Distinguishing range expansions from previously undocumented populations using background data from museum records

Aim Knowledge of the distribution of a species is fundamental to understanding the species’ biology, and changes in known distribution may reflect response to environmental change. However, in many cases, purported range expansions are not adequately justified and extra‐limital records may simply reflect previously undocumented populations. Thus, it is critical to distinguish between these hypotheses. This study aimed to provide a simple, conceptual framework for evaluating these hypotheses that depends on the use of museum background data to assess the adequacy of historical sampling. Location American Southwest and worldwide. Methods Background data are records of species other than the taxon of interest that are likely to be documented using the same sampling methods. If evaluation of the background group determines that the taxon of interest would have been documented if present, then the extra‐limital record can be considered a range expansion. Conversely, if evaluation of the background group indicates that historical sampling was inadequate to have documented the taxon of interest, then the most parsimonious explanation for the extra‐limital record is an undocumented population, which should be presented as a range extension. As an example, I applied the methods to a purported range expansion of the yellow‐nosed cotton rat (Sigmodon ochrognathus) in the Rincon Mountains in south‐eastern Arizona. Results Evaluation of the background group revealed that sampling was inadequate to have documented S. ochrognathus in the Rincon Mountains if present. Thus, the record of S. ochrognathus in the Rincon Mountains was interpreted as a previously undocumented population rather than a range expansion. Main conclusion Range expansions can reflect factors that are of important conservation concern, such as climate change or habitat modification. Thus, it is essential that the cause of extra‐limital records be accurately interpreted. The method provides a simple means for testing between hypotheses of range extension and range expansion.     

Conflicting selection on diaspore traits limits the evolutionary potential of seed dispersal by ants

Conflicts of selection on diaspore traits throughout the dispersal cycle can limit the evolutionary consequences of seed dispersal. However, these conflicts have never been investigated in directed dispersal systems. We explored conflicts of selection through life stages of dispersal in the myrmecochorous herb Helleborus foetidus. Seeds are subject to two contrasting partial selective scenarios. Undispersed seeds are subject to positive directional selection on seed size characters, whereas seeds dispersed are subject to stabilizing selection for size. In both scenarios, seedling establishment determined the magnitude and direction of selection. This does not reflect ant preferences for seed size. However, total selection still depends largely on ant activity, as ants control the relative importance of each selective scenario. We advocate the use of analytical approaches combining multiplicative fitness and microenvironment‐specific selection to more realistically estimate the realized selection on traits functional during several life stages. This approach may be extended to any organism dispersing offspring to different environments.     

矮牵牛组织培养及变异苗的RAPD分析

探索了矮牵牛组织培养的配方,对组培过程中产生的表型变异植株进行了DNA水平的分析。并对矮牵牛叶片组织培养及产生变异的影响因素等进行探讨。     

盐胁迫对黄瓜幼苗根系脯氨酸和多胺代谢的影响

以2个黄瓜品种‘长春密刺’(抗盐性较强)和‘津春2号’(抗盐性较弱)为材料,采用营养液栽培,研究了盐胁迫对幼苗根系脯氨酸(Pro)和多胺(PAs)代谢的影响。结果表明,盐胁迫能提高黄瓜幼苗根系吡咯啉-5-羧酸合成酶(P5CS)活性,抑制脯氨酸脱氢酶(ProDH)活性,从而显著增加Pro含量,且‘长春密刺’变化幅度显著大于‘津春2号’;盐胁迫下,‘长春密刺’根系精氨酸脱羧酶(ADC)、鸟氨酸脱羧酶(ODC)和S-腺苷蛋氨酸脱羧酶(SAMDC)活性升高幅度显著大于‘津春2号’,而多胺氧化酶(PAO)活性升高幅度显著低于‘津春2号’,引起其根系内亚精胺(Spd)和精胺(Spm)含量显著增加;盐胁迫下,2品种根系腐胺(Put)含量呈先上升后下降的变化趋势,随着Put积累降低,Pro含量显著增加。可见,盐胁迫诱导根系较高的Pro、Spd和Spm积累有利于提高黄瓜幼苗对盐胁迫逆境的适应能力,盐胁迫下PAs代谢和Pro代谢密切相关,Put的积累一定程度上促进了Pro含量的增加。     

苔藓植物对植物天然更新的影响

种子是天然更新的基础,幼苗和幼树的生长是天然更新过程中最敏感的阶段。苔藓植物作为许多生态系统的主要地被物,在维管植物天然更新过程中发挥着不容忽视的作用。在许多植被类型中,都有发育良好的苔藓群落,大量的研究证明它们的存在影响到维管植物的萌发、建成和生长,并且可能进一步影响到物种的共生,有一些种类甚至可能指示树种的更新。本文就苔藓植物对物种更新早期阶段的作用和影响进行了综述。包括苔藓植物的生理特性造成的微气候变化;苔藓群落对种子传播、萌发及幼苗建成的影响。并讨论了苔藓植物与更新物种的种间关系及其对幼苗生长的化感作用。     

棉花两品种耐盐性与抗氧化能力的相关性

对‘新陆早17’和‘中棉49’两个棉花（Gossypium hirsutumL.）品种在氧化剂甲基紫精（MV）和NaCl胁迫下的生理应答进行了研究,以期阐明棉花抗氧化能力与耐盐性的关系。研究结果表明,在40μmol·L-1MV胁迫3d,‘新陆早17’的丙二醛（MDA）和活性氧含量比‘中棉49’低,而抗坏血酸（AsA）、超氧化物岐化酶（SOD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）活性则高于‘中棉49’,表明‘新陆早17’抗氧化能力更强。在200mmol·L-1NaCl胁迫25d,‘新陆早17’的株高和叶绿素降低量、根部Na＋含量、相对电导率都低于‘中棉49’,说明‘新陆早17’耐盐更强。盐胁迫下‘新陆早17’的抗氧化酶活性上升而‘中棉49’却降低,表明‘新陆早17’通过上调SOD、CAT和APX活性来提高其耐盐性。结合棉花两品种的抗氧化和耐盐性差异,说明棉花抗氧化能力的高低能够影响品种的耐盐性。     

Classification of Rotylenchulus reniformis Numbers in Cotton Using Remotely Sensed Hyperspectral Data on Self-Organizing Maps

Rotylenchulus reniformis is one of the major nematode pests capable of reducing cotton yields by more than 60%, causing estimated losses that may exceed millions of dollars U.S. Therefore, early detection of nematode numbers is necessary to reduce these losses. This study investigates the feasibility of using remotely sensed hyperspectral data (reflectances) of cotton plants affected with different nematode population numbers with self-organizing maps (SOM) in correlating and classifying nematode population numbers extant in a plant's rhizosphere. The hyperspectral reflectances were classified into three classes based on R. renifomis population numbers present in plant's rhizosphere. Hyperspectral data (350-2500 nm) were also sub-divided into Visible, Red Edge + Near Infrared (NIR) and Mid-IR region to determine the sub-region most effective in spectrally classifying the nematode population numbers. Various combinations of different feature extraction and dimensionality reduction methods were applied in different regions to extract reduced sets of features. These features were then classified using a supervised-SOM classification method. Our results suggest that the overall classification accuracies, in general, for most methods in most regions (except visible region) varied from 60% to 80%, thereby, indicating a positive correlation between the nematode numbers present in plant's rhizosphere and the corresponding plant's hyperspectral signatures. Results showed that classification accuracies in the Mid-IR region were comparable to the accuracies obtained in other sub-regions. Finally, based on our findings, the use of remotely-sensed hyperspectral data with SOM could prove to be extremely time efficient in detecting nematode numbers present in the soil.     

新疆南疆不同连作年限棉田土壤微生物群落结构的变化

通过传统培养和PCR-DGGE技术,分析了新疆南疆不同连作年限的棉田土壤微生物的变化情况,结果表明:随着连作年限的增加,土壤中细菌、真菌的数量、比例、多样性指数的变化表现为先增加后下降,至连作15年时达到较低值,之后随着连作年限的继续增加又表现为回升的趋势。细菌的种类数、优势种在不同连作年限的样品中的变化不明显,多样性指数变化幅度较小,群落结构变化不大;真菌的种类数、优势种在不同连作年限的土样中的变化较大,群落结构变化较大,随着连作时间的增加,优势种的种类趋于单一化,真菌的群落结构受到连作年限的影响更明显。     

夏块菌与青刚栎形成外生菌根形态变化的研究

夏块菌（Tuber aestivum）是一种具有较高经济价值的菌根食用菌。对夏块菌与青刚栎（Cycloba-lanopsis glauca）在形成菌根过程中不同阶段的菌根形态变化进行了研究,结果显示：用夏块菌孢子液接种青刚栎苗后,第14天起开始形成淡乳色的外生菌根,外延菌丝刚毛状;第一至第二个月可形成黄褐色、褐色外生菌根,外延菌丝刚毛或羊毛状。外生菌根为单根,长1～4mm,直径150～250μm。菌套厚12～20μm,平坦或自菌根延伸出刚毛状菌丝,外延菌丝束黄绿色;哈替氏网菌丝直径1～1.5μm。菌根老化后变暗褐或萎缩。外延菌丝束呈黄绿色是夏块菌菌根区别于其它块菌菌根最重要的形态特征。