Large‐scale patterns of fish diversity and assemblage structure in the longest tropical river in Asia

Although the Mekong River is one of the world's 35 biodiversity hot spots, the large‐scale patterns of fish diversity and assemblage structure remain poorly addressed. This study aimed to investigate the fish distribution patterns in the Lower Mekong River (LMR) and to identify their environmental determinants. Daily fish catch data (i.e. from December 2000 to November 2001) at 38 sites distributed along the LMR were related to 15 physicochemical and 19 climatic variables. As a result, four different clusters were defined according to the similarity in assemblage composition and 80 indicator species were identified. While fish species richness was highest in the Mekong delta and lowest in the upper part of the LMR, the diversity index was highest in the middle part of the LMR and lowest in the delta. We found that fish assemblages changed along the environmental gradients and that the main drivers affecting the fish assemblage structure were the seasonal variation of temperature, precipitation, dissolved oxygen, pH and total phosphorus. Specifically, upstream assemblages were characterised by cyprinids and Pangasius catfish, well suited to low temperature, high dissolved oxygen and high pH. Fish assemblages in the delta were dominated by perch‐like fish and clupeids, more tolerant to high temperatures, and high levels of nutrients (nitrates and total phosphorus) and salinity. Overall, the patterns were consistent between seasons. Our study contributes to establishing the first holistic fish community study in the LMR.     

Optimization of carbon stock models to local conditions using farmers' soil tests: A case study with AMGv2 for a cereal plain in central France

Soil organic carbon (SOC) is associated with environmental benefits and crop productivity; therefore, monitoring of SOC stocks is important when assessing the sustainability of agricultural systems. This study applied a hybrid method and the results of on-farm soil tests to calibrate the AMGv2 model and adapt it to local conditions. The method was applied to soils in the Limagne plain (France), which shifted to cereal production since the 1960s. Based on analysing 988 soil test data, covering the period from 1954 to 2019, it was found that SOC stocks showed a significant decrease in the three main soil types of the study area. An optimization procedure estimated that the initial ratios of stable to total carbon fall in the ranges 0.42 and 0.46 for vertisols, 0.48 and 0.52 for calcisols, and 0.56 and 0.60 for fluvisols. Simulations using these values estimated that SOC stocks declined between 1960 and 2018 by between −31 and −17%, depending on soil type. The optimized model was used to forecast the evolution of SOC stocks up to 2050. These simulations showed a further decline in SOC stocks with continuation of current practices, even assuming a 15% increase in crop yields. They indicated that stopping straw exports would stabilize stocks, while a systematic introduction of cover crops would increase stocks about 3.8% over the period considered. It is concluded that this hybrid procedure can improve the adaptation of predictive models to local conditions.     

A novel epidemiological model to better understand and predict the observed seasonal spread of Pestivirus in Pyrenean chamois populations

Seasonal variations in individual contacts give rise to a complex interplay between host demography and pathogen transmission. This is particularly true for wild populations, which highly depend on their natural habitat. These seasonal cycles induce variations in pathogen transmission. The seasonality of these biological processes should therefore be considered to better represent and predict pathogen spread. In this study, we sought to better understand how the seasonality of both the demography and social contacts of a mountain ungulate population impacts the spread of a pestivirus within, and the dynamics of, this population. We propose a mathematical model to represent this complex biological system. The pestivirus can be transmitted both horizontally through direct contact and vertically in utero. Vertical transmission leads to abortion or to the birth of persistently infected animals with a short life expectancy. Horizontal transmission involves a complex dynamics because of seasonal variations in contact among sexes and age classes. We performed a sensitivity analysis that identified transmission rates and disease-related mortality as key parameters. We then used data from a long-term demographic and epidemiological survey of the studied population to estimate these mostly unknown epidemiological parameters. Our model adequately represents the system dynamics, observations and model predictions showing similar seasonal patterns. We show that the virus has a significant impact on population dynamics, and that persistently infected animals play a major role in the epidemic dynamics. Modeling the seasonal dynamics allowed us to obtain realistic prediction and to identify key parameters of transmission.

Electronic supplementary material

The online version of this article (doi:10.1186/s13567-015-0218-8) contains supplementary material, which is available to authorized users.     

基于EST-SSR和SNP标记的大麦麦芽纯度检测

大麦麦芽作为啤酒酿造的主要原料之一,其纯度决定了麦芽原料的均一性,进而影响加工工艺和啤酒品质。为高效准确地鉴定麦芽纯度,在啤酒企业进行麦芽原料采购和质量监测时提供参考依据。本研究分别利用EST-SSR和SNP标记定性检测了按比例预混的麦芽样品纯度,并利用SNP标记定量检测了4份送检的麦芽盲样纯度。结果表明,EST-SSR标记能定性检测混杂度高于10%的麦芽样品,而SNP标记能够有效鉴定混杂度低至5%的麦芽样品。SNP标记对纯度定量检测的单次抽样的测定值与真实值之间的误差在3%以内。比较发现,本研究所用的两类分子标记均可用于麦芽样品的纯度检测,但基于KASP技术的SNP标记可以满足麦芽纯度的快速定量检测需要。     

Environmental correlates of body size distribution in Cyprinidae (Actinopterygians) depend on phylogenetic scale

The pattern of increasing species body size with increasing latitude has been noticed in different groups of animals. Here, we used seven key environmental factors and independent contrasts to assess body size latitudinal clines in Cyprinidae at two phylogenetic levels (inter‐ and intragenera), which were defined using a genus‐level supertree. Model selection procedures revealed that environmental factors shaping body size variation in Cyprinidae differed according to the phylogenetic scale considered. At the higher phylogenetic level, we found that both temperature (negative effect) and habitat availability (positive effect of drainage basin surface area) constituted mechanistic explanations of large‐scale body size distribution. No temperature‐related body size cline was observed at the intragenus level. Instead, competitive interaction (negative effect of species richness), habitat availability (positive effect of drainage basin surface area), migration ability and available energy (positive effects of glacial coverage and actual evapotranspiration) constitute alternative explanations at this lower phylogenetic scale. We conclude that (i) at the intergenus level, cyprinids do show a tendency to be smaller at high temperatures and larger at low temperatures, (ii) this tendency no longer exists at the intragenus level, (iii) latitude per se is a weak predictor of body size clines whatever the taxonomic level analysed, (iv) generalising geographical body size patterns may be rendered difficult by the superimposition of a series of mechanisms across different taxonomic scales, and (v) habitat size, here acting positively at both taxonomic scales, may play a major role in shaping riverine species body size clines.     

A variance-covariance structure to take into account repeated measurements and heteroscedasticity in growth modeling

This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover, compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates are valid when the number of observations is large.     

针叶树苗圃病害调查与主要病害发生规律研究

本文调查了针叶树苗期病害的种类和苗期病害的发生规律，结果表明针叶树苗期病害有8种，其中侵染性病害有6种，生理性病害有2种。猝倒病是针叶树苗期主要的病害，表现为3种症状类型。日灼型猝倒是气象性病害的主要形式，由丝核菌Rhizoctonia和镰刀菌Fusarium引起的生物猝倒型和立枯型病害是针叶树育苗的主要病害，其发生与育苗地所处的环境、营养土基质有关,同时提出了对针叶树苗期病害防治的对策。     

Stand biometry and leaf area distribution in an old olive grove at Andria, southern Italy

The objectives of this paper were (1) to provide general biometry data for an 80-year-old olive (Olea europea L., cv. Coratina) grove in Andria, southern Italy, and (2) to compare different methods for estimating leaf area distributions. Stand biometry was represented by a stocking density of 132 trees ha^?1, mean spacing of 8.7 m and mean social area (proportional to spacing and tree size) of about 76 m² per tree. Trunk total circumference averaged 110 cm and after subtraction of missing or dead parts of stems averaged 81 cm, projected area of crowns averaged 17.7 m² and the mean tree height was 4.9 m. Leaf distribution was evaluated using calibrated ground-based side photographs through image analysis and through using a simple canopy-layer model (considering hollow volume within tree crowns) and double-Gaussian curves. The mean leaf size was about 5 cm² (distributed in a log-normal manner over the range of 2 to 12 cm²). Considering whole tree crowns, the mean leaf density was about 2.6 m²m^?3; the maximum leaf area occurred in canopy layers between 1.5 to 3 m, tailing with a steeper slope to the crown base and a less steep slope to the tree-top. The foliated volume of olive crowns (mean 33.2 m³) contained on average 145 thousand leaves of the total area of 72.6 m². The corresponding leaf area index on the stand level (LAI _grove = 0.96), was rather low due to low stocking density. However when taking into account only the projected crown areas (and avoiding free space between trees), the mean LAI reached about 3.5 (range from 1–7). The radial pattern of leaf distribution derived from image analysis indicated peak LAI _rad values at a distance from the stem of about 60 to 70% of crown radius in trees of different size. The applicability of different approaches to the estimation of the necessary allometric parameters is discussed.     

Thigmomorphogenesis versus light in biomechanical growth strategies of saplings of two tropical rain forest tree species

? In the dense tropical rainforest understorey, saplings exhibit different growth strategies aiming at reaching light levels better fitting their ecology. Investing mainly in height growth, at the expense of their width, a lot are close to mechanical instability. Tachigali melinonii, a long living heliophilic tree species, is frequently observed to be extremely slender and supported by neighbours. Such observations suggest an active growth control through the perception of mechanical environment.

? Mechanical environment or light availability, which one is the most influent on growth and slenderness (H/D)? To test this question, we recorded growth of control and staked saplings of two species with contrasting habits and ecology: T. melinonii, and Dicorynia guianensis, along a natural light gradient.

? Dicorynia, the more stable, responded more clearly to the staking treatment, showing slenderness increase when light is available, whereas for Tachigali, only light availability governed growth.

? For Tachigali, growth allocation is mainly governed by light availability and ontogeny, whereas Dicorynia is probably similar to the average tree strategy, using the thigmomorphogenetic physiological process to control its stability.

     

Degradation pathway of dicyclanil in water in the presence of titanium dioxide. Comparison with photolysis

The solar photolytic behavior of the pesticide 4,6-diamino-2-cyclopropyl-pyrimidine-5-carbonitrile, currently known as dicyclanil, has been mimicked in a photoreactor operating with an artificial light flux. The rate and pathway of degradation were performed. An additional study, using TiO(2) photocatalysis, has been achieved in order to determine the efficiency of photocatalysis to degrade the molecule. The catalyst was titania Degussa P-25. The aim of this article was the identification of the intermediate products formed during the irradiation, to establish the degradation pathway of dicyclanil. The kinetics of the reactions were followed by liquid chromatography with a diode array detector (LC-DAD). Most of the organic compounds occurring during the photodegradation have been identified by means of liquid chromatography and mass spectrometry coupled techniques (HPLC-MS). Additional analyses were carried out to evaluate the mineralization rates into nitrate and ammonium ions.