蜂猴线粒体细胞色素b基因变异特点及系统发育分析

测定了蜂猴属（Nycticebus)1个蜂猴（N.coucang)和2个矮蜂猴（N,pygmaseus)个体的线粒体细胞色素b(cyt-b)基因全序列，比较现有的司猴科其他种序列，分析了核苷酸序列差异和碱基替换特点，以指猴为外群重建了系统发育树，结果表明，在所研究的个体中，2个蜂猴物种碱基组成具有哺乳动物的共同特点，它们之间转换比（特别是密码子第3位）是颠换比的6倍多，大于其他种间比较；低的Ka/Ks值（＜0．1），说明懒猴科cyt-b基因的异义突位点受到强的选择压力作用。由cyt-b基因构建的系统发育树符合懒猴科化石记录和形态学分类观点，根据化石记录和与分化时间有一定线性关系的第3位颠换和同义突变速率，估算蜂猴与倭蜂猴种间，蜂猴与蜂属间可能的分化时间分别为300和600万年。

Divergence and Phylogeny of Mitochondrial Cytochrome b Gene from Species in Nycticebus

Mitochondrial cytochrome b (cyt b) genes were sequenced from one individual of N.coucang and two individuals of N.pygmaeus . By comparing with the cyt b sequences of three species in Lorisidae,the divergence and base substitution among these sequences were analyzed. The phylogenetic tree,in agreement with the fossil and morphologic data,was reconstructed with Daubentonia madagascariensis as the outgroup. The base composition of N.coucang and N.pygmaeus showed the same character as that of other mammals. The Tv/Ts ratio between the two Nycticebus species was as 6 times as other pairwise comparisons. The low values (<0 1) of Ka/Ks ratio implied a strong selective constraint against the nonsynonymous sites of the cyt b genes from the species in Lorisidae. Based on the fossil data,the transitions and synonymous mutations at the third codon position that have shown a linear relation with time,the estimations of 3 Myr (million years) and 6 Myr were the divergent time between N.coucang and N.pygmaeus ,and between Lorisines and Galagines groups,respectively.