From regionally predictable to locally complex population structure in a freshwater top predator: river systems are not always the unit of connectivity in Northern Pike Esox lucius          下载免费PDF全文

Dorte Bekkevold  Lene Jacobsen  Jakob Hemmer‐Hansen  Søren Berg  Christian Skov 《Ecology of Freshwater Fish》2015,24(2):305-316

Contemporary genetic diversity is the product of both historical and contemporary forces, such as climatic and geological processes affecting range distribution and continuously moulded by evolutionary forces selection, gene flow and genetic drift. Predatory freshwater fishes, such as Northern Pike Esox lucius, commonly exhibit small population sizes, and several local populations are considered endangered. Pike inhabit diverse habitat types, including lakes, rivers and brackish marine waters, thus spanning from small isolated patches to large open marine systems. However, pike population structure from local to regional scales is relatively poorly described, in spite of its significance to developing conservation measures. We analysed microsatellite variation in a total of 1185 North European pike from 46 samples collected across both local and regional scales, as well as over time, to address two overarching questions: Is pike population structure associated with local and/or regional connectivity patterns, and which factors likely have the main influence on the contemporary distribution of genetic diversity? To answer this, we combined estimators of population diversity and structure to assess evidence of whether populations within (i) habitats, (ii) drainage systems and (iii) geographical regions are closer related than among these ranges, and whether patterns are temporally stable. Contrasting previous predictions that genetic drift obscures signals of postglacial colonisation history, we identified clear regional differences in population genetic signatures, suggesting a major effect of drainage divides on colonisation history and connectivity. However, several populations deviated from the general pattern, showing that local processes may be complex and need to be examined case‐by‐case.  相似文献   

Design of Automatic Quasi-synchronizing Device in Rural Small Hydropower Station     

LI Anxiang  ZHAO Yulin  LIU Jihong 《东北农业大学学报(英文版)》2011,18(4):60-64

Generator synchronization is an important and frequent operation in rural small hydropower station. In order to ensure that generator can be paralleled in the grid automatically, efficiently, and stably in the rural small hydropower station whose parallel in operation still needs to be accomplished manually. This paper described an automatic quasi-synchronizing device, based on 89C52 Single-chip Microcomputer （SCM）. Its hardware includes three modules and its software is structuralized. The device structure is simple, and its reliability is high and the maintenance is easy. Besides, convenient Human Machine Interface （HMI） makes the parameter setting simple and flexible  相似文献   

中密度纤维板的尺寸稳定性改良技术   总被引：1，自引：0，他引：1  

欧阳靓  曹金珍  朱愿 《林产工业》2013,40(4)

中密度纤维板(MDF)是目前家具、室内装修等最常用的木质复合材料之一,其尺寸稳定性直接影响到产品的使用性能、使用寿命以及产品应用领域的拓展和附加值的提高.笔者概述了中密度纤维板尺寸稳定性的影响因素以及中密度纤维板尺寸稳定性方面的相关研究进展,并在此基础上提出今后研究的方向.  相似文献   

Emerging issues in genomic selection     

Ignacy Misztal  Ignacio Aguilar  Daniela Lourenco  Li Ma  Juan Pedro Steibel  Miguel Toro 《Journal of animal science》2021,99(6)

Genomic selection (GS) is now practiced successfully across many species. However, many questions remain, such as long-term effects, estimations of genomic parameters, robustness of genome-wide association study (GWAS) with small and large datasets, and stability of genomic predictions. This study summarizes presentations from the authors at the 2020 American Society of Animal Science (ASAS) symposium. The focus of many studies until now is on linkage disequilibrium between two loci. Ignoring higher-level equilibrium may lead to phantom dominance and epistasis. The Bulmer effect leads to a reduction of the additive variance; however, the selection for increased recombination rate can release anew genetic variance. With genomic information, estimates of genetic parameters may be biased by genomic preselection, but costs of estimation can increase drastically due to the dense form of the genomic information. To make the computation of estimates feasible, genotypes could be retained only for the most important animals, and methods of estimation should use algorithms that can recognize dense blocks in sparse matrices. GWASs using small genomic datasets frequently find many marker-trait associations, whereas studies using much bigger datasets find only a few. Most of the current tools use very simple models for GWAS, possibly causing artifacts. These models are adequate for large datasets where pseudo-phenotypes such as deregressed proofs indirectly account for important effects for traits of interest. Artifacts arising in GWAS with small datasets can be minimized by using data from all animals (whether genotyped or not), realistic models, and methods that account for population structure. Recent developments permit the computation of P-values from genomic best linear unbiased prediction (GBLUP), where models can be arbitrarily complex but restricted to genotyped animals only, and single-step GBLUP that also uses phenotypes from ungenotyped animals. Stability was an important part of nongenomic evaluations, where genetic predictions were stable in the absence of new data even with low prediction accuracies. Unfortunately, genomic evaluations for such animals change because all animals with genotypes are connected. A top-ranked animal can easily drop in the next evaluation, causing a crisis of confidence in genomic evaluations. While correlations between consecutive genomic evaluations are high, outliers can have differences as high as 1 SD. A solution to fluctuating genomic evaluations is to base selection decisions on groups of animals. Although many issues in GS have been solved, many new issues that require additional research continue to surface.  相似文献   

通信设备运营和电力的维护     

王宇 《湖南农机》2015,(1):52-53

文章结合中国网通近两年来内部控制项目实施的实际情况和圆满通过外部审计师审计的经验,对目前通信网络设备维护工作中存在的问题和相应带来的风险进行剖析  相似文献   

水头可调薄壁堰式渠道流量智能测控系统优化试验研究     

甄晶博  吕宏兴  庞凯文  王露  王家琪 《节水灌溉》2015,(3):62-65

采用巴赞堰流公式计算流量的水头可调薄壁堰式渠道流量智能测控系统通过渠道流量量测与控制试验,验证了其精准的测流功能和智能控制技术的可行性。为进一步提高该测控系统运行的效率和稳定性,减少运行能耗,对矩形薄壁堰堰流公式进行水力试验研究,通过分析堰上水头和流量关系,拟合出矩形薄壁堰流量计算公式。通过向该拟合公式引入修正系数λ=0.848,将测控系统测得的堰上水头数据值代入该拟合公式求得的流量值与电磁流量计测得流量值的差值的平均值为-0.004L/s,标准差为0.119,线性相关系数R2=0.989 1。该拟合公式相对于巴赞堰流公式形式简单、参数较少、运算简便,同时也满足节水灌溉对精准测流的要求,更适用于水头可调薄壁堰式渠道流量智能测控系统,对于在灌区推广和使用该测控系统具有重要的意义。  相似文献   

电压空间矢量脉宽调制的简单算法     

袁帆 《湖南农机》2015,(4)

在电压空间矢量脉宽调制(SVPWM)控制技术原理的基础上,提出了一种简单快速算法,该算法只有普通的四则运算,计算变得非常简单,消除了常规的空间矢量控制算法中由于三角函数和无理数的近似计算而带来的计算误差及影响计算精度和速度的缺点,使结果更加准确。因而更适合应用于基于DSP 的数字化控制。理论分析和大量的MATLAB仿真结果表明,该算法具有谐波含量低、直流电压利用率高的优点。  相似文献   

一个水稻三倍体×二倍体杂交F2群体的微卫星杂合性丧失     

谢兆辉 《安徽农业科学》2007,35(11):3163-3164,3166

DB102为一田间发现的三倍体水稻,利用它做母本与二倍体水稻中作59杂交,得到一个早世代(F2)稳定群体,通过微卫星分析发现,该群体中有一些微卫星位点发生了杂合性丧失,且至少6条染色体上发生微卫星位点杂合性丧失(loss of heterzygoisity LOH)可能有DNA序列变化。而微卫星位点的杂合性丧失又可能与该杂交组合早世代稳定有关。  相似文献   

黑豆色素的研究进展     

李玉美 《安徽农学通报》2007,13(21):37-38

本文综述了近年来黑豆色素的研究进展.提出了综合开发利用的前景.  相似文献   

土质边坡稳定安全系数影响因素的     

邹沐  段亚辉 《中国农村水利水电》2006,(6):73-75

土质边坡稳定安全系数的计算值主要与采用的简化计算方法和土工参数有关。采用正交试验法计算分析了不同的计算方法、材料参数、水位及其相关荷载、地震作用等对边坡安全系数计算值的影响，进而对设计中的计算方法和材料参数提出了一些有益的建议，并提出了在工程运行管理中应尽量避免低水位或水位骤降情况的意见，为土石坝类工程的设计与运行管理提供了重要参考。  相似文献