Cai Yu-Ting, Li Qin, Zhang Jia-Yong, Storey Kenneth B, Yu Dan-Na
College of Chemistry and Life Science, Zhejiang Normal University, Jinhua, Zhejiang Province, China.
Key Lab of Wildlife Biotechnology, Conservation and Utilization of Zhejiang Province, Zhejiang Normal University, Jinhua, Zhejiang, China.
PeerJ. 2020 Apr 14;8:e8901. doi: 10.7717/peerj.8901. eCollection 2020.
Mitogenomes are useful in analyzing phylogenetic relationships and also appear to influence energy metabolism, thermoregulation and osmoregulation. Much evidence has accumulated for positive selection acting on mitochondrial genes associated with environmental adaptation. Hence, the mitogenome is a likely target for environmental selection. The family Bufonidae (true toads) has only nine complete and four partial mitogenomes published compared to the 610 known species of this family. More mitogenomes are needed in order to obtain a clearer understanding of the phylogenetic relationships within Bufonidae that are currently controversial. To date, no mitogenomes have been reported from the genera and . can live in low temperature environments and can live in high salinity environments. We sequenced the mitogenomes of these two species to discuss the phylogenetic relationships within Bufonidae and the selection pressures experienced by specimens living in low temperature or saline environments. Like other toads, the circular mitogenomes of both species contained the typical 37 genes. had the highest A+T content of the complete mitogenome among the Bufonidae. In addition, showed a negative AT-skew in the control region, whereas showed a positive AT-skew. Additionally, both toad species had unique molecular features in common: an gene that uses TTG as the start codon, an extra unpaired adenine (A) in the anticodon arm of (AGY), and the loss of the DHU loop in . The monophyly of Bufonidae was corroborated by both BI and ML trees. An analysis of selective pressure based on the 13 protein coding genes was conducted using the EasyCodeML program. In the branch model analysis, we found two branches of and that were under negative selection. Additionally, we found two positively selected sites (at positions 115 and 119, BEB value > 0.90) in the ND6 protein in the site model analysis. The residue D (119) was located only in and may be related to adaptive evolution in low temperature environments. However, there was no evidence of a positively selected site in in this study.
线粒体基因组在分析系统发育关系方面很有用，而且似乎还会影响能量代谢、体温调节和渗透压调节。有大量证据表明，正向选择作用于与环境适应相关的线粒体基因。因此，线粒体基因组很可能是环境选择的目标。蟾蜍科（真蟾蜍）与该科已知的610个物种相比，仅公布了9个完整的和4个部分的线粒体基因组。为了更清楚地了解目前存在争议的蟾蜍科内部的系统发育关系，还需要更多的线粒体基因组。迄今为止，尚未有关于 属和 属的线粒体基因组的报道。 可以生活在低温环境中， 可以生活在高盐环境中。我们对这两个物种的线粒体基因组进行了测序，以探讨蟾蜍科内部的系统发育关系以及生活在低温或盐环境中的标本所经历的选择压力。与其他蟾蜍一样，这两个物种的环状线粒体基因组都包含典型的37个基因。 在蟾蜍科中，其完整线粒体基因组的A+T含量最高。此外， 在控制区表现出负的AT偏斜，而 表现出正的AT偏斜。此外，这两种蟾蜍物种还有一些共同的独特分子特征：一个使用TTG作为起始密码子的 基因，在 （AGY）的反密码子臂中有一个额外的未配对腺嘌呤（A），以及 在 中DHU环的缺失。BI树和ML树都证实了蟾蜍科的单系性。使用EasyCodeML程序对基于13个蛋白质编码基因的选择压力进行了分析。在分支模型分析中，我们发现 和 的两个分支处于负选择之下。此外，在位点模型分析中，我们在ND6蛋白中发现了两个正选择位点（第115和119位，BEB值>0.90）。残基D（119）仅存在于 中，可能与低温环境中的适应性进化有关。然而，在本研究中没有证据表明 在 中有正选择位点。
