A BAC-based physical map of the Drosophila buzzatii genome

A variety of genomic resources have been developed as part of the Drosophila Genome Project, including the high-quality sequence and annotation of the Drosophila melanogaster genome (Adams et al. 2000; Celniker and Rubin 2003). Comparatively few genomic resources have been available for other species within the genus Drosophila. Phylogenetic analyses indicate that two main lineages exist within the Drosophila genus, which diverged ∼60 million years ago (Powell 1997; Tamura et al. 2004). One lineage leads to the Sophophora subgenus with ∼300 species (including D. melanogaster and D. pseudoobscura), whereas the other one leads to the subgenera Drosophila (including Drosophila virilis and Drosophila buzzatii) and Idiomyia (Hawaiian species), with ∼700 and 375 described species, respectively (Powell 1997; http://taxodros.unizh.ch/). Thus, many Drosophila species are relatively distantly related to D. melanogaster, and genomic resources developed for this species therefore have a somewhat limited applicability to them (Segarra et al. 1995; Podemski et al. 2001; Ranz et al. 2001; Gonzalez et al. 2002). Fosmid and BAC libraries for some Drosophila species have been produced or are currently in production (http://www.genome.gov/; http://tdgc.arl.arizona.edu/baclibraries.htm). Recently, the genome sequence of Drosophila pseudoobscura became available (Richards et al. 2005), and whole-genome shotgun sequences of 10 other Drosophila species are available or in progress (http://rana.lbl.gov/drosophila/multipleflies.html). Here, we describe the construction of a BAC library and a BAC-based physical map of the D. buzzatii genome. D. buzzatii belongs to the repleta species group of the Drosophila subgenus (Wasserman 1992), a group comprising ∼100 species that has been used for studies of ecological adaptation and speciation for more than 60 years (Spencer 1941; Crow 1942; Wharton 1942; Barker and Starmer 1982; Barker et al. 1990). Efforts to map the genome of D. buzzatii began 50 years ago with the comparative analysis of its salivary gland chromosomes to establish the phylogenetic relationships between repleta group species (Wasserman 1954, 1962; Ruiz et al. 1982; Ruiz and Wasserman 1993). This was followed by the linkage mapping of a small number of visible mutants (Schafer et al. 1993). In the last 10 years, ∼400 DNA markers have been mapped by in situ hybridization to the D. buzzatii chromosomes (Ranz et al. 1997, 2003; Laayouni et al. 2000; Casals et al. 2003). No large-insert genomic libraries or clone-based physical maps were previously available for this species.