A Genomic Comparison of Drosophila melanogaster and Drosophila pseudoobscura: Evidence for Faster-X, Faster-sex and Faster-male Evolution

Abstract

<p>A genomic comparison of Drosophila melanogaster and Drosophila pseudoobscura provides a unique opportunity to investigate factors involved in sequence divergence. The chromosomal arrangements of these species include an autosomal segment in D. melanogaster which is homologous to part of the X chromosome in D. pseudoobscura. Using orthologs to calculate sequence divergence and ratios of nonsynonymous to synonymous substitutions, we found sequences on the X chromosome significantly more diverged than sequences on the autosomes. Mean divergence for sequences having sex-related functions are higher than sequences without reproductive function and even higher for sequences with male-specific reproductive functions. These estimates of divergence for sex-related sequences are most likely underestimates, as the very rapidly evolving sex-genes would tend to loose homology sooner and thus not be included in the comparison of orthologs. These results suggest that the role of sexual selection in genomic evolution is more pervasive than imagined from the interplay of female choice and secondary sexual male traits.</p>