Maughan Heather
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
Evolution. 2007 Feb;61(2):280-8. doi: 10.1111/j.1558-5646.2007.00026.x.
Rates of molecular evolution are known to vary considerably among lineages, partially due to differences in life-history traits such as generation time. The generation-time effect has been well documented in some eukaryotes, but its prevalence in prokaryotes is unknown. "Because many species of Firmicute bacteria spend long periods of time as metabolically dormant spores, which could result in fewer DNA substitutions per unit time, they present an excellent system for testing predictions of the molecular clock hypothesis." To test whether spore-forming bacteria evolve more slowly than their non-spore-forming relatives, I used phylogenetic methods to determine if there were differences in rates of amino acid substitution between spore-forming and non-spore-forming lineages of Firmicute bacteria. Although rates of evolution do vary among lineages, I find no evidence for an effect of spore-formation on evolutionary rate and, furthermore, evolutionary rates are similar to those calculated for enteric bacteria. These results support the notion that variation in generation time does not affect evolutionary rates in bacterial lineages.
已知分子进化速率在不同谱系间差异很大，部分原因是诸如世代时间等生活史特征的差异。世代时间效应在一些真核生物中已有充分记载，但在原核生物中的普遍性尚不清楚。“由于许多厚壁菌门细菌会以代谢休眠孢子的形式存在很长时间，这可能导致单位时间内的DNA替换较少，所以它们是检验分子钟假说预测的绝佳系统。”为了测试形成孢子的细菌是否比不形成孢子的亲缘细菌进化得更慢，我使用系统发育方法来确定厚壁菌门细菌中形成孢子和不形成孢子的谱系之间氨基酸替换率是否存在差异。尽管进化速率在不同谱系间确实存在差异，但我没有发现孢子形成对进化速率有影响的证据，此外，进化速率与针对肠道细菌计算出的速率相似。这些结果支持了世代时间的变化不会影响细菌谱系进化速率这一观点。
