Positive and negative selection in the beta-esterase gene cluster of the Drosophila melanogaster subgroup.
We examine the pattern of molecular evolution of the beta-esterase gene cluster, including the Est-6 and psiEst-6 genes, in eight species of the Drosophila melanogaster subgroup. Using maximum likelihood estimates of nonsynonymous/synonymous rate ratios, we show that the majority of Est-6 sites evolves under strong (48% of sites) or moderate (50% of sites) negative selection and a minority of sites (1.5%) is under significant positive selection. Est-6 sites likely to be under positive selection are associated with increased intraspecific variability. One positively selected site is responsible for the EST-6 F/S allozyme polymorphism; the same site is responsible for the EST-6 functional divergence between species of the melanogaster subgroup. For psiEst-6 83.7% sites evolve under negative selection, 16% sites evolve neutrally, and 0.3% sites are under positive selection. The positively selected sites of psiEst-6 are located at the beginning and at the end of the gene, where there is reduced divergence between D. melanogaster and D. simulans; these regions of psiEst-6 could be involved in regulation or some other function. Branch-site-specific analysis shows that the evolution of the melanogaster subgroup underwent episodic positive selection. Collating the present data with previous results for the beta-esterase genes, we propose that positive and negative selection are involved in a complex relationship that may be typical of the divergence of duplicate genes as one or both duplicates evolve a new function.
Balakirev
Evgeniy S
ES
Department of Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697-2525, USA. esbalak@bio.dvgu.ru
Anisimova
Maria
M
Ayala
Francisco J
FJ
D000818:Animals; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster / Q000201:enzymology / Q000235:genetics*; D004950:Esterases / Q000737:chemistry / Q000235:genetics*; D019143:Evolution, Molecular; D049810:Genetic Speciation; D005810:Multigene Family; D010802:Phylogeny; D012641:Selection, Genetic
D029721:Drosophila Proteins; D004950:Esterases