Effective Pollen Flow Research Articles

A decade of genetic makeup in the aerial seed bank of a fire-evader tree

BackgroundAerial seed banks occur in plants that postpone the release of viable seeds, thereby providing a mechanism for population maintenance in unpredictable environments. Seeds retained on the mother trees offer a reservoir of genetic diversity across years, but the pattern and evolutionary consequences of such accumulated diversity are poorly understood. We characterize the genetic layout of an aerial seed bank composed of serotinous cones formed in 2003 and in 2014 in a historically fire-prone area. Our hypothesis is that within this timeframe, recurrent fires could have modified the genetic makeup of the seed bank.ResultsOur results did not reveal any genetic difference along the 12-year period, but indicated a significant genetic variation (13%) of seed banks among trees within the same year. Moreover, progeny from the seed bank showed a 4% increase of observed heterozygosity, together with 14 new alleles, compared to mother trees. Finally, a strong homogenization effect of pollen flow on the genetic diversity was detected, with a very high effective number of fathers in 2003 and 2014.ConclusionsOur results highlight the temporal stability of the genetic makeup of aerial seed banks in this fire-prone area. The maternal genetic differences and an increase of genetic diversity (linked to effective pollen flow) in new generations compared to their maternal progenitors are also noteworthy. Together, these characteristics represent key assets for serotinous forest adaptation and persistence in the face of increasing wildfire activity.

Stepping stones or stone dead? Fecundity, pollen dispersal and mating patterns of roadside Qualea grandiflora Mart. trees

Forest fragmentation may affect mating and pollen dispersal patterns through conversion of continuous forests into small, spatially isolated remnant patches and individual trees in an anthropogenic landscape. We investigated reproductive investment and success, pollen dispersal, mating system, and genetic diversity and spatial structure of Qualea grandiflora trees in two environmental contexts: a continuous natural Cerrado area and isolated individuals on roadsides. Roadside trees produced more flowers and more fruit than Cerrado trees. Pollen dispersal kernels were fat-tailed in both contexts, indicating long-distance dispersal, but in Cerrado the mean pollen dispersal distance (524.7 m) and the effective number of pollen donors per mother-tree (Nep = 12.7) were higher than for roadside trees (60.9 m, Nep = 4.6). The levels and structure of genetic diversity, outcrossing rates ( $$t_{m}$$ > 0.98), and mating among relatives ( $$t_{m} - t_{s}$$ < 0.1) were similar in both environmental contexts. Allelic richness and number of private alleles were similar between the two environments. The fixation index was significantly lower in adults (minimum of 0.08) than in offspring (minimum of 0.23) in both contexts, suggesting selection against inbred individuals between offspring and adult stage. Our results indicate that the spatial isolation of roadside trees, by increasing the number of flowers produced, decreased pollinator movements, thereby reducing effective pollen flow and the number of pollen donors. All these results suggest that roadside trees can be used for harvesting seeds for recovery plans, and that these trees are a biological legacy, and reservoir of Q. grandiflora genetic diversity, from the original Cerrado forest.

Contemporary pollen and seed dispersal in natural populations of Bertholletia excelsa (Bonpl.).

Due to the nutritional content and commercial value of its seeds, Bertholletia excelsa is one of the most important species exploited in the Amazon region. The species is hermaphroditic, insect pollinated, and its seeds are dispersed by barochory and animals. Because the fruit set is dependent on natural pollinator activity, gene flow plays a key role in fruit production. However, to date, there have been no studies on pollen and seed flow in natural populations of B. excelsa. Herein, we used microsatellite loci and parentage analysis to investigate the spatial genetic structure (SGS), realized pollen and seed dispersal, and effective pollen dispersal for two B. excelsa populations in the Brazilian Amazon forest. Two plots were established in natural forests from which adults, juveniles, and seeds were sampled. Realized and effective pollen flow was greater than realized seed flow. The distance of realized pollen dispersal ranged from 36 to 2060 m, and the distance of realized seed dispersal ranged from 30 to 1742 m. Both pollen and seeds showed a dispersal pattern of isolation by distance, indicating a high frequency of mating among near-neighbor trees and seed dispersal near to mother trees. Both populations present SGS up to 175 m, which can be explained by isolation by distance pollen and seed dispersal patterns. Our results suggested that fragmentation of these forest populations may result in a significant decrease in gene flow, due to the isolation by distance pollen and seed dispersal patterns.

Female fruit production depends on female flower production and crown size rather than male density in a continuous population of a tropical dioecious tree (Virola surinamensis).

Factors related to pollen and resource limitation were evaluated to predict female fruit production in a tropical dioecious tree. Pollen limitation via variation in the male density at local scales is expected to limit female reproduction success in dioecious plants. We modeled the roles of local male density, female crown size, crown illumination, and female flower production on female fruit initiation and mature fruit production in a continuous population (62 ha plot) of a tropical dioecious tree (Virola surinamensis). In addition, we used microsatellites to describe the scale of effective pollen flow, the male effective population size, and the spatial genetic structure within/between progenies and males. The local male density was not related to female fruit initiation or mature fruit production. Female floral production had a positive effect on fruit initiation. The female crown size was positively related to fruit maturation. Seeds from the same female and seeds from different but spatially proximal females were generally half-siblings; however, proximal females showed greater variation. Proximal male-female adult pairs were not significantly more genetically related than distant pairs. The probability of paternity was negatively affected by the distance between seeds and males; most effective pollen dispersal events (∼85%) occurred from males located less than 150 m from females. The number of males siring progenies was greater than the number of males found at local scales. Female fecundity in this continuous population of Virola surinamensis is not limited by the availability of pollen from proximal males. Rather, resource allocation to floral production may ultimately determine female reproductive success.

Determinants of functional connectivity of holm oak woodlands: Fragment size and mouse foraging behavior

Demographic and genetic connectivity of fragmented plant populations will depend on effective propagule flow across the landscape. We analyze functional connectivity in a holm oak (Quercus ilex) fragmented landscape by considering three important stages driving recruitment: effective pollination, acorn production and acorn dispersal. We used a network approach to (1) determine if pollen-mediated gene exchange across the landscape was spatially structured; (2) estimate the effects of limited acorn dispersal on functional connectivity; (3) identify which landscape traits could drive source–sink dynamics of gene flow.Although long distance dispersal was relatively frequent, most effective pollen flow occurred over short distances (<100m). This resulted in a significantly modular structure of the mating network, yielding higher gene flow among nearby fragments. Limited mouse acorn hoarding activity had a strong impact on landscape connectivity, decreasing male gametic immigration rates into forest patches by one order of magnitude Besides, our results show that big forest fragments (>10ha) are the main pollen sources, while small ones (<1ha) are important pollen sinks. Thus, big fragments are critical to maintain functional connectivity, while small forest fragments may provide acorn crops better representing regional genetic diversity. In addition to area effects, less isolated and more central fragments showed higher migration rates and exchanged effective pollen with more fragments. Hence, we expected that landscapes with uniform or clumped distribution of big forest fragments would show optimal connectivity traits. However, despite that simulated gene flow was more evenly distributed across the landscape, connectance and migration rates decreased. Our results call for caution before translating patch-level management guidelines to the landscape scale. They also show that the level of functional connectivity may change throughout the recruitment process, suggesting that large-scale conservation strategies may fail if local effective seed establishment is disregarded.

Interpreting realized pollen flow in terms of pollinator travel paths and land-use resistance in heterogeneous landscapes

Widespread ecosystem change has led to declines in species world-wide. The loss of pollinators in particular constitutes a problem for ecosystem function and crop production. Understanding how landscape change affects pollinator movement, effective pollen flow, and plant and pollinator survival is therefore a global priority. In this study we investigated patterns of effective pollen flow, using wild cherry tree (Prunus avium) progeny arrays, to address two questions in three case studies: Do land-use types present different resistances to pollinator movement? Which pollinator travel path best explains the pollination data (straight lines, weighted straight lines, least cost paths or pair-wise resistance)? Trees and progeny arrays were genotyped and effective pollen flow and pollinator movement were estimated using the spatially explicit mating model. We found that pollinators did modify their travel paths in response to land-use type and arrangement, but the travel path that best described pollinator movement and the resistance rank of the land uses depended on the type and size of land-use patches and the landscape context. We propose a novel theoretical framework rooted in behavioural ecology, the resource model, for interpreting pollinator behaviour in heterogeneous landscapes. We conclude by discussing the importance and practicality of conservation and management strategies in which native and non-native land-use types together provide functional habitat and support ecosystem services across economic landscapes.

Genetic structure and diversity ofPolylepis australis(Rosaceae) tree populations from central Argentina: Implications for forest conservation

AbstractWorldwide, large areas of forest are being transformed to other land cover types and the resulting fragmented populations may suffer from restricted gene flow leading to genetic pauperization and increased inbreeding. To assess the genetic constitution of fragmentedPolylepis australismountain forests of central Argentina, analyses of the structure and diversity of ISSR markers were carried out for 90 trees distributed throughout five river basins with differing degrees of fragmentation. Overall, average polymorphism (P) ranged between 87.2 and 94.9% (95% criterion) while marker diversity index (M) varied between 0.35 and 0.39; values which are comparable with other wind-pollinated tree species. Analysis of molecular variance (AMOVA) revealed that most genetic variation occurred within river basins (97.8%), with only a little occurring between river basins (2.2%; ΦST= 0.02). In addition, Mantel’s test indicated thatP. australisdoes not follow the usual pattern of isolation by distance; instead the UPGMA method showed that trees from the two most degraded river basins formed a group while trees from the three better preserved basins formed another. As such, either effective pollen flow has maintained high levels of genetic diversity, or present day genetic variability is a remnant of a recently fragmented ancestral panmictic population. We conclude that, at present, genetic degradation inP. australispopulations of central Argentina is not as important as ecological degradation – such as soil loss, intensive browsing by livestock or increased frequencies of wildfires, and that genetic variability is still fully available for forest restoration.

Pollen flows within and between rice and millet fields in relation to farmer variety development in The Gambia

In areas with less favourable conditions for agriculture, informal seed systems permit gene flow through pollen to play a crucial role in the development of new varieties. An important factor with great impact on cross-pollination is the plant breeding system, but so far this is little studied within the context of low-input farming systems. This research studied the chances of cross-pollination within and between rice fields in The Gambia. Size and time of flowering were measured for 28 rice fields in one village. The level of mixture was measured in 90 seed lots of rice collected from four villages. Based on the results, we suggest that in general cross-pollination between different rice genotypes occurs more often within fields than between fields. No clear relationship was found between the level of within-field mixture and socio-economic status of farmers. Some comparison was made with millet, which allowed the identification of various factors influencing pollen flow between different genotypes. Effective pollen flow (between genotypes) is a function of a number of factors, such as the rate of cross-pollination of a crop, number of off-types within fields, variety distinctiveness, farmer expert knowledge, length and reliability of the rainy season, growth duration of different varieties, availability of fields, pest pressure and number of varieties grown per field or per farmer. We hypothesize that a low cross-pollination rate is more favourable for the development of new varieties in farmer fields than a high cross-pollination rate.

Wind pollination over mesoscale distances: an investigation with Scots pine

There is a gap between the order of magnitude of maximum documented distances of airborne tree pollen transport (up to 10(2)-10(3) km) and effective wind pollination (up to 10(1) km), which may partly derive from greater difficulties in detecting the latter. This study aims to assess wind pollination over scales closer to the maximum observed physical pollen transport distances. The origin of effective pollen immigrants into a strongly isolated Iberian Pinus sylvestris remnant was investigated using paternally inherited microsatellite markers and maximum-likelihood estimation combined with Monte Carlo assessment of parameter uncertainty. The results revealed significant effective pollen flow (up to 4.4%) from a large population located 100 km away, suggesting that the well-known mesoscale airborne transport of viable pine pollen can result in successful pollination over larger scales than previously reported for wind-pollinated tree species. This study supports the view that the gap between documented potential and effective wind pollen dispersal scales might not accurately reflect biological reality. Expanding the expected range of effective wind pollination has an impact on the assessment of a wide range of ecological and evolutionary processes, including reproductive assurance on fragmentation or colonization, metapopulation connectivity and interactions with local adaptation in heterogeneous habitats.

Gene flow pattern and mating system in a small population of Quercus semiserrata Roxb. (Fagaceae)

Pollen flow from external sources is important for the conservation of tree species in fragmented forests or small populations, because it can be sufficient to prevent differentiation among them, and appears to be able to prevent the loss of their genetic diversity through genetic drift. In this study, we examined the genetic heterogeneity of pollen pools accepted by each Quercus semiserrata seed parent at the Khun Wang Royal Agriculture Research Center, Thailand, both within and among two mast fruiting years (2005 and 2007), using paternity analysis and analysis of molecular variance (AMOVA). The mating systems of the trees were also examined using the multilocus mating system model (MLTR), after determining the genotypes at eight microsatellite loci of 26 seed-trees and 435 seeds from 8 seed-trees in the 2 mast fruiting years. The average distance of effective pollen flow within the plot was estimated to be 52.4 m, and 95% of effective pollen was dispersed within 200 m, indicating that effective pollen flow is highly localized and that most effective pollen is contributed by near-neighbor trees. The proportion of effective pollen that immigrated from external sources was estimated to be 26.2%. The AMOVA analysis based on the pollen haplotypes showed that the pollen pools, both total and for each reproductive year, significantly genetically differed among the seed parents. Using a mixed mating model, the estimate of biparental inbreeding for the total population ( t m − t s) was 0.013, indicating that a low proportion of mating occurred among close relatives. The effective number of pollen donors ( N ep) was estimated to be 9.987 using the TwoGener model, or 10.989 using the mixed mating model. The effective number of pollen donors of seeds was higher in the mast fruiting year 2005 than in the other examined year, 2007. Consequently the allelic richness and genetic diversity of seeds produced in 2005 were higher than those produced in 2007. Overall, the results show that high outcrossing rates, high levels of gene flow from other populations and heterogeneity in the pollen received by an individual may enhance the ability of populations to maintain effective population sizes. Therefore, these processes may be sufficient to prevent loss of genetic diversity through genetic drift of Q. semiserrata at this study site.

Preliminary development of a genetic strategy to prevent transgene escape by blocking effective pollen flow from transgenic plants.

Genetic modification (GM) of plants has great potential in the production of food and industrial compounds, and in molecular pharming. One of the greatest public concerns regarding this technology is effective pollen flow, in which wind- or insect-borne transgenic pollen is able to fertilise either non-GM crops of the same species, or closely related weed species, and lead to viable seed formation. In this paper we describe a novel concept, based on epigenetic inheritance (imprinting) and post-transcriptional gene silencing (PTGS)/RNA interference (RNAi), designed to prevent transgene escape via pollen flow from transgenic plants. A key advantage of this strategy is that it would allow all seeds from self-pollinated transgenic plants to be harvested and re-sown, without the need for specific treatments, while retaining all of the transgenes present in the parent. Thus, this strategy is not a Genetic Use Restriction Technology (GURT) and if implemented would not prevent seed saving by end-users.

Pollen flow and the intrapopulation genetic structure of Heloniopsis orientalis on the forest floor as determined using microsatellite markers

Pollenflow, seedling dynamics, and the genetic structure of Heloniopsis orientalis (Thunb.) C. Tanaka (Liliaceae) were analyzed as part of an effort to understand the reproduction system of perennial herbs foundon the forest floor by means of microsatellite markers. It was possible to assign paternity to all offspring within this population by paternity analysis. Although no ordinary pollinator visits were observed during the flowering period, effective pollen flow occurred throughout the population. It appears that low frequencies of pollinator visits nonetheless permitted adequate pollen flow. Studies of seedling dynamics suggested restricted recruitment by means of seed. Gene flow in the present population seemed to depend mainly on pollen. Local genetic structuring caused by seeds falling near the mother plant and by vegetative reproduction was detected by means of spatial autocorrelation. Three main modes of development of genetic structure were found for this species: (1) asexual reproduction by adventitious buds, which was dominant (up to 20 cm from the parent plants); (2) sexual reproduction by seeds that fell from flower stalks (up to 60 cm from the parent plants); and (3) pollen that dispersed over a wide area (throughout the population).

Cryptic dioecy and insect pollination in Rosa setigera Michx. (Rosaceae), a rare plant of Carolinian Canada

Rosa setigera is unique among known roses because it is truly dioecious, yet the plants and flowers are almost impossible to sex. Subtle differences in the inflorescences have been detected, for example, there are more flowers per inflorescence on male plants than on female plants and petal expansion from the day of opening to the next day is greater in females than in males; in addition, pollen from female plants appears somewhat collapsed and does not germinate. Pollinators (Apis mellifera, other bees (Apidae), Eristalis tenax and other Syrphidae: Diptera) visit the blossoms mostly in the morning to collect pollen (there is no nectar) and in choice experiments do not discriminate between male flowers and female flowers on landing, but do spend significantly more time on the former. They do discriminate between freshly opened flowers and day-old flowers, and show marked preference for bouquets of five flowers vs. single flowers. The female plants, with smaller inflorescences and lesser interest to pollen foraging insects, seem to encourage them to forage at more flowers than do their male counterparts. This may be biologically significant for effective pollen flow in a dioecious pollenonly plant with pollenivorous pollinators.

Use of Electrophoresis in Tree Improvement Programs

Some application of isozyme technology in tree improvement programs are discussed. The connection between single-gene enzyme products and classical Mendelian genes is developed to provide the framework for an understanding of the utility of single genes. Three main applications for this technology in tree improvement programs are identified. The first is for registration and certification of pedigrees of families and clones. Secondly, isozymes can often be used to more accurately ascribe relative species purity in cases where hybridization occurs between two parental taxa Finally, these single gene markers can be used extensively in seed orchards to estimate mating systems, elucidate mating patterns among orchard clones, establish relative fertility, determine relative proportions of contamination, and quantitatively describe patterns of effective pollen flow in the orchard. Costs of running an electrophoresis laboratory are discussed.