Outcrossing Rate Research Articles

Study on Mating System of <i>Pinus koraiensis</i> in Natural Population Based on cpSSR Technology

Chloroplast simple sequence repeat (cpSSR) technique was firstly used to study mating system of natural Pinus koraiensis population. Nine pairs of primers with clear spectrum bands, high stability and polymorphism were selected from 70 pairs of cpSSR primers to analyze the mating systems of 28 individuals. 14 polymorphic loci were detected in the nine pairs of primers. The multi-locus (tm) and single-locus (ts) outcrossing rate were 0.966 (SD=0.000) and 0.939 (SD=0.000), respectively, which were slightly higher than those of other tree species. The constant index (F=-0.035) was below zero, indicating the occurrence of excessive heterozygote. Moreover, inbreeding index (tm-ts=0.027; SD=0.000) was close to zero, indicating an insignificant inbreeding. MLDT analysis showed that multi-locus outcrossing rate differed from single-locus outcrossing rate in mating systems of 28 individuals, but the differences were not statistically significant.

Pollination Efficiency of Bumblebee Queens and Workers in the Alpine Shrub Rhododendron aureum

Rhododendron aureum is a weakly self-compatible alpine shrub pollinated by bumblebees. Flower visitation frequency and foraging behavior differed between queen bumblebees and workers. Queens exhibited less frequent flower visits, longer flight distances between inflorescences, and a smaller number of sequential inflorescence visits within patches than did worker bees. Flowering in early-snowmelt populations occurred in June, when only overwintered queens were available, while flowering in late-snowmelt populations occurred from late July to August, when frequent visits by workers were common. The fruit to flower ratio per inflorescence was lower in early-snowmelt populations due to quantitative pollen limitation, while the seed to ovule ratio per fruit was lower in late-snowmelt populations. This is because geitonogamous pollination by workers was common later in the season, which resulted in a high abortion rate of self-pollinated seeds, that is, qualitative pollen limitation. Thus, pollination efficiency, or the type of pollen limitation, shifts during the flowering season, reflecting the seasonal life cycle of bumblebees in the ecosystem. Many of the self-fertilized seeds aborted due to high inbreeding depression, and the outcrossing rate was ∼80% regardless of season.

Relation between out-crossing rate and isolation distance under cool temperature conditions at the booting stage that causes the occurrence of male sterility in rice

イネ種子親の不稔発生条件下での種子親と花粉親間の距離と交雑発生との関係を解明するために，うるち花粉親圃場から風下側に，2006年には2 m，26 m，150 m，300 m，2007年には150 m，300 m，450 m，600 mに，もち種子親を各63～69ポット （2～3 個体/ポット） で設置した．種子親には穂ばらみ期に冷水を処理し （冷水区，各不稔率25，43％），2007年のみ無処理 （不稔率26％） も設け，花粉親は無処理 （不稔率10～13％） とした．種子親の稔実種子からキセニア粒を目視で選別し，次にPCR分析により花粉親品種を判別した．種子親の交雑率は，隔離距離が短い順に2006年の冷水区で1.136，0.529，0.068，0.024％，2007年の冷水区で0.084，0.023，0.012，0.035％，無処理区で0.017，0.014，0.002，0％で，2007年では各距離とも無処理区に比べ不稔率が高い冷水区で交雑率が高く，また2007年の冷水区を除き長距離ほど交雑率が低下したが，最長600 mでも交雑が認められた．この長距離での交雑発生要因として，（1） 種子親と花粉親の出穂期の重複 （両年とも4～6日間），（2） 種子親の花粉親より高い不稔率，（3） うるち花粉源の大きい圃場面積 （花粉親圃場2.3 haの他，近接の同一品種2.7 ha，種子親と交雑が生じた他の品種が2方向に2.4 ha，2.9 ha），（4） 開花期間の風向 （70～79％は花粉親から種子親への方向） と大きな平均風速 （3.6～4.0 m/s） の4点が考えられた．

Genetic evaluation of seeds of highly endangered Pinus uliginosa Neumann from Węgliniec reserve for ex-situ conservation program

Peat-bog pine <em>Pinus uliginosa</em> Neumann has become extinct or rare in many parts of Europe. We have investigated the levels of genetic variation and inbreeding in seeds collected from a highly endangered reserve of this species in Poland, using allozymes as genetic markers. Generally, a high level of genetic variation was observed. The mean expected heterozygosity was 0.376, while average (Na) and effective (Ne) numbers of alleles per locus were 2.45 and 1.67, respectively. Nevertheless, we have detected relatively low levels of outcrossing, and potential biparental inbreeding. The population-wide multilocus outcrossing rate was estimated to be 0.706 (±0.091), while the minimum variance mean of single-locus estimates was distinctly lower (ts=0.611). The estimates of outcrossing calculated for individual trees ranged widely from 0.051 to 1.017, indicating the complexity of outcrossing patterns. The investigated population of <em>P. uliginasa</em> from Węgliniec is small and surrounded by extensive forest stands of <em>P. sylvestris</em>. Our three-year records of phenological observations demonstrated that flowering periods for <em>P. uliginosa</em> and <em>P. sylvestris</em> overlap, allowing for cross-pollination. The possibility of <em>P. uliginosa</em> pollination by <em>P. sylvestris</em> creates a potential danger of genetic erosion of the <em>P. uliginosa</em> gene pool. Nonetheless, based on a species specific cpDNA marker we have found that among 533 seedlings of <em>P. uliginosa</em> there were only six seedlings carrying cpDNA marker specific for <em>P. sylvestris</em>, indicating that such hybridization seems to be rare.

Outcrossability of Brassica napus L. and B. rapa L. in an Experimental Field

The outcrossing rate of oilseed rape (Brassica napus) between two cultivars was assessed in an experimental field. During flowering (from the end April to the end of May), the wind from the pollen donor (_??_) to the seed parent (_??_) prevailed. The crossing rate (%) of the seed parent decreased as the distance from the pollen donor parent increased; 4.1% at 0.25 m distance, 1.4% at 1 m, 0.4% at 5 m, 0.15% at 10 m, 0.09% at 30 m, and 0.01% at 60 m. In another experiment, the hybridization rate between 55 cultivars of B. rapa (_??_) and B. napus (_??_) cultivars was assessed by placing rapa-planted pots in a napus field. The rate of 55 rapa cultivars ranged from 2% to 50% in the field, which might show the rapa cultivar-differences of crossability between the two species.

Estimation of outcrossing rates at small-scale flowering sites of the dwarf bamboo species, Sasa cernua

We estimated the outcrossing rates at small-scale flowering sites of an endemic dwarf bamboo species, Sasa cernua. The multi-locus estimation of the outcrossing rate of the dwarf bamboo population was 0.148 (SD 0.118). Two culms with the highest outcrossing rates had heterozygous genotypes at one locus, but other culms in the locus were homozygotes. Five culms with high outcrossing rates bore 2-17% seeds with homozygous genotypes. Due to predominant selfing, the overall inbreeding coefficient of seeds was high, although it declined in seedlings. This suggests that selection against inbred progenies began early in the establishment process in the natural habitat.

Mating system parameters and genetic structure in Argentinean populations of Acacia caven (Leguminosae, Mimosoideae)

Acacia caven (Mol.) Mol. is native to South America. The species is a leguminous, woody small tree that is considered to have certain potential as a managed silvopastoral crop. Six varieties have been described for the species based on both morphological traits and molecular markers. Little information is available on its mating system. The main objectives of this work were to test the hypothesis that A. caven is an outcrosser and to estimate parameters of its mating system and population structure on the basis of isozyme markers. In the four populations studied, a high homozygote excess was found in the progeny population but not in the mother plant genotypes. The estimate for the multi-locus outcrossing rate (tm) was high (≥0.957) in all populations, indicating that Acacia caven is a predominantly outcrosser species. The results of genetic structure analysis within each population indicated that differences in allelic frequencies among families in all of the populations studied are highly significant. The difference in F estimates between progeny and mother plants suggests some selection favouring heterozygotes between the seedling and adult stages. Therefore, a strategy for ex situ conservation might emphasise sampling more populations with a relative large number of trees per site.

Can a seed bank provide demographic and genetic rescue in a declining population of the endangered shrub Acacia pinguifolia?

Many threatened species suffer reduced genetic diversity as a result of small population size and isolation. However, species with a persistent seed bank may be buffered against genetic loss as seed banks are expected to accumulate the reproductive output of many seasons. For fire-dependent species in decline, prescribed ecological burning may be a means to stimulate germination and recover genetic diversity stored in the seed bank, providing a demographic and genetic rescue effect. Here we investigated the effectiveness of this strategy in a small, isolated and inbred population of the endangered shrub, Acacia pinguifolia. We surveyed genetic diversity and structure of remnant populations of A. pinguifolia and monitored regeneration before and after burning. Germination was stimulated by fire, but seedling numbers 18 months post-fire were low and barely above the number of adults killed by the fire. Genetic diversity was marginally higher in the post-fire seedling cohort than the pre-fire adults (HE = 0.1 vs. 0.09, respectively). Outcrossing rates of open-pollinated seed from surrounding plants suggested moderately high levels of self-fertilisation (tm = 0.65) and analysis of fine-scale genetic structure implied pollen and seed dispersal over distances of several metres, suggesting that restricted gene flow and inbreeding may act to limit genetic diversity in the seed bank. We conclude that prescribed burning has not been immediately successful as a recovery strategy for this relictual population of A. pinguifolia, though future monitoring may detect additional recruits. Alternative conservation strategies, including performing inter-population crosses, may be required to restore genetic diversity and ameliorate extinction risks.

The relative importance of factors determining genetic drift: mating system, spatial genetic structure, habitat and census size in Arabidopsis lyrata

• The mating system, dispersal and census size are predicted to determine the magnitude of genetic drift, but little is known about their relative importance in nature. • We estimated the contributions of several population-level features to genetic drift in 18 populations of Arabidopsis lyrata. The factors were outcrossing rate, within-population spatial genetic structure, census size and substrate type. The expected heterozygosity (H(E)) at 10 microsatellite loci was taken to reflect the effective population size (N(e)) and the strength of genetic drift. • The mating system explained most of the variation in H(E) (60%), followed by substrate (10%), genetic structure (9%) and census size (6%). The most outcrossing population had a +0.32 higher predicted H(E) than the most selfing population; the estimated N(e) of selfing populations was less than half that of outcrossing populations. Rocky outcrops supported populations with a +0.14 higher H(E) than did sandy substrates. The most structured population had a +0.24 higher H(E) than the least structured population, and the largest population had a +0.18 higher H(E) than the smallest population. • This study illustrates the importance of outcrossing, genetic structure and the physical environment--together with census size--in maintaining H(E), and suggests that multiple population-level characteristics influence N(e) and the action of genetic drift.

Investigation of pollen competition between wild and cultivated sorghums (Sorghum bicolor (L.) Moench) using simple sequence repeats markers

In self-compatible plant species stigmata receive a mixture of self and outcrossed pollen and competition between them is expected to play a major role in determining the pollen-mediated gene flow. The use of male sterile bait plants in field trials to demonstrate the rate of gene flow is questionable due to lack of pollination competition. However, little direct evidence has been published. A field experiment of male sterile and male fertile sorghum pollen recipient bait plants was conducted to evaluate pollen competition between wild and cultivated sorghums and the effects of pollen competition on gene flow assessment. Pollen competition between wild and cultivated sorghums was estimated from two-component pollen mixtures of wild and cultivated sorghum (1:1 ratio) applied to wild, cultivated and male-sterile maternal bait plants. Paternity was determined in the progeny using two diagnostic Simple Sequence Repeat markers. The study found that self pollen has higher seed-siring success. Maternal genotype influences the siring ability of the pollen donor components which significantly deviated from the 1:1 pollen loads. The study showed that published estimates of gene flow derived from studies using male-sterile bait plants seriously overestimate gene flow and that pollen competition may be a significant factor influencing outcrossing rates. The results suggest that the predominant direction of gene flow is from cultivated to wild sorghum, potentially leading to introgression of crop genes into wild sorghum. Pollen competition should be taken into account in gene flow estimation, since presence of self-pollen can account for over half of seed produced irrespective of maternal genotype.

Microsatellite Based Paternity Analysis in a Clonal Eucalyptus nitens Seed Orchard

Abstract Microsatellite markers were used to determine paternity in 473 open-pollinated progenies from a clonal Eucalyptus nitens seed orchard of 50 trees from 12 different genotypes. The outcrossing rate in this orchard was high, averaging 0.85 (weighted by capsule crop) but variable between trees (ranging from 0.6-1.0). Paternal contribution of each genotype to the open-pollinated seed crop was predicted by the size of the flower crop of each genotype (r = 0.76), but not the number of ramets. While the detectable contamination in this orchard is relatively low (4.5%), it is atypical when compared to other published estimates in eucalypt seed orchards suggesting that with suitable buffering low levels of contamination can be achieved.

Outcrossing rate in sweet passion fruit based on molecular markers

With 3 tables AbstractYellow and sweet passion fruit are insect‐pollinated species native to the tropics. Fruits are used commercially for human consumption worldwide. The yellow passion fruit is an outcrossing species with self‐incompatible flowers. However, the reproductive system of the sweet passion fruit (Passiflora alata) has not been well elucidated. The objective of this work was to characterize aspects of the mating system in the sweet passion fruit using random amplified polymorphic DNA (RAPD) and microsatellite markers, particularly the rate of outcrossing in P. alata progenies. A multilocus outcrossing rate of tm = 0.994 was determined from RAPD and tm = 0.940 from microsatellites, supporting P. alata as an outcrossing species. The fixation indices of the maternal generation (Fm) were −0.200 and 0.071 with RAPD and microsatellite loci, respectively, indicating the absence of inbreeding in the maternal generation. The paternity correlation (rp) varied from −0.008 with RAPD markers to 0.208 with microsatellite markers, suggesting a low probability of finding full sibs within the progenies. The results demonstrated that all progenies assessed in this study were derived from outcrossing.

Mating systems in tropical forages: Stylosanthes capitata Vog. and Stylosanthes guianensis (Aubl.) Sw.

Stylosanthes capitata and S. guianensis are important forage legumes for tropical areas. The only available estimates of S. capitata and S. guianensis outcrossing rates were based on morphological markers, and the genus is considered as being mainly self-pollinated. Here we describe an estimation of the outcrossing rate in S. capitata and S. guianensis using microsatellite markers. The outcrossing rates were estimated in S. capitata and S. guianensis open-pollinated populations of 20 progenies consisting of ten individuals each. The multi locus outcrossing rate for S. capitata was estimated using 10 polymorphic loci, whereas five microsatellites were used for S. guianensis. The multi locus outcrossing rates for S. capitata and S. guianensis were 31 and 26%, respectively, suggesting a mixed mating system with predominance of autogamy. Comparison of single locus and multi locus estimates of outcrossing rates indicated that little inbreeding other than selfing occurred. The estimated Wright’s fixation index of the parental generation was lower than expected based on the multi locus outcrossing rate, possibly resulting from the use of some heterozygous breeding genotypes for the study. The data on the outcrossing rate described here are potentially useful for breeding programs and for maintenance of germplasm collections of these Stylosanthes species.

The natural history of Caenorhabditis elegans

Summary In the laboratory, the nematode Caenorhabditis elegans lives on the surface of nutrient agar in Petri dishes, feeding on a lawn of the uracil auxotroph strain OP50, an Escherichia coli mutant strain. This sentence sums up the fundamentals of C. elegans ecology, as most of us know it. While over 15,000 articles on diverse biological aspects of C. elegans attest to the worm's undisputable virtues as a major model organism, its biology in the wild remains mysterious. To properly interpret and fully understand the available wealth of genetic, molecular and other biological observations made in the laboratory, it will be important to know its natural history and to place the species in its ecological and evolutionary context. With the aim of connecting the discoveries that have been made about C. elegans biology to its ‘real life', we shall discuss recent studies on the worm's natural habitat and population biology, and outline key issues in attaining a modern natural history of C. elegans.

Seed dispersal and population structure in Vriesea gigantea, a bromeliad from the Brazilian Atlantic Rainforest

Seed dispersal, population structure and the mating system of plant species can have great consequences on the genetic structure of populations. Vriesea gigantea is a bromeliad from southeastern Brazil which is self-compatible and pollinator dependent for fruit set. Its populations are fertile in terms of the production of flowers, pollen, fruits and seeds. To assess the importance of seed supply for gene flow, colonization and distribution of adult individuals, the seed dispersal and population structure of V. gigantea were studied. Seeds are dispersed over short distances; most seeds land close to the mother plant. This pattern coincides with the reported aggregate distribution of bromeliad seedlings. Population structure results showed high seedling recruitment, because 51.3% developed into adults, although few juveniles reached this stage. This result is different from that for other bromeliad species from different habitat conditions. Seed dispersal and population structural patterns are consistent with previous molecular studies, revealing that V. gigantea populations are genetically structured, with low gene flow and a moderate outcrossing rate. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164, 317–325.

An evaluation of small-scale genetic diversity and the mating system in Zostera noltii on an intertidal sandflat in the Wadden Sea

The dwarf eelgrass, Zostera noltii, is a predominant inhabitant of soft-bottom intertidal regions along the coasts of northern Europe. It is a monoecious, protogynous angiosperm in which the potential for self-fertilization and inbreeding are high, especially if clone sizes exceed pollen dispersal distances. The aim of the present study was to determine the relationship between mating system and clonal structure, examine the relative roles of geitonogamous selfing and biparental inbreeding, measure pollen availability (multiple paternities) and estimate pollen dispersal. A 100-m(2) plot was established in a large, intertidal Z. noltii meadow on the island of Sylt in the German Wadden Sea. A total of 256 adult shoots was sampled: one from the centre of 100 fixed 1-m(2) quadrats (large scale resolution) and an additional 156 from within eight randomly selected 1-m(2) sub-quadrats (small-scale resolution). DNA was extracted from seeds and leaf tissue of all samples and genotyped with nine microsatellite loci. Mating system analysis revealed high multilocus and single locus outcrossing rates. Average pollen dispersal distance was nearly the same as the average genet (clone) size. Multiple paternity was common and 20-30 % of mature seeds originated from matings within the plot. Among inbred seeds, most resulted from geitonogamy rather than biparental inbreeding. Moderate disturbances intrinsic to the intertidal habitat appear to facilitate seed recruitment by gap formation. Pollen dispersal distances are sufficient to maintain outcrossing and high clonal diversity.

Significant differences in outcrossing rate, self-incompatibility, and inbreeding depression between two widely hybridizing species of Geum

Geum urbanum and Geum rivale are two widely hybridizing perennial herbs. Estimation of the breeding systems of these taxa using nuclear microsatellite markers scored in mother–progeny arrays demonstrated that, in pure populations, G. urbanum is predominantly selfing (outcrossing rate, t = 0.058 to 0.177), whereas G. rivale is predominantly outcrossing (t = 0.686–0.775). Theory suggests that hybridization between inbreeding and outcrossing species can potentially generate novel inbreeding lineages. However, the establishment of such lineages may be restricted either by self-incompatibility loci or deleterious recessive alleles derived from the outcrossing parent. To assess the likelihood that hybridization between G. urbanum and G. rivale will generate novel inbreeding lineages, self-incompatibility and inbreeding depression were investigated in the two taxa. Seed set in the absence of pollinators, and after controlled self- and cross-pollination, was measured to study self-incompatibility. Inbreeding depression was measured by estimating the relative fitness of offspring from controlled self-and cross-pollinations. Geum urbanum was fully self-compatible [self-compatibility index (SCI) = 1] and bagged flowers showed full seed set. By contrast, only 3% of bagged flowers set seed in G. rivale and controlled self-pollinations showed a 60–80% reduction in seed set compared to controlled outcross pollinations (SCI = 0.28). There was no evidence for inbreeding depression in G. urbanum, although significant, albeit low levels of inbreeding depression were detected in one of two G. rivale populations (δ = 0.33). The implication of these results is that if genetic material from G. rivale was incorporated into a hybrid with a selfing morphology, the establishment of this selfing lineage could be compromised by self-incompatibility and inbreeding depression. The wider implications of these results for evolution in hybrid swarms between G. urbanum and G. rivale are discussed.

Early Inbreeding Depression Selects for High Outcrossing Rates inAquilegia formosaandAquilegia pubescens

Theory suggests that mating‐system parameters in plants may be strongly influenced by pollinator type. We examined the outcrossing rate, biparental inbreeding, and inbreeding depression in two closely related species of Aquilegia, A. formosa and A. pubescens, that differ in their major floral visitors (hummingbird and hawkmoth, respectively). Population‐level estimates of the outcrossing rate were generally high, ranging from 0.42 to 0.89 and averaging 0.79 for A. formosa and 0.69 for A. pubescens; however, the two rates did not differ significantly. The similarities in the outcrossing rates of the two species suggest that both hummingbird and hawkmoth pollination systems provide pollen movement patterns that promote a high degree of outcrossing. However, we also found that a substantial amount of outcrossing (13%–46%) was due to mating between relatives (biparental inbreeding). Using Ritland’s genetic marker–based approach to estimate inbreeding depression, we found complete selection against inbred prog...

ANALISIS SISTEM PERKAWINAN MERBAU (Intsia bijuga O. Ktze) DI PAPUA BERDASARKAN PENANDA ISOENZIM

Merbau (Intsia bijuga O. Ktze) is an important species to supply wood in Indonesia. Mating system on natural population of merbau can influence genetic diversity of merbau. The objectives of this study were to investigate mating system on natural forest of merbau in Papua. The research used 200 samples of merbau from 10 mother trees in Gunung Meja Forest Research Manokwari-Papua. Isoenzyme analysis was done using four enzyme systems i. e. Peroxidase (POD), Esterase (EST), Glutamate Oxaloacetate Transaminase (GOT) dan Diaphorase (DIA). Data were analysed using MLTR program. The result showed that average genetic diversity (He) 0.463 and total heterozygosity (HT) 0.496. The multilocus population outcrossing rate (t m ) and singlelocus population outcrossing rate (t s ) were t m = 1.00 and t s = 0.992. Probability of inbreeding rate (t m - t s ) = 0.008.

Reproductive traits associated with invasiveness in Coreopsis lanceolata

Aims The invasive plant Coreopsis lanceolata can reproduce sexually and clonally,but the relative importance of these remains largely unknown. Our objective was to determine if reproductive characteristics affect the inva-siveness of C. lanceolata. Methods We observed the flowering dynamics of inflorescence,self-compatibility,germination traits of seed and clonal reproductive traits of C. lanceolata. Important findings Most C. lanceolata flowered and fruited between April and November. The florescence of a single capitulum persisted approximately 5 to 6 days,and the fruits matured after 18 days. Bagged capitula showed there were no seed set in single capitulum,and they were geitonogamous,which indicated self-incompatibility. The pollen-ovule (P/O) ratio was 103 549.40 ± 7 162.44. There was high pollen viability during flowering,and pollinator movement ensured endogamy,which improved the rate of out-crossing. Under natural conditions,the germination percentage is 50%,and germination occurs within 2–3 days. Coreopsis lanceolata has strong asexual capacity; there were many phalanx ramets from roots during the growing season,and the guerrilla ramets only occurred beginning in the last ten days of August,which is beneficial to C. lanceolata in excluding other species and forming mono-culture populations. These results suggest that the invasiveness of C. lanceolata is closely related to its reproductive traits.