; in subpollen particles released from ragweed pollen; and at the inner surface or in the cytoplasm but not on the outer wall, which was sloughed off after the rupture, of pollen of Japanese cedar and Japanese cypress. The activity was mostly concentrated within insoluble fractions, suggesting that it facilitates the exposure of tissues to ROS generated by this enzyme. The extent of exposure to pollen-generated ROS could differ among the plant families.     

Numerical assessment of plant species as indicators of the groundwater regime

Abstract. The relation between the occurrence of plant species in environments varying in moisture status and groundwater regime was tested using numerical methods. The groundwater regime during the vegetation period was expressed by means of four parameters, the average (AVG), mean highest (HIGH), mean lowest (LOW) groundwater level and the maximum fluctuation (AMP). 67 records of five vegetation types were selected from hydrologically stable sites in brook valleys in the northern part of The Netherlands. Response curves were calculated for 30 representative species. Calculated optima for AVG, HIGH and LOW are strongly correlated to each other. The vegetation reacts independently from overall wetness to the amount of fluctuation of the groundwater level (AMP). Response curves of single species as well as combinations of both present and absent species were used to find the best set of indicators for each parameter. The use of combinations of species clearly improves the indicating value of vegetation records. The vegetation appears to be the most sensitive to the parameter HIGH, which can thus be considered to be a key factor in controlling vegetation composition. The four parameters can be predicted satisfactorily only in the middle part of the investigated gradient. This is not only due to arithmetic artifacts, inherent to the applied method, but also to the fact that at average groundwater levels below - 60 cm or above 0 cm other factors become predominant.     

Long-distance pollen flow and tolerance to selfing in a neotropical tree species

Outcrossing rates, pollen dispersal and male mating success were assessed in Dicorynia guianensis Amshoff, a neotropical tree endemic to the Guiana shield. All adult trees within a continuous area of 40 ha (n = 157) were mapped, and were genotyped with six microsatellite loci. In addition, progenies were genotyped from 22 mature trees. At the population level, the species was mostly outcrossing (tm = 0.89) but there was marked variation among individuals. One tree exhibited mixed mating, confirming earlier results obtained with isozymes that D. guianensis can tolerate selfing. A Bayesian extension of the fractional paternity method was used for paternity analysis, and was compared with the neighbourhood method used widely for forest trees. Both methods indicated that pollen dispersal was only weakly related to distance between trees within the study area, and that the majority (62%) of pollen came from outside the study stand. Using maximum likelihood, male potential population size was estimated to be 1119, corresponding to a neighbourhood size of 560 hectares. Male mating success was, however, related to the diameter of the stem and to flowering intensity assessed visually. The mating behaviour of D. guianensis is a combination of long-distance pollen flow and occasional selfing. The species can still reproduce when it is extremely rare, either by selfing or by dispersing pollen at long distances. These results, together with the observation that male mating success was correlated with the size of the trees, could be implemented in management procedures aiming at regenerating the species.     

Effect of smoke derivatives on in vitro pollen germination and pollen tube elongation of species from different plant families

Plant‐derived smoke stimulates seed germination in numerous plant species. Smoke also has a positive stimulatory effect on pollen germination and pollen tube growth. The range of plant families affected my smoke still needs to be established since the initial study was restricted to only three species from the Amaryllidaceae. The effects of smoke‐water (SW) and the smoke‐derived compounds, karrikinolide (KAR₁) and trimethylbutenolide (TMB) on pollen growth characteristics were evaluated in seven different plant families. Smoke‐water (1:1000 and 1:2000 v:v) combined with either Brewbaker and Kwack's (BWK) medium or sucrose and boric acid (SB) medium significantly improved pollen germination and pollen tube growth in Aloe maculata All., Kniphofia uvaria Oken, Lachenalia aloides (L.f.) Engl. var. aloides and Tulbaghia simmleri P. Beauv. Karrikinolide (10^?6 and 10^?7 m ) treatment significantly improved pollen tube growth in A. maculata, K. uvaria, L. aloides and Nematanthus crassifolius (Schott) Wiehle compared to the controls. BWK or SB medium containing TMB (10^?3 m ) produced significantly longer pollen tubes in A. maculata, K. uvaria and N. crassifolius. These results indicate that plant‐derived smoke and the smoke‐isolated compounds may stimulate pollen growth in a wide range of plant species.     

Optical trait indicators for remote sensing of plant species composition: Predictive power and seasonal variability

Most plant species feature similar biochemical compositions and thus similar spectral signals. Still, empirical evidence suggests that the spectral discrimination of species and plant assemblages is possible. Success depends on the presence or absence of faint but detectable differences in biochemical (e.g., pigments, leaf water and dry matter content) and structural properties (e.g., leaf area, angle, and leaf structure), i.e., optical traits. A systematic analysis of the contributions and spatio-temporal variability of optical traits for the remote sensing of organismic vegetation patterns has not yet been conducted. We thus use time series of optical trait values retrieved from the reflectance signal using physical models (optical trait indicators, OTIs) to answer the following questions: How are optical traits related among patterns of floristic composition and reflectance? How variable are these relations in space and time? Are OTIs suitable predictors of plant species composition?We conducted a case study of three temperate open study sites with semi-natural vegetation. The canopy reflectance of permanent vegetation plots was measured on multiple dates over the vegetation period using a field spectrometer. We recorded the cover fractions of all plant species found in the vegetation plots and extracted gradients of species composition from these data. The physical PROSAIL leaf and canopy optical properties model was inverted with random forest regression models to retrieve time series of OTIs for each plot from the reflectance spectra. We analyzed these data sets using correlation analyses. This approach allowed us to assess the distribution of optical traits across gradients of species composition. The predictive performance of OTIs was tested in relation to canopy reflectance using random forest models.OTIs showed pronounced relationships with floristic patterns in all three study sites. These relationships were subject to considerable temporal variability. Such variability was driven by short-term vegetation dynamics introduced by local resource stress. In 72% of all cases OTIs out-performed the original canopy reflectance spectra as indicators of plant species composition. OTIs are also easier to interpret in an ecological sense than spectral bands or features. We thus conclude that optical traits retrieved from reflectance data have a high indicative value for ecological research and applications.     

Using wild plant species as indicators for the accumulation of emissions from a thermal power plant, Candiota, South Brazil

The impact of Candiota coal-fired thermal power plant on air quality was evaluated during two years by means of passive biomonitoring. The monitoring consisted of the quarterly collection of leaf samples of Baccharis dracunculifolia, Elephantopus mollis, Eryngium horridum, Paspalum notatum and Piptochaetium montevidense or the shoot of Baccharis trimera at five sites located in the area around the power plant. The element load of these plants was used as indicator for atmospheric pollution. In the samples collected, sulphur and heavy metal cadmium contents were measured. Among the species evaluated, E. mollis presented the highest potential to accumulate metal, followed by B. trimera. The Aeroporto and AFUCAN sampling sites, located in the prevailing wind directions, presented the highest level of metal contamination.