Inversion polymorphism in populations of Drosophila sulphurigaster albostrigata and Drosophila nasuta albomicans from Phuket, Thailand.

Two species of the Drosophila nasuta subgroup of the Drosophila immigrans group, D. sulphurigaster albostrigata and D. nasuta albomicans were investigated in this study. Collections of both species were made from Phuket, Thailand. Both species have similar salivary chromosomes, with four autosomal arms and one sex chromosome arm, and both are highly polymorphic for paracentric inversions. D.s. albostrigata accounted for the majority of the isolines collected and exhibited the greater number of inversions. One inversion, C14 was common to both species, indicating common ancestry. A non-random distribution of inversions was observed on the proximal end of chromosome III in both D.s. albostrigata and D. n. albomicans. An inter-collection comparison revealed that both rigid and flexible chromosomal polymorphism were operating in the two species, with a seasonal variation noted for one inversion in D. s. albostrigata. A non-random association of two inversions was observed in D. n. albomicans. Based on a comparison of the indices of crossing over, both D. s. albostrigata and D. n. albomicans were found to be more heterozygous than in previous studies, with D. n. albomicans appearing to have evolved further than D. s. albostrigata.