Pollen Pool Research Articles

Effects of forest fragmentation on the mating system of a cool-temperate heterodichogamous tree Acer mono

Pollination is a key process for reproduction and gene flow in flowering plants. Anthropogenic habitat fragmentation, however, can disrupt plant–pollinator interactions, and may have a negative impact on the reproductive success and population viability of entomophilous plants. Heterodichogamous plants containing protandrous and protogynous individuals within a population may be susceptible to habitat fragmentation due to a lack of available mating partners. In this study, we investigated the effects of forest fragmentation on the mating system in the heterodichogamous plant Acer mono, a major constituent of cool-temperate deciduous forests in Japan. Microsatellite analysis was applied to 212 adult trees and 17 seed families from continuous and fragmented forests. Dispersal kernel modeling using the neighborhood model indicated that pollen dispersal of A. mono was highly fat-tailed. The estimated parameters of the model suggested that the siring success of a pollen donor increased approximately fivefold, with a 100 cm increase in its diameter at breast height (DBH), and that disassortative mating was five times more frequent than assortative mating. The mating system parameters of each mother tree, outcrossing rate (tm), biparental inbreeding (tm−ts), and paternity correlation (rpm) varied among sites and conditions, depending on the local density of potential pollen donors. Whereas A. mono was effectively outcrossed (tm=0.901, tm−ts=0.052, and the number of effective sires was 1/rpm=14.93) in the continuous forest, clumped trees within the fragmented forest showed increased biparental inbreeding and reduced pollen pool genetic diversity (tm=0.959, tm−ts=0.245,1/rpm=1.742) as a result of localized mating combined with spatial genetic structures. In contrast, the isolated trees had a higher selfing rate, but the pollen pool diversity was maintained (tm=0.801, tm−ts=0.022, and 1/rpm=15.63) due to frequent long-distance pollination. These results suggest that although pollen limitation following habitat fragmentation could result in negative genetic consequences, enhanced long-distance pollination across a fragmented landscape could partly compensate for this limitation depending on the degree of forest fragmentation.

Extensive pollen flow in a natural fragmented population of Patagonian cypress Austrocedrus chilensis

Habitat fragmentation might significantly affect mating and pollen dispersal patterns in plant populations, contributing to the decline of remnant populations. However, wind-pollinated species are able to disperse pollen at longer distances after opening of the canopy. Our objectives were to characterize the mating system parameters and to estimate the average distance of effective pollen dispersal in the wind- pollinated conifer Austrocedrus chilensis. We sampled 19 "mother trees," 200 progeny, and 81 additional adults (both male and female), in a fragmented population at the Argentinean Patagonian steppe. We registered the spatial po- sitions of individuals and genotyped all samples with five microsatellite markers. We found a high genetic diversity, a moderated rate of biparental inbreeding (tmts=0.105), and a complete absence of correlated paternity (rp=−0.015). The effective number of pollen donors contributing to a single mother (Nep) was 13.9. Applying TWOGENER,weestimated a low but significant differentiation among the inferred pollen pools (ΦFT=0.036,p=0.001) and a very large average pollen dispersal distance (d=1,032.3 m). The leptokurtic distribution (b=0.18) presumes a potential for even larger dispersal dis- tances. The high genetic diversity, the mating patterns, and the extensive pollen dispersal presume that habitat fragmentation did not have a negative impact on pollen movement in this population of A. chilensis. Genetic connectivity among fragmented populations scattered in the Patagonian region is possible, and we stress the need of management policies at the landscape level.

The gravity of pollination: integrating at-site features into spatial analysis of contemporary pollen movement.

Pollen-mediated gene flow is a major driver of spatial genetic structure in plant populations. Both individual plant characteristics and site-specific features of the landscape can modify the perceived attractiveness of plants to their pollinators and thus play an important role in shaping spatial genetic variation. Most studies of landscape-level genetic connectivity in plants have focused on the effects of interindividual distance using spatial and increasingly ecological separation, yet have not incorporated individual plant characteristics or other at-site ecological variables. Using spatially explicit simulations, we first tested the extent to which the inclusion of at-site variables influencing local pollination success improved the statistical characterization of genetic connectivity based upon examination of pollen pool genetic structure. The addition of at-site characteristics provided better models than those that only considered interindividual spatial distance (e.g. IBD). Models parameterized using conditional genetic covariance (e.g. population graphs) also outperformed those assuming panmixia. In a natural population of Cornus florida L. (Cornaceae), we showed that the addition of at-site characteristics (clumping of primary canopy opening above each maternal tree and maternal tree floral output) provided significantly better models describing gene flow than models including only between-site spatial (IBD) and ecological (isolation by resistance) variables. Overall, our results show that including interindividual and local ecological variation greatly aids in characterizing landscape-level measures of contemporary gene flow.

Tree density and population size affect pollen flow and mating patterns in small fragmented forest stands of pedunculate oak (Quercus robur L.)

In many parts of the world, once large and continuous forests have been replaced by a mosaic of isolated forest fragments embedded in an agricultural or urban landscape matrix. At the same time, stand characteristics such as tree population size and tree density have been strongly modified as a result of anthropogenic activities. Because increased geographical isolation can impede gene flow among forest fragments, and because decreased population size and tree density may reduce the number of local mating partners, this can be expected to lower the opportunity to trees for outcrossing, and to result in increased inbreeding, negatively impacting the viability of fragmented tree populations. In this study, we examined eight isolated stands of the wind-pollinated tree species Q. robur that strongly differed in population size, tree density and spatial isolation. In the centre of each Q. robur stand, adult leaves and seeds were collected in a circular plot, in which we evaluated the diversity and differentiation of the local pollen pool, and examined mating patterns. Most forest stands showed high proportions of out-of-plot pollen flow (range: 0.24–0.77), which were positively correlated with the number and density of adult trees within the forest stands. Despite high outcrossing rates (>0.998), seeds within seed families were stronger related than what could be expected under panmixia, which could be attributed to small but significant levels of correlated paternity (0.018–0.107) and biparental inbreeding (0.025–0.118) within the study plots. Next to increased coancestry coefficients, deviations from random mating also resulted in significant pollen pool differentiation (0.008–0.059) among seed parents. We also found that stand population size and tree density were significantly correlated to the relatedness of the seedlings and the degree of pollen differentiation within the study plots. These results suggest that, in small and isolated low density forest stands, reduced mate availability may decrease local pollen pool diversity, increasing the likelihood of consanguineous mating and pollen pool differentiation in the next generations. We conclude that preserving high levels of pollen flow within and between forest fragments may be more important in wind-pollinated tree species than what was previously thought.

Genetic diversity, spatial genetic structure and realised seed and pollen dispersal of Himatanthus drasticus (Apocynaceae) in the Brazilian savanna

We assessed the pollen and seed dispersal patterns, genetic diversity, inbreeding and spatial genetic structure of Himatanthus drasticus (Apocynaceae), a tree native to the Brazilian Savanna (Cerrado) that is heavily exploited for its medicinal latex. The study was conducted in the Araripe National Forest, Ceara State, Brazil. Within a one-hectare plot, samples were collected from all adult trees, adult trees located in the immediate vicinity of the plot, and seedlings. All sampled individuals were mapped and genotyped using microsatellite markers. High levels of polymorphism and significant levels of inbreeding were found, which indicates that self-fertilisation and mating among relatives occur in this population. Both the adults and seedlings had significant spatial genetic structure up to ~40 m and our results confirmed the occurrence of isolation by distance. Pollen and seeds were dispersed over short distances and immigration of pollen and seeds into the plot was estimated at 13 and 9 %, respectively. Taking into consideration the degree of inbreeding, relatedness, intrapopulation spatial genetic structure and pollen dispersal distance, we recommend collecting seeds from a large number of trees spaced at least 150 m apart to avoid collecting seeds from related individuals and an overlap of pollen pools among seed trees.

Development of a regional-scale pollen emission and transport modeling framework for investigating the impact of climate change on allergic airway disease.

Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O3, PM2.5, and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.

Development of a regional-scale pollen emission and transport modeling framework for investigating the impact of climate change on allergic airway disease

Abstract. Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF/CMAQ) modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California (USA) for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O3, PM2.5, and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.

Mating between Echinacea angustifolia (Asteraceae) individuals increases with their flowering synchrony and spatial proximity

Although spatial distance is considered the primary factor in determining plant mating patterns, flowering time and synchrony are also likely to be important. We quantified the relationships of both distance and flowering phenology to the probability of mating between individual plants. In an experimental plot, we followed daily flowering phenology in Echinacea angustifolia, a self-incompatible perennial pollinated by solitary bees. We assigned paternity to 832 of 927 seedlings from 37 maternal plants using 11 microsatellite loci. Potential pollen donors included the experiment plot's 202 flowering plants and a nearby plot's 19 flowering plants. For each maternal plant sampled, we examined the pollen pool by quantifying correlated paternity and the effective number of pollen donors. Significantly more pollinations occurred between neighboring and synchronous plants than expected under random mating, with distance being more important than flowering synchrony. The distance pollen moved varied over the course of the season, with late flowering plants mating with more distant plants compared to early or peak flowering plants. All maternal plants had a diverse set of mates (mean number of effective pollen donors = 23.7), and the composition of the pollen pools overlapped little between maternal plants. Both distance and flowering synchrony influenced pollination patterns in E. angustifolia. Our results suggest that pollen movement between incompatible mates and flowering asynchrony could be contributing to the reduced seed set observed in small E. angustifolia remnants. However, we also found that individual plants receive pollen from a diverse group of pollen donors.

Pollen, wind and fire: how to investigate genetic effects of disturbance‐induced change in forest trees

Understanding the consequences of habitat disturbance on mating patterns although pollen and seed dispersal in forest trees has been a long-standing theme of forest and conservation genetics. Forest ecosystems face global environmental pressures from timber exploitation to genetic pollution and climate change, and it is therefore essential to comprehend how disturbances may alter the dispersal of genes and their establishment in tree populations in order to formulate relevant recommendations for sustainable resource management practices and realistic predictions of potential adaptation to climate change by means of range shift or expansion (Kremer et al. 2012). However, obtaining reliable evidence of disturbance-induced effects on gene dispersal processes from empirical evaluation of forest tree populations is difficult. Indeed, tree species share characteristics such as high longevity, long generation time and large reproductive population size, which may impede the experimenter's ability to assess parameters at the spatial and time scales at which any change may occur (Petit and Hampe 2006). It has been suggested that appropriate study designs should encompass comparison of populations before and after disturbance as well as account for demonstrated variation in conspecific density, that is, the spatial distribution of mates, and forest density, including all species and relating to alteration in landscape openness (Bacles & Jump 2011). However, more often than not, empirical studies aiming to assess the consequences of habitat disturbance on genetic processes in tree populations assume rather than quantify a change in tree densities in forests under disturbance and generally fail to account for population history, which may lead to inappropriate interpretation of a causal relationship between population genetic structure and habitat disturbance due to effects of unmonitored confounding variables (Gauzere et al. 2013). In this issue, Shohami and Nathan (2014) take advantage of the distinctive features of the fire-adapted wind-pollinated Aleppo pine Pinus halepensis (Fig. 1) to provide an elegant example of best practice. Thanks to long-term monitoring of the study site, a natural stand in Israel, Shohami and Nathan witnessed the direct impact of habitat disturbance, here taking the shape of fire, on conspecific and forest densities and compared pre- and postdisturbance mating patterns estimated from cones of different ages sampled on the same surviving maternal individuals (Fig. 2). This excellent study design is all the more strong that Shohami and Nathan took further analytical steps to account for confounding variables, such as historical population genetic structure and possible interannual variation in wind conditions, thus giving high credibility to their findings of unequivocal fire-induced alteration of mating patterns in P. halepensis. Most notably, the authors found, at the pollen pool level, a disruption of local genetic structure which, furthermore, they were able to attribute explicitly to enhanced pollen-mediated gene immigration into the low-density fire-disturbed stand. This cleverly designed research provides a model approach to be followed if we are to advance our understanding of disturbance-induced dispersal and genetic change in forest trees.

BREAKDOWN OF DIOECY: MODELS WHERE MALES ACQUIRE COSEXUAL FUNCTIONS

We have reanalyzed models of the breakdown of dioecy involving modified males to investigate female frequencies in the resulting gynodioecious populations. We extend and simplify previous treatments to deal with biologically relevant factors including pollen limitation, partial selfing of modified males, and inbreeding depression, to highlight the different empirically detectable advantages that may be gained by modified males that can reproduce as cosexes (i.e., can produce some seeds); these include "inconstant males," which can sometimes display some female function. Males reproducing wholly or occasionally as cosexual phenotypes can gain the transmission advantage of selfing, if partial self-fertilization is possible, and from reproductive assurance when pollen is limiting. If, because of resource limitation, such cosexual phenotypes produce fewer ovules than females, their nonselfed ovules will require a lower pollen pool size for full seed-set, compared with females. We investigate the conditions for these benefits to allow modified males to invade dioecious populations. Sometimes, such invasion leads to replacement of dioecy by the cosexual type, but sometimes the breakdown populations remain sexually polymorphic. When competition occurs between genotypes in the pollen load on a flower, high female frequencies can arise when Y chromosome-bearing pollen competes poorly with X pollen.

Extensive pollen immigration and no evidence of disrupted mating patterns or reproduction in a highly fragmented holm oak stand

Aims Forest fragmentation and reduced tree population densities can potentially have negative impacts on mating patterns, offspring genetic diversity and reproductive performance. The aim of the present study is to test these hypotheses comparing an extremely fragmented, low tree density (~0.02 trees/ha) holm oak (Quercus ilex L.) stand from Central Spain with a nearby high tree density stand (~50 trees/ha). Methods We genotyped adult trees and seeds from the low-density stand (436 seeds from 15 families) and the high-density stand (404 seeds from 11 families) using nine microsatellite markers. With these data, we performed paternity analyses, determined pollen flow, mating patterns and pollen pool structure, and estimated progeny genetic diversity in both stands. We also studied seed set and production and performed a pollen supplementation experiment to determine whether reduced tree density has limited foreign pollen availability. Important Findings We have found extensive pollen immigration (>75%) into the low tree density stand and Monte Carlo simulations revealed that pollen moves larger distances than expected from null models of random dispersal. Mating patterns and differentiation of pollen pools were similar in the high-density stand and the low-density stand but we found higher inter-annual differentiation of pollen pools in the for mer. Progeny genetic diversity and self-fertilization rates did not differ between the low-density stand and the high-density stand. Seed set rates were significantly lower in the low-density stand than in the high-density stand and experimental cross-pollen supplementation evidenced that foreign pollen availability is indeed a limiting factor in the former. However, seed crops did not differ between the low-density stand and the high-density stand, indicating that limitation of foreign pollen is not likely to be of great concern in terms of reduced seed production and potential recruitment. Poor forest regeneration due to other ecological and human factors is probably a more important threat for the persistence of fragmented and low tree density stands than reduced pollen flow and only extremely small and isolated tree populations would be expected to suffer severe loss of genetic diversity in the long term.

Seeing the forest through the trees: comprehensive inference on individual mating patterns in a mixed stand of Quercus robur and Q. petraea

Sexual reproduction is one of the most important moments in a life cycle, determining the genetic composition of individual offspring. Controlled pollination experiments often show high variation in the mating system at the individual level, suggesting a persistence of individual variation in natural populations. Individual variation in mating patterns may have significant adaptive implications for a population and for the entire species. Nevertheless, field data rarely address individual differences in mating patterns, focusing rather on averages. This study aimed to quantify individual variation in the different components of mating patterns. Microsatellite data were used from 421 adult trees and 1911 seeds, structured in 72 half-sib families collected in a single mixed stand of Quercus robur and Q. petraea in northern Poland. Using a Bayesian approach, mating patterns were investigated, taking into account pollen dispersal, male fecundity, possible hybridization and heterogeneity in immigrant pollen pools. Pollen dispersal followed a heavy-tailed distribution (283 m on average). In spite of high pollen mobility, immigrant pollen pools showed strong genetic structuring among mothers. At the individual level, immigrant pollen pools showed highly variable divergence rates, revealing that sources of immigrant pollen can vary greatly among particular trees. Within the stand, the distribution of male fecundity appeared highly skewed, with a small number of dominant males, resulting in a ratio of census to effective density of pollen donors of 5·3. Male fecundity was not correlated with tree diameter but showed strong cline-like spatial variation. This pattern can be attributed to environmental variation. Quercus petraea revealed a greater preference (74 %) towards intraspecific mating than Q. robur (36 %), although mating preferences varied among trees. Mating patterns can reveal great variation among individuals, even within a single even-age stand. The results show that trees can mate assortatively, with little respect for spatial proximity. Such selective mating may be a result of variable combining compatibility among trees due to genetic and/or environmental factors.

Long‐term effects of habitat fragmentation on mating patterns and gene flow of a tropical dry forest tree, Ceiba aesculifolia (Malvaceae: Bombacoideae)

Tropical forest loss and fragmentation isolate and reduce the size of remnant populations with negative consequences for mating patterns and genetic structure of plant species. In a 4-yr study, we determined the effect of fragmentation on mating patterns and pollen pool genetic structure of the tropical tree Ceiba aesculifolia in two habitat conditions: isolated trees in disturbed areas (≤3 trees/ha), and trees (≥6 trees/ha) in undisturbed mature forest. • Using six allozyme loci, we estimated the outcrossing rate (tm), the mean relatedness of progeny (rp) within and between fruits, the degree of genetic structure of pollen pools (Φft), and the effective number of pollen donors (Nep). • The outcrossing rates reflected a strict self-incompatible species. Relatedness of progeny within fruits was similar for all populations, revealing single sires within fruits. However, relatedness of progeny between fruits within trees was consistently greater for trees in fragmented conditions across 4 yr. We found high levels of genetic structure of pollen pools in all populations with more structure in isolated trees. The effective number of pollen donors was greater for trees in undisturbed forest than in disturbed conditions. • Our study showed that the progeny produced by isolated trees in disturbed habitats are sired by a fraction of the diversity of pollen donors found in conserved forests. The foraging behavior of bats limits the exchange of pollen between trees, causing higher levels of progeny relatedness in isolated trees.

PATTERNS OF MATING, GENERATION OF DIVERSITY, AND FITNESS OF OFFSPRING IN AGEUMHYBRID SWARM

To understand the evolutionary consequences of hybridization between the outcrossing plant Geum rivale (Rosaceae) and the selfer Geum urbanum, we tested the predictions of two simple models that assume either (A) low or (B) high pollen fitness in hybrids. Model A predicts only four genotypic classes (G. rivale, G. rivale backcross [BC(R)], F1, and Geum urbanum) and asymmetric introgression from inbreeding to outbreeding species. Model B predicts additional genotypic classes and potential generation of novel inbreeding lines in the hybrid swarm. Amplified fragment length polymorphism (AFLP) analysis of adults revealed only the four genotypes predicted by model A. However, microsatellite analysis of parent-progeny arrays demonstrated production of selfed offspring by F1 and BC(R) maternal parents and contribution of these genotypes to outcross pollen pools, as predicted by model B. Moreover, AFLP and morphological analysis showed that the offspring generation comprised genotypes and phenotypes covering the entire spectrum of variation between the two parental species, in line with model B. A common garden experiment indicated no systematic reduction in fitness of offspring derived from hybrid parents. The genetic structure of the adults in the Geum hybrid swarm cannot be explained by restricted mating patterns but may result from ecological selection acting on a diverse offspring population.

Note on the Applicability of the F-model in Analysis of Pollen Pool Heterogeneity

Measuring genetic structure of pollen gametes has become the standard approach in studies on plant mating system and pollen flow. However, the popular statistical procedure, TwoGener, provides the point estimate of the pollen pool heterogeneity based on AMOVA, implying any statistical tests regarding pollen pool structure to be based on permutation procedures. In this article, the Bayesian approach was developed based on the Dirichlet-multinomial model (the so-called F-model). Computer simulations revealed the applicability of the Bayesian method in the analysis of pollen pool heterogeneity. Compared with TwoGener, the Bayesian method appeared to have better statistical properties when estimating the inverse of heterogeneity index, mostly due to the relatively high accuracy of the Bayesian estimate when the actual heterogeneity is low. Hence, the Bayesian approach may be preferred, for example, when the effective number of pollen parents is to be assessed. Other applications and potential further developments of the Bayesian method are also briefly discussed.

Resilient Plant–Bird Interactions in a Volcanic Island Ecosystem: Pollination of Japanese Camellia Mediated by the Japanese White-Eye

Observations of interspecies interactions during volcanic activity provide important opportunities to study how organisms respond to environmental devastation. Japanese camellia (Camellia japonica L.) and its main avian pollinator, the Japanese White-eye (Zosterops japonica), offer an excellent example of such an interaction as key members of the biotic community on Miyake-jima, which erupted in 2000 and continues to emit volcanic gases. Both species exhibit higher resistance to volcanic damage than other species. We examined the effects of volcanic activity on this plant–pollinator system by estimating pollen flow and the genetic diversity of the next generation. The results showed that despite a decrease in Camellia flowers, the partitioning of allelic richness among mother-tree pollen pools and seeds decreased while the migration rate of pollen from outside the study plot and the pollen donor diversity within a fruit increased as the index of volcanic damage increased. In areas with low food (flower) density due to volcanic damage, Z. japonica ranged over larger areas to satisfy its energy needs rather than moving to areas with higher food density. Consequently, the genetic diversity of the seeds (the next plant generation) increased with the index of volcanic damage. The results were consistent with previously published data on the movement of Z. japonica based on radio tracking and the genetic diversity of Camellia pollen adhering to pollinators. Overall, our results indicated that compensation mechanisms ensured better pollination after volcanic disturbance.

Edge effects enhance selfing and seed harvesting efforts in the insect-pollinated Neotropical tree Copaifera langsdorffii (Fabaceae)

Edge effects may affect the mating system of tropical tree species and reduce the genetic diversity and variance effective size of collected seeds at the boundaries of forest fragments because of a reduction in the density of reproductive trees, neighbour size and changes in the behaviour of pollinators. Here, edge effects on the genetic diversity, mating system and pollen pool of the insect-pollinated Neotropical tree Copaifera langsdorffii were investigated using eight microsatellite loci. Open-pollinated seeds were collected from 17 seed trees within continuous savannah woodland (SW) and were compared with seeds from 11 seed trees at the edge of the savannah remnant. Seeds collected from the SW had significantly higher heterozygosity levels (Ho=0.780; He=0.831) than seeds from the edge (Ho=0.702; He=0.800). The multilocus outcrossing rate was significantly higher in the SW (tm=0.859) than in the edge (tm=0.759). Pollen pool differentiation was significant, however, it did not differ between the SW (=0.105) and the edge (=0.135). The variance effective size within the progenies was significantly higher in the SW (Ne=2.65) than at the edge (Ne=2.30). The number of seed trees to retain the reference variance effective size of 500 was 189 at the SW and 217 at the edge. Therefore, it is preferable that seed harvesting for conservation and environmental restoration strategies be conducted in the SW, where genetic diversity and variance effective size within progenies are higher.

Estimating coancestry within open-pollinated progenies of a dioecious species: the case study of Myracrodruon urundeuva

AbstractUnderstanding the coancestry coefficient within openpollinated progenies has long been an area of interest because of the implications of coancestry on estimates of additive genetic variation, variance effective size and the number of seed trees required for seed collection for ex situ conservation, tree breeding and environmental restoration. This study compares three methods to calculate the coancestry coefficient within open-pollinated progenies of the dioecious tree species, Myracrodruon urundeuva, using six microsatellite loci. The methods compared were: i) correlated mating model (CMM) (RITLAND, 1989); ii) TWOGENER method (SMOUSE et al., 2001) to estimate the differentiation among pollen pools (TGM); and iii) HARDY et al.’s 2004 method using the estimate of coancestry from LOISELLE et al. (1995) (HLM) and from RITLAND (1996) (HRM). The data analysis was based on four data sets: two populations were composed of 12 progenies, two of 24 progenies, and all progenies consisted of 15 plants. The coancestry estimated using CMM ranged among populations from 0.145 to 0.158, using TGM it ranged from 0.153 to 0.181, using HLM from 0.153 to 0.162, and HRM from 0.144 to 0.147. To investigate the bias of the estimates of true relatedness within progenies we simulated two half-sib and two full-sib populations. The most accurate method found in the study was CMM because the estimated values presented no bias for true half- or full-sib progenies and these values were very similar to those expected (0.125 and 0.25, respectively). These results have significant implications for breeding and conservation programs because coancestry-within-progenies is a key parameter in assessing the variance effective size.

Genetic diversity of Pinus densiflora pollen flowing over fragmented populations during a mating season

We attempted to evaluate the genetic diversity of long-distance transported pollen flowing over fragmented Pinus densiflora populations during a mating season. A P. densiflora clonal seed orchard, which was located in a rural area where many fragmented populations exist, was selected for pollen capture. Immigrant pollen captured by three clones having different flowering times was regarded as the pollen flowing over fragmented populations during a mating season. The genetic diversity (He) values of the immigrant pollen captured by the three clones were high (He > 0.894). The correlation of paternity (rp) values of the seeds having immigrant parent generated from the three clones were calculated to be negative. From these parameters, the pollen cloud is considered to have maintained high genetic diversity during the mating season. The genetic composition of the pollen cloud showed slight variation. The pollen captured by different trees (i.e., clonal ramets of the three clones) was significantly different based on analysis of molecular variance. Especially, the pollen pools captured by trees planted in the western side of the orchard were significantly different from the gene pool of the surrounding populations. Factors affecting this differentiation could be that the donors of the pollen transported to the orchard vary with time, as well as nonuniform dispersal of the pollen. From these results, the pollen flowing over fragmented P. densiflora populations is considered to have high genetic diversity, compensating to some extent for fragmentation.

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.