Taxonomic status of Drosophila pallidosa and the biological species concept

The genus Drosophila is an interesting biological model which shows extensive diversity at the level of species. About 50 years ago, Bock and Wheeler described a new species of Drosophila, D. pallidosa just on the basis of sexual isolation and differences in sex comb teeth number. However, there is similarity in male genitalia and absence of post mating reproductive isolation and it is considered sibling to D. ananassae, which is a domestic and cosmopolitan species. On the other hand, D. pallidosa is endemic to certain islands such as South Pacific Island of Samoa and Fijii where they are sympatric and remain reproductively isolated by sexual isolation.In these two sibling species, results of various investigations have been reported pertaining to taxonomic status, morphometric traits, metaphase karyotypes, etc. show similarities and differences which is basis of suggestion that D. pallidosa is in statu nascendi. However, its description as a new species fits well with the biological species concept and it provides interesting material for future studies in the area of speciation genetics.