The non-regular orbit: three satellite DNAs in Drosophila martensis (buzzatii complex, repleta group) followed three different evolutionary pathways

The genome of species from the buzzatii cluster (buzzatii complex, repleta group) is hosted by a number of satellite DNAs (satDNAs) showing contrasting structural characteristics, genomic organization and evolution, such as pBuM-alpha (similar to 190 bp repeats), pBuM-alpha/beta (similar to 370 bp repeats) and the DBC-150 (similar to 150 bp repeats). In the present study, we aimed to investigate the evolution of these three satDNAs by looking for homologous sequences in the genome of the closest outgroup species: Drosophila martensis (buzzatii complex). After PCR, we isolated and sequenced 9 alpha, 8 alpha/beta and 11 DBC-150 sequences from this species. The results were compared to all pBuM and DBC-150 sequences available in literature. After D. martensis split from the buzzatii cluster some 6 Mya, the three satDNAs evolved differently in the genome of D. martensis by: (1) maintenance of a collection of major types of ancestral repeats in the genome (alpha); (2) fixation for a single major type of ancestral repeats (alpha/beta) or (3) fixation for new divergent species-specific repeat types (DBC-150). Curiously, D. seriema and D. martensis, although belonging to different and allopatric clusters, became independently fixed for the same major type of alpha/beta ancestral repeats, illustrating a rare case of parallelism in satDNA evolution. The contrasting pictures illustrate the diversity of evolutionary pathways a satDNA can follow, defining a non-regular orbit with outcomes difficult to predict.