Verneau O, Catzeflis F, Furano A V
Laboratory of Molecular and Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0830, USA.
Proc Natl Acad Sci U S A. 1998 Sep 15;95(19):11284-9. doi: 10.1073/pnas.95.19.11284.
Phylogenies based on the inheritance of shared derived characters will be ambiguous when the shared characters are not the result of common ancestry. Such characters are called homoplasies. Phylogenetic analysis also can be problematic if the characters have not changed sufficiently, as might be the case for rapid or recent speciations. The latter are of particular interest because evolutionary processes may be more accessible the more recent the speciation. The repeated DNA subfamilies generated by the mammalian L1 (LINE-1) retrotransposon are apparently homoplasy-free phylogenetic characters. L1 retrotransposons are transmitted only by inheritance and rapidly generate novel variants that produce distinct subfamilies of mostly defective copies, which then "age" as they diverge. Here we show that the L1 character can both resolve and date recent speciation events within the large group of very closely related rats known as Rattus sensu stricto. This lineage arose 5-6 million years ago (Mya) and subsequently underwent two episodes of speciation: an intense one, approximately 2.7 Mya, produced at least five lineages in <0.3 My; a second began approximately 1.2 Mya and may still be continuing.
当共享特征并非共同祖先的结果时，基于共享衍生特征遗传的系统发育树将会模糊不清。此类特征被称为同塑性。如果特征变化不够充分，系统发育分析也可能存在问题，快速或近期的物种形成可能就是这种情况。后者尤其令人感兴趣，因为物种形成越近，进化过程可能越容易理解。哺乳动物L1（长散在核元件1）逆转录转座子产生的重复DNA亚家族显然是无同塑性的系统发育特征。L1逆转录转座子仅通过遗传传递，并迅速产生新的变体，这些变体产生大多有缺陷拷贝的不同亚家族，然后随着它们的分化而“老化”。在这里，我们表明，L1特征既可以解析也可以确定在被称为狭义鼠属的一大群亲缘关系非常密切的大鼠中的近期物种形成事件的时间。这个谱系起源于500-600万年前（百万年前），随后经历了两次物种形成事件：一次强烈的事件，大约在270万年前，在不到30万年的时间里产生了至少五个谱系；第二次事件大约始于120万年前，可能仍在继续。
