Genetics. Published Articles Ahead of Print: May 16, 2007, Copyright © 2007
doi:10.1534/genetics.107.071191


A more recent version of this article appeared on August 1, 2007.

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Patterns of molecular variation and evolution in Drosophila americana and its relatives

Xulio Maside 1* and Brian Charlesworth 2

1 Universidade de Santiago de Compostela
2 University of Edinburgh

* To whom correspondence should be addressed. E-mail: xmaside{at}usc.es.

Submitted on January 23, 2007
Revised on March 23, 2007
Accepted on 11 May 2007


Abstract

We present the results of a survey of DNA sequence variability at X-linked and autosomal loci in Drosophila americana, and of patterns of DNA sequence evolution among D. americana and five other related species in the virilis group of Drosophila. D. americana shows a typical level of silent polymorphism for a Drosophila species, but has an unusually low ratio of nonsynonymous to silent variation. Both D. virilis and D. americana also show a low ratio of nonsynonymous to synonymous substitutions along their respective lineages since the split from their common ancestor. The proportion of amino-acid substitutions between D. americana and its relatives that are caused by positive selection, as estimated by extensions of the McDonald-Kreitman test, appears to be unusually high. We cannot, however, exclude the possibility that this reflects a recent increase in the intensity of selection on nonsynonymous mutations in D. americana and D. virilis. We also find that base composition at neutral sites appears to be in overall equilibrium among these species, but there is some evidence for departure from equilibrium for codon usage in some lineages.

Key Words: Drosophila americana, Drosophila virilis group, adaptive protein evolution, codon usage, nucleotide composition