DETERMINING AND DATING RECENT RODENT SPECIATION EVENTS BY USING L1 (LINE-1) RETROTRANSPOSONS

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 analysi s also can be problematic if the characters have not changed sufficien tly, 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 subfamilie s generated by the mammalian L1 (LINE-1) retrotransposon are apparentl y homoplasy-freee phylogenetic characters. L1 retrotransposons are tra nsmitted 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 res olve 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 o f speciation: an intense one, approximate to 2.7 Mya, produced at leas t five lineages in <0.3 My; a second began approximate to 1.2 Mya and may still be continuing.