Relationships within the melanogaster species subgroup of the genus Drosophila ( Sophophora ) - II. Phylogenetic relationships between six species based upon polytene chromosome banding sequences
The melanogaster species subgroup of Drosophila comprises six sibling species. The interrelationship between these species has been studied by analysis of the banding patterns of their polytene chromosomes. The species fall into two groups: (1) melanogaster, simulans and mauritiana and (2) erecta, teissieri and yakuba. The former group are chromosomally closely related, indeed simulans and mauritiana are homosequential. The latter group (all African endemic species) are less closely related although they all share eight autosomal inversions of the standard (i.e. melanogaster) sequence. From this shared sequence the chromosomes of the three African endemic species have diverged considerably by many paracentric inversions. Both D. teissieri and D. yakuba are polymorphic; we describe nine and four inversion sequences in them respectively. D. erecta is monomorphic although our sample size is very small (only two populations). We discuss both the origin of interspecific inversions, especially the problem of inversion breakpoint coincidence, and the light this study throws upon evolutionary relationships within this group of species.