Paper

A multispecies approach for comparing sequence evolution of X-linked and autosomal sites in Drosophila

BEATRIZ VICOSO^a1 c1, PENELOPE R. HADDRILL and BRIAN CHARLESWORTH^a1

^a1 Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK

Summary

Population genetics models show that, under certain conditions, the X chromosome is expected to be under more efficient selection than the autosomes. This could lead to ‘faster-X evolution’, if a large proportion of mutations are fixed by positive selection, as suggested by recent studies in Drosophila. We used a multispecies approach to test this: Muller's element D, an autosomal arm, is fused to the ancestral X chromosome in Drosophila pseudoobscura and its sister species, Drosophila affinis. We tested whether the same set of genes had higher rates of non-synonymous evolution when they were X-linked (in the D. pseudoobscura/D. affinis comparison) than when they were autosomal (in Drosophila melanogaster/Drosophila yakuba). Although not significant, our results suggest this may be the case, but only for genes under particularly strong positive selection/weak purifying selection. They also suggest that genes that have become X-linked have higher levels of codon bias and slower synonymous site evolution, consistent with more effective selection on codon usage at X-linked sites.

(Received May 21 2008)

(Revised September 02 2008)

Correspondence:

^c1 Corresponding author: Institute of Evolutionary Biology, King's Buildings, Ashworth Laboratories, West Mains Road, Edinburgh EH9 3JT, UK. Tel: +44 131 650 5476. Fax. +44 131 650 6564. e-mail: b.vicoso@ed.ac.uk

Footnotes

Sequence data reported in this article have been deposited in the GenBank Data Libraries under accession numbers EU931120–EU931205.