Differences in genome size between closely related species: the Drosophila melanogaster species subgroup

Genome size varies considerably among organisms due to differences in the amplification, deletion, and divergence of various kinds of repetitive sequences, including the transposable elements, which constitute a large fraction of the genome. However, while the changes in genome size observed at a wide taxonomic level have been thoroughly investigated, we still know little about the process involved in closely related species. We estimated genome sizes and the reverse transcriptase-related sequence (RTRS) content in the nine species of the Drosophila melanogaster species subgroup. We showed that the species differ with regard to their genome size and that the RTRS content is correlated with genome size for all species except Drosophila orena. The genome of D. orena, which is 1.6-fold as big as that of D. melanogaster, has in fact not undergone any major increase in its RTRS content.