Friedrich M, Tautz D
Zoologisches Institut, Universität München, Germany.
Mol Biol Evol. 1997 Jun;14(6):644-53. doi: 10.1093/oxfordjournals.molbev.a025804.
We have studied the potential reasons for a conspicuous deviation of substitution rates in Dipteran ribosomal genes. Systematic pairwise relative-rate tests reveal that a significant increase in substitution rate is characteristic for Diptera, but not for the other insects analyzed. Estimation of sequence change in specific lineages reveals that most of these substitutions took place during the evolution of the Dipteran stem lineage. When related to the paleontologically documented periods of absolute time, the substitution rate in the stem lineage of the Diptera underwent an at least 20-fold increase compared to other insect groups and subsequently dropped by a factor of 10 before the diversification of the major Dipteran subgroups. Systematic comparisons of nucleotide composition show that this episodic change in substitution rate was accompanied by a significant increase in A+T content of Dipteran rDNA. Our data suggest that the episodic evolution of the Dipteran rDNA has most probably been caused by a change of directional mutation pressure which must have occurred during the evolution of the stem lineage of the Diptera.
我们研究了双翅目核糖体基因替换率显著偏差的潜在原因。系统的成对相对速率测试表明，替换率显著增加是双翅目的特征，但在所分析的其他昆虫中并非如此。特定谱系中序列变化的估计表明，这些替换大多发生在双翅目主干谱系的进化过程中。与古生物学记录的绝对时间周期相关时，双翅目主干谱系的替换率与其他昆虫类群相比至少增加了20倍，随后在主要双翅目亚群分化之前下降了10倍。核苷酸组成的系统比较表明，这种替换率的阶段性变化伴随着双翅目rDNA中A+T含量的显著增加。我们的数据表明，双翅目rDNA的阶段性进化很可能是由定向突变压力的变化引起的，这种变化一定发生在双翅目主干谱系的进化过程中。
