Contrasting population genetic structures using allozymes and the inversion polymorphism in Drosophila buzzatii

Second chromosome inversion and genotypic frequencies at seven allozyme loc i, differentially associated with inversions, were determined in seven natu ral populations of Drosophila buzzatii. The patterns of variation of allozy mes and the inversion polymorphisms were significantly different, indicatin g the role of adaptive differentiation for the latter. Moreover, the patter ns of population structure varied among allozyme loci, suggesting the opera tion of diversifying selection for certain loci. Differentiation was neglig ible for Leucyl-amino peptidase (Lap) and Peptidase-2 (Pep-2), low to moder ate for Aldehyde oxidase (Aldox), Peptidase-1 (Pep-1) and Esterase-1 (Est-1 ) and high for Esterase-2 (Est-2) and Xanthine dehydrogenase (Xdh). Signifi cant linkage disequilibria were detected between inversions and Aldox; Est- 1, Est-2 and Xdh. Multiple regression analyses of inversion and allele freq uencies on environmental variables revealed the existence of dines for inve rsions, Est-1, Est-2, Xdh and Aldox along altitudinal, latitudinal and/or c limatic gradients. Tests using conditional allele frequencies showed that E st-1 and Alder dines could he accounted for by hitchhiking with inversions, whereas natural selection should be invoked to explain the dines observed for Est-2 and Xdh.