南门峡裂腹鱼亚科鱼类形态相似种的分类学地位——形态趋同进化实例

受高原抬升所致的水系变迁及人类活动的影响,分布于南门峡河流的裂腹鱼亚科鱼类与黄河干支流种群间的基因交流受到长期限制。作为孤立小群体,探讨其分类学地位及其在小生境中的进化机制对了解青藏高原鱼类多样性和物种的形成、进化具有重要意义。本文采用聚合酶链式反应(PCR)和直接测序方法获得了南门峡裂腹鱼亚科鱼类(n=29)及其近缘种(n=19)共48个个体的线粒体DNA(mtDNA)细胞色素b(cytb)基因的全序列(1140bp),并以厚唇裸重鱼和尖裸鲤为外群构建了MP和Bayesian系统进化树。南门峡裂腹鱼亚科鱼类29个个体的序列经排序后,发现有100个(8·77%)多态性位点,共定义了16个单倍型,在系统进化树上分布于截然不同的两个族群中。其中5个单倍型(NMX3、6、7、13、15)与其近缘种花斑裸鲤和青海湖裸鲤形成单系群(MP99%,Bayesian98%),而其余11个单倍型(NMX1、2、4、5、8、9、10、11、12、14、16)与黄河干支流的黄河裸裂尻鱼形成另一个单系群(MP99%,Bayesian99%)。序列差异分析显示,分布于不同族群的南门峡裂腹鱼亚科鱼类之间存在较大的碱基差异(平均为7·42%),显示出种间差异水平,表明分布于南门峡河流的裂腹鱼亚科鱼类可能是花斑裸鲤和黄河裸裂尻鱼形态相似种的复合体。结合青藏高原隆升所致的气候环境变化和高原北部水系变迁的事件,推断形态趋同进化可能导致了南门峡河流裂腹鱼亚科鱼类形态相似种的共存,而小生境自然选择压力是引发适应性形态趋同进化的主要原因。

Molecular systematics of morphologically similar fishes in the Schizothoracinae in Nanmenxia River, with implication for morphological convergent evolution

With the human activities and changes in water systems due to uplifting of the Qinghai-Tibetan Plateau, gene flow between the schizothoracine fishes distributed in the Nanmenxia River and other upper reaches of the Yellow River has been limited for a long time. As a small and isolated group in a special niche, the investigation of the taxonomic status and evolutionary status of these fishes is important to further understand what has caused the rapid speciation and high levels of biodiversity in the Qinghai-Tibetan Plateau. In this study, the complete sequences of the mitochondrial cyt b gene from 29 individuals of schizothoracine fishes in the Nanmanxia River and 19 individuals representing other relatively closed species were sequenced. Among the aligned sequences of 29 individuals of schizothoracine fishes in the Nanmanxia River, 100(8.77%) nucleotide sites were variable, and a total of 16 haplotypes was identified. The phylogenetic analyses showed that 5 haplotypes(NMX3, 6, 7, 13, 15)from the Nanmanxia River clustered with the relatively closed species Gymnocypris eckloni and Gymnocypris przewalskii, and together formed a monophyletic clade with high boostrap values(99% for the MP tree and 98% for Bayesian tree). The remaining 11 haplotypes(NMX1, 2, 4, 5, 8, 9, 10, 11, 12, 14, 16) together with Schizopygopsis pylzovi from the upper reaches of the Yellow River formed another monophyletic clade(99% for both the MP tree and Bayesian tree). The sequence divergence between two groups distributed in different clades showed significant(average 7.42%), and together with the results of phylogenetic analyses suggested that schizothoracine fishes in the Nanmanxia River may be a morphologically similar species complex, consisting of two species, Gymnocypris eckloni and Schizopygopsis pylzovi. The natural selective pressure resulted from the changes of the water system and climatic conditions due to uplifts of the plateau, may have promoted adaptive convergence of their morphological characters.