Hill-Robertson interference in Drosophila melanogaster: reply to Marais, Mouchiroud and Duret.

The usage of preferred codons in Drosophila melanogaster is reduced in regions of lower recombination. This is consistent with population genetics theory, whereby the effectiveness of selection on multiple targets is limited by stochastic effects caused by linkage. However, because the selectively preferred codons in D. melanogaster end in C or G, it has been argued that base-composition-biasing effects of recombination can account for the observed relationship between preferred codon usage and recombination rate (Marais et al., 2003). Here, we show that the correlation between base composition (of protein-coding and intron regions) and recombination rate holds only for lower values of the latter. This is consistent with a Hill-Robertson interference model and does not support a model whereby the entire effect of recombination on codon usage can be attributed to its potential role in generating compositional bias.