A major difference between the divergence patterns within the lines-1 families in mice and voles

L1 retroposons are represented in mice by subfamilies of interspersedsequences of varied abundance. Previous analyses have indicated thatsubfamilies are generated by duplicative transposition of a small number ofmembers of the L1 family, the progeny of which then become a majorcomponent of the murine L1 population, and are not due to any activeprocesses generating homology within preexisting groups of elements in aparticular species. In mice, more than a third of the L1 elements belong toa clade that became active approximately 5 Mya and whose elements are >or = 95% identical. We have collected sequence information from 13 L1elements isolated from two species of voles (Rodentia: Microtinae: Microtusand Arvicola) and have found that divergence within the vole L1 populationis quite different from that in mice, in that there is no abundantsubfamily of homologous elements. Individual L1 elements from voles arevery divergent from one another and belong to a clade that began a periodof elevated duplicative transposition approximately 13 Mya. Sequenceanalyses of portions of these divergent L1 elements (approximately 250 bpeach) gave no evidence for concerted evolution having acted on the vole L1elements since the split of the two vole lineages approximately 3.5 Mya;that is, the observed interspecific divergence (6.7%-24.7%) is not largerthan the intraspecific divergence (7.9%-27.2%), and phylogenetic analysesshowed no clustering into Arvicola and Microtus clades.