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A. J. Cannone 《African Zoology》2013,48(2):179-190
The freshwater snails belonging to the genus Melanoides Olivier, 1804 are widespread across tropical regions of the world and endemic species have evolved in the African Lakes Malawi, Mweru and Tanganyika. The endemic Melanoides species of Lake Malawi have been investigated several times during the last century, due to their large conchological variation, but no unambiguous answer regarding the number of species has been given. The phylogenetic relationship between morphs or genetic clones of Melanoides in Lake Malawi was inferred by phylogenetic analyses of DNA sequence data from the mitochondrial genes 16S and COI. Additional sequences from GenBank were included to investigate the relationship to other morphs from different parts of the world. For the first time, a putative secondary structure was developed for a partial region of 16S in this genus to identify the variability of the secondary structure in stems and loops. The molecular analyses indicated that several genetic clones exist in Lake Malawi and that M. tuberculata is a paraphyletic taxon. It is not clear from the results whether invasions or dispersals account for the complex situation in Lake Malawi. The basal position of M. admirabilis, endemic to Lake Tanganyika, in the inferred phylogeny indicates that Africa might be the origin of the genus. The results further indicate that three major clades of Melanoides, consisting of several genetic clones, are present in Lake Malawi; one clade consisting of invasive M. tuberculata, another of native M. tuberculata and a third consisting of the M. polymorpha- complex. It appears as if the unique development of morphs within the Melanoides genus in Lake Malawi has evolved primarily by divergence of genetic clones instead of species differentiation. 相似文献
84.
W-OH新材料特性及在青海湖周边地区沙化地植生固沙中的应用 总被引:1,自引:0,他引:1
郭凯先 《中国农村水利水电》2012,(4):30-32,37
W-OH是一种新型的化学植生固沙材料,通过室内试验及青海湖周边地区的不同处理方式植生固沙试验表明,3%~5%浓度的W-OH材料在抗冻、抗压、抗拉、抗紫外线等性能均能达到青海湖周边地区植生固沙的要求,在处理方式喷涂W-OH+沟处理试验中取得了良好的植被恢复和治沙效果,适合在青海湖周边地区类似条件的地区进行推广应用。 相似文献
85.
对于具有耦合关系的流域复杂系统,从演化过程、驱动机制和政策效应等方面分析生态-农业耦合效应,是实现流域生态文明的方法论。论文采用系统耦合测度模型,对洱海流域系统耦合度及动态耦合过程进行分析,揭示流域生态文明下洱海流域生态农业政策的效应。结果表明:①生态农业措施对洱海流域生态-农业系统协调耦合产生积极作用。②1994-2015年,洱海流域生态-农业系统耦合度由0.48提升到0.75,接近0.8的协调耦合阈值,表明生态-农业系统由磨合阶段进入高水平耦合阶段。③耦合态势可分为磨合消耗、快速消耗、快速协调与磨合协调四个阶段,既揭示了初期生态农业政策的短期效益,又预示出中远期流域农业面源污染治理的困境。 相似文献
86.
试论结合场地特征的杭州湖滨和北山路景区规划设计 总被引:2,自引:0,他引:2
探讨了风景园林师如何正确理解场地特征,在保留场地原有景观典型性的基础上,营造出最适宜这片土地的地域性景观。杭州是一个历史悠久的山水风景城市,西湖风景区既有得天独厚的自然景观,又有大量的历史人文景观及传统街区。杭州西湖风景区中的湖滨景区和北山路景区是探索场地特征营造的典型案例。 相似文献
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88.
环太湖地区休闲农业旅游的发展探析 总被引:2,自引:0,他引:2
综述了环太湖地区丰富的农村人文资源,探讨了其开发经营休闲农业的优劣势,并提出了建议对策。 相似文献
89.
为了防止南湖水质进一步恶化,改善与提高南湖水环境质量,针对南湖水环境污染现状,提出了集中治理,分散治理及综合治理3种方案,并对这些方案进行了优化分析。 相似文献
90.
O. Seehausen 《Ecology of Freshwater Fish》1996,5(4):195-202
Geographical, macro- and microhabitat distribution of and mate recognition among color morphs of a complex of Lake Victoria cichlids was studied. The distribution of most morphs was mutually exclusive but two morphs overlapped extensively and differed only in microhabitat requirements. Coloration differences between them were inherited, and wild fishes were homozygous in this respect. Positive morph assortative female mate choice was demonstrated. Over the largest part of their common geographical range intermediate phenotypes are absent and the two morphs are to be considered two biological species. However, in populations at one end of the range intermediate phenotypes with continuously varying male coloration make up the majority of the individuals. It is suggested that the status of color morphs as phenotypes of one species or as separate biological species is a function of environmental conditions that vary considerably between the localities. The data support the hypothesis that polymorphisms can be a step preceding speciation in cichlid fish. 相似文献