Genome-Wide Patterns of Sequence Divergence of Protein-Coding Genes Between Drosophila buzzatii and D. mojavensis

Evolutionary rates for protein-coding genes are determined not only by natural selection but also by multiple genomic factors including mutation rates, recombination, gene expression levels, and chromosomal location. To investigate the joint effects of different genomic determinants on protein evolution, we compared the coding sequences of 9017 single-copy orthologs between 2 cactophilic species from the Drosophila subgenus, Drosophila mojavensis and D. buzzatii, whose genomes have been previously sequenced. We assessed the impact of 7 genomic determinants, that is, chromosome type, recombination, chromosomal inversions, expression breadth, expression level, gene length, and the number of exons, on divergence rates of protein-coding genes to understand patterns of evolutionary variation. Integrative analysis of these factors revealed that 1) X-linked and autosomal genes evolve at significantly different rates in agreement with the faster-X hypothesis, 2) genes located on the dot chromosome and pericentromeric regions have higher divergence rates, 3) genes located at chromosomes with more fixed inversions have higher pairwise divergence than those located at nearly collinear chromosomes, and 4) gene expression patterns can be considered the strongest determinant of protein evolution. In addition, the number of exons and protein length had a significant effect on pairwise divergence at synonymous sites. All in all, our results show the relative importance of each genomic factor on the rates of protein evolution and functional constraint in these 2 cactophilic Drosophila species.