Op-gbev130065 998..1009

Transposable elements (TEs) are repetitive DNA sequences that can make new copies of themselves that are inserted elsewhere in a host genome. The abundance and distributions of TEs vary considerably among phylogenetically diverse hosts. With the aim of exploring thebasis of this variation,we evaluatedcorrelations between several genomic variables and the presence of TEsand non-TE repeats in thecompletegenomesequenceof theWesternclawedfrog (Silurana tropicalis). Thisanalysis revealspatternsofTE insertion consistent with gene disruption but not with the insertional preference model. Analysis of non-TE repeats recovered unique features of their genome-wide distribution when compared with TE repeats, including no strong correlation with exons and a particularly strong negative correlation with GC content. We also collected polymorphism data from 25 TE insertion sites in 19 wild-caught S. tropicalis individuals. DNA transposon insertions were fixed at eight of nine sites and at a high frequency at one of nine, whereas insertionsof long terminal repeat (LTR)andnon-LTR retrotransposonswerefixedatonly4of16sites andat lowfrequencyat12of16. Amaximumlikelihoodmodel failed toattribute thesedifferences in insertion frequencies tovariation in selectionpressureondifferent classes of TE, opening the possibility that other phenomena such as variation in rates of replication or duration of residence in the genome could play a role. Taken together, these results identify factors that sculpt heterogeneity in TE distribution in S. tropicalis and illustrate that genomic dynamics differ markedly among TE classes and between TE and non-TE repeats.