Pollen Flow Research Articles

The reproductive strategy of a typical distylous Ophiorrhiza alatiflora (Rubiaceae), in fragmented habitat

IntroductionHeterostyly is a genetically controlled style polymorphism, that plays an important role in promoting outcrossing and improving reproductive fitness. Although distyly is often studied in plants of the Rubiaceae family, little attention has been paid to the reproductive strategies of distylous species in fragmented habitats. Here, We report for the first time the growth of Ophiorrhiza alatiflora, a type distylous species, in karst areas and evaluate its reciprocity between long styled morph and short one. We analyze the two distyly morph differences in the ancillary polymorphic of flowers and explore their reproductive strategy in fragmented habitats.MethodsIn this study, we measured the floral characteristics of different morphs and performed differential secondary metabolite analysis on different morphs and tissue organs; Different pollination treatments were carried out to observe the fruit set, pollen germination, and pollen tube elongation of O. alatiflora.Results and discussionOur research indicates that O. alatiflora is a typical distylous plant for the distyly has high reciprocity. Both morphs exhibit the highest fruit set of intermorph outcrossing; The pollen germination and pollen tube elongation experiments have also demonstrated that the affinity of pollen from intermorph outcrossing is highest, regardless of whether it is the long or short morph as the maternal parent; Meanwhile, O. alatiflora is an incompletely self-incompatible plant that exhibits a certain degree of self-pollination and intramorph outcrossing, which may be one of the important means to ensure sustainable reproduction in severely disturbed habitats. In the ancillary polymorphic of flowers, L-morphs flowers produce more pollen, and S-morph flowers produce more ovules to improve their male-female fitness and compensate for the asymmetry of pollen flow; Compared with S-morphs, L-morphs contain significantly higher levels of several kinds of terpenoids. S-morphs produce more flavonoids than L-morphs. The differences in secondary metabolites between L-morphs and S-morphs are mainly reflected in the different nutritional organs (including stems and leaves). Overall, our work has revealed the unique reproductive strategy of O. alatiflora in fragmented habitats based on the characteristics of distyly, verifying the hypothesis that the distyly of O. alatiflora promotes outcrossing and avoids male-female interference, improving male-female fitness and this is the first time in the Ophiorrhiza genus.

Composition and Quality of Honey Bee Feed: The Methodology and Monitoring of Candy Boards.

The nutritional status of a honey bee colony is recognized as a key factor in ensuring a healthy hive. A deficient flow of nectar and pollen in the honey bee colony immediately affects its development, making room for pathogen proliferation and, consequently, for a reduction in the activities and strength of the colony. It is, therefore, urgent for the beekeepers to use more food supplements and/or substitutes in apiary management, allowing them to address colony nutritional imbalances according to the beekeeper's desired results. In this context, the commercial market for beekeeping products is growing rapidly due to low regulation of animal food products and the beekeeper's willingness to guarantee healthy colonies. There are numerous products (bee food additives) currently available on the worldwide market, with a highly variable and sometimes even undefined composition, claiming a set of actions at the level of brood stimulation, energy supplementation, queen rearing support, reduction of Varroa reproduction levels, improvement of the intestinal microflora of bees, Nosema prevention, and improvement of the health of honey bee colonies infested by American foulbrood, among others. To address this issue, the members of the COLOSS (Honey Bee Research Association) NUTRITION Task Force are proposing, for the first time, action on honey bee feed control and monitoring. In our common study, we focused on candy board composition and quality parameters. For that, a selected number of commercial candy boards usually found in Europe were analyzed in terms of water and ash content, pH, acidity, 5-hydroxymethylfurfural, sugars, C3-C4 sugar origin, and texture. Results revealed differences between the values found and the ones displayed on the label, demonstrating the need for regulation of the quality of these products.

Floral scents of the protogynous aroid Spathiphyllum cannifolium: Investigating the chemistry and timing of emission at female and male phases

AbstractSpathiphyllum is a Neotropical aroid genus whose inflorescences are composed of protogynous bisexual flowers that emit strong perfumes. These scents serve as both attractants and rewards for male euglossine pollinators. We investigated the inflorescence scent of S. cannifolium, asking whether inflorescence at female and male phases differ in scent traits. For this, we collected scent samples from inflorescence at the two phases using dynamic headspace methods and analyzed them by a gas chromatograph coupled to a mass spectrometer (GC‐MS). The inflorescence scent of S. cannifolium consisted of 26 compounds, with benzyl acetate as major component (ca. 80% of the scent bouquet). We found no quantitative or qualitative differences between scents of inflorescences at female and male phases, nor in the emission time. However, when considering the timing of scent emission among individuals, we observed two general plant groups. Some individuals emitted more scent at 06:00, while others emitted more scent at 09:00, independent of the sexual phase. The similarity of floral scents between the sexes might promote floral constancy by male euglossine pollinators and consequently alternate pollinator flow between inflorescences at female and male phases. The occurrence of the two general patterns of scent emission can be interpreted as a way to ensure the pollination service. Since plants emit scents in the morning, even outside the peak emission period, this would enable these plants to attract pollinators that are active at different times than the peak emission of floral scents. This way, it would ensure the flow of pollen, even if it occurs at a low frequency.

Spatial genetic structure of Ficus superba (Moraceae) in mainland and insular Singapore

Monoecious Ficus L. (Moraceae) species have putatively effective long-distance pollen dispersal and low population densities. The lack of spatially defined populations and the assumption of high gene flow led to the dearth of work on the Spatial Genetic Structure (SGS) of monoecious species. Furthermore, as only forest or inland species were studied, the effects of landscape heterogeneity and discontinuous habitats have been overlooked. To address this, Ficus superba (Miq.) Miq., a monoecious spatially aggregated coastal and insular species from Singapore, was studied to ascertain if population homogenisation could result from pollen flow even when the assumptions of spatial and landscape homogeneity were violated. Individuals were genotyped using dominant Amplified Fragment Length Polymorphism (AFLP) markers. Bayesian clustering software and Principal Component Analysis (PCA) were used to test for population genetic structure. SGS analyses and Mantel’s Tests were performed to test for the presence of significant fine-scale SGS and Isolation By Distance (IBD). Significant population genetic structure and SGS were found, with one mainland population more differentiated from the remaining insular and mainland populations. It is hypothesised that the spatial aggregation and landscape heterogeneity significantly distort gene flow through aggregated seed dispersal and greater impedance to pollen flow over land than sea. This calls into question the supposed dichotomy in gene flow characteristics of monoecious versus dioecious figs attributed to pollinator behaviour.

Pollen dispersal distance is determined by phenology and ancillary traits but not floral gender in an andromonoecious, fly-pollinated alpine herb

Pollen-mediated gene flow and spatial genetic structure have rarely been studied in alpine plants that are pollinated by dipteran insects. In particular, it is not clear how different floral traits, such as floral gender, phenology, and ancillary traits, may affect pollen dispersal distance within alpine plant populations. In this study, we conducted a paternity analysis to track pollen flow in a population of Pulsatilla alpina, an andromonoecious alpine herb producing male and bisexual flowers. We found that the pollen was dispersed over short distances (mean = 3.16 m), with a dispersal kernel following a Weibull distribution. Nonetheless, spatial genetic structure was weak in the population (Sp statistic = 0.013), pointing to effective seed dispersal and/or high inbreeding depression. The pollen dispersal distance was independent of the gender of the flower of origin but depended positively on floral stalk height and negatively on flowering date and tepal length. Although male siring success did not correlate with pollen dispersal distance, selection may favour traits that increase the pollen dispersal distance as a result of reduced bi-parental inbreeding. Our study not only provides new insights into the nature of pollen dispersal of alpine plants, but also reveals the effects of floral traits on a component of male reproductive success.

Multilayer diffusion networks as a tool to assess the structure and functioning of fine grain sub‐specific plant–pollinator networks

Interaction networks are a widely used tool to understand the dynamics of plant–pollinator ecological communities. However, while most mutualistic networks have been defined at the species level, ecological processes such as pollination take place at different scales, including the individual or patch levels. Yet, current approaches studying fine‐grain sub‐specific plant–pollinator networks only account for interactions among nodes belonging to a single plant species due to the conceptual and mathematical limitations of modeling simultaneously several plant species each composed of several nodes. Here, we introduce a multilayer diffusion network framework that allows modeling simple diffusion processes between nodes pertaining to the same or different layers (i.e. species). It is designed to depict from the network structure the potential conspecific and heterospecific pollen flows among plant individuals or patches. This potential pollen flow is modeled as a transport‐like system, in which pollen grain movements are represented as random‐walkers that diffuse on an ensemble of bipartite layers of conspecific plants and their shared pollinators. We exemplify this physical conceptualization using a dataset of nine fine‐grain sub‐specific plant–pollinator networks from a Mediterranean grassland of annual plants, where plant nodes represent groups of conspecifics within patches of 1 m2. The diffusion networks show pollinators effectively connecting sets of patches of the same and different plant species, forming a modular structure. Interestingly, different properties of the network structure, such as the conspecific pollen arrival probability and the number of conspecific subgraphs in which plants are embedded, are critical for the seed production of different plant species. We provide a simple but robust set of metrics to calculate potential pollen flow and scale down network ecology to functioning properties at the individual or patch level, where most ecological processes take place, hence moving forward the description and interpretation of species‐rich communities across scales.

Simulating pollen flow and field sampling constraints helps revise seed sampling recommendations for conserving genetic diversity.

In this study, we use simulations to determine how pollen flow and sampling constraints can influence the genetic conservation found in seed collections. We simulated genotypes of parental individuals and crossed the parentals based on three different ranges of pollen flow (panmictic, limited, and highly limited) to create new seed sets for sampling. We tested a variety of sampling scenarios modeled on those occurring in nature and calculated the proportion of alleles conserved in each scenario. We found that pollen flow greatly influences collection outcomes, with panmictic pollen flow resulting in seed sets containing 21.6% more alleles than limited pollen flow and 48.6% more alleles than highly limited pollen flow, although this impact diminishes when large numbers of maternal plants are sampled. Simulations of realistic seed sampling (sampling more seed from some plants and fewer from others) showed a relatively minor impact (<2.5%) on genetic diversity conserved compared to ideal sampling (uniform sampling across all maternal plants). We conclude that future work must consider limited pollen flow, but collectors can be flexible with their sampling in the field as long as many unique maternal plants are sampled. Simulations remain a fruitful method to advance ex situ sampling guidelines.

Floral morph variation mediated by clonal growth and pollinator functional groups of Limonium otolepis in a heterostylous fragmented population.

Abstract. Heterostyly, a genetic style polymorphism, is linked to symmetric pollen transfer, vital for its maintenance. Clonal growth typically impacts sexual reproduction by influencing pollen transfer. However, the floral morph variation remains poorly understood under the combined effects of pollinators and clonal growth in heterostyly characterized by negative frequency-dependent selection and disassortative mating. We estimated morph ratios, ramets per genet and heterostylous syndrome and quantified legitimate pollen transfer via clonal growth, pollinators and reciprocal herkogamy between floral morphs in Limonium otolepis, a fragmented population composed of five subpopulations in the desert environment of northwestern China, with small flower and large floral morph variation. All subpopulations but one exhibited pollen-stigma morphology dimorphism. The compatibility between mating types with different pollen-stigma morphologies remained consistent regardless of reciprocal herkogamy. Biased ratios and ramets per genet of the two mating types with distinct pollen-stigma morphologies caused asymmetric pollen flow and varying fruit sets in all subpopulations. Short-tongued insects were the primary pollinators due to small flower sizes. However, pollen-feeding Syrphidae sp. triggered asymmetry in pollen flow between high and low sex organs, with short-styled morphs having lower stigma pollen depositions and greater variation. Clonal growth amplified this variation by reducing intermorph pollen transfer. All in all,pollinators and clonal growth jointly drive floral morph variation. H-morphs with the same stigma-anther position and self-incompatibility, which mitigate the disadvantages of sunken low sex organs with differing from the classical homostyly, might arise from long- and short-styled morphs through a 'relaxed selection'. This study is the first to uncover the occurrence of the H-morph and its associated influencing factors in a distylous plant featuring clonal growth, small flowers and a fragmented population.

Diversity and genetic structure of yellow passion fruit in Boyacá-Colombia using microsatellite DNA markers.

The Yellow passion fruit belongs to the Passifloraceae family with great economic, nutritional and social importance in Colombia. It presents a great phenotypic and genotypic diversity, which has not yet been explored or used in genetic improvement programs. The objective of this study was to evaluate the genetic diversity of 84 cultivars of Passiflora edulis f. flavicarpa from nine farms in the municipality of Miraflores, Boyacá, using eight microsatellite markers (SSR). On the basis of this information, estimates of genetic diversity parameters, molecular variance analysis (AMOVA), genetic distances, and cluster of cultivars were obtained. Low levels of genetic differentiation between cultivars were observed in the Bayesian analysis using Structure software, as well as the absence of correlation between genetic and geographic distances. The observed heterozygosity (0.50) was greater than the expected heterozygosity (0.43), suggesting a significant number of heterozygous individuals. The number of alleles per locus varied from 2 to 4, with a mean 2.88. In general, SSR were classified as informative (0.36). The average value of the Shannon Index was 0.71, which shows moderate variability in this cultivar. AMOVA showed higher diversity within cultivars (98%). The gene flow (Nm=28.4) was moderate, this can be explained by the flow of pollen between the different cultivars, the reproduction system of the species, self-incompatibility and the introduction of genotypes from other sites by farmers. The genetic diversity identified in this study is sufficient to initiate breeding programs aimed at identifying cultivars with higher yields.

Disrupted connectivity within a metapopulation of a wind-pollinated declining conifer, Taxus baccata L.

Population connectivity through seed and pollen dispersal determines the genetic diversity, adaptive potential, and demography of plant metapopulations. In wind-pollinated trees, population connectivity is typically maintained by long-distance pollen flow, counteracting the genetic differentiation generated by drift and restricted seed dispersal. Although strong population fragmentation is theoretically expected to disrupt connectivity in forest trees, empirical evidence remains scarce and inconclusive. We investigated contemporary connectivity within a network of small remnant populations of a declining conifer (Taxus baccata L.), which have been hypothesized to be largely isolated from each other. We tested this hypothesis using molecular data for adult trees and naturally recruited seedlings from all known remnants across a fragmented landscape spanning a length of 20 ​km, and a specifically designed statistical approach to quantify contemporary pollen and seed migration rates between populations. We additionally assessed dispersal potential using a spatially explicit parentage analysis to estimate seed and pollen dispersal kernels within one of the remnants. Estimated pairwise migration rates between populations were barely detectable for seeds, while they were larger (up to 1.1%) and significant for pollen. Both seed and pollen migration rates decreased with geographic distance between populations, more steeply in the case of pollen migration. According to parentage-based dispersal kernels, 51.8% of seeds and 11.4% of pollen travel less than 25 ​m, whereas 0.2% of seeds and 36.1% of pollen travel more than 250 ​m from a source tree. In addition, 1.2% of pollen can travel more than 2.5 ​km. We showed that strong present-day population fragmentation, with separation distances over a few kilometers between small fragments, can substantially limit the connectivity of a wind-pollinated declining tree, leading to low pollen-mediated contemporary gene flow and null or virtually null demographic connectivity via seed dispersal.

Evaluation of the YOLO models for discrimination of the alfalfa pollinating bee species

Identifying insect pollinators and their roles in mediating pollen flow is critical to understand the potential gene flow risks of insect pollination-dependent crop species, such as alfalfa. This study was conducted to evaluate and compare the feasibility of You Only Look Once (YOLO) version 3 (YOLOv3), YOLOv5, YOLOv7, and YOLO Representation (YOLOR) to discriminate the three most common alfalfa pollinating bee species, including honeybee, bumblebee, and leafcutting bee. The metrics comparison results showed YOLOv3 and YOLOv5 outperformed YOLOv7 and YOLOR regarding model precision, recall, F1 score, and mAP50 values. YOLOv3 and YOLOv5 could successfully discriminate the three different bee species with an accuracy of almost 100% (99.9%, 99.8%, and 100% accuracy for honeybee, bumblebee, and leafcutting bee for the two models, respectively). Comparatively, YOLOv7 could discriminate honeybee with an accuracy of 95% but was more likely to mistakenly discriminate bumblebee and leafcutting bee due to the relatively lower discriminating accuracy (87.3% and 66.2%, respectively). While the values of determined parameters for YOLOR were lower than YOLOv3 and YOLOv5, the higher precision (0.99680) along with recall (0.98721), F1 (0.99198), mAP50 (0.99323), and mAP50-100 (0.89076) values indicate that this model could be able to obtain a favorable performance in discriminating the three bee species. In summary, the proposed method in this study has the potential for identifying the alfalfa pollinating bee species, studying the bees’ flower-visiting behaviors, evaluating the risks of insect-mediated pollen flow, and thus contributing to the management of genetically engineered (GE) alfalfa transgene flow.

Partial and asymmetrical reproductive isolation between two sympatric tropical shrub species: Cnidoscolus aconitifolius and C. souzae (Euphorbiaceae).

Reproductive isolation is conferred by several barriers that occur at different stages of reproduction. Comprehensive reviews on the topic have identified that barriers occurring prior to zygote formation are often stronger than those that occur afterward. However, the overrepresentation of temperate perennial herbs in the current literature precludes any generalization of this pattern to plants that present other life forms and patterns of distribution. Here, we assessed reproductive isolation barriers and their absolute contribution to reproductive isolation and asymmetry in Cnidoscolus aconitifolius and C. souzae, two closely related tropical shrub species that co-occur on the Yucatan peninsula. The reproductive barriers assessed were phenological mismatch, pollinator differentiation, pollen-pistil incompatibility (three pre-zygotic barriers), fruit set failure, and seed unviability (post-zygotic barriers). Reproductive isolation between the study species was found to be complete in the direction C. aconitifolius to C. souzae, but only partial in the opposite direction. One post-zygotic barrier was the strongest example. Most barriers, particularly the pre-zygotic examples, were asymmetrical and predicted the direction of heterospecific pollen flow and hybrid formation from C. souzae to C. aconitifolius. Both parental species, as well as the hybrids, were diploid and had a chromosome number 2n = 36. More studies with tropical woody perennials are required to fully determine whether this group of plants consistently shows stronger post-zygotic barriers.

Optimizing a Regional White Spruce Tree Improvement Program: SNP Genotyping for Enhanced Breeding Values, Genetic Diversity Assessment, and Estimation of Pollen Contamination

The utilization of genotyping has gained significant popularity in tree improvement programs, aiding in enhancing the precision of breeding values, removing pedigree errors, the assessment of genetic diversity, and evaluating pollen contamination. Our study explores the impact of utilizing 5308 SNP markers to genotype seed orchard parents (166), progeny in progeny trials (667), and seedlot orchard seedlings (780), to simultaneously enhance variance components, breeding values, genetic diversity estimates, and pollen flow in the Region I white spruce (Picea glauca) breeding program in central Alberta (Canada). We compared different individual tree mixed models, including pedigree-based (ABLUP), genomic-based (GBLUP), and single-step pedigree-genomic-based (ssGBLUP) models, to estimate variance components and predict breeding values for the height and diameter at breast height traits. The highest heritability estimates were achieved using the ssGBLUP approach, resulting in improved breeding value accuracy compared to the ABLUP and GBLUP models for the studied growth traits. In the six orchard seedlots tested, the genetic diversity of the seedlings remained stable, characterized by an average of approximately 2.00 alleles per SNP, a Shannon Index of approximately 0.44, and an expected and observed heterozygosity of approximately 0.29. The pedigree reconstruction of seed orchard seedlings successfully identified consistent parental contributions and equal genotype contributions in different years. Pollen contamination levels varied between 11% and 70% using SNP markers and 8% to 81% using pollen traps, with traps both over- and under-estimating contamination. Overall, integrating genomic information from parents and offspring empowers forest geneticists and breeders in the Region I white spruce breeding program to correct errors, conduct backward and forward selections with greater precision, gain a deeper understanding of the orchard’s genetic structure, select superior seedlots, and accurately estimate the genetic worth of each orchard lot, which can ultimately result in increased and more precise estimates of genetic gain in the studied growth traits.

The effects of altitude and rearing period on some characteristics of honey bee queens, Apis mellifera caucasica Gorbachev, 1916 (Hymenoptera: Apidae)

In the study, some characteristics of honey bee queens, Apis mellifera caucasica Gorbachev, 1916 (Hymenoptera: Apidae), reared at two different altitudes (140 m vs 920 m) and three rearing seasons (May, June-I, June-II) in 2019-2020 were examined in Ordu. These are larvae grafting, length of the queen cell, weight of queens at various periods, and spermathecae parameters of queens. One-day old 50 larvae were grafted at each period and altitude. The effect of period and period*altitude interaction on the weight at emergence of queen was significant (p&amp;lt;0.001) while the effect of altitude and year was nonsignificant. Weights at emergence of queens were lower in May at high altitudes and in June-II at low altitudes. The effects of year, period and altitude were significant (p&amp;lt;0.001) in the terms of the diameter and volume of the spermathecae, and the number of spermatozoa in the spermathecae. When the two-year data was evaluated together, the number of spermatozoa in the spermathecae was higher in the queen bees reared in May. It is recommended to pay attention to the period and altitude when pollen and nectar flow is intense in queen rearing in Ordu and similar climatic conditions.

Fine-scale genetic structure of co-occurring seagrass species highlights the importance of repeated seedling recruitment (Leyte Island, Philippines)

Seagrasses are recognized for their fundamental and ecological functions in coastal environments. Movement ecology and dispersal mechanism of organisms are hypothesized to have a profound significance for the dynamics and resilience of populations and ecosystems. We tested this hypothesis by comparing the genetic diversity and fine-scaled structure of co-occurring seagrass populations of Thalassia hemprichii and Cymodocea serrulata, which differ in their survival strategy and movement ecology. Two hundred eighty-four and two hundred sixty-three individuals of T. hemprichii and C. serrulata from 6 seagrass meadows along Leyte, Philippines were genotyped using 15 and 9 microsatellite markers, respectively. Thalassia hemprichii was observed to have higher genotypic diversity, while clonal elongation was more pronounced for C. serrulata. Repeated seedling recruitment followed by rhizome elongation was observed as an important strategy of resilience and indicated the complementary importance of both sexual and asexual reproduction of these species. Moreover, fine-scale spatial structure analysis revealed that repeated seed recruitment and pollen flow occurred locally, yielding higher kinship values at very close distances of < 5 m, indicating its importance for the maintenance of genetic diversity. An individual based STRUCTURE analysis showed three putative gene pools for both species. Overall, our findings have important implications for understanding the processes and dynamics of populations before conservation efforts. Depending on the strategy of the species, efforts should focus on preserving natural expansion of existing beds and enabling local seed recruitment for successful conservation.

Comparative analysis of molecular and morphological diversity in two diploid Paspalum species (Poaceae) with contrasting mating systems.

Interspecific comparison of two Paspalum species has demonstrated that mating systems (selfing and outcrossing) contribute to variation (genetically and morphologically) within species through similar but mutually exclusive processes. Mating systems play a key role in the genetic dynamics of populations. Studies show that populations of selfing plants have less genetic diversity than outcrossing plants. Yet, many such studies have ignored morphological diversity. Here, we compared the morphological and molecular diversity patterns in populations of two phylogenetically-related sexual diploids that differ in their mating system: self-sterile Paspalum indecorum and self-fertile P. pumilum. We assessed the morphological variation using 16 morpho-phenological characters and the molecular diversity using three combinations of AFLPs. We compared the morphological and molecular diversity within and among populations in each mating system. Contrary to expectations, selfers showed higher morphological variation within populations, mainly in vegetative and phenological traits, compared to outcrossers. The high morphological variation within populations of selfers led to a low differentiation among populations. At molecular level, selfing populations showed lower levels of genotypic and genetic diversity than outcrossing populations. As expected, selfers showed higher population structure than outcrossers (PhiST = 0.301 and PhiST = 0.108, respectively). Increased homozygous combinations for the same trait/locus enhance morphological variation and reduce molecular variation within populations in selfing P. pumilum. Thus, selfing outcomes are opposite when comparing morphological and molecular variation in P. pumilum. Meanwhile, pollen flow in obligate outcrossing populations of P. indecorum increases within-population molecular variation, but tends to homogenize phenotypes within-population. Pollen flow in obligate outcrossers tends to merge geographically closer populations; but isolation by distance can lead to a weak differentiation among distant populations of P. indecorum.

The effect of species role and trait-matching on plant fitness in a plant-hummingbird interaction network

In animal-pollinated plants, fitness is affected by pollinator attraction and plant-pollinator trait matching. Plant-pollinator interactions are often characterized using metrics derived from mutualistic networks, such as centrality and interaction selectivity. This approach often focuses on the species level, thus neglecting significant among-individual variation in attracting foraging pollinators and associated fitness consequences for plants. Here, we tested if centrality and interaction selectivity were related to fitness at the species and the individual level for 14 hummingbird-pollinated plant species in the Atlantic Forest. In addition, we tested if plant-pollinator trait-matching influenced plant fitness. At the species-level, we did not find a relationship between plant fitness and centrality nor interaction selectivity; we found instead that plant fitness increased with higher trait-matching between bill and corolla lengths. At the individual-level we found that individuals with higher centrality values produced less seeds, likely due to lower quality in pollen deposition. Moreover, individuals with a lower interaction selectivity also produced more seeds, probably because of higher conspecific pollen flow. Our results show that individual position and interaction selectivity within pollination networks may have important implications for pollination effectiveness and hence plant fitness.

Direct tracking of pollen with quantum dots reveals surprising uniformity in dispersal distance across 11 populations of an annual plant.

Pollen movement is a crucial component of dispersal in seed plants. Although pollen dispersal is well studied, methodological constraints have made it challenging to directly track pollen flow within multiple populations across landscapes. We labeled pollen with quantum dots, a new technique that overcomes past limitations, to evaluate the spatial scale of pollen dispersal and its relationship with conspecific density within 11 populations of Clarkia xantiana subsp. xantiana, a bee-pollinated annual plant. We used experimental arrays in two years to track pollen movement across distances of 5-35 m within nine populations and across distances of 10-70 m within two additional populations. We tested for distance decay of pollen dispersal, whether conspecific density modulated dispersal distance, and whether dispersal kernels varied among populations across an environmentally complex landscape. Labeled pollen receipt did not decline with distance over 35 m within eight of nine populations or over 70 m within either of two populations. Pollen receipt increased with conspecific density. Overall, dispersal kernels were consistent across populations. The surprising uniformity in dispersal distance within different populations was likely influenced by low precipitation and plant density in our study years. This suggests that spatiotemporal variation in the abiotic environment substantially influences the extent of gene flow within and among populations.

Pollination success of Fraxinus excelsior L. in the context of ash dieback

Key messagePaternity analyses show that effective pollination of ash (Fraxinus excelsior L.) in a seed orchard and a floodplain forest affected by ash dieback is more likely to be facilitated by healthier males. Thereby, natural selection can have a positive effect on the health of future generations.ContextOngoing ash dieback and increasing fragmentation of ash populations may result in reduced pollen flow, which can reduce pollination success of future generations of ash trees. Therefore, it is essential to further improve our understanding of gene flow patterns, especially with respect to ash dieback.AimsIn this study, paternity analyses were conducted in a seed orchard and a floodplain forest in Germany in 2018 to explain the relationship between pollination success and the health status of ash trees and distances of effective pollen transport.MethodsCambium samples (i.e., from twigs and stumps) were collected from 251 ash trees (putative father and mother trees) for genotyping, and the health status of each tree was documented using a scoring system to evaluate vitality. Additionally, seeds were harvested from 12 mother trees per site. Genetic analyses using nuclear microsatellites were performed to determine paternal trees. Paternities were assigned based on the likelihood model implemented in the Cervus 3.0.7 software.ResultsOur results showed that the average pollination distance was 76 m in the seed orchard and 166 m in the floodplain forest. In general, pollination success decreased substantially with increasing distance to the mother tree. Despite the dense tree cover in the floodplain forest, pollen were transported over long distances (greater than 550 m), suggesting that non-local sources also play a role in pollination. This is supported by the foreign pollen input identified in the seed orchard (66.5%). Self-pollination was detected only to a very small extent, and thus had no major influence on reproduction. In addition, both healthy and slightly diseased father trees showed similar mating success. However, this was not the case for the severely diseased ash trees (more than 50% of crown damage) because only a few offspring could be assigned to them. Nevertheless, in contrast to the floodplain forest, there was no significant correlation between damage classes and pollination success in the seed orchard.ConclusionLong-distance pollen transport contributes to the connectivity of ash trees in the landscape. Additionally, both healthy and slightly diseased fathers have a greater contribution to pollination, thus potentially improving the health of the next generation of ash trees. Moreover, gene flow between stepping stone populations is necessary to ensure the positive impact on the genetic diversity of ash populations in the future.

Protective nets reduce pollen flow in blueberry orchards

Protective covers are commonly employed in agricultural systems to reduce the impacts of extreme weather events, pest species and to control the environmental conditions in which crop plants are grown. As protected cropping systems are expanding rapidly, there is an urgent need to better understand how variations in netting practices might impact pollination service delivery by wild and managed insects to pollinator dependent crops. We used southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid) crops to investigate (i) how variations in protected cropping structures (fully netted, partially netted and unnetted blocks) influence the amount and composition of pollen deposited on crop stigmas; (ii) to what extent blueberry floral abundance and plant richness in remnant vegetation influence pollen composition on crop stigmas; and (iii) the difference between stigmatic pollen load composition in the middle and at the edge of crop blocks. We collected data from 15 field blocks of 6 different cultivars distributed on 10 farms. We collected blueberry stigmas to analyse the pollen load and measured blueberry floral abundance and richness of flowering plant taxa in remnant vegetation every two weeks. Our results indicate that blueberry pollen abundance on stigmas was reduced by up to 81% under full netting and 36% by partial netting. On blueberry stigmas, we identified a total of 31 morphospecies of non-blueberry pollen from 20 plant families. There was no relationship between blueberry stigmatic pollen loads and blueberry floral abundance. Moreover, the composition of non-blueberry pollen on stigmas differed between blueberry blocks under different netting categories. However, there was no relationship between plant taxa present in the surrounding remnant vegetation of each block and the pollen load on the stigmas of each block. Combining all netting treatments, stigmas located at the edge of the blocks received a greater amount of both conspecific (5% more) and heterospecific (40% more) pollen grains than those within the middle of blocks. Pollen flow in fields is reduced under netting structures as well as in the middle of blocks. Reduced blueberry pollen flow under nets may be detrimental to fruit yield and quality for some varieties of pollinator dependent crops, particularly those that are self-incompatible.