基于两个核基因序列研究龟鳖类的系统进化特征

摘要

R35 intron segment sequences of 2 turtles and RAG2 gene segment sequences of 6 turtles were obtained by using PCR amplification and sequencing in order to evaluate the evolutionary character and phylogenetic relationships of turtles from the point of nuclear gene sequences. The homologous sequences of other turtles were downloaded from NCBI and the phylogenetic characters were analyzed together with the sequences the authors provided here. The results showed that 941 bp consensus sequences of R35 and 620 bp consensus sequences of RAG2 were obtained after aligned. 1561 bp consensus sequences of combined R35/RAG2 date set were acquired. Thereinto,505 variable sites were detected, accounting for 32. 35% of total sites, with 239 parsim-informative and 139 indels. The average contents were found to be 29.5%in A,28.5%in T,22. 8%in G, and 19.2% in C, with the Ts/Tv ratio of 1.64. And Kimura-2-parameter (K-2-P) distance was the minimum (0.025) between the Cheloniidae and Chelydridae. The K-2-P distance between the Trionychidae and Podocnemididae was the maximum (0.182). The phylogenetic trees indicate that 1) Geoemydidae is firstly clustered with Testudinidae, forming a monophyletic clade, and then they clustered with Emydidae,2) it strongly support that Testudinoidea is the sister taxon to Chelydridae plus Chelonioidea, and 3) Family Chelydridae is the sister taxon to Chelonioidea.%为从核基因的角度探讨龟鳖类的系统发育特征,采用PCR扩增和测序的方法,获得两种龟的R35内含子部分序列以及6种龟的RAG2基因部分序列,结合NCBI其它龟鳖的同源序列一并进行分析.结果表明:将R35序列比对后得到941 bp的一致序列,将RAG2比对后得到620 bp的一致序列,二者合并后,比对排序后得到1561 bp的一致序列,其中共有505个可变核苷酸位点,总变异率为32.35％；简约信息位点为239个,插入/缺失为139个,转换/颠换比率为1.64.碱基A、T、G、C的平均含量分别为29.5％、28.5％、22.8％、19.2％.海龟科和鳄龟科之间Kimura双参数(K-2-P)遗传距离最小(0.025),鳖科和南美侧颈龟科之间的遗传距离最大(0.182).分子系统树结果显示:1)陆龟科与潮龟科先聚在一起,再与龟科聚在一起,陆龟科与潮龟科构成一个单系类群；2)支持陆龟总科与鳄龟科+海龟总科构成姐妹群；3)鳄龟科和海龟总科是姐妹群的关系.