Comparative mitochondrial genome analysis of Varunidae and its phylogenetic implications

Complete mitochondrial genomes(mitogenomes)can indicate phylogenetic relationships,as well as useful information for gene rearrangement mechanisms and molecular evolution.Currently,the phylogenetic location of the genus Varuna(Brachyura:Varunidae)has not been well resolved mainly because of limited representatives(only two extant species).Here,we determined a new mitogenome of this genus(Varuna litterata)and added the published mitogenomes to reconstruct the phylogeny of Varunidae.The 16368-bp mitogenome contains the entire set of 37 genes and a putative control region.The characteristics of this newly sequenced mitogenome were described and compared with the other 15 Varunidae mitogenomes.All 16 analyzed mitogenomes have identical gene order and similar molecular features.The sliding window and genetic distance analyses demonstrate highly variable nucleotide diversity,with comparatively low variability of COI and COII,and high variability of ND6.The nonsynonymous/synonymous substitution rates(dN/dS ratio)analysis shows that all 13 PCGs are under purifying selection and ATP8 gene evolves under the least selective pressure.Twelve tRNA genes,two rRNAs,one PCG,and the putative control region are found to be rearranged with respect to the pancrustacean ground pattern gene order.Tandem duplication/random loss model is adopted to explain the large-scale gene rearrangement events occurring in Varunidae mitogenomes.Phylogenetic analyses show that all Varunidae species are placed into one group,and form a sister clade with Macrophthalmidae.Nevertheless,the phylogenetic relationships within Varunidae are not completely consistent based on the two different datasets used in this study.These findings will contribute to a better understanding of gene rearrangement and molecular evolution in Varunidae mitogenomes,as well as provide insights into the phylogenetic studies of Brachyura.

长江口中华绒螯蟹与其它几种同科蟹的同工酶比较

对长江口中华绒螯蟹、天津厚蟹、无齿相手蟹、红螯相手蟹和字纹弓蟹等五种蟹的肌肉、肝进行了６种同工酶的聚丙烯酰胺凝胶电泳。结果表明，五种蟹的同工酶酶谱存在明显的物种特异性和组织特异性，种间同工酶差异与它们的分类地位一致。

白纹方蟹、字纹弓蟹与角眼沙蟹rDNA序列变异及结构分析

用特异性引物分别扩增、测得白纹方蟹、字纹弓蟹和角眼沙蟹18SrDNA序列片段长度为826bp、825bp和833bp；分析得出3种蟹18SrDNA序列的A＋T碱基百分含量基本相同，其平均含量为49．3％，略低于G＋C的百分含量（50．7%）；3条18SrDNA序列对位排列后共836位点，其中存在20个变异位点，包括插入／缺失位点13个，转换4个，颠换3个；并通过RNAstructure软件对变异较大的第601～836位点序列进行了二级结构预测。

蜑螺属Nerita几个混淆种的比较研究(腹足纲,珍珠蜑螺目,蜑螺科)

蜑螺科Neritidae蜑螺属Nerita的一些种类形态近似,形态鉴定上存在种类混淆、同物异名或错误鉴定等现象。作者在整理中国科学院南海海洋生物标本馆和中国科学院海洋生物标本馆历年来采集的蜑螺科标本时,对4种隶属于蜑螺属的易混淆种进行了比较研究。通过对标本的反复对比,分别找出了它们之间外部形态、地理分布以及生活习性方面的差异,澄清了混淆,确立了其分类地位:1)矮狮蜑螺Nerita chamaeleon Linnaeus,1758和圆蜑螺Nerita histrio Linnaeus,1758两者贝壳形态相近,在我国海区分布重叠,存在混淆以及错误鉴定的现象,根据螺旋部以及壳面雕刻可将它们区分开,即前者壳面螺肋光滑,后者螺肋粗糙,而前者螺旋部较后者高;2)锦蜑螺Nerita polita Linnaeus,1758和杂色蜑螺Nerita litterata Gmelin,1791两个种常被混淆在一起,都鉴定为锦蜑螺,前者在我国见于台湾、海南岛和西沙群岛,后者在我国见于台湾、福建、广东、广西和西沙群岛,其中杂色蜑螺此前在我国仅见于台湾,本文的报道进一步完善了该种的地理分布信息。