Effects of biotic interactions on modeled species' distribution can be masked by environmental gradients

A fundamental goal of ecology is to understand the determinants of species' distributions (i.e., the set of locations where a species is present). Competition among species (i.e., interactions among species that harms each of the species involved) is common in nature and it would be tremendously useful to quantify its effects on species' distributions. An approach to studying the large‐scale effects of competition or other biotic interactions is to fit species' distributions models (SDMs) and assess the effect of competitors on the distribution and abundance of the species of interest. It is often difficult to validate the accuracy of this approach with available data. Here, we simulate virtual species that experience competition. In these simulated datasets, we can unambiguously identify the effects that competition has on a species' distribution. We then fit SDMs to the simulated datasets and test whether we can use the outputs of the SDMs to infer the true effect of competition in each simulated dataset. In our simulations, the abiotic environment influenced the effects of competition. Thus, our SDMs often inferred that the abiotic environment was a strong predictor of species abundance, even when the species' distribution was strongly affected by competition. The severity of this problem depended on whether the competitor excluded the focal species from highly suitable sites or marginally suitable sites. Our results highlight how correlations between biotic interactions and the abiotic environment make it difficult to infer the effects of competition using SDMs.     

三种兰科植物的保护遗传学研究初探

采用随机扩增多态 DNA(RAPD)分析研究了中国3种珍稀濒危兰科植物硬叶兜兰(Paphiopedilum micranthum Tang et Wang)、麻栗坡兜兰(P. malipoense S.C.Chen et Tsi)和独花兰(Changnienia amoena Chien)的遗传多样性与群体遗传结构.12个RAPD引物在2种兜兰中共扩增出131条带.对4个硬叶兜兰群体的检测表明其物种水平的多态条带百分率(PPB)为 71.6%,Nei 的基因多样度(h)为 0.217 1,Shannon多样性指数 (I) 为 0.330 1;4个群体的平均多样性水平为 PPB = 45.2%,h = 0.145 7,I = 0.220 4,低于远交兰花的平均水平.在总遗传变异中,群体间遗传变异占20.31%,略高于远交物种的平均水平.在物种水平上,麻栗坡兜兰的PPB为49.5%,h为0.117 4,I为0.176 4,均大大低于硬叶兜兰.对11个独花兰群体采用16个RAPD引物共扩增出119条带.物种水平PPB=76.5%,h=0.194 1,I=0.305 8;在群体水平上,上述3个指标的平均值则分别为37.2%、0.119 7和0.181 0,均低于远交兰花的平均水平.群体间的遗传变异占45.27%,遗传分化明显高于远交物种的平均水平.导致3个物种遗传多样性偏低而群体间遗传分化较高的主要原因在于人为的过度采挖和生境的片断化.研究结果为兰花保护策略和措施的制定提供了理论基础.     

Molecular model, calcium sensitivity, and disease specificity of a conformational thyroperoxidase B-cell epitope

While studying the humoral mechanisms involved in thyroid autoimmunity, we located a B-cell autoepitope in the extracellular C-terminal region of human thyroperoxidase. Structural modeling showed that this region encompasses both a Sushi-like and an epidermal growth factor-like domain, the flexible arrangement of which was putatively stabilized by calcium. The recombinant peptide was found to contain the previously identified conformational thyroperoxidase autoepitope. The occurrence of a calcium-induced conformational change was confirmed using a recombinant peptide monoclonal antibody, the decrease of which in binding to calcium-saturated thyroperoxidase was reversed by a chelating agent. The disease specificity of recombinant peptide, which was more frequently recognized by Hashimoto's than by Graves' patients, adds to its potential value as a diagnostic and preventive tool in the context of B-cell autoimmunity.     

Evaluation of dHPLC for CX26 mutation screening in patients from southern France with sensorineural deafness

The GJB2 gene (or CX26 for connexin 26) is one of the major genes causing nonsyndromic sensorineural hearing loss (NSSNHL). More than 50 sequence variations have been identified as polymorphisms or associated with autosomal or recessive forms of deafness. Though a major mutation, 35delG, is easily detectable by PCR digest; it is often present in the compound heterozygous state in our population in trans with recurrent, but less frequent, mutations. The CX26 gene is composed of a single coding exon that facilitates sequencing strategies. However, for mutation screening purposes, it is necessary to use high-throughput and cost-effective genotyping methods. Therefore, we have assessed denaturing high-performance liquid chromatography (dHPLC) in patients with known mutations in the CX26 gene. We conclude that dHPLC analysis is suitable for rapid and reliable scanning of the gene in deaf patients.     

Capillary gas chromatographic determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine

This article describes two methods for the determination of 1,4-butanediol and gamma-hydroxybutyrate in human plasma and urine using capillary gas chromatography. For 1,4-butanediol, plasma or urine samples (500 microl) were extracted by protein precipitation whereas for gamma-hydroxybutyrate, plasma or urine samples (500 microl) were extracted and derivatised with BF3-butanol. The compounds were separated on a Supelcowax-10 column and detection was achieved using a flame ionization detector. The methods are linear over the specific ranges investigated, accurate (with a percentage of the nominal concentration <109.8%) and showed intra-day and inter-day precision within the ranges of 5.0-12.0 and 7.0-10.1%, respectively. No interferences were observed in plasma and urine from hospitalized patients.     

Pitx3 is required for motor activity and for survival of a subset of midbrain dopaminergic neurons

Mesencephalic dopaminergic (MesDA) neurons play crucial roles in motor and behavioral processes; their loss in Parkinson's disease (PD) results in striatal dopamine (DA) deficiency and hypokinetic movement disorder. The Pitx3 homeobox gene is expressed in the MesDA system. We now show that only a subset of MesDA neurons express Pitx3 and that in Pitx3-deficient aphakia mice, this subset is progressively lost by apoptosis during fetal (substantia nigra, SN) and postnatal (ventral tegmental area) development, resulting in very low striatal DA and akinesia. Similar to human PD, dorsal SN neurons (which are Pitx3 negative) are spared in mutant mice. Thus, Pitx3 defines a pathway for survival of neurons that are implicated in PD and that are required for spontaneous locomotor activity.     

Effects of long-term fixation on histological quality of undecalcified murine bones embedded in methylmethacrylate

While long-term fixation and storage of specimens is common and useful for many research projects, it is particularly important for space flight investigations where samples may not be returned to Earth for several months (International Space Station) or years (manned mission to Mars). We examined two critical challenges of space flight experimentation: the effect of long-term fixation on the quality of mouse bone preservation and the preservation of antigens and enzymes for both histochemical and immunohistochemical analyses, and how the animal/sample processing affects the preservation. We show that long-term fixation minimally affects standard histological staining, but that enzyme histochemistry and immunolabeling are greatly compromised. Further, we demonstrate that whole animal preservation is not as suitable as whole leg or stripped leg preservation for long-term fixation and all histological analyses. Overall, we recommend whole leg processing for long-term storage of bone specimens in fixative prior to embedding in plastic for histological examination.     

Early life antibiotic-driven changes in microbiota enhance susceptibility to allergic asthma

Allergic asthma rates have increased steadily in developed countries, arguing for an environmental aetiology. To assess the influence of gut microbiota on experimental murine allergic asthma, we treated neonatal mice with clinical doses of two widely used antibiotics--streptomycin and vancomycin--and evaluated resulting shifts in resident flora and subsequent susceptibility to allergic asthma. Streptomycin treatment had little effect on the microbiota and on disease, whereas vancomycin reduced microbial diversity, shifted the composition of the bacterial population and enhanced disease severity. Neither antibiotic had a significant effect when administered to adult mice. Consistent with the 'hygiene hypothesis', our data support a neonatal, microbiota-driven, specific increase in susceptibility to experimental murine allergic asthma.     

Factors influencing in the response of <i>Schizolobium parahybum</i> (Vell) Blake to <i>Ceratocystis paradoxa</i> and <i>C. moniliformis</i>

In the Ecuadorian coast one of the most destructive diseases of the pachaco is vascular wilt or stem rot caused by Ceratocystis complex, so the aim of this study was to determine the factors that affect the efficiency of the reaction of bark pachaco to this disease. This research was conducted under laboratory conditions, using trees pachaco S38, S41, S98, AE-1, AE-2 and AE-3, and pathogenic species Ceratocystis paradoxa and C. moniliformis. The method utilized was tissue stem bark,with bark sections with 4.5 cm², and a suspension of 3x10⁴ units infection and remained in a humid chamber for 96 hours at 25 ± 5 °C. Were determined grades of resistance/ susceptibility using a scale from 0 to 4, depending on the amount of mycelia and peritecio in each plant sample. Three factors were used: four colonies obtained by several transfers from each fungal specie, four ages of colonies of each fungal specie and four volumes of inoculum applied (units of infection), using for each experiment separately Completely Randomized Design with 4 replications factorial arrangement. For comparison between treatment means was used Tukey test at 5% probability of error. For future trials using this technique, you could use 30-day colonies for C. paradoxa and 40 days for C. moniliformis, and an application volume of 100 μL/cm², it would improve the level of response for the formation of perithecium and mycelia in samples cortex.