Latitudinal clines for nucleotide polymorphisms in the Esterase 6 gene of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> |
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Authors: | Christopher W Coppin Wendy A Odgers John G Oakeshott |
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Institution: | (1) CSIRO Entomology, GPO Box 1700, Canberra , ACT, 2601, Australia;(2) School of Biochemistry and Molecular Biology, Australian National University, Canberra , ACT, 0200, Australia;(3) BioSecurity Australia, AFFA, GPO Box 858, Canberra, ACT, 2601, Australia |
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Abstract: | Previous studies have found non-neutral patterns of nucleotide polymorphism in the promoter and coding regions of Est6 in D. melanogaster. Coding region polymorphism peaks around two closely linked replacement differences associated with the EST6-F/EST6-S allozyme
polymorphism. The promoter contains two common, highly diverged haplotype groups, P1 and P7, that differentially affect Est6 expression. Allozyme studies have also revealed latitudinal clines in EST6-F and EST6-S frequencies that recur across continents.
Here we analyse nucleotide polymorphisms across the promoter and the region of peak coding sequence polymorphism in 10 Australian
populations along a 25° latitudinal gradient in order to examine the basis for the allozyme clines. As with the earlier studies,
we find an excess of intermediate to high frequency variants in both the P1/P7 region and around the two EST6-F/EST6-S replacements
in some populations. The two EST6-F/EST6-S replacement polymorphisms show latitudinal clines whereas the P1 and P7 groups
of promoter haplotypes do not. However the strongest clines are for three co-segregating silent site polymorphisms in a 4 bp
stretch at the 3′ end of the sequenced region. Monte Carlo simulations show that the clines for those three sites can explain
all others in the data but none of the others can explain those three. Thus the allozyme clines may not reflect selection
on either the P1/P7 polymorphism or the two replacements previously associated with the EST6-F/EST-S difference. |
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Keywords: | Drosophila melanogaster Esterase 6 Latitudinal cline Nucleotide polymorphism |
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