马尾松二代无性系种子园子代父本分析及花粉散布

目前国内较早建立的马尾松(Pinus massoniana)二代种子园正陆续进入正常开花结实期。研究马尾松二代种子园花粉散布和自由授粉子代的父本组成, 可为生产上指导马尾松高世代种子园的规划设计和遗传管理提供理论依据。该文利用筛选的11对SSR引物, 对马尾松二代无性系种子园内8个无性系单株的320个自由授粉子代和48个候选父本进行了扩增, 并采用最大似然法对子代进行父本分析。结果表明: 11个位点共检测到61个等位基因, 每个位点的等位基因数在2-11之间, 平均为5.55个。试验亲本和子代群体的总平均观测杂合度(H_o)、期望杂合度(H_e)及多态信息含量(PIC)分别为0.428、0.433和0.387。在80%的可信度水平下可为232 (72.50%)个子代确定其父本。平均每个采种母树与19个父本产生子代。在自由授粉状态下, 马尾松二代种子园自交率为1.72%, 自交现象很弱, 其交配方式以异交为主。绝大多数亲本无性系的雄性繁殖适合度在1.00%-4.00%之间, 候选父本平均繁殖适合度为2.17%, 平均形成5个后代。马尾松有效花粉的散布距离和固定交配距离的父本繁殖适合度均符合正态分布, 两者呈极显著负相关, 其主要散布距离集中在0-100 m, 而检测到的最大散布距离为192 m。种子园花粉污染率较低, 仅为4.06%。总体看来, 树冠南面子代亲本交配距离较北面有增加的趋势, 但树冠南、北面子代父本组成数并未表现明显的规律。     

基于DNA分子标记的花粉流动态分析

花粉介导的基因流是植物有性繁殖世代之间的桥梁, 花粉散布属性是植物繁殖生态学、保护生物学和进化生物学研究关注的焦点。随着DNA分子技术的发展, 花粉流分析所使用的分子标记(尤其是微卫星标记)逐步替代了早期物理标记, 基于最大似然法估计以及新兴的基于贝叶斯推断的父本指派算法的发展, 能有效地估计花粉流散布的方向、距离和强度等重要特征。花粉散布曲线由单一参数向多参数模型发展, 以更好地获得花粉散布特征的拟合效果, 双组分的复合模型利用相互独立的参数空间使得散布曲线在长距离和短距离形状上呈现更大的可塑性。这些革新的技术和方法被成功应用于植物性别表型、隔离种群和杂交物种间花粉流分析, 以探讨进化、生态和保护等多领域的基础理论问题。近年来, 高通量测序技术的发展将进一步加快以分子标记为基础的花粉流动态分析在更广泛的植物类群中运用。     

A comment on García et al. (2005, 2007) and related papers on mating patterns and gene dispersal in Prunus mahaleb

In two studies on mating patterns and spatial components of pollen and seed dispersal of Prunus mahaleb based on parentage analysis, García et al. (2005, 2007) depicted their 196 focal trees as a spatially isolated population where all reproductive trees had been genotyped. Additional distributional data for P. mahaleb trees in their study area, however, revealed that García and colleagues’ depiction of their study system bears little resemblance to reality. The trees these authors studied did not form a discrete, geographically isolated population. Around 300 ungenotyped reproductive trees occurred within the 1.5‐km distributional gap to the nearest population proclaimed by García and colleagues. Since exhaustive sampling of potential parental genotypes is essential in parentage analyses, the occurrence of a large number of ungenotyped trees in the immediate neighbourhood of focal trees can severely affect the main conclusions of García et al. (2005, 2007) as well as of several related publications on gene dispersal and mating patterns of P. mahaleb conducted on the same trees and relying on the same false premises of spatial isolation and exhaustive sampling.     

High diversity of oilseed rape pollen clouds over an agro-ecosystem indicates long-distance dispersal

Abstract Estimating the frequency of long-distance pollination is important in cultivated species, particularly to assess the risk of gene transfer following the release of genetically modified crops. For this purpose, we estimated the diversity and origin of fertilizing pollen in a 10 x 10 km French oilseed rape production area. First, the cultivar grown in each field was identified through surveys to farmers and using microsatellite markers. Examination of the seed set in fields indicated high rates of seed contamination (8.7%) and pollination from other sources (5%). Then, male-sterile plants were scattered over the study area and their seed genotyped using the same markers. Most pollination was local: 65% of the seeds had a compatible sire in the closest field, i.e. at 50 or 300 m depending on site, but the nearest compatible field was found more than 1000 m away for 13% of the seeds. To assess the diversity of fertilizing pollen, each seed was assigned to the nearest putative siring cultivar. The observed diversity of pollen was then compared to that predicted by simulations using three empirical dispersal models with increasing proportion of long-distance pollination. The diversity was sensitive to the dispersal kernel used in the simulations, fatter-tailed functions predicting higher diversities. The dispersal kernel that was more consistent with our data predicted more long-distance dispersal than the exponential function.     

Fine-scale genetic structure and gene dispersal in Centaurea corymbosa (Asteraceae) I. Pattern of pollen dispersal

Pollen dispersal was characterized within a population of the narrowly endemic perennial herb, Centaurea corymbosa, using exclusion-based and likelihood-based paternity analyses carried out on microsatellite data. Data were used to fit a model of pollen dispersal and to estimate the rates of pollen flow and mutation/genotyping error, by developing a new method. Selfing was rare (1.6%). Pollen dispersed isotropically around each flowering plant following a leptokurtic distribution, with 50% of mating pairs separated by less than 11 m, but 22% by more than 40 m. Estimates of pollen flow lacked precision (0-25%), partially because mutations and/or genotyping errors (0.03-1%) could also explain the occurrence of offspring without a compatible candidate father. However, the pollen pool that fertilized these offspring was little differentiated from the adults of the population whereas strongly differentiated from the other populations, suggesting that pollen flow rate among populations was low. Our results suggest that pollen dispersal is too extended to allow differentiation by local adaptation within a population. However, among populations, gene flow might be low enough for such processes to occur.     

orchard: Paternity program for autotetraploid species

Advances in molecular marker technology have provided new opportunities to study the population genetics of polyploid taxa. Paternity analysis using microsatellite markers can be used in detection of gene flow between individuals and populations, in mating system analysis, to identify factors that influence fecundity and fertility, to identify behaviour of parent–offspring relationships and in the analysis of the reproductive success of different ecological groups. As there is no specific program for carrying out paternity analysis in tetraploid species, specialized software was designed for the assignment of paternity for autotetraploid species. orchard is a novel implementation of exclusion and likelihood statistics for carrying out paternity analysis of autotetraploids. First, the program performs an exclusion method, and then, a likelihood statistic is used with nonexcluded candidate fathers. Optional features include estimation of allele dosage of known mother trees and the estimation of pollen flow distances. orchard was tested using a data set of microsatellite data of Dipteryx odorata, a tetraploid Amazonian tree species.     

Extensive long-distance pollen dispersal and highly outcrossed mating in historically small and disjunct populations of Acacia woodmaniorum (Fabaceae), a rare banded iron formation endemic

Background and Aims

Understanding patterns of pollen dispersal and variation in mating systems provides insights into the evolutionary potential of plant species and how historically rare species with small disjunct populations persist over long time frames. This study aims to quantify the role of pollen dispersal and the mating system in maintaining contemporary levels of connectivity and facilitating persistence of small populations of the historically rare Acacia woodmaniorum.

Methods

Progeny arrays of A. woodmaniorum were genotyped with nine polymorphic microsatellite markers. A low number of fathers contributed to seed within single pods; therefore, sampling to remove bias of correlated paternity was implemented for further analysis. Pollen immigration and mating system parameters were then assessed in eight populations of varying size and degree of isolation.

Key Results

Pollen immigration into small disjunct populations was extensive (mean minimum estimate 40 % and mean maximum estimate 57 % of progeny) and dispersal occurred over large distances (≤1870m). Pollen immigration resulted in large effective population sizes and was sufficient to ensure adaptive and inbreeding connectivity in small disjunct populations. High outcrossing (mean t_m = 0·975) and a lack of apparent inbreeding suggested that a self-incompatibility mechanism is operating. Population parameters, including size and degree of geographic disjunction, were not useful predictors of pollen dispersal or components of the mating system.

Conclusions

Extensive long-distance pollen dispersal and a highly outcrossed mating system are likely to play a key role in maintaining genetic diversity and limiting negative genetic effects of inbreeding and drift in small disjunct populations of A. woodmaniorum. It is proposed that maintenance of genetic connectivity through habitat and pollinator conservation will be a key factor in the persistence of this and other historically rare species with similar extensive long-distance pollen dispersal and highly outcrossed mating systems.     

Primary pollinator exclusion has divergent consequences for pollen dispersal and mating in different populations of a bird‐pollinated tree

Pollination by nectarivorous birds is predicted to result in different patterns of pollen dispersal and plant mating compared to pollination by insects. We tested the prediction that paternal genetic diversity, outcrossing rate and realized pollen dispersal will be reduced when the primary pollinator group is excluded from bird‐pollinated plants. Pollinator exclusion experiments in conjunction with paternity analysis of progeny were applied to Eucalyptus caesia Benth. (Myrtaceae), a predominantly honeyeater‐pollinated tree that is visited by native insects and the introduced Apis mellifera (Apidae). Microsatellite genotyping at 14 loci of all adult E. caesia at two populations (n = 580 and 315), followed by paternity analysis of 705 progeny, revealed contrasting results between populations. Honeyeater exclusion did not significantly impact pollen dispersal or plant mating at Mount Caroline. In contrast, at the Chiddarcooping site, the exclusion of honeyeaters led to lower outcrossing rates, a threefold reduction in the average number of sires per fruit, a decrease in intermediate‐distance mating and an increase in near‐neighbour mating. The results from Chiddarcooping suggest that bird pollination may increase paternal genetic diversity, potentially leading to higher fitness of progeny and favouring the evolution of this strategy. However, further experimentation involving additional trees and study sites is required to test this hypothesis. Alternatively, insects may be effective pollinators in some populations of bird‐adapted plants, but ineffective in others.     

Characterization of microsatellite loci in the African fig Ficus sycomorus L. (Moraceae)

Microsatellite loci were characterized in the African fig tree Ficus sycomorus in order to investigate patterns of pollination and gene flow in this species. The loci characterized included new loci isolated from F. sycomorus and a single locus originally developed in Ficus carica. In total 12 loci were polymorphic when tested in between eight and 79 Namibian F. sycomorus individuals. Three of the new F. sycomorus loci were found to be polymorphic in cultivars of the edible fig F. carica suggesting a selection of these loci will be useful for population studies in other fig species.     

Host associations of the strangler fig Ficus watkinsiana in a subtropical Queensland rain forest

Abstract The distribution of epiphytic organisms is limited by the availability of, and dispersal to suitable hosts. We examined the distribution of a hemi‐epiphytic strangler fig, Ficus watkinsiana (Moraceae) in Cooloola National Park (Queensland, Australia), in order to determine whether this species exhibits a preference for certain host species and why. We assessed host bark roughness and flakiness, fruit type, and size to explain the observed distribution of F. watkinsiana. We surveyed over 1900 potential host trees of the 30 most common forest canopy species and found that host size measured by diameter at breast height accounted for most variation in fig prevalence (Binary Logistic Regression log‐likelihood = ?588.178, G = 314.494, d.f. = 1, P < 0.005). After controlling for host size, F. watkinsiana prevalence still differed significantly between host species (χ² = 54.612, d.f. = 24, P < 0.005), a difference that was only partly explained by variation in the bark roughness of host trunks. These results suggest that variation in the rate at which tree species host strangler figs are primarily related to individual tree size – figs may simply be more likely to colonize and thrive upon host species that grow larger.     

Paternity analysis-based inference of pollen dispersal patterns, male fecundity variation, and influence of flowering tree density and general flowering magnitude in two dipterocarp species

Background and Aims

Knowledge of pollen dispersal patterns and variation of fecundity is essential to understanding plant evolutionary processes and to formulating strategies to conserve forest genetic resources. Nevertheless, the pollen dispersal pattern of dipterocarp, main canopy tree species in palaeo-tropical forest remains unclear, and flowering intensity variation in the field suggests heterogeneity of fecundity.

Methods

Pollen dispersal patterns and male fecundity variation of Shorea leprosula and Shorea parvifolia ssp. parvifolia on Peninsular Malaysian were investigated during two general flowering seasons (2001 and 2002), using a neighbourhood model modified by including terms accounting for variation in male fecundity among individual trees to express heterogeneity in flowering.

Key Results

The pollen dispersal patterns of the two dipterocarp species were affected by differences in conspecific tree flowering density, and reductions in conspecific tree flowering density led to an increased selfing rate. Active pollen dispersal and a larger number of effective paternal parents were observed for both species in the season of greater magnitude of general flowering (2002).

Conclusions

The magnitude of general flowering, male fecundity variation, and distance between pollen donors and mother trees should be taken into account when attempting to predict the effects of management practices on the self-fertilization and genetic structure of key tree species in tropical forest, and also the sustainability of possible management strategies, especially selective logging regimes.     

Mating patterns and gene flow in the neotropical epiphytic orchid, Laelia rubescens

Understanding mating patterns and gene movement in plant populations occupying highly disturbed landscapes is essential for insights into their long-term survival. We used allozyme genetic markers to examine mating patterns and to directly measure pollen flow in the Central American epiphytic orchid, Laelia rubescens. Study populations were located in disturbed, seasonally dry tropical forest in Costa Rica. Every flowering individual within 15 populations and 12-18 seedlings from each maternal individual were genotyped over two reproductive seasons. Strict correlated mating by orchids produces full-sib progeny arrays from which the multilocus diploid genotype of the pollen parent can be inferred. These paternity analyses produced detailed quantitative estimates of pollen movement within and among populations of this species. Although our data illustrate that mating patterns vary spatially and temporally among trees, among pastures, and between years, overall patterns were surprisingly consistent. Thirty-four per cent of the capsules produced in both years resulted from gene flow events. Where pollen parents were identified, pollen moved mean distances of 279 m and 519 m in 1999 and 2000 respectively and a maximum documented distance of 1034 m. A substantially larger floral display in 2000 corresponded to a marked increase in pollen dispersal distances. Smaller populations, which more closely resembled those in undisturbed forest, had higher rates of gene flow than the large populations that characterize disturbed sites. We predict the occurrence of greater gene flow between low-density populations occupying undisturbed habitats.     

Parentage versus two-generation analyses for estimating pollen-mediated gene flow in plant populations

Assessment of contemporary pollen-mediated gene flow in plants is important for various aspects of plant population biology, genetic conservation and breeding. Here, through simulations we compare the two alternative approaches for measuring pollen-mediated gene flow: (i) the NEIGHBORHOOD model--a representative of parentage analyses, and (ii) the recently developed TWOGENER analysis of pollen pool structure. We investigate their properties in estimating the effective number of pollen parents (N(ep)) and the mean pollen dispersal distance (delta). We demonstrate that both methods provide very congruent estimates of N(ep) and delta, when the methods' assumptions considering the shape of pollen dispersal curve and the mating system follow those used in data simulations, although the NEIGHBORHOOD model exhibits generally lower variances of the estimates. The violations of the assumptions, especially increased selfing or long-distance pollen dispersal, affect the two methods to a different degree; however, they are still capable to provide comparable estimates of N(ep). The NEIGHBORHOOD model inherently allows to estimate both self-fertilization and outcrossing due to the long-distance pollen dispersal; however, the TWOGENER method is particularly sensitive to inflated selfing levels, which in turn may confound and suppress the effects of distant pollen movement. As a solution we demonstrate that in case of TWOGENER it is possible to extract the fraction of intraclass correlation that results from outcrossing only, which seems to be very relevant for measuring pollen-mediated gene flow. The two approaches differ in estimation precision and experimental efforts but they seem to be complementary depending on the main research focus and type of a population studied.     

Influence of pollinator grooming on pollen‐mediated gene dispersal in Mimulus ringens (Phrymaceae)

Pollinator foraging patterns and the dynamics of pollen transport influence the quality and diversity of flowering plant mating opportunities. For species pollinated by grooming pollinators, such as bees, the amount of pollen carried between a donor flower and potential recipient flowers depends on how grooming influences pollen transfer. To investigate the relationship between grooming and pollen‐mediated gene dispersal, we studied bumblebee (Bombus fervidus) foraging behavior and resulting gene dispersal in linear arrays of Mimulus ringens. Each of the 14 plants in an array had a unique multilocus genotype, facilitating unambiguous assignment of paternity to 1050 progeny. Each plant was trimmed to a single flower so that pollinator movements could be linked directly to resulting gene dispersal patterns. Pollen‐mediated gene dispersal was very limited. More than 95% of the seeds sired by a donor flower were distributed over the first three recipient flowers in the visitation sequence. However, seeds were occasionally sired on flowers visited later in the pollinator's floral visitation sequence. Intensive grooming immediately following pollen removal from a donor flower significantly increased the decay rate of the donor flower's gene dispersal curve. These results suggest that the frequency and relative intensity of grooming can have significant effects on patterns of pollen‐mediated gene dispersal from individual pollen donors.     

Experimental evidence for extreme dispersal limitation in tropical forest birds

Movements of organisms between habitat remnants can affect metapopulation structure, community assembly dynamics, gene flow and conservation strategy. In the tropical landscapes that support the majority of global biodiversity and where forest fragmentation is accelerating, there is particular urgency to understand how dispersal across habitats mediates the demography, distribution and differentiation of organisms. By employing unique dispersal challenge experiments coupled with exhaustive inventories of birds in a Panamanian lacustrine archipelago, we show that the ability to fly even short distances (< 100 m) between habitat fragments varies dramatically and consistently among species of forest birds, and that this variation correlates strongly with species' extinction histories and current distributions across the archipelago. This extreme variation in flight capability indicates that species' persistence in isolated forest remnants will be differentially mediated by their respective dispersal abilities, and that corridors connecting such fragments will be essential for the maintenance of avian diversity in fragmented tropical landscapes.     

Immigration history and gene dispersal: allozyme variation in Nordic populations of the red campion, Silene dioica (Caryophyllaceae)

Most of the Nordic region was ice-covered during the last (Weichselian) glaciation. During the postglacial period, plant and animal species recolonized the region from several directions and the geographic structuring of genetic variation within Nordic species may still contain a historic component that reflects patterns of postglacial immigration. The present investigation of 69 populations of Silene dioica represents the first large-scale allozyme study of a widespread herbaceous plant in the Nordic region. Although the frequencies of individual alleles showed a range of different geographic patterns, mapping of the axis scores from an ordination of variation at eight polymorphic loci revealed a division into two main geographic groups of populations. The broadly south-western and north-eastern distributions of these two groups of populations suggest that immigration into the region may have involved both eastern and southern geographic sources. However, the geographic boundaries between the two groups of populations are diffuse, and the relatively low between-population component of genetic diversity (G_ST = 16.4%) suggests a history of extensive gene dispersal by pollen.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 23–34.     

Genetic evidence of frequent long-distance recruitment in a vertebrate-dispersed tree

The importance of dispersal for the maintenance of biodiversity, while long-recognized, has remained unresolved. We used molecular markers to measure effective dispersal in a natural population of the vertebrate-dispersed Neotropical tree, Simarouba amara (Simaroubaceae) by comparing the distances between maternal parents and their offspring and comparing gene movement via seed and pollen in the 50 ha plot of the Barro Colorado Island forest, Central Panama. In all cases (parent-pair, mother-offspring, father-offspring, sib-sib) distances between related pairs were significantly greater than distances to nearest possible neighbours within each category. Long-distance seedling establishment was frequent: 74% of assigned seedlings established > 100 m from the maternal parent [mean = 392 +/- 234.6 m (SD), range = 9.3-1000.5 m] and pollen-mediated gene flow was comparable to that of seed [mean = 345.0 +/- 157.7 m (SD), range 57.6-739.7 m]. For S. amara we found approximately a 10-fold difference between distances estimated by inverse modelling and mean seedling recruitment distances (39 m vs. 392 m). Our findings have important implications for future studies in forest demography and regeneration, with most seedlings establishing at distances far exceeding those demonstrated by negative density-dependent effects.     

Fine-scale spatial genetic structure and gene dispersal in Silene latifolia

Plants are sessile organisms, often characterized by limited dispersal. Seeds and pollen are the critical stages for gene flow. Here we investigate spatial genetic structure, gene dispersal and the relative contribution of pollen vs seed in the movement of genes in a stable metapopulation of the white campion Silene latifolia within its native range. This short-lived perennial plant is dioecious, has gravity-dispersed seeds and moth-mediated pollination. Direct measures of pollen dispersal suggested that large populations receive more pollen than small isolated populations and that most gene flow occurs within tens of meters. However, these studies were performed in the newly colonized range (North America) where the specialist pollinator is absent. In the native range (Europe), gene dispersal could fall on a different spatial scale. We genotyped 258 individuals from large and small (15) subpopulations along a 60 km, elongated metapopulation in Europe using six highly variable microsatellite markers, two X-linked and four autosomal. We found substantial genetic differentiation among subpopulations (global F_ST=0.11) and a general pattern of isolation by distance over the whole sampled area. Spatial autocorrelation revealed high relatedness among neighboring individuals over hundreds of meters. Estimates of gene dispersal revealed gene flow at the scale of tens of meters (5–30 m), similar to the newly colonized range. Contrary to expectations, estimates of dispersal based on X and autosomal markers showed very similar ranges, suggesting similar levels of pollen and seed dispersal. This may be explained by stochastic events of extensive seed dispersal in this area and limited pollen dispersal.     

Isolation of six microsatellite loci in the pollinating fig wasp,Platyscapa awekei

Platyscapa awekei DNA was enriched for several repeat motifs. Sequencing of 48 transformed colonies showed that 22 contained microsatellite loci. Eleven of these loci were tested and six of them proved to be reliable and variable. As expected from these wasps’ biology, F_IS was high (= 0.423), indicating frequent sibmating. Notwithstanding, we estimate that dispersing males may secure as much as 8% of all matings.     

Population genetic structure and long-distance dispersal among seabird populations: implications for colony persistence

Dramatic local population decline brought about by anthropogenic-driven change is an increasingly common threat to biodiversity. Seabird life history traits make them particularly vulnerable to such change; therefore, understanding population connectivity and dispersal dynamics is vital for successful management. Our study used a 357-base pair mitochondrial control region locus sequenced for 103 individuals and 18 nuclear microsatellite loci genotyped for 245 individuals to investigate population structure in the Atlantic and Pacific populations of the pelagic seabird, Leach's storm-petrel Oceanodroma leucorhoa leucorhoa. This species is under intense predation pressure at one regionally important colony on St Kilda, Scotland, where a disparity between population decline and predation rates hints at immigration from other large colonies. AMOVA, F(ST), Φ(ST) and Bayesian cluster analyses revealed no genetic structure among Atlantic colonies (Global Φ(ST) = -0.02 P > 0.05, Global F(ST) = 0.003, P > 0.05, STRUCTURE K = 1), consistent with either contemporary gene flow or strong historical association within the ocean basin. The Pacific and Atlantic populations are genetically distinct (Global Φ(ST) = 0.32 P < 0.0001, Global F(ST) = 0.04, P < 0.0001, STRUCTURE K = 2), but evidence for interocean exchange was found with individual exclusion/assignment and population coalescent analyses. These findings highlight the importance of conserving multiple colonies at a number of different sites and suggest that management of this seabird may be best viewed at an oceanic scale. Moreover, our study provides an illustration of how long-distance movement may ameliorate the potentially deleterious impacts of localized environmental change, although direct measures of dispersal are still required to better understand this process.