Is genome size influenced by colonization of new environments in dipteran species?

Genome size differences are usually attributed to the amplification and deletion of various repeated DNA sequences, including transposable elements (TEs). Because environmental changes may promote modifications in the amount of these repeated sequences, it has been postulated that when a species colonizes new environments this could be followed by an increase in its genome size. We tested this hypothesis by estimating the genome size of geographically distinct populations of Drosophila ananassae, Drosophila malerkotliana, Drosophila melanogaster, Drosophila simulans, Drosophila subobscura, and Zaprionus indianus, all of which have known colonization capacities.

Worldwide distribution of transposable element copy number in natural populations of Drosophila simulans.

Transposable elements (TEs), which promote various kinds of mutations, constitute a large fraction of the genome. How they invade natural populations and species is therefore of fundamental importance for understanding the dynamics of genetic diversity and genome composition. On the basis of 85 samples of natural populations of Drosophila simulans, we report the distributions of the genome insertion site numbers of nine TEs that were chosen because they have a low average number of sites.

Tissue-specificity of 412 retrotransposon expression in Drosophila simulans and D. melanogaster.

We analyse the expression of the retrotransposon 412 in the soma, testes, and ovaries in populations of Drosophila simulans and D. melanogaster, using RT-PCR and in situ hybridization. We find that expression of 412 is highly variable in the soma, confirming previous findings based on Northern blots.

Developmental expression of the 412 retrotransposon in natural populations of D. melanogaster and D. simulans.

We analysed the pattern of expression of retrotransposon 412 through developmental stages in various populations of Drosophila simulans and D. melanogaster differing in 412 copy number. We found that the 412 expression pattern varied greatly between populations of both species, indicating that such patterns were not entirely species-specific.

Distribution of the retrotransposable element 412 in Drosophila species.

Copy numbers of sequences homologous to the Drosophila melanogaster retrotransposable element 412, their distribution between the chromosome arms and the chromocenter, and whether they contain full-size copies were analyzed for 55 species of the Drosophila genus. Element 412 insertion sites were detected on the chromosome arms of D. melanogaster, Drosophila simulans, and a few species of the obscura group, but the chromocenter was labeled in almost all species.