Relationship between measures of balance and strength in middle-aged adults

The purpose of this study was to investigate the relationship between variables of static and dynamic postural control as well as between isometric and dynamic muscle strength. A single-group design was used. Thirty-two middle-aged healthy adults (mean age: 56 ± 4 years) performed measurements of static (unperturbed)/dynamic (perturbed) balance and of isometric (i.e., maximal isometric torque [MIT]; rate of torque development [RTD] of the plantar flexor)/dynamic (i.e., countermovement jump [CMJ] height and power) lower extremity muscle strength. No significant associations were observed between variables of static and dynamic postural control (r = +0.128-0.341, p > 0.05) and between measures of balance and strength (r = -0.189 to +0.316, p > 0.05). Significant positive correlations were detected between variables of isometric and dynamic strength ranging from r = +0.361 to +0.501 (p < 0.05). Further, simple regression analyses revealed that a 10% increase in the mean CMJ height (3.1 cm) was associated with 44.4 N·m and 118.4 N·m·s better MIT and RTD, respectively. The nonsignificant correlations between static and dynamic balance measures and between balance and strength variables imply that static and dynamic postural control and balance and strength are independent of each other and may have to be tested and trained complementarily.     

Plant dispersal, neighbourhood size and isolation by distance

A theoretical relationship between isolation by distance or spatial genetic structure (SGS) and seed and pollen dispersal is tested using extensive spatial-temporal simulations. Although for animals Wright's neighbourhood size N(e) = 4pisigma(2)(t) has been ascertained also, where sigma(2)(t) is the axial variance of distances between parents and offspring, and it was recently confirmed that N(e) = 4pi(sigma(2)(f) + sigma(2)(m))/2 when dispersal of females and males differ, the situation for plants had not been established. This article shows that for a very wide range of conditions, neighbourhood size defined by Crawford's formula N(e) = 4pi(sigma(2)(s) + sigma(2)(p)/2) fully determines SGS, even when dispersal variances of seed (sigma(2)(s)) and pollen sigma(2)(p)) differ strongly. Further, self-fertilization with rate s acts as zero-distance pollen dispersal, and N(e) = 4pi[sigma(2)(s) + sigma(2)(p)(1 - s)/2] fully determines SGS, for most cases where there are both likely parameter values and substantial SGS. Moreover, for most cases, there is a loglinear relationship, I(1) = 0.587 - 0.117 ln(N(e)), between SGS, as measured by I(1), Moran's coefficient for adjacent individuals, and N(e). However, there are several biologically significant exceptions, namely for very low or large N(e), SGS exceeds the loglinear values. There are also important exceptions to Crawford's formula. First, plants with low seed dispersal, high outcross pollen dispersal and high selfing rate show larger SGS than predicted. Second, in plants with very low (near zero) seed dispersal, selfing decreases SGS, opposite expectations. Finally, in some cases seed dispersal is more critical than pollen dispersal, in a manner inconsistent with Crawford's formula.     

Linkage and the Limits to Natural Selection

The probability of fixation of a favorable mutation is reduced if selection at other loci causes inherited variation in fitness. A general method for calculating the fixation probability of an allele that can find itself in a variety of genetic backgrounds is applied to find the effect of substitutions, fluctuating polymorphisms, and deleterious mutations in a large population. With loose linkage, r, the effects depend on the additive genetic variance in relative fitness, var (W), and act by reducing effective population size by (N/N(e)) = 1 + var (W)/2r(2). However, tightly linked loci can have a substantial effect not predictable from N(e). Linked deleterious mutations reduce the fixation probability of weakly favored alleles by exp(-2U/R), where U is the total mutation rate and R is the map length in Morgans. Substitutions can cause a greater reduction: an allele with advantage s < s(crit) = (π(2)/6) log(e) (S/s)[var(W)/R] is very unlikely to be fixed. (S is the advantage of the substitution impeding fixation.) Fluctuating polymorphisms at many (n) linked loci can also have a substantial effect, reducing fixation probability by exp [ &2Kn var(W)/R] [K = -1/E((u - u)(2)/uv) depending on the frequencies (u,v) at the selected polymorphisms]. Hitchhiking due to all three kinds of selection may substantially impede adaptation that depends on weakly favored alleles.     

Comparative quantitative structure toxicity relationships for flavonoids evaluated in isolated rat hepatocytes and HeLa tumor cells

Quantitative structure activity relationship (QSAR) equations were obtained to describe the cytotoxicity of 22 polyphenols using toxicity (logLD50) representing the concentration for 50% cell survival in 2 h for isolated rat hepatocytes, log P representing octanol/water partitioning, and/or E(p/2) representing redox potential. One- and two-parameter equations were derived for the quantitative structure toxicity relationships (QSTR) for polyphenol induced hepatocyte cytotoxicity: e.g. log C(hepatocyte) (microM)=-0.65(-0.08)log P+4.12(-0.15) (n=19, r(2)=0.80, s=0.33, P<1 x 10(-6)). One- and two-parameter QSAR equations were also derived to describe the inhibitory effects of 13 polyphenols on tumor cell growth when incubated with HeLa cells for 3 days: e.g. log C(tumor) (microM)=-0.34(+/-0.04)log P+2.40(+/-0.07) (n=11, r(2)=0.90, s=0.13, P<1 x 10(-5)). These findings point to lipophilicity as a major characteristic determining polyphenol cytotoxicity. The E(p/2) also played a significant role in polyphenol cytotoxicity towards both cell types: e.g. log C(hepatocyte) (microM)=-0.60(+/-0.06)log P+2.01(+/-0.43)E(p/2) (V)+3.86(+/-0.12) (n=9, r(2)=0.96, s=0.15, P<0.005). The involvement of log P and E(p/2) could be explained if polyphenol cytotoxicity involved the formation of radicals, which interacted with the mitochondrial inner membrane resulting in a disruption of the membrane potential.     

On the persistence and pervasiveness of a new mutation

It has frequently been assumed that the persistence of a deleterious mutation (the average number of generations before its loss) and its pervasiveness (the average number of individuals carrying the gene before its loss) are equal. This is true for a particular simple, widely used infinite model, but this agreement is not general. If hs > 1/(4N(e)), where hs is the selective disadvantage of mutant heterozygotes and N(e) is the effective population number, the contribution of homozygous mutants can be neglected and the simple approximate formula 1/hs gives the mean pervasiveness. But the expected persistence is usually much smaller, 2(log(e)(1/2hs) + 1 - gamma) where gamma = 0.5772. For neutral mutations, the total number of heterozygotes until fixation or loss is often the quantity of interest, and its expected value is 2N(e), with remarkable generality for various population structures. In contrast, the number of generations until fixation or loss, 2(N(e)/N)(1 + log(e)2N), is much smaller than the total number of heterozygotes. In general the number of generations is less than the number of individuals.     

Quantitative structure toxicity relationships for phenols in isolated rat hepatocytes

Quantitative structure toxicity relationship (QSTR) equations were obtained to predict and describe the cytotoxicity of 31 phenols using logLD(50) as a concentration to induce 50% cytotoxicity of isolated rat hepatocytes in 2 h and logP as octanol/water partitioning: logLD(50) (microM)=-0.588(+/-0.059)logP+4.652(+/-0.153) (n=27, r(2)=0.801, s=0.261, P<1 x 10(-9)). Hydroquinone, catechol, 4-nitrophenol, and 2,4-dinitrophenol were outliers for this equation. When the ionization constant pK(a) was considered as a contributing factor a two-parameter QSTR equation was derived: logLD(50) (microM)=-0.595(+/-0.051)logP+0.197(+/-0.029)pK(a)+2.665(+/-0.281) (n=28, r(2)=0.859, s=0.218, P<1 x 10(-6)). Using sigma+, the Brown variation of the Hammet electronic constant, as a contributing parameter, the cytotoxicity of phenols towards hepatocytes were defined by logLD(50) (microM)=-0.594(+/-0.052)logP-0.552(+/-0.085)sigma+ +4.540(+/-0.132) (n=28, r(2)=0.853, s=0.223, P<1 x 10(-6)). Replacing sigma+ with the homolytic bond dissociation energy (BDE) for (X-PhOH+PhO.-->X-PhO.+PhOH) led to logLD(50) (microM)=-0.601(+/-0.066)logP-0.040(+/-0.018)BDE+4.611(+/-0.166) (n=23, r(2)=0.827, s=0.223, P<0.05). Hydroquinone, catechol and 2-nitrophenol were outliers for the above equations. Using redox potential and logP led to a new correlation: logLD(50) (microM)=-0.529(+/-0.135)logP+2.077(+/-0.892)E(p/2)+2.806(+/-0.592) (n=15, r(2)=0.561, s=0.383, P<0.05) with 4-nitrophenol as an outlier. Our findings indicate that phenols with higher lipophilicity, BDE, or sigma+ values or with lower pK(a) and redox potential were more toxic towards hepatocytes. We also showed that a collapse of hepatocyte mitochondrial membrane potential preceded the cytotoxicity of most phenols. Our study indicates that one or a combination of mechanisms; i.e. mitochondrial uncoupling, phenoxy radicals, or phenol metabolism to quinone methides and quinones, contribute to phenol cytotoxicity towards hepatocytes depending on the phenol chemical structure.     

"Anti-platelet antibodies" in HIV infected haemophiliacs.

We have studied anti platelet antibodies and circulating immunocomplexes in 16 haemophiliacs with mild thrombocytopenia eight of which were infected by human immunodeficiency virus (HIV). No difference in platelet count was observed between HIV+ (143 +/- 31 x 10(9)/l) and HIV- patients (148 +/- 30 x 10(9)/l). On the contrary, HIV+ haemophiliacs had serum platelet bindable IgG (SPBIgG), normal platelet associated IgG (PAIgG), high serum IgG and circulating immunocomplexes (CIC). Considering all 16 patients serum IgG correlated with CIC (r = 0.7 p less than 0.01) and SPBIgG (r = 0.6 p less than 0.01) respectively. We obtained also a positive correlation between serum CIC and SPBIgG (r = 0.51 p less than 0.05). Immunoblotting of patients' sera showed no specific binding to target platelet antigens. In conclusion there is no evidence of HIV related immune thrombocytopenia in our haemophiliacs but the study confirms the appearance of immunocomplexes in the HIV+ subjects.     

A quantitative framework for the design of acellular hemoglobins as blood substitutes: implications of dynamic flow conditions

The delivery of oxygen to tissue by cell-free carriers eliminates intraluminal barriers associated with red blood cells. This is important in arterioles, since arteriolar tone controls capillary perfusion. We describe a mathematical model for O(2) transport by hemoglobin solutions and red blood cells flowing through arteriolar-sized tubes to optimize values of p50, Hill number, hemoglobin molecular diffusivity and concentration. Oxygen release is evaluated by including an extra-luminal resistance term to reflect tissue oxygen consumption. For low consumption (i.e., high resistance to O(2) release) a hemoglobin solution with p50=15 mmHg, n=1, D(HBO2)=3 x 10(-7) cm(2)/s delivers O(2) at a rate similar to that of red blood cells. For high consumption, the p50 must be decreased to 5 mmHg. The model predicts that regardless of size, hemoglobin solutions with higher p50 will present excess O(2) to arteriolar walls. Oversupply of O(2) to arteriolar walls may cause constriction and paradoxically reduced capillary perfusion.     

The numbers of Sertoli cells in mature Holstein bulls and their relationship to quantitative aspects of spermatogenesis

Testes from 37 Holstein bulls, 38-99 mo of age, were used to investigate the relationship of Sertoli cell number, Sertoli cell-germ cell ratios and other related factors to daily sperm production (DSP). DSP was assessed by enumeration of spermatids in testicular homogenates, whereas Sertoli cell and germ cell ratios were based on direct counts in 20 round Stage VIII seminiferous tubular cross sections per bull. Numbers of Sertoli cells were calculated as (total homogenization resistant spermatids:spermatid:Sertoli cell ratio)/0.394; the factor of 0.394 adjusted for the presence of homogenization resistant spermatids during only 39.4% of the spermatogenic cycle. Data were subjected to simple linear and second-order regression analyses. Positive linear relationships were observed between DSP and testicular parenchymal weight (p less than 0.005, R = +0.71), DSP per gram (p less than 0.005, R = +0.79), total Sertoli cells (p less than 0.005, R = +0.83), Sertoli cells per gram (p less than 0.01, R = +0.47) and the yield of Step 8 spermatids per Type A spermatogonium (p less than 0.05, R = +0.34). DSP was not related (p greater than 0.10) to the number of germ cells supported per Sertoli cell. Testicular parenchymal weight and DSP per gram were unrelated to each other (p greater than 0.10), but both were related (p less than 0.005) to the total Sertoli cell number (R = +0.61 and +0.62, respectively). Total number of Sertoli cells accounted for more of the variation in DSP between bulls (R2 = 68.2%) than did any other factor examined. It was suggested that total Sertoli cell number may be an important determinant of a bull's spermatogenic potential.     

Probability of fixation under weak selection: a branching process unifying approach

We link two-allele population models by Haldane and Fisher with Kimura's diffusion approximations of the Wright-Fisher model, by considering continuous-state branching (CB) processes which are either independent (model I) or conditioned to have constant sum (model II). Recent works by the author allow us to further include logistic density-dependence (model III), which is ubiquitous in ecology. In all models, each allele (mutant or resident) is then characterized by a triple demographic trait: intrinsic growth rate r, reproduction variance sigma and competition sensitivity c. Generally, the fixation probability u of the mutant depends on its initial proportion p, the total initial population size z, and the six demographic traits. Under weak selection, we can linearize u in all models thanks to the same master formula u = p + p(1 - p)[g(r)s(r) + g(sigma)s(sigma) + g(c)s(c)] + o(s(r),s(sigma),s(c), where s(r) = r' - r, s(sigma) = sigma-sigma' and s(c) = c - c' are selection coefficients, and g(r), g(sigma), g(c) are invasibility coefficients (' refers to the mutant traits), which are positive and do not depend on p. In particular, increased reproduction variance is always deleterious. We prove that in all three models g(sigma) = 1/sigma and g(r) = z/sigma for small initial population sizes z. In model II, g(r) = z/sigma for all z, and we display invasion isoclines of the 'mean vs variance' type. A slight departure from the isocline is shown to be more beneficial to alleles with low sigma than with high r. In model III, g(c) increases with z like ln(z)/c, and g(r)(z) converges to a finite limit L > K/sigma, where K = r/c is the carrying capacity. For r > 0 the growth invasibility is above z/sigma when z < K, and below z/sigma when z > K, showing that classical models I and II underestimate the fixation probabilities in growing populations, and overestimate them in declining populations.     

安徽沿江圩丘农区夏收作物田杂草群落分布规律的研究

作者创用了七级目测调查取样,进行数量分析的方法,对夏收作物田杂草群落进行分类研究,揭示了安徽沿江圩丘农区夏收作物田杂草群落的分布规律主要受土壤类型和轮作制度制约。看麦娘杂草群落分布于水稻土田,猪殃殃,野燕麦杂草群落分布于丘岗区旱地,卷耳、婆婆纳杂草群落分布于灰潮土旱地。首次提出综合草害指数,用以评定杂草群落类型中每种杂草的危害性,从而,提出了不同土壤类型和轮作制度的田块中恶性杂草的定量化指标与防除策略。     

Effective Size of Populations under Selection

Equations to approximate the effective size (N(e)) of populations under continued selection are obtained that include the possibility of partial full-sib mating and other systems such as assortative mating. The general equation for the case of equal number of sexes and constant number of breeding individuals (N) is N(e) = 4N/[2(1 - α(I)) + (S(k)(2) + 4Q(2)C(2)) (1 + α(I) + 2α(O))], where S(k)(2) is the variance of family size due to sampling without selection, C(2) is the variance of selective advantages among families (the squared coefficient of variation of the expected number of offspring per family), α(I) is the deviation from Hardy-Weinberg proportions, α(O) is the correlation between genes of male and female parents, and Q(2) is the term accounting for the cumulative effect of selection on an inherited trait. This is obtained as Q = 2/[2 - G(1 + r)], where G is the remaining proportion of genetic variance in selected individuals and r is the correlation of the expected selective values of male and female parents. The method is also extended to the general case of different numbers of male and female parents. The predictive value of the formulae is tested under a model of truncation selection with the infinitesimal model of gene effects, where C(2) and G are a function of the selection intensity, the heritability and the intraclass correlation of sibs. Under random mating r = α(I) = -1/(N - 1) and α(O) = 0. Under partial full-sib mating with an average proportion β of full-sib matings per generation, r & β and α(O) & α(I) & β/ (4 - 3β). The prediction equation is compared to other approximations based on the long-term contributions of ancestors to descendants. Finally, based on the approach followed, a system of mating (compensatory mating) is proposed to reduce rates of inbreeding without loss of response in selection programs in which selected individuals from the largest families are mated to those from the smallest families.     

Forecasting seasonal population growth of Aphis glycines (Hemiptera: Aphididae) in soybean in Illinois

From 2001 to 2004, 252 fifty-plant samples were collected from commercial soybean, Glycine max L., fields in three townships (93-km2 area) in Illinois. Townships were sampled every 3 wk from late June or early July when aphids (Aphis glycines Matsumura) first invaded the townships to early August. We used linear regression of 18 mean township field densities to calibrate several simple models to predict the change in aphid population density in a township from one sampling date to the next. The best exponential model for the complete data set has an r2 = 0.54, Y2 = Ylexp (0.09659 x DAY), where Y1 and Y2 are the first and second samples of aphids separated by a 3-wk period (the number of days, DAY). Our intrinsic rate of increase for the population is much lower than rates calculated in other studies. The best single-variable linear model has an r2 = 0.88, Y2 = Y1 + 0.1084 x Y1 x DAY. The latter model indicates the value of including monitoring data in the prediction. The best two-variable model has an R2 = 0.98, Y2 = Y1 + 0.08136 x Y1 x DAY + 0.000080 x N1(2) x DAY, where N1(2) x DAY is the interaction term for initial, squared, sample density of the season multiplied by the number of days between samples. The latter two models indicate that the change in the population density is greater for more dense populations. Degree-days were generally inferior to days as the time component in the simple models.     

Reduced selective constraint in endosymbionts: elevation in radical amino acid replacements occurs genome-wide

As predicted by the nearly neutral model of evolution, numerous studies have shown that reduced N(e) accelerates the accumulation of slightly deleterious changes under genetic drift. While such studies have mostly focused on eukaryotes, bacteria also offer excellent models to explore the effects of N(e). Most notably, the genomes of host-dependent bacteria with small N(e) show signatures of genetic drift, including elevated K(a)/K(s). Here, I explore the utility of an alternative measure of selective constraint: the per-site rate of radical and conservative amino acid substitutions (D(r)/D(c)). I test the hypothesis that purifying selection against radical amino acid changes is less effective in two insect endosymbiont groups (Blochmannia of ants and Buchnera of aphids), compared to related gamma-Proteobacteria. Genome comparisons demonstrate a significant elevation in D(r)/D(c) in endosymbionts that affects the majority (66-79%) of shared orthologs examined. The elevation of D(r)/D(c) in endosymbionts affects all functional categories examined. Simulations indicate that D(r)/D(c) estimates are sensitive to codon frequencies and mutational parameters; however, estimation biases occur in the opposite direction as the patterns observed in genome comparisons, thereby making the inference of elevated D(r)/D(c) more conservative. Increased D(r)/D(c) and other signatures of genome degradation in endosymbionts are consistent with strong effects of genetic drift in their small populations, as well as linkage to selected sites in these asexual bacteria. While relaxed selection against radical substitutions may contribute, genome-wide processes such as genetic drift and linkage best explain the pervasive elevation in D(r)/D(c) across diverse functional categories that include basic cellular processes. Although the current study focuses on a few bacterial lineages, it suggests D(r)/D(c) is a useful gauge of selective constraint and may provide a valuable alternative to K(a)/K(s) when high sequence divergences preclude estimates of K(s). Broader application of D(r)/D(c) will benefit from approaches less prone to estimation biases.     

武汉东湖星形柄裸藻种群与宿主的关系以及生态因子对它的影响

星形柄裸藻与附生宿主之间的相互作用为:它是偏利者,而对宿主无很大影响;当其在宿主体表大量附着时,才对宿主有偏害作用。它的种群密度(N,个/L)与宿主密度(Na,个/L)有密切的正相关关系:N=0.0858e0.0528Na(r=0921,pT,天)对星形柄裸藻的平均附着量(m,个/每个甲壳动物)和附着量(B,个/L)的影响是:在一定的蜕皮间隔时间范围内呈正相关性:m=aebT和B=aebT(a和b为方程常数,下同);超过这个范围呈负相关性:m=aT-b和B=aT-b。而宿主蜕皮间隔时间(T,天)对星形柄裸藻附着率(R,%)的影响则仅为正相关性:R=a+blnT。星形柄裸藻对宿主的附生有一定的选择性。水温(t,℃)与星形柄裸藻种群密度(N,个/L)的关系为:在5-12℃时呈正相关性,N=0.309e0.624t(r=0.914,pN=0.0000617e190.2/t(r=0.941,pR,%)的影响则仅呈负相关关系:R=bln(30-t)-a。水的透明度(d,cm)与星形柄裸藻种群密度(N,个/L)的相关方程为:N=0.020e0.037d(r=0.838,pS,mg/L)与种群密度(N,个/L)有一定的正相关性:N=0.00254e0.178S(r=0.816,pN,个/L)与4个主要因子:宿主密度(N,个/L),透明度(d,cm),水温(t,℃),含钙量(S,mg/L)的多元回归方程为:N=1.208Na+0.698d+5.584t+2.942S-357.957(R=0.853,df=11,k=4,p<0.01)。       

Characterization of the partially reduced cyanide-inhibited derivative of cytochrome c oxidase by optical, electron-paramagnetic-resonance and magnetic-circular-dichroism spectroscopy.

Optical. e.p.r. and near-infrared low-temperature m.c.d. (magnetic-circular-dichroism) spectroscopy were used to characterize the partially reduced cyanide-inhibited derivative of cytochrome c oxidase produced by anaerobic reductive titration with dithionite. The reductions of cytochrome a3+ and Cu2+a were followed by observation of the e.p.r. signals at g = 3.03, 2.21 and 1.5 and at g = 2.18, 2.03 and 1.99. As reduction proceeds new e.p.r. signals (g = 3.58 and 1.56) appear that quantify to give one haem per enzyme unit when a small excess of dithionite has been titrated in. The e.p.r. signal of the Cu2+a titrates in parallel with the disappearance of the band and 820nm in the optical absorption spectrum. The near-infrared m.c.d. spectrum shows the presence of the low-spin ferric haem, a3+, in the oxidized state of the enzyme, as a well-resolved positive peak at 1650nm. As reduction proceeds this band is replaced by one at 1550nm due to haem a3+(3)--CN in the partially reduced state. Hence as haem a3+(3)--CN becomes e.p.r.-detectable it also shows a near-infrared m.c.d. spectrum characteristic of a low-spin ferric haem. It is concluded that the partially reduced state of cyanide-inhibited cytochrome c oxidase contains a2+ . Cu+a . a3+(3)--CN . Cu+a3.     

T-cell receptor excision circles (TREC) in SHIV 89.6p and SIVmac251 models of HIV-1 infection

T-cell receptor excision circles (TREC) may be a useful surrogate marker in HIV-1 infection for evaluating the likelihood of continued clinical stability and/or the response to therapeutics, including vaccines. Analysis of TREC in SHIV and SIV models of HIV-1 infection may provide additional information concerning the utility of TREC as a marker. We measured TREC in peripheral blood mononuclear cells (PBMC) from rhesus macaques in SHIV89.6p (n = 20) and SIVmac251 (n = 11) models of HIV-1 infection. TREC were also evaluated in tissues in the SIVmac251 model at end-point. In the SHIV89.6p model, TREC in PBMC were significantly lower at 12 weeks postinfection compared to preinfection levels. The decrease in TREC correlated with the decline in CD4+ T cells (r(s) = 0.496; P = 0.026), which in turn correlated inversely with serum viral loads at end-point (r(s) = -0.517; P = 0.019). Macaques that controlled SHIV89.6p infection to some degree (n = 6) had higher TREC at study end-point (P = 0.017). In the SIVmac251 model, TREC in PBMC were significantly reduced after 17 months of infection (P = 0.012) despite receiving highly active antiretroviral therapy (HAART) consisting of didanosine (ddI) and (R)-9-(2-phosphonylmethoxypropyl)-adenine (PMPA) when not cycling off therapy during scheduled treatment interruptions (STI). However, macaques that received continuous hydroxyurea (HU) in addition to the HAART regimen had higher end-point TREC compared to the non-HU group (P = 0.041), and the reduction in TREC observed at end-point within the HU group was not significant. In the SIVmac251 model, TREC correlated with the percentage of CD4+ T cells (r(s) = 0.426; P = 0.048) and CD4+CD28+ T cells (r(s) = 0.624; P = 0.002), and inversely with CD8+ T cells (r(s) = -0.622; P = 0.002), CD8+CD28- T cells (r(s) = -0.516; P = 0.014), and serum viral loads (r(s) = -0.627; P = 0.039). High levels of TREC were observed in the thymus, levels comparable to PBMC were seen in the lymph node, and low but detectable levels of TREC were present in bone marrow. The use of correlates of TREC as covariates in ANCOVA revealed that the decline in TREC in the SHIV 89.6p model reflected the decline in the percentage of CD4+ T-cells due to viral cytopathogenicity. In the SIVmac251 model, the decline in TREC was related to increased immune activation and proliferation due to viral replication, as reflected by decreases in percentages of CD4+CD28+ T cells and increases in CD8+ and CD8+CD28- T cells.     

Determinants of effective population size for loci with different modes of inheritance

Here we report an assessment of the determinants of effective population size (N(e)) in species with overlapping generations. Specifically, we used a stochastic demographic model to investigate the influence of different life-history variables on N(e)/N (where N = population census number) and the influence of sex differences in life-history variables on N(e) for loci with different modes of inheritance. We applied an individual-based modeling approach to two datasets: one from a natural population of savannah baboons (Papio cynocephalus) in the Amboseli basin of southern Kenya and one from a human tribal population (the Gainj of Papua New Guinea). Simulation-based estimates of N(e)/N averaged 0.329 for the Amboseli baboon population (SD = 0.116, 95% CI = 0.172 - 0.537) and 0.786 for the Gainj (SD = 0.184, 95% CI = 0.498 - 1.115). Although variance in male fitness had a substantial impact on N(e)/N in each of the two primate populations, ratios of N(e) values for autosomal and sex-linked loci exhibited no significant departures from Poisson-expected values. In each case, similarities in sex-specific N(e) values were attributable to the unexpectedly high variance in female fitness. Variance in male fitness resulted primarily from age-dependent variance in reproductive success, whereas variance in female fitness resulted primarily from stochastic variance in survival during the reproductive phase.     

Local increases in intracellular calcium elicit local filopodial responses in Helisoma neuronal growth cones.

Highly localized changes in intracellular Ca2+ concentration ([Ca2+]i) can be evoked in neuronal growth cones; these are followed by local changes in filopodia. Focally applied electric fields evoked spatially restricted, high magnitude increases in growth cone [Ca2+]i. The earliest and greatest increases were localized to small regions within a growth cone. Such fields also produced characteristic changes in the disposition of filopodia: both filopodial length and number were significantly increased on the cathode side of growth cones. The requirement for extracellular Ca2+ and the strong correlation between the evoked rise in [Ca2+]i and the changes in filopodia (r = 0.98) indicate that cathode stimulation results in local Ca2+ influx, leading to locally increased [Ca2+]i and local changes in filopodial behavior.