Patterns of pollen dispersal in a small population of the Canarian endemic palm (Phoenix canariensis)

The genetic diversity of small populations is greatly influenced by local dispersal patterns and genetic connectivity among populations, with pollen dispersal being the major component of gene flow in many plants species. Patterns of pollen dispersal, mating system parameters and spatial genetic structure were investigated in a small isolated population of the emblematic palm Phoenix canariensis in Gran Canaria island (Canary Islands). All adult palms present in the study population (n=182), as well as 616 seeds collected from 22 female palms, were mapped and genotyped at 8 microsatellite loci. Mating system analysis revealed an average of 5.8 effective pollen donors (N_ep) per female. There was strong variation in correlated paternity rates across maternal progenies (ranging from null to 0.9) that could not be explained by the location and density of local males around focal females. Paternity analysis revealed a mean effective pollen dispersal distance of ∼71 m, with ∼70% of effective pollen originating from a distance of <75 m, and 90% from <200 m. A spatially explicit mating model indicated a leptokurtic pollen dispersal kernel, significant pollen immigration (12%) from external palm groves and a directional pollen dispersal pattern that seems consistent with local altitudinal air movement. No evidence of inbreeding or genetic diversity erosion was found, but spatial genetic structure was detected in the small palm population. Overall, the results suggest substantial pollen dispersal over the studied population, genetic connectivity among different palm groves and some resilience to neutral genetic erosion and subsequently to fragmentation.     

Mating system,pollen and propagule dispersal,and spatial genetic structure in a high-density population of the mangrove tree Kandelia candel

Mangrove tree species form ecologically and economically important forests along the tropical and subtropical coastlines of the world. Although low intrapopulation genetic diversity and high interpopulation genetic differentiation have been detected in most mangrove tree species, no direct investigation of pollen and propagule dispersal through paternity and/or parentage analysis and spatial genetic structure within populations has been conducted. We surveyed the mating system, pollen and propagule dispersal, and spatial genetic structure in a natural population of Kandelia candel, one of the typical viviparous mangrove tree species, using nuclear and chloroplast microsatellite markers. High diversity and outcrossing rates were observed. Paternity and parentage analysis and modelling estimations revealed the presence of an extremely short-distance component of pollen and propagule dispersal (pollen: 15.2 ± 14.9 m (SD) by paternity analysis and 34.4 m by modelling; propagule: 9.4 ± 13.8 m (SD) by parentage analysis, and 18.6 m by modelling). Genetic structure was significant at short distances, and a clumped distribution of chloroplast microsatellite genotypes was seen in K. candel adults. We conclude that the K. candel population was initiated by limited propagule founders from outside by long-distance dispersal followed by limited propagule dispersal from the founders, resulting in a half-sib family structure.     

Evaluating the influence of different aspects of habitat fragmentation on mating patterns and pollen dispersal in the bird-pollinated Banksia sphaerocarpa var. caesia

Habitat fragmentation can significantly affect mating and pollen dispersal patterns in plant populations, although the differential effects of the various aspects of fragmentation are poorly understood. In this study, we used eight microsatellite loci to investigate the effect of fragmentation on the mating system and pollen dispersal within one large and eight small population remnants of Banksia sphaerocarpa var. caesia, a bird-pollinated shrub in the southern agricultural region of Western Australia. The large population had a much larger neighbourhood size and lower selfing rate, maternal pollen pool differentiation and within-plot mean pollen dispersal distance than the small populations. Outcrossing was consistently high and ranged from 85.7% ± 2.6 to 98.5% ± 0.9, and mating patterns suggested nearest-neighbour pollination. Pollen immigration into small populations ranged from 2.8% ± 1.8 to 16.5% ± 3.2. Using the small populations, we tested for correlations between various fragmentation variables and mating system and pollen dispersal parameters. We found significant negative linear relationships between population isolation and outcrossing rate; population shape and neighbourhood size; and conspecific density and mean pollen dispersal distance. There were significant positive linear relationships between population shape and pollen pool differentiation and between population size and number of different fathers per seed crop. Our results suggest that birds may use a series of fragmented populations as a vegetation corridor while foraging across the landscape and that population connectivity is a critical determinant of pollinator visitation. Our results also suggest that the effect of a linear population shape on the mating system and pollen dispersal is routinely underestimated.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Limited pollen-mediated dispersal and partial self-incompatibility in the rare ironstone endemic <Emphasis Type="Italic">Tetratheca paynterae</Emphasis> subsp. <Emphasis Type="Italic">paynterae</Emphasis> increase the risks associated with habitat loss

Patterns of mating and dispersal are key factors affecting the dynamics, viability and evolution of plant populations. Changes in mating system parameters can provide evidence of anthropogenic impacts on populations of rare plants. Tetratheca paynterae subsp. paynterae is a critically endangered perennial shrub confined to a single ironstone range in Western Australia. Mining of the range removed 25% of plants in 2004 and further plants may be removed if the viability of the remaining populations is not compromised. To provide baseline genetic data for monitoring mining impacts, we characterised the mating system and pollen dispersal over two seasons in T. paynterae subsp. paynterae and compared mating system parameters with two other ironstone endemics, T. paynterae subsp. cremnobata and T. aphylla subsp. aphylla that were not impacted by mining. T. paynterae subsp. paynterae was the only taxon showing evidence of inbreeding (t _m = 0.89), although hand pollination revealed pre-zygotic self-incompatibility limits the production of seed from self-pollen. In a year of lower fruit set (2005), the estimate of correlated paternity increased from 20 to 35%. Direct estimates of realised pollen dispersal, made by paternity assignment in two small populations where all adult plants were genotyped, revealed a leptokurtic distribution with 30% of pollen dispersed less than 3 m and 90% less than 15 m. Restricted pollen dispersal maintains the strong genetic structuring of the adult populations in succeeding generations. As a consequence of preferential outcrossing, any reduction in effective population size, flowering plant density and/or the abundance and activity of pollinators may impact negatively on population viability through reduced seed set, increased inbreeding and increased correlated paternity.     

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.     

Genetic structure and mating system of Manilkara huberi (Ducke) A. Chev., a heavily logged Amazonian timber species

In this work, we report on the population genetic structure of the endangered tree species Manilkara huberi, an Amazonian tree species intensely exploited due to the high density and resistance of its wood. We investigated the patterns of spatial distribution, genetic structure, and mating system using 7 microsatellite loci and here discuss the consequences for conservation and management of the species. To examine the population genetic structure, 481 adult trees and 810 seedlings were sampled from an area of 200 ha from a natural population in FLONA Tapajós, PA, Brazil. We found relatively high and consistent inbreeding levels (intrapopulation fixation index [f] 0.175 and 0.240) and a significant spatial genetic structure up to a radius of approximately 300 m, most likely due to a limited seed and pollen flow. The multilocus (tm) population outcrossing rate was high (0.995), suggesting that the species is predominantly allogamous with a pollen flow restricted to 47 m. These results suggest that M. huberi is spatially structured, consistent with a model of isolation by distance. Fragmentation may therefore cause the loss of subpopulations, suggesting that management programs for production and conservation should include large areas. The genetic data also revealed that for ex situ conservation, seeds should be collected from more than 175 maternal trees, in order to keep an effective population size of 500. Furthermore, as the species is widely distributed across the Amazon Forest, samples should include several populations in order to represent the highest genetic diversity possible. These results provide a blueprint to guide the production and conservation management policies of this valuable timber species.     

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

Mating systems have long been recognized as key factors determining genetic structure within and between populations. Outcrossing promotes genetic diversity and gene flow between populations, while inbreeding, on the other hand, decreases recombination rates, facilitating fixation of co-adapted genes. In small populations, selfing moderates pollen limitation because of low mate availability, but at the cost of increased inbreeding depression. These conflicts are of more than theoretical interest; they are critical for the management of endangered species. In order to help designing conservation strategies for the management of the gene pool of fragmented populations of Pinus cembra, a protected species in Poland, we have characterized pollen flow and mating structure using nuclear microsatellite markers. We demonstrated that P. cembra in the studied stands of the Tatra Mts. is characterized by an average outcrossing rate (t) of 0.72. Unlike with the existing approaches, using the newly developed Bayesian method, we found that population size and seasonal variation had confounding effects on outcrossing rates. In concordance with predictions, large populations showed significantly higher outcrossing rates (t?=?0.89) than smaller ones (t?=?0.51). Temporal variation revealed in the outcrossing rate might be linked with masting behavior of the species. On the other hand, we showed that outcrossing rates were not associated with a trunk diameter of a mother tree. Our study also demonstrated that biparental inbreeding is a significant component of mating system. However, we further show that pollen dispersal follows a fat-tailed distribution (with the average dispersal distance of 1,267 m) so that at least some long-distance pollen dispersal must be occurring. Overall, we conclude that the high inbreeding (both selfing and mating between relatives) found in P. cembra buffers for pollen limitation. We argue that small, isolated stands can be at risk of gene pool erosion, despite the potential for long-distance pollen and seed dispersal.     

Joint estimation of contemporary seed and pollen dispersal rates among plant populations

There are few statistical methods for estimating contemporary dispersal among plant populations. A maximum-likelihood procedure is introduced here that uses pre- and post-dispersal population samples of biparentally inherited genetic markers to jointly estimate contemporary seed and pollen immigration rates from a set of discrete external sources into a target population. Monte Carlo simulations indicate that accurate estimates and reliable confidence intervals can be obtained using this method for both pollen and seed migration rates at modest sample sizes (100 parents/population and 100 offspring) when population differentiation is moderate (F(ST) ≥ 0.1), or by increasing pre-dispersal samples (to about 500 parents/population) when genetic divergence is weak (F(ST) = 0.01). The method exhibited low sensitivity to the number of source populations and achieved good accuracy at affordable genetic resolution (10 loci with 10 equifrequent alleles each). Unsampled source populations introduced positive biases in migration rate estimates from sampled sources, although they were minor when the proportion of immigration from the latter was comparatively low. A practical application of the method to a metapopulation of the Australian resprouter shrub Banksia attenuata revealed comparable levels of directional seed and pollen migration among dune groups, and the estimate of seed dispersal was higher than a previous estimate based on conservative assignment tests. The method should be of interest to researchers and managers assessing broad-scale nonequilibrium seed and pollen gene flow dynamics in plants.     

The role of gene flow in shaping genetic structures of the subtropical conifer species Araucaria angustifolia

The morphological features of pollen and seed of Araucaria angustifolia have led to the proposal of limited gene dispersal for this species. We used nuclear microsatellite and AFLP markers to assess patterns of genetic variation in six natural populations at the intra- and inter-population level, and related our findings to gene dispersal in this species. Estimates of both fine-scale spatial genetic structure (SGS) and migration rate suggest relatively short-distance gene dispersal. However, gene dispersal differed among populations, and effects of more efficient dispersal within population were observed in at least one stand. In addition, even though some seed dispersal may be aggregated in this principally barochorous species, reasonable secondary seed dispersal, presumably facilitated by animals, and overlap of seed shadows within populations is suggested. Overall, no correlation was observed between levels of SGS and inbreeding, density or age structure, except that a higher level of SGS was revealed for the population with a higher number of juvenile individuals. A low estimate for the number of migrants per generation between two neighbouring populations implies limited gene flow. We expect that stepping-stone pollen flow may have contributed to low genetic differentiation among populations observed in a previous survey. Thus, strategies for maintenance of gene flow among remnant populations should be considered in order to avoid degrading effects of population fragmentation on the evolution of A. angustifolia.     

Reconciling field observations of dispersal with estimates of gene flow

Montgomery Slatkin, in a classic article concerning the role of gene flow in determining population genetic structure in natural populations noted an inconsistency between observations made in the field of limited dispersal of weakly flying insect and population genetic analyses of genetic structure which revealed extensive gene flow among populations. This phenomenon was subsequently termed Slatkin's Paradox. In this issue, Yu et al. (2010) provide an example of Slatkin's Paradox in a study of seed and pollen gene flow in the dioecious understory fig Ficus hirta in southern Asia. Given multiple field observations that showed the low vagility of fig wasp pollinators of dioecious figs and the high movement capacity of its vertebrate seed dispersers, the authors expected to see higher levels of gene movement of seed versus pollen. They compared neutral genetic differentiation across 15 populations separated by >2500km at six nuclear microsatellite and two chloroplast loci and found that F. hirta shows an order of magnitude higher level of gene flow of pollen relative to seeds that challenges observations of limited dispersal of fig wasps that pollinate dioecious figs. They propose broadening the application of Slatkin's Paradox beyond insects to include situations where an incongruity exists between ecological measures of low dispersal and high levels of effective gene flow.     

Clonal diversity and distribution in Stenocereus eruca (Cactaceae), a narrow endemic cactus of the Sonoran Desert

Stenocereus eruca (Cactaceae), a prostrate cactus endemic to the Sonoran Desert, is thought to be highly clonal. We examined its clonal diversity and distribution: (1) at the population level, in four distinct populations along its distribution range; and (2) at a micro scale level, within a single population. Our objective was to evaluate the importance of sexual versus clonal recruitment through the use of RAPD markers. Contrary to previous field observations, clonal diversity was relatively high across the distribution range. This finding suggests that sexual recruitment is an important regeneration mechanism. The proportions of distinguishable genotypes (G/N = 0.83) and genotypic diversity (D = 0.987) were greater than in other clonal cacti, suggesting that clonal propagation is not the major regeneration mechanism. Autocorrelation analyses revealed a spatial genetic structure that may be the result of restricted gene flow (via pollen or seeds) and clonal propagation. A molecular variance analysis (AMOVA) indicated that most of the variation (66.3%) was found within and not across populations. Future studies on pollen and seed dispersal are needed to understand the role of the clonal habit in the mating system of S. eruca.     

植物种群交配系统、亲本分析以及基因流动研究

 在过去的二十年中,有关植物种群交配与散布过程的研究与日俱增,重点集中在利用母本子代系列(Maternal progeny arrays)来估计种群间自交与异交的相对比例,种群的花粉散布与雄性育性变异的模式。早期的研究主要依靠排除法来确定亲本,但几乎同时也意识到基因流动事件几乎是检测不到的。在大多数估计中,难以做到为大多数非迁移子代确定唯一的亲本。因此,基因流动与雄性育性的最大似然性方法得以引入该领域的研究。本文介绍了用单位点和多位点模型来估计家系与种群自交与异交的相对频率,着重阐述了目前可用于亲本分析与基因流的估计方法。最后介绍了我们对木根麦冬交配系统与亲本分析的研究以及亲本分析将来的研究方向。     

Population differentiation and gene flow within a metapopulation of a threatened tree, Magnolia stellata (Magnoliaceae)

We examined genetic differentiation among eight local populations of a metapopulation of Magnolia stellata using 10 nuclear and three chloroplast microsatellite (nSSR and cpSSR) markers and evaluated the influence of historical gene flow on population differentiation. The coefficient of genetic differentiation among populations for nSSR (F(ST) = 0.053) was less than half that for cpSSR (0.137). An isolation-by-distance pattern was detected for nSSRs, but not cpSSRs. These results suggest that pollen flow, as well as seed dispersal, has significantly reduced genetic differentiation among populations. We also examined patterns of contemporary pollen flow by paternity analysis of seeds from nine seed parents in one of the populations using the nSSR markers and found it to be greatly restricted by the distance between parents. Although most pollen flow occurred within the population, pollen flow from outside the population accounted for 2.5% of the total. When historical and contemporary pollen flows among populations were compared, the levels of pollen flow seem to have declined recently. We conclude that to conserve M. stellata, it is important to preserve the whole population by maintaining its metapopulation structure and the gene flow among its populations.     

Fire‐induced population reduction and landscape opening increases gene flow via pollen dispersal in Pinus halepensis

Population reduction and disturbances may alter dispersal, mating patterns and gene flow. Rather than taking the common approach of comparing different populations or sites, here we studied gene flow via wind‐mediated effective pollen dispersal on the same plant individuals before and after a fire‐induced population drop, in a natural stand of Pinus halepensis. The fire killed 96% of the pine trees in the stand and cleared the vegetation in the area. Thirteen trees survived in two groups separated by ~80 m, and seven of these trees had serotinous (closed) prefire cones that did not open despite the fire. We analysed pollen from closed pre and postfire cones using microsatellites. The two groups of surviving trees were highly genetically differentiated, and the pollen they produced also showed strong among‐group differentiation and very high kinship both before and after the fire, indicating limited and very local pollen dispersal. The pollen not produced by the survivors also showed significant prefire spatial genetic structure and high kinship, indicating mainly within‐population origin and limited gene flow from outside, but became spatially homogeneous with random kinship after the fire. We suggest that postfire gene flow via wind‐mediated pollen dispersal increased by two putative mechanisms: (i) a drastic reduction in local pollen production due to population thinning, effectively increasing pollen immigration through reduced dilution effect; (ii) an increase in wind speeds in the vegetation‐free postfire landscape. This research shows that dispersal can alleviate negative genetic effects of population size reduction and that disturbances might enhance gene flow, rather than reduce it.     

Paternity analysis of the breeding structure of strangler fig populations: evidence for substantial long-distance wasp dispersal

Abstract. The mutualistic interaction of figs with their species-specific wasp pollinators and the role of figs as 'keystone' plant resources in tropical communities has received substantial attention from both plant and animal ecologists. Despite this focus on the reproductive biology of figs, the minute size of the wasps has effectively precluded our ability to monitor patterns of wasp dispersal and fig mating relationships in natural forest habitats. In this paper we use genetic markers and genealogy reconstruction techniques to examine the breeding structure of populations of four strangler fig species occurring in central Panama. The natural history of figs facilitates the genetic analysis of full-sib progeny arrays from which the genotypes of successful pollen donors can be reconstructed precisely. Paternity reconstruction in the four study species reveals that individual flowering trees may routinely receive pollen from numerous donors despite characteristically low densities of co-flowering individuals. These data indicate not only that breeding populations of these figs are larger than the minimum critical sizes predicted to be necessary to support populations of their species-specific pollinators, but are more extensive in size and area than has been described for any plant species yet examined. Further, the fig wasps are shown to be efficient agents of long-distance dispersal, routinely moving up to 10 km between flowering trees. In accord with the potential for substantial long-distance gene flow and large effective population sizes, ten of eleven species of Panamanian figs assayed were found to maintain exceptionally high levels of genetic variation within their populations. Combined with other reports of occasional long-distance dispersal, the results of this study suggest that fig wasps may be more effective at colonizing isolated fig populations than previously thought.     

Genetic evidence for female-biased dispersal and gene flow in a polygynous primate

Many models of sex-biased dispersal predict that the direction of sex-bias depends upon a species' mating system. In agreement with this, almost all polygynous mammals show male-biased dispersal whereas largely monogamous birds show female-biased dispersal (FBD). The hamadryas baboon (Papio hamadryas hamadryas) is polygynous and so dispersal is predicted to be male biased, as is found in all other baboon subspecies, but there are conflicting field data showing both female and male dispersal. Using 19 autosomal genetic markers genotyped in baboons from four Saudi Arabian populations, we found strong evidence for FBD in post-dispersal adults but not, as expected, in pre-dispersal infants and young juveniles, when we compared male and female: population structure (F(st)), inbreeding (F(is)), relatedness (r), and the mean assignment index (mAIc). Furthermore, we found evidence for female-biased gene flow as population genetic structure (F(st)), was about four times higher for the paternally inherited Y, than for either autosomal markers or for maternally inherited mtDNA. These results contradict the direction of sex-bias predicted by the mating system and show that FBD has evolved recently from an ancestral state of male-biased dispersal. We suggest that the cost-benefit balance of dispersal to males and females is tightly linked to the unique hierarchical social structure of hamadryas baboons and that dispersal and social organization have coevolved.     

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.     

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.     

Pollen dispersal and gene flow within and into a population of the alpine monocarpic plant Campanula thyrsoides

Background and Aims

Gene flow by seed and pollen largely shapes the genetic structure within and among plant populations. Seed dispersal is often strongly spatially restricted, making gene flow primarily dependent on pollen dispersal within and into populations. To understand distance-dependent pollination success, pollen dispersal and gene flow were studied within and into a population of the alpine monocarpic perennial Campanula thyrsoides.

Methods

A paternity analysis was performed on sampled seed families using microsatellites, genotyping 22 flowering adults and 331 germinated offspring to estimate gene flow, and pollen analogues were used to estimate pollen dispersal. The focal population was situated among 23 genetically differentiated populations on a subalpine mountain plateau (<10 km²) in central Switzerland.

Key Results

Paternity analysis assigned 110 offspring (33·2 %) to a specific pollen donor (i.e. ‘father’) in the focal population. Mean pollination distance was 17·4 m for these offspring, and the pollen dispersal curve based on positive LOD scores of all 331 offspring was strongly decreasing with distance. The paternal contribution from 20–35 offspring (6·0–10·5 %) originated outside the population, probably from nearby populations on the plateau. Multiple potential fathers were assigned to each of 186 offspring (56·2 %). The pollination distance to ‘mother’ plants was negatively affected by the mothers'' degree of spatial isolation in the population. Variability in male mating success was not related to the degree of isolation of father plants.

Conclusions

Pollen dispersal patterns within the C. thyrsoides population are affected by spatial positioning of flowering individuals and pollen dispersal may therefore contribute to the course of evolution of populations of this species. Pollen dispersal into the population was high but apparently not strong enough to prevent the previously described substantial among-population differentiation on the plateau, which may be due to the monocarpic perenniality of this species.