A MAJOR DIFFERENCE BETWEEN THE DIVERGENCE PATTERNS WITHIN THE LINES-1FAMILIES IN MICE AND VOLES

L1 retroposons are represented in mice by subfamilies of interspersed sequences of varied abundance. Previous analysis have indicated that s ubfamilies are generated by duplicative transposition of a small numbe r of members of the L1 family, the progeny of which then become a majo r component of the murine L1 population, and are not due to any active processes generating homology within preexisting groups of elements i n a particular species. In mice, more than a third of the L1 elements belong to a clade that became active approximately 5 Mya and whose ele ments are greater-than-or-equal-to 95% identical. We have collected se quence information from 13 L1 elements isolated from two species of vo les (Rodentia: Microtinae: Microtus and Arvicola) and have found that divergence within the vole L1 population is quite different from that in mice, in that there is no abundant subfamily of homologous elements . Individual L1 elements from voles are very divergent from one anothe r and belong to a clade that began a period of elevated duplicative tr ansposition approximately 13 Mya. Sequence analyses of portions of the se divergent L1 elements (approximately 250 bp each) gave no evidence for concerted evolution having acted on the vole L1 elements since the split of the two vole lineages approximately 3.5 Mya; that is, the ob served interspecific divergence (6.7%-24.7%) is not larger than the in traspecific divergence (7.9%-27.2%), and phylogenetic analyses showed no clustering into Arvicola and Microtus clades.