Genetic diversity,genetic drift and mixed mating system in small subpopulations of <Emphasis Type="Italic">Dyckia ibiramensis</Emphasis>, a rare endemic bromeliad from Southern Brazil

Dyckia ibiramensis is a naturally rare, endemic and threatened bromeliad which occurs naturally on 4 km of rocky river outcroppings in Southern Brazil. For this study, subpopulations of the species were characterized based on size and genetics, to compile information for in situ and ex situ conservation strategies. A census of the rosettes was undertaken for each subpopulation and seven allozyme polymorphic loci were used to estimate genetic diversity and structure of adults and offspring and assess the mating system. In general, the subpopulations were small and most of the rosettes were aggregated into clumps. The species showed a high genetic diversity ([^(H)]_e = 0.219 \hat{H}_{e} = 0.219 ) and significant fixation index ([^(f)] = 0.642, \hat{f} = 0.642, P ≤ 0.05). The estimate of differentiation among all adult subpopulations indicate pronounced genetic structure ([^(G)]^￠_ST = 0.674 \hat{G}^{\prime}_{ST} = 0.674 ). D. ibiramensis has a mixed mating system and multilocus outcrossing rates [^(t)]_m \hat{t}_{m} were variable between subpopulations. This study demonstrates the importance of in situ preservation of all subpopulations for the maintenance of species diversity. For effective ex situ conservation, it would be necessary to collect seeds from 52 to 99 seed-rosettes, depending on the target population.     

Genetic effects of forest fragmentation in high-density Araucaria angustifolia populations in Southern Brazil

Araucaria angustifolia is an endangered tropical/subtropical coniferous of great interest for conservation due its economical, ecological, and social value. Only 3% of original Araucaria forests remain, which are generally confined to small forest fragments. Forest fragmentation can have serious consequences on genetic process in tree population, affecting long-term fitness and adaptability. To investigate the effects of forest fragmentation on genetic diversity and the structure of A. angustifolia populations, the genetic diversity of eight microsatellite loci was compared in four small fragmented populations (<22 ha), four tree groups (five to 11 trees) occurring in pastures and in three plots in a large continuous population. The clearest effect of fragmentation was the loss of rare alleles (p ≤ 0.05) in fragmented populations (19.4% to 47.2%) and intermediate frequency (0.05 < p ≤ 0.25) and rare alleles (p ≤ 0.05) in tree groups (19% to 86.1%) in comparison to continuous populations. Fragmented populations have significant higher fixation index ( [^(F)]_\textIS = 0.121 \widehat{F}_{\text{IS}} = 0.121 , P < 0.05) than continuous populations ( [^(F)]_\textIS = 0.083 \widehat{F}_{\text{IS}} = 0.083 , P < 0.05). High genetic differentiation was detected among tree groups ( [^(G)]_\textST^￠ = 0.258 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.258 , P < 0.01) and low among fragments ( [^(G)]_\textST^￠ = 0.031 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.031 , P < 0.05) and continuous populations ( [^(G)]_\textST^￠ = 0.026 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.026 , P < 0.05), showing a significant bottleneck effect in tree groups. Evidence that forest fragments have experienced a recent bottleneck was confirmed in at least two studied fragments. The implications of the results for conservation of the fragmented A. angustifolia populations are discussed.     

Genetic parameters and predicted selection responses for timber production traits in a Castanea sativa progeny trial: developing a breeding program

Total height, diameter, index volume, stem straightness, apical dominance, and survival were assessed at 8 years from seed in an open-pollinated progeny test of 36 families of European chestnut (Castanea sativa Miller) established at two sites in the Atlantic area of Galicia, Spain. Iterative spatial analysis was applied to eliminate the effect of the spatial dependence in the original data and to estimate accurately genetic parameters for evaluating the potential for selection of the measured trees. Spatial analysis was very beneficial for growth traits and survival, but less so if at all for form traits. Estimated individual heritabilities ranged from moderate to high for growth traits ([^(h)]_i² = 0.29 - 0.42 \widehat{h}_i^2 = 0.29 - 0.42 ) and stem straightness ([^(h)]_i² = 0.24 - 0.42 \widehat{h}_i^2 = 0.{24} - 0.{42} ). High coefficients of additive genetic variance were obtained for volume ( [^(\textC)]\textV_\textA = 36.5 - 41.5% \widehat{\text{C}}{{\text{V}}_{\text{A}}} = {36}.{5} - {41}.{5}\% ) and straightness ( [^(\textC)]\textV_\textA = 44.26 - 53.84% \widehat{\text{C}}{{\text{V}}_{\text{A}}} = {44}.{26} - {53}.{84}\% ). Phenotypic and estimated genetic correlations between growth traits were very high, and correlations between sites indicated that there was no important family × site interaction. No adverse correlations between traits were evident. The results indicate the ample potential for selection in the current progeny trial, where responses to within-family and combined selection for growth traits may be high. Accordingly, three selection scenarios were addressed with the aim to initiate the selection of individuals for implementing the Forest Breeding Plan of Galicia for European chestnut.     

Effective size of an Atlantic salmon (Salmo salar L.) metapopulation in Northern Spain

The genetic diversity of metapopulations is influenced not only by the effective sizes (N _e ) of individual subpopulations, but also by the total effective size of the metapopulation (meta-N _e ). We estimated meta-N _e of four neighbouring Atlantic salmon populations connected by gene flow using genetic estimates of subpopulation N _e s and migration rates derived from capture–recapture data. The meta-[^(N)]_e meta{\hbox{-}}\hat{N}_{e} was lower than the sum of [^(N)]_e \hat{N}_{e} s of the subpopulations, suggesting that genetic diversity harboured by the four river salmon metapopulation is lower than what would have been expected by viewing individual subpopulations separately. In addition, meta-[^(N)]_e meta{\hbox{-}}\hat{N}_{e} was found to be sensitive to changes in [^(N)]_e \hat{N}_{e} of the subpopulation from which net emigration rate was largest, so as that the genetic diversity of the metapopulation would be best preserved by avoiding any reductions in N _e of this subpopulation. Yet, this subpopulation is the one that has historically—and still is—experiencing the highest exploitation rate in the metapopulation system.     

Self-thinning lines of organs and aboveground parts based on allometric relationships in overcrowded Pinus densiflora stands

The allometric relationships of mean tree height [`(H)]( μ [`(w)]_x^q ) \bar{H}( \propto \bar{w}_{\rm {x}}^{\theta } ) and of organ mass density [`(d)]<sub>x</sub> ( μ [`(w)]_x^d ) \bar{d}_{\rm {x}} ( \propto \bar{w}_{\rm {x}}^{\delta } ) to mean organ mass [`(w)]_x \bar{w}_{\rm {x}} were studied in self-thinning Pinus densiflora Sieb. et Zucc. stands. Tree height increased significantly with increasing mean mass of organs and aboveground parts on log–log coordinates. The value of the allometric constant θ ranged from 0.2878 to 0.3349. On the other hand, the constant value δ was not significantly different from zero, except for leaves. The value of the allometric constant δ ranged from −0.2926 to 0.0120. According to Weller’s allometric model, the slope of the self-thinning line was calculated from the allometric constants θ and δ. The thinning slope was estimated to be −1.51 in stem, −1.39 in branches, −1.00 in leaf and −1.41 in aboveground parts, respectively. Mass density was high in stem, medium in branches and low in leaves. Mean leaf mass density decreased significantly with decreasing stand density on log–log coordinates, which could be interpreted as indicating the importance of the constant final leaf biomass in overcrowded P. densiflora stands. The self-thinning exponents of branch, stem and aboveground parts were not significantly different from 3/2, which indicated that the 3/2 power law of self-thinning holds for stem mass, branch mass and aboveground mass in overcrowded P. densiflora stands.     

Wild genetic diversity preservation in a small-sized first generation breeding population of <Emphasis Type="Italic">Allanblackia floribunda</Emphasis> (Clusiaceae)

Founder group size is of prime importance in tree breeding programs. We determined whether sampling 20-plus trees for breeding in Allanblackia floribunda, a tropical forest tree species that has been recently enrolled in tree improvement program for fruit and seed production, would affect neutral genetic diversity and inbreeding level in both breeding and production populations. Using eight informative microsatellite loci, we: (a) assessed the nuclear genetic diversity of ten natural populations, and of the breeding population in the humid forest zone of Cameroon; (b) investigated temporal effective-size fluctuations in A. floribunda natural populations, with a view to identifying the role of past demographic events in the genetic structure of the studied species; and (c) tested the hypothesis that genetic diversity in a founder group of 20 individuals is not different from that existing in the wild. The eight loci were variable. High levels of genetic diversity (A = 4.96; H _E = 0.59) and moderate differentiation (R _ST = 0.061) were found within and among populations in wild stands. High genetic distances existed between populations ( \textaverage chord distance = 0.\text2769 ±0.00\text554 ) \left( {{\text{average chord distance}} = 0.{\text{2769}} \pm 0.00{\text{554}}} \right) . Eight of the ten surveyed populations showed signs of deviation from mutation-drift equilibrium, suggesting Pleistocene population bottlenecks and fluctuations in effective population size. Mantel tests did not reveal any relationships between genetic and geographic distances. A neighbor-joining dendrogram showed a population structure that could be explained by historical factors. The hypothesis tested has been accepted. However, a slight increase in inbreeding was observed in the breeding population.     

Gene stacking strategies with doubled haploids derived from biparental crosses: theory and simulations assuming a finite number of loci

Recent progress in genotyping and doubled haploid (DH) techniques has created new opportunities for development of improved selection methods in numerous crops. Assuming a finite number of unlinked loci (ℓ) and a given total number (n) of individuals to be genotyped, we compared, by theory and simulations, three methods of marker-assisted selection (MAS) for gene stacking in DH lines derived from biparental crosses: (1) MAS for high values of the marker score (T, corresponding to the total number of target alleles) in the F₂ generation and subsequently among DH lines derived from the selected F₂ individual (Method 1), (2) MAS for augmented F₂ enrichment and subsequently for T among DH lines from the best carrier F₂ individual (Method 2), and (3) MAS for T among DH lines derived from the F₁ generation (Method 3). Our objectives were to (a) determine the optimum allocation of resources to the F₂ ( n₁^* \, n_{1}^{*} ) and DH generations (n - n₁^* ) (n - n_{1}^{*} ) for Methods 1 and 2 by simulations, (b) compare the efficiency of all three methods for gene stacking by simulations, and (c) develop theory to explain the general effect of selection on the segregation variance and interpret our simulation results. By theory, we proved that for smaller values of ℓ, the segregation variance of T among DH lines derived from F₂ individuals, selected for high values of T, can be much smaller than expected in the absence of selection. This explained our simulation results, showing that for Method 1, it is best to genotype more F₂ individuals than DH lines ($ n_{1}^{*} :n > 0.5 $ n_{1}^{*} :n > 0.5 ), whereas under Method 2, the optimal ratio n₁^* :n n_{1}^{*} :n was close to 0.5. However, for ratios deviating moderately from the optimum, the mean [`(X)] \overline{X} of T in the finally selected DH line ( T<sub>\textDH</sub><sup>*</sup> T_{\text{DH}}^{*} ) was hardly reduced. Method 3 had always the lowest mean [`(X)] \overline{X} of T_\textDH^* T_{\text{DH}}^{*} except for small numbers of loci (ℓ = 4) and is favorable only if a small number of loci are to be stacked in one genotype and/or saving one generation is of crucial importance in cultivar development. Method 2 is under most circumstances the superior method, because it generally showed the highest mean [`(X)] \overline{X} and lowest SD of T_\textDH^* T_{\text{DH}}^{*} for the finally selected DH.     

Influence of {\text{NH - }}{{\text{S}}^\gamma } bonding interactions on the structure and dynamics of metallothioneins

Mammalian metallothioneins ( \textM₇^\textIIMTs {\text{M}}_7^{\text{IIMTs}} ) show a clustered arrangement of the metal ions and a nonregular protein structure. The solution structures of Cd₃-thiolate cluster containing β-domain of mouse β-MT-1 and rat β-MT-2 show high structural similarities, but widely differing structure dynamics. Molecular dynamics simulations revealed a substantially increased number of \textNH - \textS^g {\text{NH - }}{{\text{S}}^\gamma } hydrogen bonds in β-MT-2, features likely responsible for the increased stability of the Cd₃-thiolate cluster and the enfolding protein domain. Alterations in the \textNH - \textS^g {\text{NH - }}{{\text{S}}^\gamma } hydrogen-bonding network may provide a rationale for the differences in dynamic properties encountered in the β-domains of MT-1, -2, and -3 isoforms, believed to be essential for their different biological function.     

A bias correction for estimates of effective population size based on linkage disequilibrium at unlinked gene loci*

Analysis of linkage disequilibrium (=mean squared correlation of allele frequencies at different gene loci) provides a means of estimating effective population size (N _e) from a single sample, but this method has seen much less use than the temporal method (which requires at least two samples). It is shown that for realistic numbers of loci and alleles, the linkage disequilibrium method can provide precision comparable to that of the temporal method. However, computer simulations show that estimates of N _e based on for unlinked, diallelic gene loci are sharply biased downwards ( in some cases) if sample size (S) is less than true N _e. The bias is shown to arise from inaccuracies in published formula for when S and/or N _e are small. Empirically derived modifications to for two mating systems (random mating and lifetime monogamy) effectively eliminate the bias (residual bias in % in most cases). The modified method also performs well in estimating N _e in non-ideal populations with skewed sex ratio or non-random variance in reproductive success. Recent population declines are not likely to seriously affect , but if N has recently increased from a bottleneck can be biased downwards for a few generations. These results should facilitate application of the disequilibrium method for estimating contemporary N _e in natural populations. However, a comprehensive assessment of performance of with highly polymorphic markers such as microsatellites is needed.The US Governmentȁ9s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Genetic effects on wood quality traits of plantation-grown white spruce (Picea glauca) and their relationships with growth

Clonal repeatabilities on individual tree (H_i² H_i^2 ) and clonal mean (H_{[`(C)]</sub> <sup>2</sup> H_{{\overline C }}^2 ) bases for growth (14-year height and volume), wood quality traits (latewood proportion, wood density, fiber length, and microfibril angle), and genotypic correlations among the traits were estimated, using 30 white spruce (Picea glauca [Moench] Voss) clones from six full-sib families (five per family). These families were selected from a clonally replicated test to represent different early growth categories: fast, moderate, and slow. Wood increment cores of the 30 clones were collected from two contrasting sites at age 19 years. For growth traits, in contrast to most wood quality traits, more genetic variation was accounted for by clone within family than by family within growth category. Both growth and wood quality traits appear to be under moderate genetic control, with [^(H)]<sub>i</sub><sup>2</sup> = 0.20 - 0.36 \widehat{H}_i^2 = 0.20 - 0.36 and [^(H)]<sub>[`(C)]} ² = 0.70 - 0.83 \widehat{H}_{{\overline C }}^2 = 0.70 - 0.83 . The only exception was microfibril angle ( [^(H)]_i² = 0.10  \textand  [^(H)]_[`(C)] ² = 0.34 \widehat{H}_i^2 = 0.10\;{\text{and}}\;\widehat{H}_{{\overline C }}^2 = 0.34 ). Generally, faster growth resulted in a significantly lower latewood proportion and lower overall wood density. Selection for faster growth does not appear to impact on either fiber length or microfibril angle. Among the wood quality traits, significant genotypic association was observed only between latewood proportion and wood density. Despite the generally negative association between growth and wood density among families, several fast-growing clones maintained above-average density. This implies that, by adopting multiclonal forestry, one can simultaneously improve growth and wood density.     

HNCA-TOCSY-CANH experiments with alternate <Superscript>13</Superscript>C-<Superscript>12</Superscript>C labeling: a set of 3D experiment with unique supra-sequential information for mainchain resonance assignment

Described here is a set of three-dimensional (3D) NMR experiments that rely on CACA-TOCSY magnetization transfer via the weak ³ \textJ_{\textCa\textCa} ^{ 3} {\text{J}}_{{{\text{C}}\alpha {\text{C}}\alpha }} coupling. These pulse sequences, which resemble recently described ¹³C detected CACA-TOCSY (Takeuchi et al. 2010) experiments, are recorded in ¹H₂O, and use ¹H excitation and detection. These experiments require alternate ¹³C-¹²C labeling together with perdeuteration, which allows utilizing the small ³ \textJ_{\textCa\textCa} ^{ 3} {\text{J}}_{{{\text{C}}\alpha {\text{C}}\alpha }} scalar coupling that is otherwise masked by the stronger ¹J_CC couplings in uniformly ¹³C labeled samples. These new experiments provide a unique assignment ladder-mark that yields bidirectional supra-sequential information and can readily straddle proline residues. Unlike the conventional HNCA experiment, which contains only sequential information to the ^{1 3} \textC^a ^{ 1 3} {\text{C}}^{\alpha } of the preceding residue, the 3D hnCA-TOCSY-caNH experiment can yield sequential correlations to alpha carbons in positions i−1, i + 1 and i−2. Furthermore, the 3D hNca-TOCSY-caNH and Hnca-TOCSY-caNH experiments, which share the same magnetization pathway but use a different chemical shift encoding, directly couple the ¹⁵N-¹H spin pair of residue i to adjacent amide protons and nitrogens at positions i−2, i−1, i + 1 and i + 2, respectively. These new experimental features make protein backbone assignments more robust by reducing the degeneracy problem associated with the conventional 3D NMR experiments.     

Transition from octahedral to tetrahedral geometry causes the activation or inhibition by Zn<Superscript>2+</Superscript> of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> phosphorylcholine phosphatase

Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine, which is produced by the action of hemolytic phospholipase C on phosphatidylcholine or sphyngomielin, to generate choline and inorganic phosphate. Among divalent cations, its activity is dependent on Mg²⁺ or Zn²⁺. Mg²⁺ produced identical activation at pH 5.0 and 7.4, but Zn²⁺ was an activator at pH 5.0 and became an inhibitor at pH 7.4. At this higher pH, very low concentrations of Zn²⁺ inhibited enzymatic activity even in the presence of saturating Mg²⁺ concentrations. Considering experimental and theoretical physicochemical calculations performed by different authors, we conclude that at pH 5.0, Mg²⁺ and Zn²⁺ are hexacoordinated in an octahedral arrangement in the PchP active site. At pH 7.4, Mg²⁺ conserves the octahedral coordination maintaining enzymatic activity. The inhibition produced by Zn²⁺ at 7.4 is interpreted as a change from octahedral to tetrahedral coordination geometry which is produced by hydrolysis of the [ \textZn ²⁺ \textL ₂ ^{- 1} \textL ₂⁰ ( \textH ₂ \textO ) ₂ ] \left[ {{\text{Zn}}^{ 2+ } {\text{L}}_{ 2}^{ - 1} {\text{L}}_{ 2}^{0} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{ 2} } \right] complex.     

Patterns of genetic parameters for height in field genetic tests of Picea abies and Pinus sylvestris in Sweden

We reviewed the genetic parameter estimates carried out from 1992 to 2006 for height increment in genetic tests of Norway spruce and Scots pine, to describe patterns of genetic variation, heritability, and genetic correlations. The material included seedling and clonal tests in Sweden, aged between 5 and 20 years. Multiple regression was used to explore relationships between parameter values and test environments. Results showed moderate narrow-sense heritabilities ([^(h)]² {\hat{h}^2} : mean =0.29 in Norway spruce; mean =0.23 in Scots pine) that decreased with test site latitude for both species. In Norway spruce, [^(h)]² {\hat{h}^2} increased with better growth and decreased with tree age, while for Scots pine, [^(h)]² {\hat{h}^2} increased with tree age and southward transfer. The additive genetic coefficient of variation (; mean 15%), in Norway spruce, decreased with growth as well as site latitude. in Scots pine (mean =8.5%) increased with southward transfer and more southerly test latitude. Additive and genotypic within-site genetic age-age correlations in Norway spruce were high, with mean r _A and r _G of 0.92 and 0.85, respectively. Corresponding across-sites estimates were on average lower. Genetic parameters were better expressed on favorable sites, at younger ages in Norway spruce and at older ages in Scots pine. The results imply that gain calculations should be based on different parameters in the two species. For maximizing genetic gain in the Swedish breeding program, testing times could be shorter for Norway spruce than for Scots pine. The investigation showed a large variation in parameter estimates from different field experiments, highlighting the importance of testing over multiple sites.     

Genetic structure of an insect-pollinated and bird-dispersed tropical tree in vegetation fragments and corridors: implications for conservation

In the vegetation corridors that connect small remnants of undisturbed primary forest in the Lavras landscape (Brazil), Protium spruceanum is a representative of a mass-flowering insect-pollinated and bird-dispersed tree. Allozyme variation was quantified from five forest remnants (N = 150) from secondary vegetation corridors linking them (N = 80) to generate information for genetic conservation. The species adhered to H-W equilibrium in all fragments in most of the loci. The results indicated high gene diversity in the fragments and corridors positively correlated with the plant density (r = 0.742, R ² = 0.551, d.f. = 4). We did not find evidence of inbreeding within fragments nor overall The genetic differentiation among remnants was low Evidence of recent bottlenecks by anthropogenic disturbance was detected in fragments (P < 0.05, Wilcoxon sign-rank test). The minimal viable population was estimated for conservation in situ, indicating fragments with possibilities of maintaining genetic equilibrium diversity in the short term (except F3) and in the long term (only F5). The ratios was also calculated to contribute to vegetation enrichment, area recovery or creation of new vegetation corridors. We found high levels of gene diversity in the vegetation corridors, genetic identity with the fragments and absence of inbreeding. Thus, our results suggest that landscape management strategies should therefore consider both the creation of new vegetation corridors and the protection of extant ones.     

The mechanism and kinetics of decomposition of 5-aminotetrazole

The pathway and ab initio direct kinetics of the decomposition 5-aminotetrazole (5-ATZ) to HN₃ and NH₂CN was investigated. Reactant, products and transition state were optimized with MP2 and B3LYP methods using 6–311G** and aug-cc-pVDZ basis sets. The intrinsic reaction coordinate curve of the reaction was calculated using the MP2 method with 6–311G** basis set. The energies were refined using CCSD(T)/6–311G**. Rate constants were evaluated by conventional transition-state theory (CVT) and canonical variational transition-state theory (TST), with tunneling effect over 300 to 2,500 K. The results indicated that the tunneling effect and the variational effect are small for the calculated rate constants. The fitted three-parameter expression calculated using the CVT and TST methods are and , respectively. Figure The mechanism of the decomposition process of 5-ATZ to HN₃ and NH₂CN     

Sampling bias in estimating Design II variance components with S1 families

Summary The use of several S₁ individuals to represent an S₀ individual permits the use of a Design II mating scheme for plants with only one pistillate flower per plant. Estimates of additive (V _A ) and dominance (V _D ) variance from this mating scheme will be biased upwards, when a small number (10) of individuals of each S₁ line are used. This bias can be computed, and the additive and dominance estimates can be corrected. Of particular interest is the observation that the additive genetic variance contributes to bias in estimates of V _D . When S₀ plants are non inbred and their selfedprogeny (S₁ lines) are used to represent them in developing families for use in the Design II, where m₁ is the number of individuals used to represent an S₁ line in developing half sib-families and m₂ is the number of individuals used to represent the S₁ line in making up full sib-families. For example, in a 3×3 Design II, with about 10 individuals used to represent each S₁ line in each cross, m₂ = 10 and m₁ = 30. When m₁ = m₂ = 1, and Joint contribution from Department of Agronomy, University of Nebraska 68583, and the S. S. Cameron Laboratory, Werribee, Victoria 3030, Australia. Published as paper No. 7395, Journal Series     

Understanding the effects of isolation on seed and pollen flow,spatial genetic structure and effective population size of the dioecious tropical tree species <Emphasis Type="Italic">Myracrodruon urundeuva</Emphasis>

This study examines the levels of gene flow, the distance and the patterns of pollen and seed dispersal, the intra-population spatial genetic structure (SGS) and the effective population size of a spatially isolated Myracrodruon urundeuva population using five microsatellite loci. The study was carried out in the Paulo de Faria Ecological Station, São Paulo State, Brazil and included the sampling and mapping of 467 adult-trees and 149 juveniles. Open-pollinated seeds (514) from 29 seed-trees were also sampled and genotyped. Significant SGS was detected in both adult (S _p  = 0.0269) and juveniles trees (S _p  = 0.0246), indicating short-distance seed dispersal. Using maternity analysis, all juveniles had the mother-tree assigned within the stand. A father-tree within the stand was also assigned for 97.3% of the juveniles and 98.4% of offspring. The average pollen dispersal distance measured in juveniles \( \left( {\hat{\delta } = 1 3 8\pm 1 6 9 {\text{ m}},{\text{ mean}} \pm {\text{SD}}} \right) \) and offspring \( \left( {\hat{\delta } = 2 5 2\pm 20 4 {\text{ m}}} \right) \) were higher than the average seed dispersal distance measured in juveniles \( \left( {\hat{\delta } = 1 2 4\pm 1 50{\text{ m}}} \right) \). About 70% of the pollen from juveniles and 51% from offspring traveled less than 200 m and, 72% of the seeds traveled less than 50 m. The effective population size of the studied sample indicates that the 467 adult-trees and 145 juveniles correspond respectively to 335 and 63 individuals that are neither inbred nor relatives. The results are discussed in relation to their impact on seed collection practices and genetic conservation.     

A standard quantitative method to measure acid tolerance of probiotic cells

The aim of this work was to develop a standard quantitative method to measure the acid tolerance of probiotic cells when exposed to a simulated gastric fluid. Three model strains of different cell concentrations were exposed to a standard simulated gastric fluid of fixed volume. The fluid pH ranged from pH 1.5 to 2.5. In general, the death kinetics followed an exponential trend. The overall death constant, k _d, for all strains was found to be in a power relationship with the pH value and the initial cell concentration, and it can be expressed as