MBE Advance Access published online on March 5, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg033
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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1 Department of Agricultural Biotechnology, Lab. of Genetics, Agricultural University of Athens, Iera Odos 75, Votanikos, 118 55 Athens, Greece
* To whom correspondence should be addressed. E-mail: goulielmos{at}imbb.forth.gr.
In the olive fruit fly Bactrocera oleae previous studies have described an one-locus three-allele electrophoretic polymorphism of the enzyme alcohol dehydrogenase and provided evidence that the polymorphism is under the influence of selection. A recent study has shown that this species carries a two-locus duplication for alcohol dehydrogenase. Here we show that the polymorphism maps at one of the duplicated loci, Adh2, and identify the nucleotide and, therefore, the inferred amino acid differences among the three allozymes. At the amino acid level, the polymorphism is of the simplest possible form: there is no intra-allozyme variation, and inter-allozyme differences are restricted to one amino acid for two pairs of alleles and to two for the third pair. Consideration of the amino acid residues at the sites that segregate in B. oleae in four congeneric species and the phylogenetic trees produced from the nucleotide sequences of the Adh2 gene of these species point to the same allozyme as the ancestral form of the polymorphism. Interestingly, this allozyme comprises less than 1% of the gene pool of present-day natural populations of B. oleae, where the other two allozymes appear to form a stable polymorphism. Previous studies have shown that the frequency of the rare allozyme rises rapidly in laboratory colonies maintained on artificial diet and declines again when the artificial diet is replaced with olive fruit, the natural substrate of B. oleae. The geographical distribution of several congeneric species suggests that B. oleae originated in the Indian subcontinent where the olive tree is practically absent. The poor performance of the ancestral allele on the olive fruit suggests the possibility that the decline of this allele and the concomitant rise of the presently common alleles might be associated with the expansion of the insect's geographical distribution to areas where the olive tree has become its main and perhaps sole host. The estimated age of the polymorphism is compatible with this hypothesis, but firmer support could be difficult to obtain. Key Words:
Alcohol dehydrogenase, olive fruit fly, amino acid polymorphism
© 2003 Society for Molecular Biology and Evolution
Original Articles
Tracing the History of an Enzyme Polymorphism: The Case of Alcohol Dehydrogenase-2 (Adh-2) of the Olive Fruit Fly Bactrocera oleae
2 Department of Biology, University of Crete, Vasilika Vouton, 714 09 Iraklion, Crete
3 Department of Biology, University of Crete, Vasilika Vouton, 714 09 Iraklion, Crete; Institute of Marine Biology of Crete, Iraklion, Crete, Greece
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