Inversion polymorphism in species of the Drosophila nasuta subgroup from Thailand.

Thailand populations of three species of the D. nasuta complex have been analysed for the presence of paracentric inversions. D. albomicans and D. sulfurigaster albostrigata were collected from Phuket, Chiang Mai and the River Kwai, whilst D. kohkoa was found only in Phuket and the River Kwai. Chromosomal polymorphism was studied in respect to geographical distribution. The Phuket populations of all three species proved to be highly polymorphic by comparison with the River Kwai and Chiang Mai populations. The heterozygosity frequencies of inversions were calculated and the variations interpreted as a result of adaptation to local ecogeographical conditions. Shared polymorphisms revealed that D. kohkoa and D. s. albostrigata are more closely related to D. albomicans than they are to each other.