Department of Comparative Anatomy, Institute of Zoology, Jagiellonian University, ul. Gronostajowa 9, 30-387 Kraków, Poland.
Gene. 2012 Jan 1;491(1):71-80. doi: 10.1016/j.gene.2011.08.004. Epub 2011 Sep 17.
Natural transfer of mitochondrial DNA has occurred between three western Palaearctic waterfrog taxa: Pelophylax lessonae, Pelophylax ridibundus and their hybridogenetic hybrid, Pelophylax kl. esculentus. The transfer is asymmetric with most P. kl. esculentus and approximately one third of all central European P. ridibundus having mtDNA derived from P. lessonae (L-mtDNA). We obtained complete nucleotide sequences of multiple mitochondrial genomes (15,376-78 bp without control regions) from all 3 taxa, including a P. ridibundus frog with introgressed L-mtDNA. The gene content and organization of the mitogenomes correspond to those typical of neobatrachians. Divergence between the mtDNAs of P. lessonae and P. ridibundus is high with an uncorrected p-distance of 11.9% across the entire mitogenome. However, the rate of nucleotide substitution depends on the degree of functional constraint with up to 30-fold differences in levels of divergence. In general, mitochondrial genes encoding the translational machinery evolve very slowly, whereas genes encoding polypeptides of the electron transport system, especially the ND genes, evolve rapidly. Only 25 of 211-213 observed amino acid replacements could be classified as radical and are therefore more likely to be exposed to selection. A disproportionately high number of amino acid substitutions has occurred in the ND4, ND4L and cytb genes of the P. lessonae lineage (including 36% of all radical changes). In contrast to the interspecific divergence, nucleotide polymorphism within L- and R-mtDNA is very low: L-mtDNA haplotypes differed on average by only 19 nucleotides, while there was no variation within two mtDNAs derived from P. ridibundus. This is an expected finding considering that we have sampled a post-glacial expansion area. Moreover, the introgressed L-mtDNA on a P. ridibundus background differed from other L-mtDNAs by only a few substitutions, indicative of a very recent introgression event. We discuss our findings in the context of natural selection acting on L-mtDNA and its potential significance in cytonuclear epistasis.
线粒体 DNA 的自然转移发生在三个西部古北界水蛙类群之间：泽蛙、金线蛙及其杂种化杂种金线蛙。这种转移是不对称的，大多数金线蛙和大约三分之一的中欧金线蛙的 mtDNA 来自泽蛙（L-mtDNA）。我们从这 3 个类群中获得了多个线粒体基因组的完整核苷酸序列（不包括控制区的 15376-78bp），包括一只具有 L-mtDNA 渗入的金线蛙。线粒体基因组的基因组成和组织与新蛙类的典型基因组成和组织相对应。泽蛙和金线蛙的 mtDNA 之间的分化很高，整个线粒体基因组的未校正 p-距离为 11.9%。然而，核苷酸取代的速度取决于功能约束的程度，在不同程度的分化中，差异可达 30 倍。一般来说，线粒体基因编码翻译机器的进化非常缓慢，而编码电子传递系统多肽的基因，特别是 ND 基因，进化迅速。在 211-213 个观察到的氨基酸替换中，只有 25 个可以被归类为激进的，因此更有可能受到选择的影响。在泽蛙谱系的 ND4、ND4L 和 cytb 基因中发生了不成比例的大量氨基酸替换（包括所有激进变化的 36%）。与种间分化相反，L-和 R-mtDNA 内的核苷酸多态性非常低：L-mtDNA 单倍型平均仅相差 19 个核苷酸，而来自金线蛙的两个 mtDNA 内没有变异。考虑到我们已经采样了一个后冰河时代扩张的区域，这是一个预期的发现。此外，在金线蛙背景下的渗入 L-mtDNA 仅与其他 L-mtDNA 有几个替换的差异，表明这是一个非常近期的渗入事件。我们在自然选择作用于 L-mtDNA 的背景下讨论了我们的发现及其在细胞质核遗传中的潜在意义。
