The evolutionary dynamics of the Helena retrotransposon revealed by sequenced Drosophila genomes

<p>Abstract</p> <p>Background</p> <p>Several studies have shown that genomes contain a mixture of transposable elements, some of which are still active and others ancient relics that have degenerated. This is true for the non-LTR retrotransposon <it>Helena</it>, of which only degenerate sequences have been shown to be present in some species (<it>Drosophila melanogaster</it>), whereas putatively active sequences are present in others (<it>D. simulans</it>). Combining experimental and population analyses with the sequence analysis of the 12 <it>Drosophila </it>genomes, we have investigated the evolution of <it>Helena</it>, and propose a possible scenario for the evolution of this element.</p> <p>Results</p> <p>We show that six species of <it>Drosophila </it>have the <it>Helena </it>transposable element at different stages of its evolution. The copy number is highly variable among these species, but most of them are truncated at the 5' ends and also harbor several internal deletions and insertions suggesting that they are inactive in all species, except in <it>D. mojavensis </it>in which quantitative RT-PCR experiments have identified a putative active copy.</p> <p>Conclusion</p> <p>Our data suggest that <it>Helena </it>was present in the common ancestor of the <it>Drosophila </it>genus, which has been vertically transmitted to the derived lineages, but that it has been lost in some of them. The wide variation in copy number and sequence degeneration in the different species suggest that the evolutionary dynamics of <it>Helena </it>depends on the genomic environment of the host species.</p

Impure Public Goods and Technological Interdependencies

Impure public goods represent an important group of goods. Almost every public good exerts not only effects which are public to all but also effects which are private to the producer of this good. What is often omitted in the analysis of impure public goods is the fact that – regularly – these private effects can also be generated independently of the public good. In our analysis we focus on the effects alternative technologies – independently generating the private effects of the public good – may have on the provision of impure public goods. After the investigation in an analytical impure public good model, we numerically simulate the effects of alternative technologies in a parameterized model for climate policy in Germany