Increase in the degree of inversion polymorphism in Drosophila bipectinata populations transfereed to laboratory conditions

Abstract

Thirteen laboratory populations (six mass cultures and seven isofemale lines) of Drosophila bipectinata were established from flies collected from six different geographic localities (four in the north and two in the south) in India. These mass cultures and isofemale lines were maintained in food bottles in the laboratory for varying number of generations by transferring about 50 flies (females and males in equal number) in each generation. After several generations, all the laboratory populations were analysed chromosomally to determine the frequency of different inversions. The results indicate that all the laboratory populations remained chromosomally polymorphic due to the persistence of inversions which were originally present in the populations. The quantitative data on the frequency of inverted gene orders and the level of inversion heterozygosity in laboratory populations are compared with those in corresponding natural populations. This comparison clearly shows that there is a considerable increase in the frequency of inverted gene orders and the level of inversion heterozygosity in laboratory populations when compared with corresponding natural populations. This is most likely to be due to selective advantage of inversion heterozygotes under stringent competition in laboratory populations. Thus heterotic buffering is associated with chromosome inversions of Drosopliilu bipectinata.

Species and genetic diversity in the genus Drosophila inhabiting the Indian subcontinent

“…D. bipectinata shows relatively less number of inversions (only 13 paracentric in versions) in its natural populations (Gupta and Panigrahy 1990). Only three inversions have been found to persist in laboratory stocks due to heterozygote superiority (Singh and Banerjee 1997). Inversions occur at low frequency in natural populations and there is no evidence for geographic differentiation in natural populations which lend support for rigid inversion polymorphism in D. bipectinata (Banerjee and Singh 1996).…”