ESTIMATION OF GENETIC NEIGHBORHOOD PARAMETERS FROM POLLEN AND SEED DISPERSAL IN THE MARINE ANGIOSPERM ZOSTERA MARINA L.

The relative importance of random genetic drift and local adaptation in causing population substructuring in plant species remains an important empirical question. Here I estimate the effective size of the genetic neighborhood, N_b, as a means of evaluating the likely role of genetic drift in creating genetic differentiation within a population of a marine plant, Zostera marina L. (eelgrass). Calculations of effective neighborhood size are based on field estimates of pollen and seed-dispersal distributions, an electrophoretic estimate of the mating system using open-pollinated progeny arrays, and determination of the effective density of reproductive individuals in the population. Neighborhood area calculated from the parent-offspring dispersal variances was equal to N_a = 524 m²; variance in the seed-dispersal distribution contributes more than twice as much as variance in pollen dispersal to N_a. Including an outcrossing rate slightly different from random, estimated neighborhood size for Z. marina is N_b = 6255. This estimate is one of the largest reported for plants or animals and indicates that genetic drift in small neighborhoods is highly unlikely to cause genetic substructuring in the study population. High gene-flow levels provided by the marine environment appear to prevent genetic isolation by distance among eelgrass patches, but the importance of drift through founder events in this population characterized by high patch turnover cannot be discounted and is the subject of ongoing study.     

POPULATION STRUCTURE AND LEVELS OF GENE FLOW IN THE MEDITERRANEAN LAND SNAIL ALBINARIA CORRUGATA (PULMONATA: CLAUSILIIDAE)

The amount of gene flow among local populations partly determines the relative importance of genetic drift and natural selection in the differentiation of such populations. Land snails, because of their limited powers for dispersal, may be particularly likely to show such differentiation. In this study, we directly estimate gene flow in Albinaria corrugata, a sedentary, rock-dwelling gastropod from Crete, by mark-recapture studies. In the same area, 23 samples were taken and studied electrophoretically for six polymorphic enzyme loci. The field studies indicate that the population structure corresponds closely to the stepping-stone model: demes are present on limestone boulders that are a few meters apart, and dispersal takes place mainly between adjacent demes. Average deme size (N) is estimated at 29 breeding individuals and the proportion of migrants per generation at 0.195 (Nm = 5.7). We find no reason to assume long-distance dispersal, apart from dispersal along occasional stretches of suitable habitat. Genetic subdivision of the population, as derived from F_ST values, corresponds to the direct estimate only at the lowest spatial level (distance between sample sites < 10 m), where values for Nm of 5.4 and 17.6 were obtained. In contrast, at the larger spatial scales, F_ST values give gene-flow estimates that are incompatible with the expected amount of gene flow at these scales. We explain these discrepancies by arguing that gene flow is in fact extremely limited, making correct estimates of Nm from F_ST impossible at the larger spatial scales. In view of these low levels of gene flow, it is concluded that both genetic drift and natural selection may play important roles in the genetic differentiation of this species, even at the lowest spatial scales.     

Seed dispersal in Erythronium grandiflorum (Liliaceae)

Primary and secondary seed dispersal was investigated for the glacier lily Erythronium grandiflorum in the Colorado Rocky Mountains. These heavy seeds have no obvious adaptations for biotic or abiotic dispersal, but can be thrown short distances when the dehiscent fruits are shaken by wind. We used sticky traps to measure primary transport of seeds up to 1 m away from individual plants. A seed cafeteria experiment examined the role of ants and rodents in secondary seed transport. Primary dispersal by wind was positively skewed and median transport distances were influenced by variation in plant height. Secondary dispersal was negligible compared to Viola nuttallii, an elaiosome-bearing species. Thus, seed dispersal was highly restricted in E. grandiflorum, and a 1 m radius encompassed the modal section of the seed dispersal curve. The seed dispersal component of gene flow was quantified and combined with previous measurements of pollen flow to yield a more complete estimate of Wright's neighborhood size, N _e, for E. grandiflorum. The lack of a special seed dispersal mechanism in E. grandiflorum is discussed in terms of a source-sink model for seedling establishment with respect to distance from the parental plants.     

Slatkin’s Paradox: when direct observation and realized gene flow disagree. A case study in Ficus

In flying insects, there is frequently a lack of congruence between empirical estimates of local demographic parameters and the prediction that differentiation between populations should decrease with increasing dispersal, a puzzling phenomenon known as Slatkin’s Paradox. Here, we generalize Slatkin’s Paradox to other taxa, drawing from available information on dispersal to predict the relative importance of pollen vs. seed migration in structuring broad‐scale patterns of genetic variation in Ficus hirta, a dioecious fig whose pollen is dispersed by minute, species‐specific fig wasps and whose seeds are disseminated by a variety of vagile vertebrates (especially bats and birds). Local‐scale observational and genetic studies of dioecious understory figs suggest comparable rates of pollen and seed migration. In contrast, we found unusually low nuclear differentiation (F_ST = 0.037, R_ST = 0.074) and high chloroplast differentiation (G_ST = 0.729, N_ST = 0.798) among populations separated by up to 2850 km, leading us to reject the hypothesis of equal pollen and seed migration rates and to obtain an equilibrium estimate of the ratio of pollen to seed migration of r = 16.2–36.3. We reconcile this example of Slatkin’s Paradox with previously published data for dioecious figs and relate it to the picture of exceptionally long‐distance wasp‐mediated pollen dispersal that is emerging for large monoecious fig trees. More generally, we argue that Slatkin’s Paradox is a general phenomenon and suggest it may be common in plants and animals.     

EVIDENCE FOR LONG-DISTANCE POLLEN DISPERSAL IN MILKWEEDS (ASCLEPIAS EXALTATA)

We investigated pollen-mediated gene flow and interspecific matings in natural populations of poke milkweed, Asclepias exaltata. Genetic data from 16 polymorphic isozymes allowed unambiguous identification of the diploid paternal genotype for 225 singly sired fruits collected from six populations in Shenandoah National Park, Virginia. Paternity analysis of progeny arrays revealed that 29%–50% (39.2%, mean) of the seeds produced in these populations were sired by plants located outside each target population. Variation among populations appears to be related to isolation distance (Kendall's τ = ?0.69, N = 6, P > 0.1), although the negative correlation was statistically significant only when the results from a previous study of A. exaltata were also included in the analysis (Kendall's τ = ?0.78, N = 7, P < 0.05). The coupling of standard paternity exclusion analysis on individual seeds (12 seeds/fruit) with estimation of cryptic gene flow from Monte Carlo simulations accounted for only 65% of the gene flow detected using the progeny-array analysis. These results suggest that standard paternity exclusion, incorporating cryptic gene flow, will inherently underestimate actual gene flow rates when the number of paternal parents is smaller than the number of seeds per fruit (i.e., matings are correlated). Indirect estimates of the number of migrants per generation (Nm ≈ 2.3) obtained from Nei's genetic diversity statistic (G_ST) are much smaller than realized gene flow measured in 1990 (Nm = 9.4, progeny-array method). In addition, interspecific hybridization with common milkweed, Asclepias syriaca, via long-distance pollen dispersal was detected in two fruits (0.8%). Thus, pollen-mediated gene flow and infrequent interspecific matings provide mechanisms to lower genetic differentiation among populations to maintain novel, low-frequency alleles within populations of A. exaltata.     

gener: a server‐based analysis of pollen pool structure

The server‐based program gener performs the two‐generation analysis of pollen flow for data consisting of mother/offspring arrays using genetic markers. The gener program decomposes the genetic variance sampled by maternal individuals within and among pollen pool components of genetic variance and is accessible from http://dyerlab.bio.vcu.edu . These estimates are used to construct the test statistic, Φ_ft , whose significance is tested via permutation. The Φ_ft statistic can subsequently be used to quantify genetic effective pollen donor population size (N_ep), effective mating area and dispersal distance. Furthermore, the gener program can calculate Φ_ft values for all pairs of substrata within the data set.     

Leptokurtic pollen-flow,non-leptokurtic gene-flow in a wind-pollinated herb,Plantago lanceolata L.

Summary The purpose of this study was to simultaneously measure pollen dispersal distance and actual pollen-mediated gene-flow distance in a wind-pollinated herb, Plantago lanceolata. The pollen dispersal distribution, measured as pollen deposition in a wind tunnel, is leptokurtic, as expected from previous studies of wind-pollinated plants. Gene-flow, measured as seeds produced on rows of male-sterile inflorescences in the wind tunnel, is non-leptokurtic, peaking at an intermediate distance. The difference between the two distributions results from the tendency of the pollen grains to cluster. These pollen clusters are the units of gene dispersal, with clusters of intermediate and large size contributing disproportionately to gene-flow. Since many wind-pollinated species show pollen clustering (see text), the common assumption for wind-pollinated plants that gene-flow is leptokurtic requires re-examination. Gene-flow was also measured in an artifical outdoor population of male-steriles, containing a single pollen source plant in the center of the array. The gene flow distribution is significantly platykurtic, and has the same general properties outdoors, where wind speed and turbulence are uncontrolled, as it does in the wind tunnel. I estimated genetic neighborhood size based on my measure of gene-flow in the outdoor population. The estimate shows that populations of Plantago lanceolata will vary in effective number from a few tens of plants to more than five hundred plants, depending on the density of the population in question. Thus, the measured pollen-mediated gene-flow distribution and population density will interact to produce effective population sizes ranging from those in which there is no random genetic drift to those in which random genetic drift plays an important role in determining gene frequencies within and among populations. Despite the platykurtosis in the distribution, pollen-mediated gene dispersal distances are still quite limited, and considerable within and among-population genetic differentiation is to be expected in this species.     

Extensive seed and pollen dispersal and assortative mating in the rain forest tree Entandrophragma cylindricum (Meliaceae) inferred from indirect and direct analyses

Pollen and seed dispersal are key processes affecting the demographic and evolutionary dynamics of plant species and are also important considerations for the sustainable management of timber trees. Through direct and indirect genetic analyses, we studied the mating system and the extent of pollen and seed dispersal in an economically important timber species, Entandrophragma cylindricum (Meliaceae). We genotyped adult trees, seeds and saplings from a 400‐ha study plot in a natural forest from East Cameroon using eight nuclear microsatellite markers. The species is mainly outcrossed (t = 0.92), but seeds from the same fruit are often pollinated by the same father (correlated paternity, r_p = 0.77). An average of 4.76 effective pollen donors (N_ep) per seed tree contributes to the pollination. Seed dispersal was as extensive as pollen dispersal, with a mean dispersal distance in the study plot approaching 600 m, and immigration rates from outside the plot to the central part of the plot reaching 40% for both pollen and seeds. Extensive pollen‐ and seed‐mediated gene flow is further supported by the weak, fine‐scale spatial genetic structure (Sp statistic = 0.0058), corresponding to historical gene dispersal distances (σ_g) reaching approximately 1,500 m. Using an original approach, we showed that the relatedness between mating individuals (F_ij = 0.06) was higher than expected by chance, given the extent of pollen dispersal distances (expected F_ij = 0.02 according to simulations). This remarkable pattern of assortative mating could be a phenomenon of potentially consequential evolutionary and management significance that deserves to be studied in other plant populations.     

The number of breeders explains genetic connectivity in an endangered bird

Connectivity is central to ecology and evolution as it focuses on the movement of individuals or genes across landscapes. Genetic connectivity approaches aim to understand gene flow but often estimate it indirectly based on metrics of genetic differentiation, which can also be affected by other evolutionary forces such as genetic drift. Gene flow and genetic drift are driven by separate ecological mechanisms with potentially differing effects on genetic differentiation and interpretations of genetic connectivity. The ecological mechanisms contributing to gene flow and genetic drift are primarily effective dispersal, or movement followed by successful reproduction, and the number of breeders in a local population, N_b, respectively. Yet, rarely are these ecological mechanisms and genetic connectivity measured simultaneously across landscapes. We examine the roles of effective dispersal and N_b on genetic connectivity across the entire range of the endangered snail kite (Rostrhamus sociabilis plumbeus), between 2006–2015. We find that both N_b and effective dispersal are important predictors of genetic connectivity across this landscape, but that N_b has a 3 × stronger effect on genetic connectivity. Furthermore, N_b is positively correlated with heterozygosity and allelic richness within patches, suggesting a potentially important role of genetic drift, in addition to gene flow, on genetic connectivity. These results emphasize that conservation efforts should focus on not only between‐patch processes of movement but also within‐patch processes regarding habitat quality and local population size for increasing genetic connectivity.     

The relative contributions of seed and pollen dispersal to gene flow and genetic diversity in seedlings of a tropical palm

Seed and pollen dispersal shape patterns of gene flow and genetic diversity in plants. Pollen is generally thought to travel longer distances than seeds, but seeds determine the ultimate location of gametes. Resolving how interactions between these two dispersal processes shape microevolutionary processes is a long‐standing research priority. We unambiguously isolated the separate and combined contributions of these two dispersal processes in seedlings of the animal‐dispersed palm Oenocarpus bataua to address two questions. First, what is the spatial extent of pollen versus seed movement in a system characterized by long‐distance seed dispersal? Second, how does seed dispersal mediate seedling genetic diversity? Despite evidence of frequent long‐distance seed dispersal, we found that pollen moves much further than seeds. Nonetheless, seed dispersal ultimately mediates genetic diversity and fine‐scale spatial genetic structure. Compared to undispersed seedlings, seedlings dispersed by vertebrates were characterized by higher female gametic and diploid seedling diversity and weaker fine‐scale spatial genetic structure for female gametes, male gametes and diploid seedlings. Interestingly, the diversity of maternal seed sources at seed deposition sites (N _em) was associated with higher effective number of pollen sources (N _ep), higher effective number of parents (N _e) and weaker spatial genetic structure, whereas seed dispersal distance had little impact on these or other parameters we measured. These findings highlight the importance maternal seed source diversity (N _em) at frugivore seed deposition sites in driving emergent patterns of fine‐scale genetic diversity and structure.     

ECOLOGICAL AND HISTORICAL ASSOCIATIONS OF GENE FLOW IN DARTERS (TELEOSTEI: PERCIDAE)

Life history should relate to gene flow (Nm) through its influence on dispersal and effective population size. Comparative studies designed to elucidate this relationship must contend with historical events that can yield misleading estimates of gene flow and statistical problems associated with inclusion of life-history traits correlated with phylogeny. We studied the relationships of life-history characters and gene flow in 15 species of darters, a monophyletic group of stream fishes. Populations of coexisting species were sampled in three geographic regions with different Pleistocene glaciation histories. Gene flow was estimated indirectly from allozymes using two methods, 8 and private alleles. Isolation-by-distance was also tested using regression of pairwise estimates of gene flow (M?) on distance. Theta and private-alleles methods produced congruent estimates of Nm, except in a study region hypothesized to have been historically fragmented and then united following Pleistocene glaciation. A relatively weak association between life-history traits and Nm (based on θ) was observed when species from the historically fragmented region were included in stepwise regression analysis, because Nm was low despite life-history differences among taxa in this region. Excluding observations from this region produced stronger associations between clutch size and Nm (r² = 0.57), and between female size, egg size, and Nm (r² = 0.95). Additional analyses that corrected for female body size and phylogenetic nonindependence agreed that darters with high fecundity and small eggs exhibited high gene flow, whereas darters with small clutches and large eggs had low gene flow. The latter combination of life-history traits primarily is exhibited in species from headwater habitats where parental investment presumably confers survivorship on offspring. Reduced gene flow and genetic divergence among demes appear to be evolutionary consequences of this strategy.     

Genetic variation, genetic structure and effective population size in the tropical holoparasitic endophyteBdallophyton bambusarum (Rafflesiaceae)

The genetic population structure inBdallophyton bambusarum, an endoparasite, was studied in ten subpopulations from a subdeciduous tropical forest in Veracruz Mexico. The sample was analyzed using seven polymorphic loci in cellulose acetate electrophoresis. Isozyme data indicated that the subpopulations ofB. bambusarum contained high genetic variability (H_ep = 0.452 ± 0.045, S.E.). Our analysis suggests that almost each inflorescence ofB. bambusarum is an individual. The subpopulations studied were genetically similar (average Nei's genetic identity 0.941 ± 0.051 and F _st values 0.097 ± 0.026), suggesting that genetic differentiation among subpopulations was small. Direct estimates of effective population size was derived from observations of three fluorescent dyes, and from the genetic neighborhood area derived from these data. The neighborhood area, multiplied by the total density of individuals, gave an N_e = 124.84 plants, and when corrected to consider the proportion of males and females gave an N_e = 118.59 individuals. An indirect estimate of Nm was obtained from the F _st values (mean Nm=2.037), giving an indirect estimate of the effective population size N_b = 12.8 individuals. Both values are relatively high when compared to other plant studies. The gene flow and/or effective populations size of the studied subpopulations ofB. bambusarum are believed to be large enough to prevent differentiation among subpopulations due to genetic drift.     

Novel polymorphic microsatellite loci and patterns of pollen-mediated gene flow in an ex situ population of <Emphasis Type="Italic">Eurycorymbus cavaleriei</Emphasis> (Sapindaceae) as revealed by categorical paternity analysis

Understanding the patterns of contemporary, pollen-mediated gene flow is of great importance for designing appropriate conservation strategies. In this study, ten novel polymorphic microsatellite loci were isolated for the rare dioecious tree, Eurycorymbus cavaleriei, and the patterns of pollen dispersal were investigated in an ex situ conserved population. A combination of microsatellite markers with high-collective exclusion power (0.932) was used to assign paternity to 240 seeds collected from eight maternal trees. The average effective pollen dispersal distance (δ) was 292.6 m and the frequency distribution of pollen movement suggested extensive pollen movement in the population. The effective pollen donors per maternal tree (N _ep) ranged from 5 to 10, and the most isolated maternal trees were observed with the largest number of N _ep = 10. Although a trend of near-neighbor mating was found in seven of eight maternal trees, no significant correlations were detected between the average effective pollen dispersal distance (δ) and the geographic distances (d1 and d2) between maternal and male trees. The increased average effective distance of pollen dispersal and number of N _ep for isolated maternal trees might be a compound consequence of low density and long-distance flight of pollinators of this species. The conservation implications of these results are discussed.     

Genetic diversity in fragmented populations of the critically endangered spider orchid Caladenia huegelii: implications for conservation

The Orchidaceae is characterised by a diverse range of life histories, reproductive strategies and geographic distribution, reflected in a variety of patterns in the population genetic structure of different species. In this study, the genetic diversity and structure was assessed within and among remnant populations of the critically endangered sexually deceptive orchid, Caladenia huegelii. This species has experienced severe recent habitat loss in a landscape marked by ancient patterns of population fragmentation within the Southwest Australian Floristic Region, a global biodiversity hotspot. Using seven polymorphic microsatellite loci, high levels of within-population diversity (mean alleles/locus = 6.73; mean H _E = 0.690), weak genetic structuring among 13 remnant populations (F _ST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean F _IS = 0.22). Positive inbreeding coefficients are most likely due to Wahlund effects and/or inbreeding effects from highly correlated paternity and typically low fruit set. Indirect estimates of gene flow (Nm = 5.09 using F _ST; Nm = 3.12 using the private alleles method) among populations reflects a historical capacity for gene flow through long distance pollen dispersal by sexually deceived wasp pollinators and/or long range dispersal of dust-like orchid seed. However, current levels of gene flow may be impacted by habitat destruction, fragmentation and reduced population size. A genetically divergent population was identified, which should be a high priority for conservation managers. Very weak genetic differentiation indicates that the movement and mixing of seeds from different populations for reintroduction programs should result in minimal negative genetic effects.     

Short-distance pollen dispersal and high self-pollination in a bat-pollinated neotropical tree

We investigated pollen dispersal and breeding structure in the tropical tree species Caryocar brasiliense Camb. (Caryocaraceae), using genetic data from ten microsatellite loci. All adult trees (101) within a patch of 8.3 ha were sampled, and from these adults 18 open-pollinated maternal progeny arrays were analyzed (280 seeds from 265 fruits). Most fruits presented only one seed (median equal to 1.000) and mean number of ripened seeds per fruit was 1.053 (SD = 0.828). Our results showed that C. brasiliense presents a mixed-mating system, with 11.4% of self-pollination, multilocus outcrossing rate of t _m = 0.891 ± 0.025, and high probability of full-sibship within progeny arrays (r _p = 0.135 ± 0.032). Outcrossing rate and self-pollination varied significantly among mother trees. We could detect a maximum pollen dispersal distance of ∼500 m and a mean pollen dispersal distance of ∼132 m. However, most pollination events (80%) occurred at distances less than 200 m. Our results also indicated that pollen dispersal is restricted to a neighborhood of 5.4 ha with rare events of immigration (∼1% N _e m = 0.35). C. brasiliense also presents a significant but weak spatial genetic structure (Sp = 0.0116), and extension of pollen dispersal distance was greater than seed dispersal (N _b = 86.20 m). These results are most likely due to the foraging behavior of pollinators that may have limited flight range. The highly within-population synchronous flowering, high population density, and clumped distribution reinforce pollinator behavior and affect residence time leading to a short-distance pollen dispersal.     

GENE FLOW IN CHAMAECRISTA FASCICULATA (LEGUMINOSAE) II. GENE ESTABLISHMENT

The role of gene establishment in gene flow was investigated in a population of the annual legume Chamaecrista fasciculata by determining the effect of interparent distance on progeny fitness throughout the entire life history. A decelerating gain in progeny fitness with increasing interparent distance was observed. Selfed progeny suffered a 2-fold fitness disadvantage compared to progeny derived from mating events between individuals in the same neighborhood. Progeny derived from within neighborhood crosses had lower fitness than progeny from crosses between neighborhoods. Coupling the effect of interparent distance on gene establishment with information on gene dispersal resulted in a considerable increase in estimated gene flow. However, gene flow was still limited, as the average neighborhood area corresponded to a circle with radius of approximately 3.0 m. Yearly fluctuations in population size and variation in reproductive output lowered the estimate of N_e below the census estimate to approximately 100 individuals. The role of a seed bank in increasing the estimate of N_e was found to be insignificant. It is likely that genetic drift plays a major role in determining the distribution of genetic variation in this population.     

Effects of population density on male and female reproductive success in the wind-pollinated, wind-dispersed tree species Betula maximowicziana

The effects of population density on male and female reproductive success of Betula maximowicziana were evaluated in two mixed and two post-fire stands, with various population densities, ranging from 1.9 to 300.0 trees per ha, in central Hokkaido, Japan. First, we investigated ecological determinants of reproductive success (seed set and germination) of both seeds collected from the trees (tree seeds) and dispersed seeds collected from seed traps (dispersed seeds). We then evaluated the effects of population density on seed set and germination of tree seeds and dispersed seeds using a generalized linear mixed model (GLMM). Subsequently, we genotyped 950 seeds collected from mother trees and 940 seeds trapped after dispersal derived from tree seeds and dispersed seeds, respectively, using eleven microsatellite loci. Using the acquired data, we then evaluated the outcrossing rate and effective number of pollen donors (N _ep) of the tree seeds, and the genetic structure of both pollen pools and dispersed seed populations. The seed set and germination rate of dispersed seeds was significantly lower both in the lowest-density stand and in the highest-density stand. The GLMM revealed that seed set and germination rates of dispersed seeds may be maximal at approximately 120 trees per hectare (optimal density). Outcrossing rates were consistently high (t _m = 0.995), regardless of the population density. In contrast, N _ep was lower in the lowest-density stands. Significant genetic structure of the dispersed seed population was found in two low-density stands, probably due to the limitation of overlapping seed shadows.     

DISPERSAL AND GENETIC STRUCTURE IN KANGAROO RATS

We used spatial autocorrelation of allele frequencies to examine local structure in a population of bannertailed kangaroo rats for which Wright's isolation-by-distance model seems applicable, and for which we can estimate neighborhood size based on 10 years of data on demography and dispersal. The uniform dispersion and strong philopatric tendencies of this species provide a test case for the idea that restricted dispersal can lead to local genetic structure in small mammals. Whether we considered such complications as nonnormal dispersal distances, variation in lifetime reproductive success, fluctuating population density, and adult as well as juvenile dispersal, our estimate of effective population size was fewer than 15 animals. Nevertheless, data from four polymorphic allozyme loci analyzed over a range of separations between 50 m (approximately one home range diameter) and 1,000 m detected no evidence for spatial clustering of alleles. One resolution of this apparent paradox is that “gamete dispersal,” caused by the movements of males away from their residences during the breeding season, may be a significant (and unmeasured) component of gene dispersal. Our analyses also demonstrate that a decline in population density may actually increase neighborhood size. A more general implication is that even extremely philopatric mammals have effective population sizes large enough to prevent the development of local genetic structure.     

Effects of tree architecture on pollen dispersal and mating patterns in Abies pinsapo Boiss. (Pinaceae)

Plant architecture is crucial to pollination and mating in wind‐pollinated species. We investigated the effect of crown architecture on pollen dispersal, mating system and offspring quality, combining phenotypic and genotypic analyses in a low‐density population of the endangered species Abies pinsapo. A total of 598 embryos from three relative crown height levels (bottom, middle and top) in five mother plants were genotyped using eleven nuclear microsatellite markers (nSSRs). Paternity analysis and mating system models were used to infer mating and pollen dispersal parameters. In addition, seeds were weighed (N = 16 110) and germinated (N = 736), and seedling vigour was measured to assess inbreeding depression. Overall, A. pinsapo shows a fat‐tailed dispersal kernel, with an average pollen dispersal distance of 113–227 m, an immigration rate of 0.84–26.92%, and a number of effective pollen donors (N_ep) ranging between 3.5 and 11.9. We found an effect of tree height and relative crown height levels on mating parameters. A higher proportion of seeds with embryo (about 50%) and a higher rate of self‐fertilization (about 60%) were found at the bottom level in comparison with the top level. Seed weight and seedling vigour are positively related. Nevertheless, no differences were found in seed weight or in seedling‐related variables such as weight and length of aerial and subterranean parts among the different relative crown height levels, suggesting that seeds from the more strongly inbred bottom level are not affected by inbreeding depression. Our results point to vertical isotropy for outcross‐pollen and they suggest that self‐pollen may ensure fertilization when outcross‐pollen is not available in low‐density population.     

Short-distance pollen dispersal and high self-pollination in a bat-pollinated neotropical tree

We investigated pollen dispersal and breeding structure in the tropical tree species Caryocar brasiliense Camb. (Caryocaraceae), using genetic data from ten microsatellite loci. All adult trees (101) within a patch of 8.3 ha were sampled, and from these adults 18 open-pollinated maternal progeny arrays were analyzed (280 seeds from 265 fruits). Most fruits presented only one seed (median equal to 1.000) and mean number of ripened seeds per fruit was 1.053 (SD?=?0.828). Our results showed that C. brasiliense presents a mixed-mating system, with 11.4% of self-pollination, multilocus outcrossing rate of t _m?=?0.891?±?0.025, and high probability of full-sibship within progeny arrays (r _p?=?0.135?±?0.032). Outcrossing rate and self-pollination varied significantly among mother trees. We could detect a maximum pollen dispersal distance of ～500 m and a mean pollen dispersal distance of ～132 m. However, most pollination events (80%) occurred at distances less than 200 m. Our results also indicated that pollen dispersal is restricted to a neighborhood of 5.4 ha with rare events of immigration (～1% N _e m?=?0.35). C. brasiliense also presents a significant but weak spatial genetic structure (Sp?=?0.0116), and extension of pollen dispersal distance was greater than seed dispersal (N _b?=?86.20 m). These results are most likely due to the foraging behavior of pollinators that may have limited flight range. The highly within-population synchronous flowering, high population density, and clumped distribution reinforce pollinator behavior and affect residence time leading to a short-distance pollen dispersal.