关键词： anurans   Hyda versicolor   predator-induced plasticity   competitor-induced plasticity   ontogeny  

摘要： Studies of phenotypic plasticity typically focus on traits in single ontogenetic stages. However, plastic responses can be induced in multiple ontogenetic stages and traits induced early in ontogeny may have lasting effects. We examined how gray treefrog larvae altered their morphology in four different larval environments and whether different larval environments affected the survival, growth, development, and morphology of juvenile frogs at metamorphosis. We then reared these juveniles in terrestrial environments under high and low intraspecific competition to determine whether the initial differences in traits at metamorphosis affected subsequent survival and growth, whether the initial phenotypic differences converged over time, and whether competition in the terrestrial environment induced further phenotypic changes. Larval and juvenile environments both affected treefrog traits. Larval predators induced relatively deep tail fins and short bodies, but there was no impact on larval development. In contrast, larval competitors induced relatively short tails and long bodies, reduced larval growth, and slowed larval development. At metamorphosis, larval predators had no effect on juvenile growth or relative morphology while larval competitors produced juveniles that were smaller and possessed relatively shorter limbs and shorter bodies. After 1 month of terrestrial competition among the juvenile frogs, the initial differences in juvenile morphology did not converge. There were no differences in growth due to larval treatment but there were differences in survival. Individuals that experienced low competition as tadpoles experienced near perfect survival as juvenile frogs but individuals that experienced high competition as tadpoles suffered an 18% decrease in survival as juvenile frogs. There were also morphological responses to juvenile competition, but these changes appear to be due, at least in part, to allometric effects. Collectively, these results demonstrate

关键词： benthic macroinvertebrates   predictive models   genetic algorithm   decision trees   physical-chemical-, ecotoxicological-   structural variables  

摘要： Predicting freshwater organisms based on machine learning is becoming more and more reliable due to the availability of appropriate datasets, advanced modelling techniques and the continuously increasing capacity of computers. A database consisting of measurements collected at 360 sampling sites in non-navigable watercourses in Flanders was applied to predict the absence/presence of benthic macroinvertebrate taxa by means of decision trees. The measured variables were a combination of physical-chemical (temperature, pH, dissolved oxygen concentration, conductivity, total organic carbon, Kjeldahl nitrogen and total phosphorus), structural (granulometric analysis of the sediment, width, depth and flow velocity of the river) and two ecotoxicological variables. The predictive power of decision trees was assessed on the basis of the number of Correctly Classified Instances (CCI). A genetic algorithm was introduced to compare the predictive power of different sets of input variables for the decision trees. The number of input variables was reduced from 15 to 2-8 variables without affecting the predictive power of the decision trees significantly. Furthermore, reducing the number of input variables allowed to ease the identification of general data trends. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： toxicokinetics   bioavailability   benzo[a]pyrene   hexachlorobiphenyl   sediment  

摘要： This study investigated the effect of long-term sediment aging on the toxicokinetics of benzo[a]pyrene (BaP) and hexachlorobiphenyl (HCBP) using three freshwater benthic invertebrates. Hyalella azteca, Chironomus tentans, and Lumbriculus variegatus were exposed to BaP- and HCBP-spiked sediments that were aged for 7 d or 1.5 years. The toxicokinetics of the two compounds were determined for each test organism using a two-compartment model. The modeling of BaP was more complex because biotransformation was included within the model. The results of this study showed that the HCBP uptake clearance rates (k(s)) for each species were generally an order of magnitude greater than those determined for BaP and this difference was most likely due to preferential and rapid binding of BaP to sediment particles. Overall, the bioavailability of HCBP in spiked sediments tended to decrease with duration of aging, based on k(s) values and bioaccumulation factors (BAFs). However, the decreases in bioavailability appear to be species specific. Benzo[a]pyrene did not decline in bioavailability for the species tested because it may resist movement into the micropores of the sediment due to its large size. In addition to the bioassays, this article outlines a method for toxicokinetic modeling of biotransformed compounds and methods for statistical comparisons of kinetic parameters (i.e., k(s), k(d)...) and BAF values.

关键词： palaeolimnology   Holocene   subalpine lake   chironomids   vegetation history   catchment-lake interactions  

摘要： Early Holocene reforestation by stone pine (Pinus cembra) and tree birch (Betula pubescens) took place ca. 500 years after the end of the Younger Dryas at Hinterburgsee, a small subalpine lake in the northern Swiss Alps. During the next ca. 3000 years the local vegetation consisted of open woodlands with many pioneer dwarf shrubs and herbs. The expansion of silver fir (Abies alba) at ca. 7400 calibrated radiocarbon years before present (cal. BP) and Norway spruce (Picea abies) at ca. 6000 cal. BP in Hinterburgsee's catchment led to a closing of the local forests with a successive decrease in erosion and a distinct change in Hinterburgsee's sediment composition. First signs of probably human-induced openings of the catchment forest are apparent at ca. 2500 cal. 13P, but it is not until the past ca. 800 years that pollen analysis suggests strong local and regional anthropogenic activity. The strongest and most abrupt changes in the Holocene development of Hinterburgsee's chironomid fauna took place at ca. 11500 cal. BP and at ca. 10 000 cal. BP, when parts of the alpine taxa that were dominant during the Younger Dryas disappeared from the lake. The first change is most likely related to the increasing temperatures after the end of the Younger Dryas, the second possibly to decreasing lake depth and increasing summer insolation in the early Holocene that may have led to warmer bottom water temperatures in the lake. No clear relationship between the changes in catchment vegetation and the development of the chironomid fauna was found. Possibly the increase in sediment organic matter associated with the denser catchment forests was responsible for a succession in the chironomid stratigraphy between 7000 and 4500 cal. BP. However, due to the high sedimentation rates in Hinterburgsee this trend could also be a consequence of, or be promoted by, the sediment infilling of the lake basin. This conjecture is supported by the increasing importance of Tanytarsus lugens-type, a ch

关键词： mammalian phylogeny   Bayesian method   credibility value  

摘要： Murphy and colleagues reported that the mammalian phylogeny was resolved by Bayesian phylogenetics. However, the DNA sequences they used had many alignment gaps and undetermined nucleotide sites. We therefore reanalyzed their data by minimizing unshared nucleotide sites and retaining as many species as possible (13 species). In constructing phylogenetic trees, we used the Bayesian, maximum likelihood (ML), maximum parsimony (MP), and neighbor-joining (NJ) methods with different substitution models. These trees were constructed by using both protein and DNA sequences. The results showed that the posterior probabilities for Bayesian trees were generally much higher than the bootstrap values for ML, MP, and NJ trees. Two different Bayesian topologies for the same set of species were sometimes supported by high posterior probabilities, implying that two different topologies can be judged to be correct by Bayesian phylogenetics. This suggests that the posterior probability in Bayesian analysis can be excessively high as an indication of statistical confidence and therefore Murphy et al.'s tree, which largely depends on Bayesian posterior probability, may not be correct.

关键词： leaf volatile   constitutive compound   induced plant defence   psyllid   pear cultivar   alder   hawthorn   honeydew   systemic and local response   methyl salicylate   alpha-farnesene  

摘要： Qualitative and quantitative differences among pear cultivars were found in constitutive and Cacopsylla-induced volatiles, depending on experimental treatment of the trees (i.e., uninfested and partly or completely infested by psyllids). Blend differences were also found between pear cultivars and wild-type pear, alder and hawthorn-the latter trees are frequently present in pear orchard hedgerows. Interesting differences were found in the presence of methyl salicylate and (E,E)-alpha-farnesene, two compounds previously found to mediate attraction of predatory bugs towards psyllid-infested pear trees. Methyl salicylate is expressed constitutively and is induced systemically by infestation in the whole plant of all four cultivars. (E,E)-alpha-farnesene on the other hand showed also systemic induction in Bartlett, NY10355 and Beurre Hardy, but in partially infested Conference trees it was induced locally, only in herbivore-damaged leaves. No methyl salicylate or (E,E)-alpha-farnesene were identified in honeydew. In field collected headspace samples of alder leaves infested by aphids and leaf beetles we found methyl salicylate but no (E,E)-alpha-farnesene, whereas in uninfested hawthorn neither were identified. Insight in the variability of damage-related pear volatiles will have important implications for integrated pest management in the field.

关键词： CALIFORNIA vole   ROCK vole   YELLOW birch   MAMMALS   TREES  

摘要： We located the endangered rock vole, Microtus chrotorrhinus, at 3 of 59 sites in mixed mesophytic forests in the southern Appalachians. Rock voles were always found within mixed mesophytic habitats characterized by yellow birch, Betula alleghaniensis, rather than mixed mesophytic habitats dominated by other tree species. We compared the tree communities, microhabitat features, and small mammals found within three groups of habitats: sites where M. chrotorrhinus was found, yellow birch habitats where M. chrotorrhinus was not found, and other mixed mesophytic habitats where M. chrotorrhinus was not found. Sites occupied by M. chrotorrhinus had greater amounts of large, rocky substrate, greater incidence of moss, and a more northwest aspect than yellow birch and other mixed mesophytic sites without M. chrotorrhinus. Moreover, sites with rock voles had larger trees and were significantly older than sites without M. chrotorrhinus. Red-backed votes, Clethrionomys gapperi, are readily sampled by live-trap methods and were significantly more abundant at sites with M. chrotorrhinus, and may thus be a promising indicator species. Our results suggest that mixed mesophytic forests, especially older stands dominated by yellow birch and rocky substrate, should be managed with care to preserve M. chrotorrhinus habitat.

关键词： X线摄影术   CT   三维重建   气管   支气管   实验研究  

摘要： 前言 低剂量CT技术从出现至今有10余年的历史，已经在胸部体检方面展示了广阔的发展前景，在检出率及检测结节直径上均具有明显优势，对于早期和Ⅰ期可切除期肺癌检出能力显著提高，而其辐射剂量仅为传统螺旋CT的1／10～1／6。文献中关于降低辐射剂量的研究较多地集中于降低管电流mAs，而对于螺距、管电压等扫描条件改变降低剂量的研究相对较少。 胸部气道疾病气管支气管树重建同样适合低剂量CT扫描，但到目前为止尚未见关于应用多层螺旋CT气道重建低剂量扫描的文献报道。为扩大低剂量CT的应用范围，我们尝试通过改变影响CT剂量的扫描参数进行气管支气管树重建，探讨低剂量多层螺旋CT气道重建的可行性。 目的 探讨低剂量CT与常规剂量CT比较对气管重建有无影响，评价低剂量多层螺旋CT气管重建图像能否提供足够的诊断信息。 材料和方法 选用中国医科大学实验动物中心提供的健康成犬8只，体重范围：11-13Kg，麻醉后采用Philips Mx8000四层螺旋CT扫描，扫描时呼吸频率范围：18-24次／分。 根据CT剂量相关因素分组：毫安设置(150、100、50、20mAs)，层厚(6.5、3.2mm)，管球电压(90、120KVp)，螺距(1.25、1.75)，标准剂量组(3.2mm层厚、150mAs、120KVp、pitchl.25)，各组参照标准组仅改变层厚、毫安秒、管球电压或螺距一项参数，每只犬分 别进行7个序列的胸部扫描，各序列扫描时间范围：4．4－9．3秒。 将横断面源图像输人 sgio。工作站进行 MPR、SSD和 VB重建，标 准内插法重建，50％重叠间隔重建。 2名诊断医师在不预知扫描条件情况下盲法评价图像质量， 采用改良 Zethere评分法门：极差；2：差；3：一般；4：佳；5：极佳X 分另根据MPR、SSD和VB重建图像评价图像伪影、气管管壁光滑 度和气管软骨环显示情况进行质量评分，与标准剂量组进行比较。 记录各组0－4级支气管显示率，与标准剂量组比较。测量重建图 像四点气管隆突上Zcm、左主支气管、左上叶支气管及左上叶尖段 支气管管径，与相应解剖标本气管内径真实测值进行比较。 统计学分析采用SPSS10．0软件，图像质量评估采用配对秩和 检验，低剂量各组与标准剂量组间两组均数相差显著性采用配对t 检验，P＜o．05为差异显著性指标。 结 果 通过改变mAS、管球电压、层厚和螺距等因素均可以降低CT 辐射剂量，辐射剂量与d S线性相关。在一定范围内增加螺距或 层厚并不引起放射剂量的显著改变。 图像质量评价：标准剂量组气管重建图像3级段支气管显示 率为75％，图像质量评估5分78％／分22％，气管管壁光滑，气 管软骨环细节显示清晰，可以提供足够的诊断信息。 MPR重建评价图像伪影：***层厚组与标准组有显著差异 瞩＜0．001）；20mAS组与标准组有差异***＜P＜0．05八其余 10030mAS组、管电压90KVp和螺距1．75组各组与标准组无差 异汐叩．05人D＊B重建评价气管管壁光滑度、气管软骨环显 示情况：层厚***组与标准剂量组质量评分存在显著性差异瞩 ＜***；二皿3OInA组气管重建图像质量与标准组无差异（P＞ 0．05＊20ed8组与标准组有差异O＜0．05＊管电压 90KVp和螺 ·2· 距二．75组与标准组无差异瞩＞o．05人 支气管显示率刃级＊级各组无差异。2级叶支气管：*** 层厚组与标准组有显著差异K＜o．001人3级段支气管：*** 层厚组

关键词： SCIENTIFIC experimentation   BIOLOGY -- Study & teaching (Higher)   MOLLUSKS -- Population biology  

摘要： Presents a guide in the execution of a laboratory project which introduces several key concepts and skills for biology course at the university level. Procedure for measuring marine mollusk shells; Background reading required prior to measuring genetic drift; Instruction for implementing a case study on leaf variability for the construction of taxonomic keys.

关键词： Voles   Predators   Seedlings   Vegetation   Odors   Foraging   Meadows   Foxes  

摘要： Herbivores are thought to respond to the increased risk of attack by predators during foraging activities by concentrating feeding in safe habitats and by reducing feeding in the presence of predators. We tested these hypotheses by comparing tree seedling predation by meadow voles within large outdoor enclosures treated either with scent of large mammalian predators (red fox, bobcat. coyote) or a control scent (vinegar). In addition, we compared the distribution of votes in relation to naturally occurring variation in vegetation cover and the tendency of votes to attack tree seedlings planted in small patches with cover manipulation (intact. reduced or removed cover). Predator scent did not affect the rate or spatial distribution of tree seedling predation by voles, nor did it affect giving up densities (a surrogate of patch quitting harvest rate), survival rates, body size or habitat distribution of voles. In both predator scent and vinegar treatments voles preferred abundant vegetation providing good cover, which was also the site of almost all tree seedling predation. We Conclude that large mammalian predator scent does not influence the perception by voles of the general safety of habitat, which is more strongly affected by the presence of cover.