鳍足类线粒体基因的选择压力比较及进化关系探讨

Selection pressure comparison and evolutionary relationships exploration of pinnipeds mitochondrial genes

鳍足类Pinnipeds是海洋哺乳动物的重要类群,现存种类包括海象科Odobenidae、海狮科Otariidae和海豹科Phocidae的所有物种。在海豹属Phoca中,atp8基因的Ka/Ks最高,仅为0.084 7(远小于1),因而海豹属所有线粒体蛋白质编码基因的选择压力均非常高。对于群海豹属Pusa,cox1、cox2和nad3基因的Ka/Ks均为0,表明在这3个基因中,所有的核苷酸的替换均为同义替换,没有出现氨基酸的改变。科内、属内基因变异位点的分析表明,nad5、nad4和nad2基因可以作为cox1和cob基因辅助的分子标记。线粒体基因组的系统发育结果,强烈支持食肉目所有12个科均为单系群,并且鳍足类(海狮科、海象科和海豹科)为食肉目Carnivora内部的一个单系群(BPM=100,BPP=100)。在鳍足类内部,海狮科与海象科亲缘关系最近,聚类为海狮总科Otarioidea,然后与海豹科聚类:(海狮科+海象科)+海豹科。在海豹科内部,线粒体基因组的证据支持将海豹科划分为2个亚科,即僧海豹亚科Monachinae和海豹亚科Phocinae。线粒体基因组的证据,强烈支持鼬科Mustelidae与浣熊科Procyonidae关系最近,臭鼬科Mephitidae与熊猫科Ailuridae近缘,同时,鳍足类与[(鼬科+浣熊科)+(臭鼬科+熊猫科)]为姊妹群,而与熊科Ursidae较远。犬科Canidae在犬型亚目Caniformia中分化较早,位于犬型亚目的基部。

Current pinnipeds is one important group of marine mammals, which including all species in three families （Odobenidae, Otariidae and Phocidae）. In the genus Phoca, the Ka/Ks rate of atp8 gene is highest and only 0. 084 7 （much less than 1）, so all Phoca mitochondrial protein-coding genes bear very high selection pressure. In Pusa, Ka/Ks rates of three genes （cox1 ,cox2 and had3） are equal to 0,indicating that replacement of all nucleotides in these three genes are synonymous substitutions and none amino acid change. Analyses of genetic variations within family and genus indicted that nariS,had4, and had2 genes can be used as molecular markers assisted to cox] and cob gene. Phylogenetic results based on mitochondrial genomes strongly support that all 12 families from Carnivora are monophyletic group, and pinnipeds （Otariidae, Odobenidae and Phocidae） are one monophyletic group within Carnivora （BPM= 100, BPP=100）. Within the pinnipeds, the relationship between Otariidae and Odobenidae is close （Otarioidea）, then cluster with Phocidae： （Otariidae＋Odobenidae）＋Phocidae. Evidences of mitochondrial genomes support that Phoeidae are divided into two subfamilies （Monachinae and Phocinae）. Mitochondrial genomic evidence strongly supports close relationship between Mustelidae and Procyonidae. Meanwhile, Mephitidae clustering with Ailuridae is supported powerfully. Pinnipeds as a sister group to [（Mustelidae＋Procyonidae）＋（Mephitidae＋Ailuridae）], then cluster with the family Ursidae. Canidae is differentiation earliest and is located in base position of the suborder Caniformia.